AIRVAC Design Manual.2008

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Design Manual

2008



2008 Design Manual

AIRVAC, Inc. : 4217 N. Old U.S. 31 • P.O. Box 528 • Rochester, Indiana 46975

Phone: 574.223.3980 • Fax: 574.223.5566 • www.airvac.com



The World Leader in Vacuum Sewer Technology

THIS DOCUMENT CONTAINS INFORMATION WHICH AIRVAC DEEMS

CONFIDENTIAL AND PROPRIETARY. THE BASIC AIRVAC SYSTEM REVEALED IN

THIS DOCUMENT IS PATENTED AS ARE CERTAIN SYSTEM COMPONENTS*. IN

CONSIDERATION FOR THE RECEIPT OF THIS DOCUMENT, RECIPIENT AGREES

NOT TO REPRODUCE, COPY, USE OR TRANSMIT THIS DOCUMENT OR THE

INFORMATION CONTAINED HEREIN, IN WHOLE OR PART, OR TO PERMIT

OTHERS TO DO SO, FOR ANY PURPOSE WITHOUT FIRST OBTAINING THE

EXPRESS WRITTEN PERMISSION FROM AIRVAC. RECIPIENT FURTHER

AGREES TO SURRENDER THIS DOCUMENT UPON REQUEST BY AIRVAC.

* FOLLOWING IS A PARTIAL LIST OF SUCH PATENTS:

4,917,143 5,326,069

5,064,314 5,515,554

5,259,427 5,570,715

5,282,281 6,397,874

COPYRIGHT AIRVACr, INC. 1976,77,78,80,86,89,92,96,00,05, 08



THIS DOCUMENT IS COPYRIGHT 2008 AIRVAC r , INC.

ALL RIGHTS RESERVED

NO PART OF THIS DOCUMENT MAY BE COPIED, OR

USED IN ANOTHER DOCUMENT, WITHOUT THE

EXPRESS WRITTEN PERMISSION OF AIRVAC, INC.



DISCLAIMER

AIRVAC is not an engineering firm, and cannot and does notprovide engineering services. AIRVAC reviews the design, plans,and specifications for a project only for their compatibility with

AIRVAC's vacuum products, and accepts no responsibility for theoverall project design. Any information provided to project

engineers is provided solely to assist the engineer in designingand engineering and maintaining an overall system that can utilize

AIRVAC vacuum products.



______________________________________________________________________TABLE OF CONTENTS

CHAPTER 1: INTRODUCTION

• History of Vacuum Collection Systems

• General Description

• Vacuum Transport Process

• Major System Components

• Applications

CHAPTER 2: DESIGN FLOWS

• Basis of Design

• Average Daily Flow

• Peaking Factor

• Peak Flow• Infiltration

• Flow Entering via Pumps

CHAPTER 3: VACUUM STATION DESIGN

• Station Sizing-General

• Collection Tank Sizing

• Sewage Pump Sizing

• Vacuum Pump Sizing

• Electrical Panel

• Level Controls

• Other Station Components

• Noise & Heat Considerations

• Standby Generator

• Odor Control

CHAPTER 4: VACUUM MAIN DESIGN

• Construction Issues

• System Layout Guidelines

• Line Sizing

• Line Lengths

• Main Line Design Parameters• Service Lateral Design Parameters

• Line Connections

• Losses Due to Friction

• Losses Due to Lifts (Static Loss)

• Pipe Volume

• Summary of Vacuum Design Fundamentals



______________________________________________________________________TABLE OF CONTENTS

CHAPTER 5: VALVE PITS

• Valve Pit Arrangements

• Components Common to Both Pit Types

• Valve Pit Components: PE 1-Piece Pits

• Valve Pit Components: Fiberglass 3-Piece Pits

• Building Sewer (House to Pit)

CHAPTER 6: BUFFER TANKS

• Description

• When & Where Used

• Effect on System Hydraulics• Buffer Tank Sizing

• Limitations on Use

• Situations to Avoid

• Potential Adverse Impacts

CHAPTER 7: PREFABRICATED VACUUM STATION SKIDS

• General

• Possible Skid Configurations

• Modifications to the Standard AIRVAC Skid

• Vacuum Station Equipment Configurations

CHAPTER 8: AIRVAC SERVICES

• The Team Approach

• Preliminary System Layout

• Detailed Design Assistance

• Construction Field Services

• System Start-Up

•

Home Hookup & Valve Installation• Initial System Operation

• Operator Training

• After-Market Services



Design Manual 2008

CHAPTER 1

INTRODUCTION

The design guidelines contained in this manual are intended for buried vacuum sewersystems serving municipalities or land developments that utilize AIRVAC’s 3” vacuumvalve. For indoor vacuum piping systems and applications that utilize vacuum valves

smaller than 3” and/or vacuum toilets, contact AIRVAC’s Environmental Group forapplication-specific design manuals.

A. HISTORY OF VACUUM COLLECTION SYSTEMS

Vacuum sewers were first used in Europe in 1882. However, it has been onlyin the last 35 years that vacuum transport has been utilized in the UnitedStates. During this time, the use and acceptance of vacuum sewers haveexpanded greatly. Entering 2008, there were nearly 300 AIRVAC vacuum

systems in operation in 27 states and 500-600 more in 27 foreign countries.

This technology is also recognized in two industry publications: the 1991United States Environmental Protection Agency (EPA), publication numberEPA/625/1-91/024, The Manual For Alternative Wastewater Collection Systems and the 2008 Water Environment Federation (WEF) Alternative SewerSystems, 2nd ed.; Manual of Practice No. FD-12. While both publicationsdescribe vacuum systems in general, the design criteria presented in both arebased on the AIRVAC system.

B. GENERAL DESCRIPTION

Vacuum sewers are a mechanized system of wastewater transport. Unlikegravity flow, vacuum sewers use differential air pressure to move the sewage.

A central source of power to operate vacuum pumps is required to maintainvacuum on the collection system (See Figure 1-1).

The vacuum sewer system requires a normally closed vacuum/gravity interfacevalve at each entry point to seal the lines so that vacuum is maintained. Theinterface valves; located in a valve pit, open when a predetermined amount ofsewage accumulates in the collecting sump. The resulting differential pressurebetween atmosphere and vacuum becomes the driving force that propels thesewage towards the vacuum station.

Vacuum sewer lines are designed to maintain a generally downward slopetoward the vacuum station so essentially they are a vacuum assisted, gravityflow piping network.

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Design Manual 2008

FIGURE 1-1: TYPICAL LAYOUT

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Design Manual 2008

C. VACUUM TRANSPORT PROCESS

When a sufficient volume of sewage accumulates in the sump, the associatedvacuum valve cycles. The differential pressure between the sewer main andatmosphere forces the sump liquid content and additional air into the collectionmain at maximum velocities. This liquid and air join with the liquid and air thatis at rest within the piping network, and is then propelled downstream. If noadditional valves are opened during this period, the liquid that has not exited themain to the collection tank once again comes to rest at downstream low points.

The magnitude of the propulsive forces starts to decline noticeably when thevacuum valve closes, but remains important as the air continues to expandwithin the pipe. Eventually friction and gravity bring the sewage to rest at a lowspot. Another valve cycle, at any location upstream of the low spot, will causethis sewage to continue its movement toward the vacuum station.

Sawtooth profileThe sawtooth profile ensures that an open passage of air between the vacuumstation and the interface valves is maintained throughout the piping network.This provides the maximum differential pressure at the interface valves toinsure self-cleansing of the valves as well as maximum energy input to thevacuum mains.

When the liquid comes to rest at the base of various lifts, it does not come incontact with the crown of the pipe and therefore does not seal the pipe (Figure1-2). Should the lift be sealed for any reason, liquid would become suspendedwithin the lift and an associated vacuum loss incurred.

The AIRVAC design philosophy includes an accounting of all lifts for all flowpaths within a system and the associated potential vacuum loss incurred. Thestatic loss limit assures that sufficient vacuum will be available for valveoperation in the event of a system upset such as 100% lift saturation.

Air to Liquid ratio (A/L ratio)Vacuum systems are designed to operate on two-phase (air/liquid) flows withthe air being admitted for a time period twice that of the liquid. Open time of the

AIRVAC valve is adjustable; hence, various air to liquid (A/L) ratios are

attainable. Sewage scouring velocities of 15 to 18 feet per second are attainedusing the standard air/liquid ratio.

The ability of the vacuum main to quickly recover to the same level of vacuumthat existed prior to the cycle, is commonly referred to as “vacuum response”,and is very important in vacuum sewer design. Vacuum response is a functionof line length, pipe diameter, number of connections, and the amount of lift inthe system.

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Design Manual 2008

Back-surgeSewage admitted to a vacuum main through an AIRVAC valve initially moves intwo directions. Approximately 80% flows toward the vacuum station and 20%flows in the opposite direction. When the back-surge slows, all of the flowmoves toward the vacuum station. (See Figure 1-3).

The 80%-20% split occurs when a wye fitting is used at the connection location.The back-surge would become 50% if a tee fitting were used. This would resultin a less efficient system. For this reason, a tee is never used in a vacuumsystem.

The vacuum transport process is clearly demonstrated at the AIRVACDemonstration Rig at the factory.

SEWAGE AT REST

FLOW

OPEN PASSAGE

OF AIR

FIGURE 1-2: VACUUM MAIN DURING PERIOD OF NO FLOW

FINAL FLOW (100%)

INITIAL FLOW (80%) INITIAL BACK-SURGE (20%) S E W A G E I N L E T

FIGURE 1-3: TYPICAL BACKSURGE

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Design Manual 2008

D. MAJOR SYSTEM COMPONENTS

There are three (3) major system components: the valve pit, the vacuum pipingand the vacuum station. These are described below:

Valve Pit The valve pit houses the vacuum valve and provides the interface between thevacuum system and the house. The sump portion of the valve pit is used toaccept the wastes from the house.

AIRVAC has two styles of valve pits; a single piece molded PE pit and a 3 piecefiberglass pit. In either style, there are two (2) separate internal chambers; anupper chamber that houses the vacuum valve and a bottom chamber that is thesump into which the building sewer is connected. These two chambers are

sealed from each other. The valve pit is able to withstand traffic loads.

The vacuum valve, which is housed in the upper chamber, operates without theuse of electricity. The AIRVAC Three Inch Valves are manufactured ofmaterials suitable for handling sanitary sewage. The valve is entirely pneumaticby design, and has a full 3-inch opening size. Some states have made this aminimum size requirement, as this is slightly larger than the throat diameter ofthe standard toilet.

The vacuum valve provides the interface between the vacuum in the collectionpiping and the atmospheric air in the building sewer. System vacuum in thecollection piping is maintained when the valve is closed. With the valveopened, system vacuum evacuates the contents of the sump.

Once the contents of the holding sump have been evacuated, an amount ofatmospheric air is admitted through the vacuum valve to provide propulsion tothe liquid. The source of this atmospheric air is either a 4” air-intake that isplaced on each house gravity line or a 6” dedicated air-terminal that isconnected to each valve pit.

With the first option, the 4” air-intake is installed downstream of all of the housetraps. This could circumvent the potential problem of inadequate house ventingwhich results in trap evacuation. While local codes may dictate exact locations,

AIRVAC recommends placing the air-intake on each gravity line connected tothe sump and at least 20 feet from the vacuum valve.

With the second option, the 6” dedicated air-terminal is located a short distancefrom the valve pit and is connected to the pit via 6” piping to one of the four (4)openings in the sump. No sewage is permitted to enter this “air-only” line.

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Design Manual 2008

Some local codes may require the installation of a backwater valves on thehomeowner’s building sewer. With most backwater valves, positioning is criticalto ensure proper operation of the AIRVAC valve (see Chapter 5); however byusing a normally opened type backwater valve, this concern can be alleviated.

AIRVAC should be consulted before such a device is installed.

Vacuum Piping AIRVAC sewers are laid in a saw tooth profile. When AIRVAC sewers areinstalled at 0.2% fall in flat land, the trench depth increases 12" every 500 feet.Profile changes, also called lifts, may be used to bring the sewer invert back tothe commencing level, keeping the trench depth to a minimum. Where thenatural ground profile has a fall in excess of 0.2% in the flow direction, thevacuum sewer profiles follow those of the ground with no profile changes.

PVC thermoplastic pipe, Schedule 40, SDR 21 or class 200, in sizes 3", 4", 6",

8" and 10" is normally used for vacuum sewers. Fittings used are of theSchedule 40 (pressure) type. Fittings include: wyes (for incoming branches or

AIRVAC valve crossovers), 45 degree ells (for making changes in direction andfabricating profile changes), and concentric reducers (for making changes inmain size). Tee fittings are not used for vacuum sewers.

Pipe and fitting joints are normally solvent welded or rubber ring type joints.Not all rubber ring pipe joints are suitable for vacuum service andengineers should require a guarantee from the manufacturer along with

test certification. When temperatures fall below 32° F, solvent weld jointscannot be reliably made, so o-ring pipe joints are recommended. AIRVAC

maintains a comprehensive recommended specification for sewer piping alongwith a list of manufacturers who have acceptable products.

The 3” pipe used to connect the valve pit to the vacuum main or branch iscalled a service lateral. Branch sewers are the tributary sewers connected tothe main. Installation of vacuum sewer pipes and fittings are depicted innumerous details shown within this manual; additional construction details areavailable on request.

Division or shut off valves are installed in branch and main lines to allowportions of the piping system to be isolated for troubleshooting and

maintenance. These valves are typically resilient-wedge gate valves usingmechanical joint connections with transition gaskets to PVC pipe that suitablefor underground vacuum service.

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Design Manual 2008

Vacuum StationThe vacuum station is the heart of the vacuum collection system. Themachinery installed is similar to that of a conventional sewage pumping stationor lift station, except vacuum is applied to the wetwell (collection tank) that issealed. Major components including the tank, are the sewage pumps, thevacuum pumps, and a control panel.

Most modern vacuum systems utilize factory pre-fabricated collection stationsmounted on skids for ease of installation and are typically housed in a two storystructure with the vacuum pumps and control panel located on the top floor andthe collection tank and sewage pumps on the lower floor (See Figure 1-4).

FIGURE 1-4: TYPICAL VACUUM STATION SCHEMATIC

FORCE MAIN

CONTROL

PANEL

VACUUM

SEWER MAIN

VACUUM PUMPS

COLLECTION TANK

SEWAGEPUMPS

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Design Manual 2008

Collection tanks are normally steel with protective coatings; fiberglass andstainless steel tanks have also been used. The vacuum sewers terminate atthis tank where vacuum is maintained automatically and passed to the sewersystem.

Duplicate sewage discharge pumps are used, with each pump capable ofpumping design peak flow. Dry- pit, horizontal, centrifugal sewage pumps aretypical, although dry-pit submersibles have been used as well.

Multiple sliding-vane type vacuum pumps are also typical. These pumps arecapable of an ultimate vacuum range near 29” Hg and offer efficient air-delivery-to-horsepower ratios. Horsepower varies with total flow rate, but isnormally 10 - 25 Hp.

Check valves for discharge pumps feature soft seats with outside weights andlevers; vacuum pump inlet check valves are also fitted with soft seats.

Typical electrical controls include:

• Vacuum switches with stainless bellows.

• Liquid level controls suitable for sanitary sewage

• Motor starters with overload

• Automatic alternators for pump cycling

• Hour run meters

• A solid state telephone alarm system

• A seven (7) day circular vacuum chart recorder

Since the systems require only one source of power, many systems utilizeexisting portable generators for emergency power; others have permanentlyinstalled back up generators.

For unusually large flow areas, a customized, built-in place vacuum station canbe utilized using similar equipment available from AIRVAC.

See Chapter 3 for design parameters and details of vacuum stations.

Introduction1 - 8





Design Manual 2008

GRAVITY SEWERSVACUUM SEWERS

TYPICAL

DEPTH

3' TO 5'

TYPICAL

DEPTH

3' TO 20'

VACUUM SEWERS ARE

INSTALLED IN THE RIGHT OF

WAYS AND REQUIRE SHALLOW

TRENCHES WITH MINIMAL

ENVIRONMENTAL IMPACT.

GRAVITY SEWERS ARE INSTALLED

ALONG THE ROAD CENTERLINE.

THEY REQUIRE DEEP TRENCHES

AND CONSIDERABLE PAVEMENT

RESTORATION.

FIGURE 1-5: VACUUM vs GRAVITY EXCAVATIONS

3' TYP.

20' TYP.

3' TYP.

5' TYP.

GRAVITY SEWERS

VACUUM SEWERS

FIGURE 1-6: VACUUM AND GRAVITY PROFILES

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Design Manual 2008

Introduction1 - 11

Advantages-Operation (general) There are several operating advantages to using vacuum sewers as describedbelow:

• High scouring velocities are attained, reducing the risk of blockages

and keeping wastewater aerated and mixed.

• Elimination of the exposure of maintenance personnel to the risk ofH2S gas hazards.

• The system will not allow major leaks to go unnoticed, resulting inreduced environmental damage from exfiltration of wastewater.

• The elimination of infiltration permits a reduction of size and cost ofthe treatment plant.

• The air/sewage mixture enters sewers at high velocity, and the airprovides some pretreatment to the sewage inside the vacuumsewers.

Advantages-Operation (in hurricane prone areas) There are several advantages to using vacuum sewers for hurricane proneareas. System operators of actual systems that have experienced hurricanesreport the following advantages:

• Vacuum systems are sealed and massive amounts of I&I cannotenter the system and overwhelm the treatment plant.

• All vacuum stations have either a fixed or portable generator, whichensures uninterrupted service to the customer.

• Vacuum systems eliminate the threat of massive I&I and sewagespills. In coastal areas where 1 vacuum station typically replaces 7 or8 lift stations, this means less hurricane preparation is required.

•

The maintenance staff is not exposed to the severe weather as thegenerators automatically start during a power outage.

• If water level rises to the point where the air-intakes are in danger offlooding, the entire system can be turned off, thus preventing damageto system components.



Design Manual 2008

CHAPTER 2DESIGN FLOWS

A. BASIS OF DESIGN

All of the major vacuum system components are sized according to peak flow,expressed in gallons per minute (gpm). Peak flow rates are calculated byapplying a peaking factor to an average daily flow rate.

B. AVERAGE DAILY FLOW

Based on the current Ten State Standards, sewage flow rates shall be basedon one of the following:

1. Documented wastewater flow for the area being served. Water userecords are typically used for this purpose.

2. 100 gallons per person per day combined with home population densitiesspecific to the service area. Most approval agencies will acceptpublished U.S. Census Bureau home density for this criterion.

C. PEAKING FACTOR

The peaking factor suggested by the design firm will be used, with oneexception: the minimum peaking factor should never be less than 2.5.

If not established by the consulting firm, regulatory agency or other applicableregulations, the peaking factor should be based on the following formula:

18 + 1000/POPULATION

4 + 1000/POPULATION

Design FlowsPage 2 - 1



Design Manual 2008

For example, if the service area has a population density of 1200, the peakingfactor would be:

2.1+18

= 3.75

2.14 +

Table 2-1 shows peak factors for various populations. Please note that theseare not the exact figures that would be returned by the formula but rather arerounded figures for presentation purposes only.

Table 2-1

Peak FactorsBased on Ten State Standards formula

Population Peak factor

100 4.25

500 4.00

1200 3.75

2500 3.50

5000 3.25

9000 3.00

D. PEAK FLOW

Applying the peak factor to the average daily flow rate and converting to gpmwill yield the peak flow to be used as the basis of design.

Qa /1440 x PF = Qmax where:

Qa = Ave daily flow (gpd)PF = Peak factorQmax = Peak Flow (gpm)




Design Manual 2008

Using local flow rates and a peak factor suggested by design firmIf the design firm provides the average daily flow based on local water recordsand recommends a peaking factor, AIRVAC will use both as the basis fordesign.

Example:

Average daily flow rate: 75 gpcdPersons/house 3.5# houses: 400Peak factor: 3.50

Qa = 75 gpcd x 3.5 per/hse x 400 hses = 105,000 gpdPF = 3.50

Qmax = 105,000 gpd/1440 x 3.50= 255 gpm

Using Ten State Standards Peak factor and flow ratesIf the design firm does not suggest average daily flow rates and peaking factors,then the Ten State Standards will be used for both.

Example Average daily flow rate: 100 gpcdPopulation (3.0 x 400): 1200Peak factor 3.75

Qa = 100 gpcd x 1200 persons = 120,000 gpdPF = 3.75

Qmax = 120,000 gpd/1440 x 3.75= 313 gpm




Design Manual 2008


E. INFILTRATION

The vacuum system is a sealed system that eliminates ground water infiltrationfrom the piping network and the interface valve pits. However, ground watercan enter the system as a result of leaking house plumbing or as a result ofbuilding roof drains being connected to the plumbing system. It is thereforeimportant for designers to consider methods of eliminating ground waterfrom plumbing systems during the design phase of a project. AIRVACengineers will be happy to share ideas and methods used successfully in thepast.

F. FLOW ENTERING VIA PUMPS

For purposes of vacuum design, any flow that enters the vacuum system via apump should be expressed in terms of the actual discharge pump rate ratherthan the standard peak flow rate from the house.



Design Manual 2008

CHAPTER 3VACUUM STATION

A. STATION SIZING-GENERAL

Nomenclature used in the station design is given below:

Term DefinitionQmax Station peak flow (gpm)Qa Station average flow (gpm)Qmin Station minimum flow (gpm)Qdp Discharge pump capacity (gpm)Qvp Vacuum pump capacity (cfm)Vo Collection tank operating volume (gal)Vct Collection tank volume (gal)

t System pump-down time (min)Vp Piping system volume (gal)Vt Total system volume (gal)TDH Total dynamic head (ft)Hs Static head (ft)Hf Friction head (ft)Hv Vacuum head (ft)

The major station components are generally sized as described in Table 3-1.Detailed formulas for each component are shown in this Chapter. A VacuumStation Calculation Sheet is included in this chapter.

Table 3-1

Vacuum Station Component Sizing

Component How Sized

Collection Tank To insure adequate operating volume to preventexcessive sewage pumping cycles and to provideemergency storage volume.

Sewage Pumps Based on total peak flow to the vacuum station oras necessary to maintain 2 ft/sec scouring velocitywithin the force-main whichever is greater.

Vacuum Pumps Based on: 1) peak flow & length of line and 2) thetotal system piping volume.

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Design Manual 2008

B COLLECTION TANK SIZING

MaterialsMild steel, Type 304 or 316 stainless steel and fiberglass tanks are acceptable.Steel and SS tanks should be of a welded construction and fabricated from notless than 1/4- in. thick steel plates. The tanks should be designed for a workingpressure of 20 in. Hg vacuum and tested to 28 in. Hg vacuum.

The tank should be furnished with the required number and size of openings,man-ways, and taps, as shown on the plans. In addition, the tank should besupplied complete with sight glass and its associated valves.

Steel tanks should be sand-blasted and painted as follows:

• Internally: Two coats of epoxy suitable for immersion in sewage.

• Externally: One coat of epoxy primer and one coat of epoxy finish.

Fiberglass tanks may be substituted using the same specifications. All tanksare to have 150 psi rated flanges.

It is recommended that only one vessel be used for most projects. Should thesingle tank concept result in a tank too large to transport, dual tanks arerecommended but this is very rare.

Tank SizingCollection Tanks are sized to insure adequate operating volume to preventsewage pump short cycles and emergency storage volume. Also, tanks may besized in anticipation of any future growth.

The tanks are sized based on peak flow to the station. To this peak flowquantity, factors are applied to establish the operation volume for sewage pumpcycling. Using these criteria, the sewage pumps will not operate more than 4times per hour at minimum flow periods (2 starts per pump), nor start more than7 times per hour at average flow (3.5 starts per pump). This is represented bythe following formulas:

QdpQQdpQVo − ÷= min)min(15

4003

Vacuum Station

+= VoVct

Vo

minQ

Qdp

Vct

Where = Operating Volume (gal)

= Minimum Flow (gpm) = Qa /2

= Sewage Pump capacity (gpm)

= Collection Tank Size (gal)

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Design Manual 2008

Vacuum Station

o the operating volume a safety factor of 3.0 is applied for emergency storage.

able 3-2 gives the value of Vo for a 15-minute cycle at Qmin for different

Table 3-2

Values of Vo for a 15-Minute Cycle at Qmin

T An additional 400 gallons is added to this subtotal as a reserve volume withinthe tank for moisture separation and vacuum pump reserve volume.

Tpeaking factors. The total volume of the collection tank should be 3 times theoperating volume (Vt = 3 x Vo) with a minimum recommended size of 1000 gal.

for Different Peaking Factors

Peaking Factor Vo

3.0 2.08 x Qmax 3.5 1.84 x Qmax 4.0 1.64 x Qmax

fter sizing the operating volume, the designer should check to ensure an

hen designing the collection tank, the sewage pump suction lines should be

he minimum recommended tank size is 1000 gallons.

IRVAC prefabricated skids are available with nominal tank sizes starting at

Aexcessive number of pump starts per hour will not occur. This check should beperformed for a sewage inflow equal to one-half the pump capacity.

Wplaced at the lowest point on the tank and as far away as possible from themain line inlets. The main line inlet elbows inside the tank should be turned atan angle away from the pump suction openings.

T

A1000 gallons and then increasing in nominal increments of 500 gallons. SeeChapter 7 for more information on AIRVAC Prefabricated skids.

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Design Manual 2008

C. SEWAGE PUMP SIZING

MaterialsDuplicate pumps, each capable of delivering the design capacity at thespecified TDH should be used. These are typically horizontal, non-clogcentrifugal pumps.

Because the pump is drawing from a tank under vacuum, the NPSHcalculations are especially critical. A certification from the pump manufacturerthat the pumps are suitable for use in a vacuum sewerage installation isstrongly recommended.

Each pump should be equipped with an enclosed, non-clog type, two port, grayiron impeller that is statically and dynamically balanced and capable of passinga 3-in sphere. The impeller should be fastened to a stress-proof steel shaft bya stainless steel lock screw or locknut. Pumps should have an inspectionopening in the discharge casing.

The sewage pumps are the most susceptible component to submergence so itwould be wise to consider dry-pit submersible pumps for flood prone areas.These pumps may operate in a dry pit under normal conditions and if necessarycontinue to operate while submerged. The obvious disadvantage is a motorcoupled to the pump casing that is sealed making maintenance more difficult.Submersible pumps tend to require slightly higher NPSHa than their non-submersible counterparts so some special arrangements may be necessary tosatisfy this criterion as well.

Pump capacityTo size the discharge pumps, use the following formula:

Qdp = Qmax = Qa x Peak Factor

Typical peak factors range from 3.0 to 4.0 (see Chapter 2).

The final selected pump capacity should be as calculated above (Qdp) or asnecessary to maintain 2 ft/sec scouring velocity within the force-main,whichever is greater.

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Design Manual 2008

TDH CalculationsThe Total Dynamic Head (TDH) is calculated using the following formula:

TDH = Hs + Hf + Hv

TDH is calculated using standard procedures for pumps with the exception thatthe head attributed to overcoming the vacuum in the collection tank (Hv) mustalso be considered. This value is usually 23 ft, which is roughly equivalent to20 in. Hg, which is the typical upper operating value.

Since Hv will vary depending on the tank vacuum level, (16-20 in Hg, withpossible operation at much lower and higher levels during problem periods) it isprudent to avoid a pump with a flat capacity/head curve.

Where possible, horizontal sewage pumps should be used, as they have lesssuction losses compared to vertical pumps. To reduce suction line frictionlosses, the pump suction line should be 2 in. larger than the discharge line.

NPSH Calculations To calculate NPSHa, use the following formulas. Nomenclature and typicalvalves used in the NPSH calculations are given in Table 3-3

NPSHa = havt + hs – hf - hvpa

where havt = ha - Vmax

NPSHa and TDH should be calculated for both the high and low vacuumoperating levels and compared to the NPSHr at the corresponding point on thehead/capacity curve.

NPSHa must be greater than NPSHr . NPSH characteristics differ frommanufacturer to manufacturer, with some better suited for use in a vacuum

system than others. Depending on the actual pump selected and where it willoperate on the pump curve, it would be prudent for the designer to includesome margin between NPSHa and NPSHr. This is especially important forpumps that will operate away from the BEP (Best Efficiency Point) of the pumpcurve.

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Design Manual 2008

Historically, NPSH has proven to be the most critical factor regarding sewagepump performance in a vacuum system. While several pumps may meet thehead, capacity and NPSH requirements, AIRVAC recommends that thedesigner choose the pump with the lowest NPSHr .

Table 3-3

Discharge Pump NPSH Calculation/ Nomenclature

Term Definition Typical Value

NPSHa Net positive suction head available, ft-

NPSHr Net positive suction head required by the pump selected, ft -

ha Head available due to atmospheric pressure, ft 33.9 @ sea level

33.2 @ 500 ft

32.8 @ 1,000 ft29.4 @ 4,000 ft

havt Head available due to atmospheric pressure at liquid level less

vacuum in collection tank, ft

-

Vmax Maximum collection tank vacuum, ft 18.1 @ 16-inHg

22.6 @ 20-inHg

hs Depth of wastewater above pump centerline, ft 1.0 (min)

hvpa Absolute vapor pressure of wastewater at its pumpingtemperature, ft

0.8

hf Friction loss in suction pipes, ft 2.0 (ver. Pump)

1.0 (hor. Pump)

Figure 3-1 is a diagram for calculation of NPSHa in a vacuum system.

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Design Manual 2008

FIGURE 3-1: NPSHa CALCULATION WITH TYPICAL VALUES

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Design Manual 2008

D. VACUUM PUMP SIZING

Materials AIRVAC recommends sliding vane type vacuum pumps, as they appear to bemore efficient (air delivered versus electrical energy usage) in the operatingrange of 16-20” Hg, are more dependable, and generate less noise than do theliquid ring type.

Vacuum pumps should be air-cooled and have a minimum (ultimate) vacuum of29.3 in. Hg at sea level. Even though the pumps operate on short cycles, theyshould be capable of continuous operation. Lubrication should be provided byan integral, fully re-circulating oil supply. The oil separation system should alsobe integral. The entire pump, motor, and exhaust should be factory assembledand tested with the unit mounted on vibration isolators, and should not requirespecial mounting or foundation considerations.

When the vacuum pump capacity calculations call for 2 pumps, duplicatepumps each capable of delivering 100 percent of the required airflow, should beprovided. When more than 2 pumps are required, 100 percent of the requiredairflow should be provided by the cumulative total capacity of all of the pumpsless 1, with the additional pump having the same capacity as the others.

Pump SizingVacuum pumps are sized based on 2 factors: 1) peak flow & A/L ratio and 2)system pump down time (‘t’) which is a function of the total system piping

volume. Both criteria should be checked and the larger value used.

System pump-down time is the controlling factor for the majority of the vacuumpumps used in municipal sewer systems.

Pump Size Based on Flow and Line LengthTo size the vacuum pumps, the following empirical formula has been usedsuccessfully:

Qvp = A x Qmax/7.5 gal/ft3

"A" varies empirically with mainline length as shown in Table 3-4.

Vacuum Station3 - 8



Design Manual 2008

Table 3- 4

“A” Factor for Use in Vacuum Pump Sizing

Longest Line Length (ft) A0 - 5,000 6

5,001 - 7,000 77,001 -10,000 8

10,001 -12,000 9>12,000 11

Pump Size Based on Pipe Volume (see page 4-30) After the initial vacuum pump size has been selected based on peak flow & A/Lratio, system pump- down time (known as ‘t’) for an operating range of 16-20 in.Hg should be checked. This calculation will show the amount of time it will takethe selected vacuum pumps to evacuate (pump-down) the collection piping

starting at a level of 16 in. Hg to a final level of 20 in. Hg.

(0.045 cfm-min) (2/3 Vp + (Vct-Vo)) galt = _______________ x ____________________________

gal Qvp cfm

where:

t = System pump-down time (min)Vp = Volume of collection system piping (gal)Vct = Volume of collection tank (gal)

Vo = Operating volume of collection tank (gal)Qvp = Vacuum pump capacity (cfm)

In no case should "t" be greater than 3 minutes nor less than 1 minute. Ifgreater than 3 minutes, the capacity of the vacuum pumps should be increasedor additional pumps added. If “t” is less than 1 minute, the capacity must bereduced.

The minimum recommended pump size is 170 cfm. AIRVAC prefabricatedskids use the following 3 vacuum pump sizes (See Chapter 7).

170 cfm 10 hp305 cfm 15 hp455 cfm 25 hp

Please contact AIRVAC if the design includes an EAAC (see NOTE on page 4-27) or system operation at levels higher than 16-20 in. Hg, as this may requirean additional vacuum pump or a larger vacuum pump.

Vacuum Station3 - 9



Design Manual 2008

PROJECT PROJECT NUMBER

STATION NUMBER DATE

FLOW CALCULATIONS

# connections x = (a)

Present growth rate Future

Residential Flow rate (gpcd) = (b) Per/hse = (c)

Ave daily flow (residential) x x = gpd (d)

(a) (b) (c)

Peak factor (e)

Peak flow (Residential) (d) x (e) = x = gpm (f)

1,440 1,440 (e)

Other Peak flow (Comm) gpm (g)

Total Peak Flow (f) + (g) = + = gpm Qmax

(f) (g)

Average Flow = Qmax = = gpm Qa

(e)

Minimum Flow = Qa = = gpm Qmin

2 2

SEWAGE PUMP CALC’s

Pump Capacity = Qmax = gpm Qdp

TDH @ 16” Hg = 18.1 + + = ft

Vacuum Static Friction

TDH @ 20” Hg = 22.6 + + = ft

Vacuum Static Friction

NPSHa @ 16” Hg = + - - = ft

(havt) (hs) (hf) (hvpa)

NPSHa @ 20” Hg = + - - = ft

(havt) (hs) (hf) (hvpa)

NOTE: Havt = [ ha - Vmax ]

COLLECTION TANK SIZING

Operating Volume = 15 Qmin (Qdp – Qmin) = 15 x x ( - )

= gal VoQdp

Tank Volume required = [Vo x 3] + 400 = ( x 3 ) + 400 = gal

Selected tank Volume (round up to nearest 500 gal) gal Vct

FIGURE 3 – 2: STATION CALCULATIONS

Vacuum Station3 - 10



Design Manual 2008



STATION NUMBER DATE

VACUUM PUMP CALCULATIONS

A. Based on Peak Flow and Line Length

Longest Line Length “A” Pump Capacity Horsepower

0 - 5,000 65,001 - 7,000 7 170 cfm 107,001 - 10,000 8 305 cfm 1510,001 - 12.000 9 455 cfm 2512,001 - 15,000 11

Longest Line = lf

Vacuum Pump capacity required = Qvp = A x Qmax = ( x )

7.5 gal/ft3 7.5 gal/ft3

= cfm

Minimum 2 vacuum pumps : cfm Qvp

1 pump used as a standby # pumps Round up tocommon size

B. Based on Pipe Volume & “ t”

LINE LENGTHS & PIPE VOLUME

Line 3” 4” 6” 8” 10”

A

B

C

D

TotalPipe footage lf lf lf lf lf

x 0.0547 ft3/lf 0.0904 ft

3/lf 0.1959 ft

3/lf 0.3321 ft

3/lf 0.5095 ft

3/lf

Pipe Volume = ft3 ft

3 ft

3 ft

3 ft

3

Vp = ft3 x 7.48 gal/ft

3 = gal

t = (.045 cfm-min) x [2/3 Vp + (Vct-Vo)] gal

gal [# pumps –1] x Qvp cfm“t” should be less than 3 min. If over,increase Qvp or add vacuum pumps t = .045 x [ (2/3 x ) + ( - )]

( - 1 ) x ( )If “t” is under 1 min, increase Vct

t = min

FIGURE 3 – 2: STATION CALCULATIONS



Design Manual 2008

VACUUM FORMULAS AND CONVERSION FACTOR

Absolute Pressure Based On U.S. Std Atmosphere

ALTITUDE PRESSURE

(Feet) In. Hg. PSI

0 29.92 14.70

500 29.38 14.43

600 29.28 14.38

700 29.18 14.33

800 29.07 14.28

900 28.97 14.23

1,000 28.86 14.18

1,500 28.33 13.90

2,000 27.82 13.67

2,500 27.31 13.41

3,000 26.81 13.19

3,500 26.32 12.92

4,000 25.84 12.70

4,500 25.36 12.45

5,000 24.89 12.23

5,500 24.43 12.00

6,000 23.98 11.77

6,500 23.53 11.56

7,000 23.09 11.34

7,500 22.65 11.12

8,000 22.22 10.90

8,500 21.80 10.70

9,000 21.38 10.50

9,500 20.98 10.30

10,000 20.58 10.10

Multiply

Vacuum Station

By

To Obtain

lb./square inch (psi) 2.036 Inches mercury

lb./square inch (psi) 27.684 Inches water

lb./square inch (psi) 5.17 Cm. mercury

lb./square inch (psi) 70.317 Cm. water

lb./square inch (psi) 703.09 Kg/m2

Inches water 0.0735 In. mercury

Inches water 0.036 Lb./sq. inch

Inches water 2.54 Cm. water

Inches mercury 0.4912 Lb./sq. inch

Inches mercury 13.60 In. water

Inches mercury 2.54 Cm. mercury

Gal. Water 8.337 Lb.

Gal. 0.1337 Cu. Ft.

Cu. Ft. 7.48 Gal.

Cu. Ft. 0.0283 Cu. Meters

Horsepower 746. Watts

Kilowatts 1.341 Horsepower

M3/min. 35.31 Cfm

cfm 1.6992 m3/hr.

AIRVAC SYSTEM PUMP DOWN TIME

The following formulas will give pump down time for anempty vacuum system.

SYSTEM PUMP DOWN TIME

t -2 .3V

S l o g

P

P

1

2

t = time in minutesV = volume of system in cubic feetS = average pump speed in CFM from P1 to P2

P1 = initial pressure - psiaP2 = final pressure - psia

The following examples illustrate two (2) typical operatingconditions

For pumping 0 to 20” Hg

t (m in ) - 0 .147

c fm - m in

gal

Vp Vct Vrt

Qvp

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟

+ +

For pumping 16” Hg to 20” Hg

t (m i n ) - 0.0 45c fm - m in

gal

Vp Vc t Vrt

Qv p

⎛

⎝ ⎜

⎞

⎠⎟

+ +

DEFINITIONS

FREE AIR (SCFM)Free Air is air at normal atmospheric pressure. Becausethe altitude, barometer and temperature vary at differentlocalities and at different times, it follows that this termdoes not mean air under identical conditions.

DELIVERED AIR (ACFM) Vacuum Pump: Delivered air is the actual volume ofexpanded air under the vacuum condition expressed inCFM at the vacuum pump intake.

SCFMStandard Cubic Feet per Minute.

Delivered, free air at 14.7 PSIA and 70°F

30"

30" V (in.Hg)

x SCFM ACFM

−=

EXPANDED AIR Expanded Air is air under a partial vacuum or belowatmospheric pressure. A true vacuum is a space without

any air or gas and represents zero absolute pressure.

ABSOLUTE PRESSURE Absolute Pressure is the total pressure above true zero.When working below atmospheric pressure it is less than14.7 pounds per square inch. When working aboveatmospheric pressure, the absolute pressure is the sum ofthe atmospheric pressure and the gauge pressure.

ATMOSPHERIC PRESSURE Atmospheric Pressure at sea level is 14.7 pounds persquare inch above zero absolute pressure or 29.93 inchesmercury.

3 - 12



Design Manual 2008

E. ELECTRICAL PANEL

Motor Control panelRather than using a Motor Control Center (MCC), most vacuum stations use asmaller control panel that is attached directly to the equipment skid. Thesecontrol panels are specifically designed for each station.

The control panel enclosure is to be NEMA Type 12 and is generally mountedon the equipment skid. A main disconnect switch, sized to handle the currentdraw for all related vacuum station equipment is to be provided.

The panel includes motor starters for each motor. Typically, IEC type motorstarters are used. To reduce in-rush current, “soft-starts” can be also used.The control panel also incorporates control relays, which then are connected tothe various functions of the control panel system design.

Discharge pump level control relays are mounted inside the panel.Conductance type level control rods are mounted through the tank wall and setto specific heights to maintain sewage pump operation and to provide alarmfunctions.

The panel should include pilot lights and hand-off-auto (HOA) switches. Hour-run meters are included for the operator to track daily run times of the vacuumand discharge pumps.

To monitor system performance, a 7-day chart recorder is installed in the

enclosure. The control panel should also include a telephone alarm dialer,which monitors (3) three alarm functions: low vacuum levels, high sewageconditions and power outages.

In small, simple vacuum station designs, the control panel is wired to eachmotor and control device by AIRVAC. Larger, more complex designs requirethe contractor to wire the control panel to the related junction boxes provided onthe equipment.

Motor Control Center

In larger vacuum stations, the controls are typically housed in a Motor ControlCenter (MCC). The Motor Control Center (MCC) is to be manufactured,assembled, wired, and tested in accordance with the latest issue of NEMAPublication ISC2-322, for Industrial Controls and Systems. The vertical sectionand the individual units should bear a UL label, where applicable, as evidenceof compliance with UL Standard 845.




Design Manual 2008

Wiring inside the MCC is to be NEMA Class II, Type B. Where Type B wiring isindicated, the terminal blocks should be located in each section of the MCC.

The enclosure should be NEMA Type 12-with-Gasketed Doors. Verticalsections shall be constructed with steel divider side sheet assemblies formed orotherwise fabricated to eliminate open framework between adjacent sections orfull-length bolted-on side sheet assemblies at ends of the MCC.

The MCC should be assembled in such a manner that it is not necessary tohave rear accessibility to remove any internal devices or components. All futurespaces and wire-ways are to be covered by blank doors.

Relay logic vs. PLCControl panels can use either relay-logic or PLC logic. Some prefer thesimplicity of relay-logic and may not want the sophistication of using a PLC.

Others wish to have more control over the system by changing the ladder logicthrough laptop computers or by phone. Many of the larger municipalities preferthis type of logic as it matches other controls they may have with lift stationsand/or their treatment plant.

F. LEVEL CONTROLS

Seven (7) probes inside the collection tank control the discharge pumps andalarms. These probes are ¼ in. stainless steel with a PVC coating. The sevenpositions are as follows:

1. Ground probe2. Both discharge pumps stop3. Lead discharge pump start4. Lag discharge pump start5. High level alarm6. Reset for probe #77. High level cut-off: stops all discharge pumps (auto position only)

and vacuum pumps (auto and manual positions)

Figure 3-3 gives approximate elevations of these probes in the collection tankrelative to the discharge pumps and incoming vacuum mains.

An acceptable alternative to the seven probes is a single capacitance-inductivetype probe capable of monitoring all seven set points. This type of proberequires a transmitter/transducer to send a 4-20 mA signal to the MCC.




Design Manual 2008


FIGURE 3-3 LEVEL CONTROL PROBE DIAGRAM



Design Manual 2008

G. OTHER STATION COMPONENTS

Equalizing Lines A 1” NPT equalizing line is installed on each sewage pump. Its purpose is toequalize the liquid level on both sides of the impeller so that air is removed.This ensures that the impeller is filled with liquid when the pump starts whichallows the sewage pump to start without having to pump against the vacuum inthe collection tank.

Clear PVC pipe is recommended for the equalizing lines because small airleaks or blockages will then be clearly visible to the system operator.

For discharge pumps with small flow, the equalizing lines should be fitted withmotorized full port valves that close after the pump is started.

Vacuum GaugesOn the upstream side of each side of each vacuum sewer isolation valve, avacuum gauge of not less than 4.5-in. diameter should be installed. Gaugesshould be positioned so that they are easily viewed when the isolation valvesare operated. Diaphragm seals should not be used with compound gauges.

All vacuum gauges should be specified to have a stainless steel bourdon tubeand socket and to be provided with ½ in. bottom outlets. Polypropylene orstainless steel ball valves should be used as gauge cocks.

The connection from the incoming main lines to the vacuum gauges should bemade of PVC or CPVC pipe. Copper pipe is not to be used for this purpose.

Vacuum Chart RecorderThe Motor Control Center of control panel should contain a 7-day circular chartrecorder. The recording range is to be 0-30 in. Hg vacuum, with the 0 positionat the center of the chart. The chart recorder should have stainless steelbellows.

Station Piping & valves Station piping includes all piping within the station, connecting piping to thecollection tank, vacuum sewer lines, and force mains. This item includes piping,valves, fittings, pipe supports, fixtures, drains, and other work involved inproviding a complete installation.




Design Manual 2008

Wastewater, vacuum, and drain lines 4-in. and larger should be ductile iron,using AWWA/ANSI C110/A21.10 as standard. Pipe and fittings with thevacuum station should be flanged with EPDM gaskets.

Exposed vacuum lines and other piping smaller than 4-in. can be Sch 80 PVC,304 Stainless Steel or galvanized. Building sanitary drains may be constructedof Sch 40 PVC with DWV fittings.

The vacuum station piping should be adequately supported to prevent saggingand vibration. It also should be installed in a manner to permit expansion,venting, and drainage. For fiberglass tanks, all piping must be supported sothat the tank flanges support no weight. Flange bolts should only be tightenedto the manufacturer's recommendations. Provisions must be allowed forinaccurate opening alignment.

All shut-off valves fitted within the vacuum station should be flanged, resilient

coated plug valves with circular ports.

Check valves fitted to the vacuum piping are to be of the 125 lb. bolted bonnet,rubber flapper, and horizontal swing variety. Check valves are to be fitted withBuna-N soft seats.

Check valves fitted to the sewage discharge piping are to be supplied with anexternal lever and weight to ensure positive closing. They also should be fittedwith soft rubber seats.

Station Sump ValveThe basement of the vacuum station should be provided with a 15 in. x 15 in. x12 in. deep sump to collect wash-down water. A vacuum valve that isconnected by piping to the collection tank empties this sump. A check valveand eccentric plug valve should be fitted between the sump valve and thecollection tank.

Fault Monitoring System A voice communication-type automatic telephone dialing alarm system istypically used to alert the operator of system abnormalities and station

emergencies. The system should be self-contained and capable ofautomatically monitoring up to four independent alarm conditions.

The telephone dialer is usually within the Motor Control Panel. When doing so,provisions must be made to isolate the system from interference. Themonitoring system should be provided with continuously charged batteries for24 hours standby operation in the event of a power outage.




Design Manual 2008

H. NOISE & HEAT CONSIDERATIONS

NoiseNoise generated by a vacuum station is typically associated with the vacuumpumps. If desired, soundproofing features can be added to the vacuum station.Of the 250+ vacuum stations in the U.S., only a handful has utilized this addedprotection. In these cases, there were 4 or 5 vacuum pumps, a large generator,and the station was located in close proximity to a house.

A study of 6 operating vacuum stations, which employed masonry construction,resulted in measured decibels range of 50 to 60 dBA at the door of the vacuumstation while vacuum pumps were in operation. Ambient readings indicated 50to 55 dBA while no pumps were operating. No difference between ambient andoperating pumps could be detected at the property line.

HeatThe vacuum station generates heat primarily from the sewage pump motorsand the vacuum pumps. Obviously this heat is added to ambient conditionsand can add up during hottest periods of the day.

To prevent heat buildup, vacuum stations should be designed with adequate airexchange rates provided through ventilation equipment. Allowing natural heatrising through roof-mounted vents with low air intakes is recommended.Maximum recommended operating temperature for station equipment is 104degrees (F).

Contact AIRVAC for recommended minimum ventilation standards.

I. STANDBY GENERATOR

A generator is used to provide standby power for duty discharge and vacuumpump operation. It can be located either inside or outside the vacuum station.

A portable generator unit is sometimes used which may provide power forseveral vacuum stations. This is more common where power interruptions arerare and allows the unit to be taken in for service when required.

J. ODOR CONTROL

Odor control for vacuum systems is normally associated with airborne H2Swithin the vacuum pump exhaust. If odor is a concern, various methods can beused to successfully eliminate H2S. The use of a bio-mass compost bed




Design Manual 2008

designed in accordance with EPA Manual for "Odor and Corrosion in SanitarySewerage Systems" have been used for many years in various locals in theU.S. and in foreign countries. Other methods employed include chemicalneutralization, activated carbon absorption systems and absorption bymanufactured bio-mass filters.

The bio-mass filter bed is recommended, assuming space is available at thesite. An Excel spreadsheet for bio-filter sizing is available from AIRVAC uponrequest. An example follows for reference only.

1 Number of vacuum pumps 4

2 Pump capacity (e.g. – 455) 455 ACFM

3Maximum vertical velocity thru filter bed(suggested 4.0 ft/min or less) 4.0 Ft/min

4Minimum area required at maximum air velocity (pumpcap x # pumps/max velocity)(455 x 4/4.0) 455 Ft2

5 Assumed Filter bed area (Length x Width)Example: 30 ft x 12 ft = 360 Ft2 360 Ft2

6 Actual filter bed loading (pump cap x # pumps/filter bedarea)(455 x 4)/360 5.06 Ft/min

7 Assumed filter bed depth (suggest 3.0 ft) 3.0 Ft

8Total filter bed volume (area x depth)(360 x 3.0) 1080 Ft3

9 Compost material density (suggest 50 lb/Ft3) 50 Lb/ft3

10Compost total weight (density x volume)(50 x 1080) 54,000 Lb.

11Bulk weight of compost (assuming 75% void space)(54,000 x .25) 13,500 Lb.

12Bulk weight of compost in Kilograms(13,500 / 2.2) 6,124 Kg

13Possible hydrogen sulfide gas removal(assuming 2.2 mg/Kg-min concentration)(6,124 x 2.2) 13,472 mg/min

14

Total possible weight of exhaust gas (in Kg)

(assume weight of exhaust gas = .075 lb/ft3)(455 x 4 x 0.075)/2.2 62.05 Kg

15Total possible H2S in gas(assuming max 60 ppm concentration (60 mg/kg)(60 x 62.05) 3,723 mg

16Factor of safety (should be minimum of 3.0)(Possible H2S removal/Total Possible H2S)(13,472 / 3,723) 3.6






Design Manual 2008

CHAPTER 4VACUUM MAINS

A. CONSTRUCTION ISSUES

Piping materialsThe piping network connects the individual valve pits to the collection tank atthe vacuum station. Typical sizes include 4-in, 6-in, 8-in and 10-in. pipe.

PVC thermoplastic pipe is normally used for vacuum sewers. Schedule 40 orSDR 21 PVC pipe have been used, with SDR 21 being recommended. In someEuropean installations, HDPE, MDPE and ABS have been successfully used. Incertain cases, DCIP has also been used, assuming the joints have been tested

and found suitable for vacuum service.

To reduce expansion- and contraction- induced stresses, flexible elastomeric joint ("rubber ring" joint) pipe is recommended. Where rubber ring joint pipe isused, a certificate is to be provided by the manufacturer stating that the pipehas been tested at 22” Hg vacuum in accordance with ASTM D-3139 and isguaranteed for use under vacuum conditions. AIRVAC recommends a double-lipped “Reiber style” gasket be used.

If solvent-welded joint pipe is used, the pipe manufacturer’s recommendationsfor installation regarding temperature considerations should be followed. The

Uni-Bell Handbook of PVC Pipe provides guidance as to proper practices.

FittingsPVC pressure rated fittings are needed for directional change as well as for thecrossover connections from the service line to the main line. Fittings for sewersand service laterals shall be schedule 40 pressure rated with solvent weldconnections in accordance with ASTM D-1784 and ASTM D-2466. Rubber ringgasket joints on fittings have been used successfully on some projects. Theshape of gasket on smaller pipe sizes is of critical importance.

For all pipe sizes, the engineer shall ensure that suitable fittings are available tosuit the requirements of the vacuum system.

Tee fittings shall not be used for vacuum service.

Vacuum Mains4 - 1



Design Manual 2008

Profile changes (lifts)Lifts or vertical profile changes are used to maintain shallow trench depths aswell as for uphill liquid transport (Figure 4.1). These lifts are made in a saw-tooth fashion.

SCHEDULE 40 OR

SDR 21 PVC PIPE

45° PVC SOLVENT WELD

SCHEDULE 40 PRESSURE

FITTING (TYP.)

FIGURE 4-1: LIFT DETAIL

A single lift consists of two (2) 45-degree fittings connected with a short lengthof pipe. AIRVAC recommends that lifts be made in either 1.0 ft. or 1.5 ft.increments depending on pipe size (see Table 4-13).

Location tape An inert polyethylene tape having a metallic core should be laid in the sewertrench at a depth not exceeding 18" below ground surface.

Vacuum Mains4 - 2



Design Manual 2008

Isolation Valves AIRVAC recommends an isolation valve at the beginning of each branch and onthe mainline near these branch connections. Should branch spacing exceed1500 feet, AIRVAC recommends an additional isolation valve for that section.The purpose of these valves is to isolate sections of the vacuum system fortrouble shooting purposes and the above listed standards have proven to besufficient in past years.

While both plug and resilient-wedge gate valves have been used, AIRVACrecommends the resilient-wedge gate valves.

Gauge taps A gauge tap, installed just downstream of the isolation valve, makes it possiblefor one person to troubleshoot without having to check vacuum at the station.

This reduces emergency maintenance expenses, both from a time andmanpower standpoint.

AIRVAC only recommends the use of gauge taps for entities with limitedoperating resources (ex- only 1 operator) where areas of the collection systemare not easily reached by vehicle within a few minutes time. If the system isfairly contained where the farthest reaches of the system are only minutes fromthe vacuum station and the operating entity has 2 or more operators, trucks,radios, etc., then gauge taps are of little value and are not recommended.

Cleanouts/Access Points AIRVAC does not recommend the use of cleanouts or inspection ports onvacuum lines. There are two very good reasons for this.

First, cleanouts/access points are unnecessary as access to the vacuum maincan be gained at any valve pit by removing the valve. A second, and perhapsmore important reason, is the potential they pose for vacuum leaks. Earlysystems that used them experienced as many, if not more, leaks due tocleanouts than were associated with the actual vacuum main itself.

While not required, cleanouts/access points may be used where line size

changes occur and at the end of the vacuum main.

Installation Tolerances-Open CutTolerances for open-cut trenching is typically ± 0.05’ per 100 ft, or 0.05%, for allpipe sizes. With a target slope of 0.20 %, this means the slope could vary from0.15% to 0.25%. There should be no sags or bellies in the line. Trench watershould not be allowed to enter the pipe during construction.

Vacuum Mains4 - 3



Design Manual 2008

Installation Tolerances –Horizontal Directional DrillingTolerances for directional drilling are the same as those required for opentrenching. The “minimum 50’ at 0.20% prior to a lift” rule applies to directionaldrilling just as it does to open trenching. Making a directional drill at a slopegreater than 0.20% and then immediately using a lift to make up the differenceis not acceptable.

At the time this Manual went to print, AIRVAC still had not endorsed the use ofhorizontal directional drilling, primarily due to grade control issues. This is likelyto change as some HDD companies are taking additional steps to ensure thatproper grade is attained. Table 4-1 shows AIRVAC’s requirements for HDD.

Table 4-1

AIRVAC requirements forHorizontal Directional Drilling

Item AIRVAC Requirement

Slope Installed pipe must meet AIRVAC’s slopetolerances (± 0.05’ per 100 ft)

Sags (bellies) &summits

Are not acceptable

Quality control HDD firm must be able to electronically verify

installed slopes at the time of the installationSystem integrity Installed pipe must be capable of passing

AIRVAC’s daily & final vacuum tests

Pipe materials Must mate up to AIRVAC products and othersystem components

On non-critical lines, it may be possible to actually design for slopes greaterthan 0.20% in areas where directional drilling is desired. This would not be aconstruction tolerance but rather a design decision that allows for a moreattainable slope (say 0.50%).

Incorrect slopes or sag and summits have larger negative affect when avacuum main is involved rather than when a branch or service line is involved.

An incorrect slope on a service line would affect the operation of just thatparticular service line, whereas an incorrect slope on a vacuum main wouldaffect not only that main, but all connected branch and service lines as well.

Vacuum Mains4 - 4



Design Manual 2008

Testing – Daily Test At the completion of each day's work, all sewer mains and lateral connectionslaid that day are to undergo a 2-hour vacuum test. A vacuum of 22" Hg isapplied to the pipes and a maximum loss of vacuum of 1% per hour for a two(2) hour test period is permissible. As pipe is laid the new section will be tested

in addition to the previously laid pipe on that main.

Testing – Final Test At the end of the construction period, and prior to the installation of the AIRVACvalve, the complete vacuum sewer system is to be vacuum tested. The testingprocedure is the same as the daily test, except the final test is a 4-hour test.

Again, the maximum permissible loss is 1% per hour over the four (4) hour testperiod (approximately 1” Hg loss).

B. SYSTEM LAYOUT GUIDELINES

There are four (4) major items to consider when laying out a vacuum system:

Multiple service zones: By locating the vacuum station centrally, it is possiblefor multiple vacuum mains to enter the station. This allows the service area toeffectively be divided into zones. The net result is smaller pipe sizes and lessoverall vacuum loss.

More importantly, this results in operational flexibility as well as service

reliability. With multiple service zones, the system operator can respond tosystem problems, i.e., low station vacuum, by analyzing the collection systemzone by zone to see which zone has the problem. The problem zone can thenbe isolated from the rest of the system so that normal service is possible in theunaffected zones while the problem is identified and solved.

Minimize pipe sizes: By dividing the service area into zones, the total peakflow to the station is also spread out among the various zones. This makes itpossible to minimize the pipe sizes. For example, a total peak flow of 350 gpmin system with only 1 service zone would require a 10-inch vacuum main to thestation with progressively smaller pipe toward the system extremities. By

spreading this peak flow equally over four vacuum service zones; only 6-inchand 4-inch pipe would be required.

Minimize vacuum loss: Vacuum loss is generally limited to 13 feet. Items thatcan result in vacuum loss are increased line length and elevation differences,utility conflicts and the relationship of the valve pit location to the vacuum main.The system layout should take these factors into consideration.

Vacuum Mains4 - 5



Design Manual 2008

Valve pit spacing: Another important consideration is the location of the valvepits along the vacuum main. To the designer, the valve pit is more than justthe connection point for the customer; it is an “energy input” location.

Movement of liquid within the vacuum main depends on differential pressure.The differential is created when a vacuum valve opens and allows atmosphericair to enter a vacuum main that is under a negative pressure. The only placethis can happen is where a vacuum valve exists. The fewer the energy inputsthat exist, the poorer the transport characteristics become. As a result,designers should avoid layouts that result in long stretches of vacuum main withno house connections.

C. LINE SIZING

Based on hydraulic testing, AIRVAC has established both absolute maximumflows as well as recommended maximum flows for the various main pipe sizes.Table 4-2 shows these recommendations.

Table 4-2

Maximum Flow for Various Pipe Sizes(Assuming SDR 21 pipe)

PipeDiameter

(in)

AbsoluteMaximum Flow

(gpm)

RecommendedMaximum Flow

(gpm)

4 55 386 152 1058 305 210

10 544 374

The minimum diameter for a vacuum main is 4 inches. Three (3) inch vacuumlines are only used for the service lateral (pit to main). Only one (1) valve pit

may be connected to a 3” service lateral.

The values in Table 4-2 should be used for planning purposes or as a startingpoint for the detailed design. In the latter case, estimated site-specific flowinputs along with the friction tables should be used in the hydraulic calculations.

A correctly sized line will yield a relatively small friction loss. If the next largerpipe size significantly reduces friction loss, the line was originally undersized.

Vacuum Mains4 - 6



Design Manual 2008

D. LINE LENGTHS

The length of vacuum mains is governed by two factors. These are static liftand friction losses. As discussed later in this chapter, the static loss generallyshould not exceed 13 ft and friction losses should not exceed 5 ft.

Due to restraints placed upon each design by topography and sewage flows, itis impossible to give a definite maximum line length. In perfectly flat terrain withno unusual subsurface obstacles present, a length of 10,000 ft can typically beachieved. Should there be some elevation difference to overcome, this lengthcould be shorter. On the other hand, with positive elevation toward the vacuumstation, this length could be longer. As an example, one operating system hasa single main line branch exceeding 16,500 feet in length.

Since most projects have a combination of uphill, downhill, and level sections, AIRVAC recommends that the 10,000 feet figure be used as a starting point bythe designer when doing the preliminary line layout. Any length in excess ofthis should only be considered if static and friction losses calculated during thefinal design allow for such additional length.

Guidelines for line lengths and sizes are shown in Table 4-3.

Table 4-3

Maximum Line Length for Various Pipe Sizes

Pipe Diameter(in) Where used

Maximum recommendedlength (ft)

3 Service lateral 300

4 Branch Line/endof main line

2,000

6, 8 & 10 Main Lines Limited by static & friction losses

AIRVAC engineers will be pleased to advise and assist clients with the designof the vacuum mains once topography and flow rates are available.

Vacuum Mains4 - 7



Design Manual 2008

E. MAIN LINE DESIGN PARAMETERS

Vacuum sewer design rules have been developed largely as a result of studyingoperating systems. Important design parameters are shown in Tables 4-4.

Table 4-4

Main Line Design Parameters

Minimum distance between lifts, ft 20

Minimum distance of 0.20% slope prior to a lift or series of lifts, ft 50

Minimum distance between top of lift and any service lateral, ft 6

Minimum slope 0.20%

Maximum # of lifts in a series (see page 4-29) 5

50 FT MINIMUM

SLOPE AT 0.20%SERIES OF LIFTS

DOWNHILL SLOPE

GREATER THAN 0.2%

FLOW

FIGURE 4-2: PROFILING BEFORE A SERIES OF LIFTS

Vacuum Mains4 - 8



Design Manual 2008

Slope on Vacuum MainsTable 4-5 provides general guidelines for vacuum main slopes.

Table 4- 5

Guidelines for Determining Line Slopes

Level 0.20% slope until depth is unacceptable; then use lifts

Uphill Use lifts spaced close together (see Table 4.6)

Downhill Follow ground profile when ground >0.20% slope

LAY SEWER TO A SLOPE

OF NOT LESS THAN 0.2%

UNIFORMLY WITHOUT

POCKETSFLOW

VACUUM MAIN

FIGURE 4-3: DOWNHILL TRANSPORT

Vacuum Mains4 - 9



Design Manual 2008

FLOW

0.25 FEET OR 0.2% TIMES DISTANCE

FALL BETWEEN LIFTS IS GREATER OF TWO VALUES:

0.2% SLOPE

0.2% SLOPE

VACUUM MAIN

20 FT MIN.

0.25 FT FALL (MIN)

0.25 FT FALL (MIN)

45 DEG ELLS

FIGURE 4-4: UPHILL TRANSPORT

FLOW

FALL BETWEEN LIFTS IS GREATER OF TWO VALUES:

0.2% SLOPE 0.2% SLOPE

0.25 FEET OR 0.2% TIMES DISTANCE

VACUUM MAIN

500 FT TYPICAL

FIGURE 4-5: LEVEL TRANSPORT

Vacuum Mains4 - 10



Design Manual 2008

Slope between liftsFor slope between lifts, Table 4-6 shows the distance at which the 0.20% slope,rather than the minimum fall, will govern the design for a given pipe diameter.

Table 4- 6

Slopes Between Lifts

Pipe Diameter(in)

Minimum fall between lifts*Use greater value of (A) or (B)

Distance atwhich (B) governs

(A) (B)

3 0.20 ft 0.20% x distance > 100 ft4 0.25 ft 0.20% x distance > 125 ft6 0.25 ft 0.20% x distance > 125 ft8 0.25 ft 0.20% x distance > 125 ft

10 0.25 ft 0.20% x distance > 125 ft

* When not between lifts, use 0.20% slope; distance measured in feet

F. SERVICE LATERAL (Pit to Main) DESIGN PARAMETERS

Vacuum sewer service laterals connect the vacuum main to the valve pit.Service laterals are 3 inches in diameter and are limited to one valve pit only.The type of pipe and fittings are the same as those used on the vacuum mains.

When lifts are required in the service lateralIf it is necessary to locate an AIRVAC valve with its invert lower than the main,the procedure shown in Figure 4-6 should be followed. Where this method isused, the maximum lift must not exceed the vacuum available in the main at thepoint of connection (less the five inches of mercury required for vacuum valveoperation). Lifts used must be included when calculating the system line losses.

Table 4- 7

Service Lateral Design Parameters

Maximum number of 1’- lifts in service lateral 5 eaMinimum distance from valve pit to 1

st lift 5 ft

Minimum distance from last lift to main 5 ftMinimum slope between lifts 0.20 ft or [0.2% x distance (ft)]

(whichever is larger)

Vacuum Mains4 - 11



Design Manual 2008

FIGURE 4-6: DIAGRAM OF 3” SERVICE LATERAL WITH LIFTS

Vacuum Mains4 - 12



Design Manual 2008

G. LINE CONNECTIONS

Two (2) types of connections are made to a vacuum sewer:

• Connections from a branch to a main

• Connections from a service lateral (valve pit) to either a branch or main.

“Tee” fittings are not acceptable for use in vacuum sewers, including both ofthese types of connections.

Connecting a branch to a mainSeveral configurations involving wyes and fittings have been used to connect abranch to a main. See AIRVAC’s standard details for the various methods thatexist for connecting branch vacuum sewers to vacuum mains.

In one method, connections to the main are made "over-the-top," by using awye fitting in the vertical position. Due to the restraints placed upon the depthof sewers by the connections entering "over the top", engineers should considerthe ground cover required on service laterals.

In another method, the invert to invert spacing can be reduced by rolling thewye fitting to a 45 degree angle. This method is acceptable, provided theinvert of the connecting pipe is at least 2 inches above the crown of the main.

Note that 90° ells are not allowed on branch connections. Also, where a lift orprofile change is required in a branch sewer prior to entering the main, it shouldbe made 20 or more feet from the main.

Connecting a Service lateral to a branch or mainSeveral configurations involving wyes and fittings have been used to connect avalve pit to a branch or main. See AIRVAC’s standard details which show thevarious methods that are acceptable.

A long turn 90° ell is allowed on a service lateral connection.

Vacuum Mains4 - 13



Design Manual 2008

H. LOSSES DUE TO FRICTION

Friction losses are only calculated for sewers that are laid on a downward slopebetween 0.20% and 2.0% and are cumulative for each flow path from thefurthest valve on the line to the vacuum station. Friction losses in sewersinstalled at greater than 2.0% percent are ignored.

Friction loss charts for SDR 21 PVC pipe and a 2:1 air/liquid ratio have beendeveloped by AIRVAC. These charts were based on the following formula:

F = 2.75 x 0.2083 x (100/C)1.85 x Q1.85

d4.8655

Where:F = friction loss (ft/100 ft)C = 150 for PVCQ = flow (gpm)d = inside pipe diameter (in.)

Table 4 – 8

PVC Pipe Sizes andRelated AIRVAC Design Information

C = 150

Rec’d

Design Flow

Absolute

Max FlowPipe Pipe Diameter I.D. (F=0.25) (F=0.50)Type (inches) (inches) (gpm) (gpm)

SDR 21 4 4.05 38 556 5.96 105 1528 7.76 210 305

10 9.67 374 544

SCH 40 4 4.00 37 53

6 * 6.03 108 1578 * 7.94 223 32410 * 9.98 406 591

* These sizes not recommended in Schedule 40 AIRVAC recommends SDR 21 and maximum flow based on F = 0.25

Vacuum Mains4 - 14



Design Manual 2008

Table 4-9

FRICTION LOSS TABLEFOR 4 INCH PIPE

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

2 .0011 20 .0769 38 .2520

3

4

.0023

.0039

21

22

.0841

.0917

39

40

.2644

.2771

5

6

7

.0059

.0083

.0110

23

24

25

.0995

.1077

.1161

41

42

43

.2900

.3032

.3167

8

9

10

.0141

.0175

.0213

26

27

28

.1249

.1339

.1432

44

45

46

.3305

.3445

.3588

11

12

13

.0254

.0299

.0346

29

30

31

.1582

.1627

.1729

47

48

49

.3734

.3882

.4033

14

15

16

.0397

.0451

.0509

32

33

34

.1834

.1941

.2051

50

51

52

.4187

.4343

.4502

17 .0569 35 .2164 53 .4663

1819

.0632

.06993637

.2280

.23995455

.4827

.4994

*SHADED AREAS NOT RECOMMENDED

Vacuum Mains4 - 15



Design Manual 2008

Table 4-10

FRICTION LOSS TABLE

FOR 6 INCH PIPE

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

3

4

5

.0004

.0006

.0009

31

32

33

.0264

.0280

.0296

59

60

61

.0867

.0895

.0922

6

7

8

.0013

.0017

.0022

34

35

36

.0313

.0330

.0348

62

63

64

.0951

.0979

.1008

9

10

11

.0027

.0033

.0039

37

38

39

.0366

.0384

.0403

65

66

67

.1037

.1067

.1097

12

13

14

.0046

.0053

.0061

40

41

42

.0423

.0442

.0462

68

69

70

.1128

.1159

.1190

15

16

17

.0069

.0078

.0087

43

44

45

.0483

.0504

.0525

71

72

73

.1222

.1254

.1286

18

19

20

.0096

.0107

.0117

46

47

48

.0547

.0569

.0592

74

75

76

.1319

.1352

.138521

22

23

.0128

.0140

.0152

49

50

51

.0615

.0638

.0662

77

78

79

.1419

.1454

.1488

24

25

26

.0164

.0177

.0190

52

53

54

.0687

.0711

.0736

80

81

82

.1523

.1559

.1594

27

28

29

.0204

.0218

.0233

55

56

57

.0762

.0787

.0814

83

84

85

.1631

.1667

.1704

30 .0248 58 .0840 86 .1741

Vacuum Mains4 - 16



Design Manual 2008

Table 4-10 (cont)

FRICTION LOSS TABLE

FOR 6 INCH PIPE

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

87

88

89

.1779

.1817

.1855

112

113

114

.2839

.2886

.2933

137

138

139

.4121

.4177

.4233

90

91

92

.1894

.1933

.1973

115

116

117

.2981

.3029

.3078

140

141

142

.4289

.4346

.4404

93

94

95

.2013

.2053

.2093

118

119

120

.3126

.3176

.3225

143

144

145

.4461

.4519

.4577

96

97

98

.2134

.2176

.2217

121

122

123

.3275

.3325

.3376

146

147

148

.4636

.4695

.4754

99

100

101

.2259

.2302

.2345

124

125

126

.3427

.3478

.3530

149

150

151

.4813

.4873

.4934

102

103

104

.2388

.2431

.2475

127

128

129

.3582

.3634

.3687

152

153

154

.4994

.5055

.5117105

106

.2519

.2564

130

131

.3740

.3793

107 .2609 132 .3847

108

109

110

.2654

.2700

.2746

133

134

135

.3901

.3956

.4010

111 .2792 136 .4065


Vacuum Mains4 - 17



Design Manual 2008

Table 4-11

FRICTION LOSS TABLE

FOR 8 INCH PIPE

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

85

86

87

.0471

.0481

.0492

113

114

115

.0798

.0811

.0824

141

142

143

.1202

.1217

.1233

88

89

90

.0502

.0513

.0524

116

117

118

.0837

.0851

.0864

144

145

146

.1249

.1265

.1282

91

92

93

.0534

.0545

.0556

119

120

121

.0878

.0892

.0905

147

148

149

.1298

.1314

.1331

94

95

96

.0568

.0579

.0590

122

123

124

.0919

.0933

.0947

150

151

152

.1347

.1364

.1381

97

98

99

.0602

.0613

.0625

125

126

127

.0962

.0967

.0990

153

154

155

.1398

.1415

.1432

100

101

102

.0636

.0648

.0660

128

129

130

.1005

.1019

.1034

156

157

158

.1449

.1466

.1483103

104

105

.0672

.0684

.0696

131

132

133

.1049

.1064

.1079

159

160

161

.1501

.1518

.1536

106

107

108

.0709

.0721

.0734

134

135

136

.1094

.1109

.1124

162

163

164

.1554

.1571

.1589

109

110

111

.0746

.0759

.0772

137

138

139

.1139

.1155

.1170

165

166

167

.1607

.1625

.1643

112 .0785 140 .1186 168 .1662

Vacuum Mains4 - 18



Design Manual 2008

Table 4-11 (cont)

FRICTION LOSS TABLE

FOR 8 INCH PIPE

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

169

170

171

.1680

.1698

.1717

197

198

199

.2231

.2252

.2273

225

226

227

.2853

.2876

.2900

172

173

174

.1736

.1754

.1773

200

201

202

.2294

.2315

.2337

228

229

230

.2923

.2947

.2971

175

176

177

.1792

.1811

.1830

203

204

205

.2358

.2380

.2401

231

232

233

.3995

.3019

.3043

178

179

180

.1849

.1869

.1888

206

207

208

.2423

.2445

.2467

234

235

236

.3067

.3092

.3116

181

182

.1907

.1927

209

210

.2489

.2511

237

238

.3141

.3165

183 .1947 211 .2533 239 .3190

184

185

186

.1966

.1986

.2006

212

213

214

.2555

.2578

.2600

240

241

242

.3214

.3239

.3264187

188

189

.2026

.2046

.2066

215

216

217

.2623

.2645

.2668

243

244

245

.3289

.3314

.3339

190

191

192

.2086

.2107

.2127

218

219

220

.2691

.2714

.2737

246

247

248

.3365

.3390

.3416

193

194

195

.2148

.2168

.2189

221

222

223

.2760

.2783

.2806

249

250

251

.3441

.3467

.3492

196 .2210 224 .2829 252 .3518


Vacuum Mains4 - 19



Design Manual 2008

Vacuum Mains4 - 20

Table 4-12

FRICTION LOSS TABLE

FOR 10 INCH PIPE

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)200 .0786 236 .1067 272 .1388

201 .0793 237 .1075 273 .1397

202 .0800 238 .1084 274 .1407

203 .0808 239 .1092 275 .1416

204 .0815 240 .1101 276 .1426

205 .0822 241 .1109 277 .1435

206 .0830 242 .1118 278 .1445

207 .0837 243 .1126 279 .1454

208 .0845 244 .1135 280 .1464

209 .0852 245 .1144 281 .1474

210 .0860 246 .1152 282 .1483

211 .0867 247 .1161 283 .1493

212 .0875 248 .1170 284 .1503

213 .0883 249 .1178 285 .1513

214 .0890 250 .1187 286 .1523

215 .0898 251 .1196 287 .1532

216 .0906 252 .1205 288 .1542

217 .0914 253 .1214 289 .1552

218 .0921 254 .1223 290 .1562

219 .0929 255 .1231 291 .1572

220 .0937 256 .1240 292 .1582221 .0945 257 .1249 293 .1592

222 .0953 258 .1258 294 .1602

223 .0961 259 .1267 295 .1612

224 .0969 260 .1276 296 .1623

225 .0977 261 .1286 297 .1633

226 .0985 262 .1295 298 .1643

227 .0993 263 .1304 299 .1653

228 .1001 264 .1313 300 .1663

229 .1009 265 .1322 301 .1674

230 .1017 266 .1332 302 .1684231 .1026 267 .1341 303 .1694

232 .1034 268 .1350 304 .1705

233 .1042 269 .1359 305 .1715

234 .1050 270 .1369 306 .1725

235 .1059 271 .1378 307 .1736



Design Manual 2008

Table 4-12 (cont)

FRICTION LOSS TABLE

FOR 10 INCH PIPE

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)

FLOW

(gpm)

HEAD LOSS

(ft/100 ft)308 .1746 344 .2143 380 .2576

309 .1757 345 .2154 381 .2588

310 .1767 346 .2166 382 .2601

311 .1778 347 .2177 383 .2614

312 .1789 348 .2189 384 .2626

313 .1799 349 .2201 385 .2639

314 .1810 350 .2212 386 .2652

315 .1821 351 .2224 387 .2664

316 .1831 352 .2236 388 .2677

317 .1842 353 .2247 389 .2690

318 .1853 354 .2259 390 .2703

319 .1863 355 .2271 391 .2715

320 .1874 356 .2283 392 .2728

321 .1885 357 .2295 393 .2741

322 .1896 358 .2307 394 .2754

323 .1907 359 .2319 395 .2767

324 .1918 360 .2331 396 .2780

325 .1929 361 .2343 397 .2793

326 .1940 362 .2355 398 .2806

327 .1951 363 .2367 399 .2819

328 .1962 364 .2379 400 .2832329 .1973 365 .2391 401 .2845

330 .1984 366 .2403 402 .2858

331 .1995 367 .2415 403 .2872

332 .2006 368 .2427 404 .2885

333 .2018 369 .2440 405 .2898

334 .2029 370 .2452 410 .2965

335 .2040 371 .2464 415 .3032

336 .2051 372 .2476 420 .3100

337 .2063 373 .2489 425 .3172

338 .2074 374 .2501 430 .3238339 .2085 375 .2513 435 .3308

340 .2097 376 .2526 440 .3378

341 .2108 377 .2538 445 .3450

342 .2120 378 .2551 450 .3522

343 .2131 379 .2563 455 .3594


Vacuum Mains4 -21



PROJECT IRV

r PROJECT # S

LINE AIR/LIQUID MAX FLOW D

STATION

TOSTATION

LINELENGTH

QMEAN

Q ACC'M

FRICT100'

FRICT

LOSSLINE

FRICT

LOSS ACCUM

STATIC

LOSSLINE

STATIC

LOSS ACCUM

PIPE SIZ

4" 6" 8"

V a c u um M ai n s

4 -2 2

FIGURE 4-7: FRICTION LOSS CALCULATION SHEET



Design Manual 2008

I. LOSSES DUE TO LIFTS (STATIC LOSS)

Operating vacuum ranges of 16 to 20 inches of mercury are typical for mostmodern vacuum systems. While deeper vacuum ranges are attainable, thisrange is generally considered the most practical in terms of equipmentoperating cost and dependability.

When considering the limit of water lifted by a vacuum, it is common to think interms of a water manometer in which the liquid is lifted in a vertical column.The height of this column is in direct proportion to the difference betweenavailable atmospheric pressure and the sub-atmospheric pressure within thevacuum.

Basis of DesignIn an AIRVAC vacuum system, the lower operating level of 16-in mercuryvacuum pressure is used as the basis of system hydraulic design. In this case,a vertical column of liquid could be suspended 18 feet at sea level (1" Hg =1.13’ water).

Five (5) feet of this liquid column must be reserved for the vacuum valveoperation and sump liquid evacuation. This results in 13 feet of liquid availablefor transportation within a vacuum system (Figure 4-8).

NORMAL OPERATING RANGE

18' TOTAL AVAILABLE LIFT (AT LOW END)

-5' REQ'D FOR VALVE OPERATION

13' AVAIL. FOR SEWAGE TRANSPORT

16" HG = 18' H O2

20" HG = 23' H O2

230" HG = 34' H O

VACUUM PUMP

FIGURE 4-8: VACUUM LIFT CAPABILITY

Vacuum Mains4 - 23





Design Manual 2008

Observations from in-house hydraulic studies

The idea behind the AIRVAC saw-tooth profile is to maintain an openpassageway throughout the top portion of the piping network. If this is the case,the same level of vacuum will be present at the end of the system as exists atthe vacuum station.

The AIRVAC system operates on the concept of moving a mixture of air andliquid only part of its intended travel distance. As propulsive forces arediminished, the liquid and air will separate and the liquid will come to rest at lowpoints within the system. Subsequent AIRVAC valve cycles will then boost thisliquid downstream to a new low point and the process repeats itself until theliquid enters the vacuum station.

In reality, the only time a vacuum loss occurs is when liquid is suspended withina vertical lift or when it is in motion; rarely will these events occursimultaneously.

Whether or not liquid is suspended in lifts is a function of many factors: pipediameter, pipe slope, air-to-liquid ratio, number of valves opening at a givenmoment, and so on. The distance liquid travels, is also a function of manyfactors.

Due to the uncertainty of predicting the exact occurrence of so many variables,previous design limits have been based on the worst-case scenario, that is, thatall lifts are completely filled or saturated.

Substantial data has been gathered from operating vacuum systems in an effortto more accurately predict exactly where and when these variables will occur.While these studies remain on-going, it has become obvious that theoccurrence of lift saturation is rare and normally associated with a temporary airto liquid imbalance.

The ability of a vacuum system to automatically recover from such animbalance (thereby restoring normal vacuum to line extremities) is the actuallimit of vacuum line design. During these brief periods, it has been shown thatall losses within the system are associated with suspended liquid with very littlefriction loss occurring. This is also supported by the fact that little or no flow

takes place.

Vacuum Mains4 - 25



Design Manual 2008

Recommended static loss limitsEmpirical studies currently indicate that system performance may be groupedas follows:

Table 4-14

Static & Friction Losses: Design Guidelines

GroupStatic

Loss (ft)FrictionLoss (ft)

Operation duringNormal conditions

Recovery from temporary A/L imbalance

A 0.0 -13.0 5 Dependable Automatic recovery withoutdisruption of service

B 13.1- 16.0 5 Dependable if

a) high static loss is limitedto 1 or 2 branches &

b) optimum placement ofvalves and lifts are

considered

Automatic recovery withmomentary low vacuum at

line extremities

C > 16.0 5 Reasonably dependable if :

a) high static loss is limitedto 1 or 2 branches &

b) optimum placement ofvalves and lifts are

considered

Recovery relies on theinjection of atmospheric air at

selected points to restoreadequate vacuum to line

extremities

AIRVAC recommends that systems be designed with the guidelines stated ingroup A:

13 Feet of Vacuum Loss due to Li fts5 Feet of Vacuum Loss due to Friction

The static loss and friction losses are separate calculations and are asummation of losses for each flow path. Simply stated, a flow path is the pipingthrough which liquid will travel from the last AIRVAC valve to the vacuumstation.

AIRVAC should be consul ted for any design fo llowing the guidelines ofgroup B or C.

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Design Manual 2008

Widespread use of deep valve pitFor any single flow path where more than 25% of the valve pits are of the deepvariety (8’ and/or 10’ deep pits), the allowable static loss of that vacuum mainmay need to be reduced from 13 ft. to a lower amount to account for theadditional lift within the valve pit. Consult AIRVAC’s Engineering Departmentfor details.

Electronic Air Admission Control (EAAC)The Electronic Air Admission Control (EAAC) is an accessory for a typical 3”

AIRVAC vacuum valve. This device monitors line vacuum and will open ifvacuum falls below a pre-set limit for an extended period of time. The openingof this valve injects large quantities of atmospheric air to boost liquid throughvarious lifts and downstream towards the vacuum station. The end result is anincrease of available vacuum for valve operation.

The primary purpose of the EAAC is to improve the transport characteristics of

a system that is already in operation. Occasionally, this device can be includedas a design feature when static losses are slightly in excess of therecommended 13 feet. In these cases, the EAAC device may be needed toinsure adequate vacuum is available for those particular sections of vacuumlines where the 13 ft limit has been exceeded. NOTE: Minimum vacuumpump capacity when utilizing EAAC units is 305 acfm.

Since there are limits to the use of these devices, AIRVAC should be involvedin the placement and parameters for their use.

J. PIPE VOLUME

It is necessary to calculate the total connected pipe volume, expressed ingallons, for use in the vacuum pump sizing process (see Chapter 3). Table 4-15shows the pipe volume per lineal foot for the various pipe sizes based on the IDof SDR 21 pipe. Multiply these factors by the length of pipe and then by 7.48 toconvert to pipe volume in gallons.

Table 4-15

Pipe Volume per Linear FootFor Various Pipe Sizes

Pipe Diameter Volume per foot (ft3/ft)

3” 0.0547

4” 0.0904

6” 0.1959

8” 0.3321

10” 0.5095

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Design Manual 2008


STATION NUMBER DATE

LINE4"

PIPE6"

PIPE8"

PIPE10"

PIPE PEAKNUMBERSERVICE

LATERALS

NUMBER AIRVAC

VALVES

HOMES

TOTALS

AVERAGE

SERVICE LATERAL

LENGTH

TOTAL3” PIPE

(VOLUME OF PIPEWORK: BASED ON SDR-21 PVC PIPE)

Vp = (.0547 x Length 3") + (.0904 x Length 4") + (.1959 x Length 6") +

(.3321 x Length 8") + (.5095 x Length 10") ft3

Vp = ( + + + + ) ft3

Vp = 7.48 gal/ft3 x ( ) ft3 = gal

2/3 Vp = gal

FIGURE 4-10: PIPE VOLUME CALCULATION SHEET

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Design Manual 2008

K. SUMMARY OF VACUUM MAIN DESIGN FUNDAMENTALS

1. SLOPES:

a. Use natural ground slope if greater than 0.2%b. Use 0.2% slope for flat terrainc. Use saw tooth profile for uphill transportd. Use 0.2% slope at 50’ minimum prior to first lift in any series

2. FALL BETWEEN LIFTS: Use larger of two (2) values

a. 0.20% x Lengthb. 0.20 ft. Fall for 3" Service Lines if lifts are less than 100 lf apart.c. 0.25 ft. Fall for ALL Vacuum Mains if lifts are less than 125 lf

apart.

3. LIFTS:

a. Use 1’-0” for 3” or 4” pipeb. Use 1’-6” for 6” or larger pipec. Static loss = Lift Height - Pipe Diameterd. Maximum vacuum loss due to lifts from any AIRVAC valve to the

vacuum station = (13 ft Static Loss + 5 ft Friction Loss)e. Maximum series of lifts = 5. Separate one series of 5 lifts from the

next lift or series of lifts by at least 100 ft of vacuum main. Inaddition, there must be at least 1 energy input in the zone ofseparation.

f. First lift on a branch minimum 20 lf from connection to main.

4. CONNECTIONS:

a. Use wye connectors for all branch and lateral connectors, wye

may be vertical or at 45° angle

b. Use long sweep 90° ell for 3” service connectors only

c. Use 45° ells for 4” and larger connectors and any directionalchange

d. Recommended minimum Invert to Invert elevation difference forconnections:

4 x 3 = 0.66 ft 6 x 3 = 0.84 ft 8 x 3 = 1.40 ft4 x 4 = 0.71 ft 6 x 4 = 0.85 ft 8 x 4 = 1.40 ft

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Design Manual 2008

5. FLOW LIMITS: (Maximum Friction Loss not to exceed 5 ft)

3” = 3 gpm4” = 38 gpm6” = 106 gpm8” = 210 gpm

10” = 375 gpm

6. MAXIMUM LINE LENGTHS:

3” = 300 lf4” = 2,000 lf6” & Larger determined by static limits

7. PIPE VOLUMES

Pipe Size Volume per foot (vf) ft /ft

3 inches .0547

4 inches .0904

6 inches .1959

8 inches .3321

10 inches .5095

Volume in a specific size of pipe is determined by multiplying the lengthof pipe by the appropriate vf factor above: L x vf = ft3

The volume of 300 lf of 6” pipe is therefore: 300 x .1959 = 58.77 ft 3.

8. ISOLATION VALVES

a. Place a line isolation or division valve for each branch vacuum sewernear its connection to main line.

b. Place isolation or division valves for main lines at 1500-foot centers ornear branch connection.

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Design Manual 2008

CHAPTER 5VALVE PITS

A. VALVE PIT ARRANGEMENTS

Pit typesTable 5-1 shows the various AIRVAC valve pit arrangements that are available.

AIRVAC recommends the use of the 1-piece PE pits for most projects. Insituations where deeper pits are required, the 3-piece fiberglass pits are used.

Table 5-1

AIRVAC Valve Pit TypesPit

Type AIRVACModel No

PitDepth

PitDescription

RecommendedMaximum # Conn

Shallow VP3030WT 5.0 ft PE 1-piece 2

Shallow VP3030 5.0 ft Fiberglass 3-piece 2

Standard VP4830WT 6.5 ft PE 1-piece 4

Standard VP3042T 6.0 ft Fiberglass 3-piece 4

Deep VP5442 8.0 ft Fiberglass 3-piece 4

Extended VP5466 10.0 ft Fiberglass 3-piece 4

1. Maximum combined peak flow to these valve pit types is limited to 3 gpm.

2. The sumps to these valve pit types can physically accept up to 4 incominglines, subject to the 3 gpm maximum (see Note 3).

3. If a Dedicated Air Terminal (DAT) is used, one of the 4 sump openings mustbe reserved for that purpose, reducing the maximum possible # of

connections from 4 to 3. The manifolding of a building sewer to the DAToutside the sump is not permitted (See page 5-17).

4. One or more 1 ft extension pieces can be added to any valve pit. Extending inthis manner will result in the valve residing lower in the upper chamber.

For larger water users with peak flows in excess of 3 gpm, see Chapter 6(Buffer Tanks).

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Design Manual 2008

Pit sharing Up to four separate building sewers can be connected to one sump, each at 90degrees to one another. However, this is rarely done as property linesconsiderations and other factors may render this impractical.

By far, the most common valve pit sharing arrangement is for two adjacenthouses to share a single valve pit. In certain cases, such as a cul-de-sac orwhen small lots exists, it may be possible to serve 3 or even 4 houses with asingle valve pit; however, all other design factors, such as limiting peak flow to 3gpm must be considered.

FIGURE 5-16.5’ AIRVAC VALVE PIT

PE 1-PIECE PIT

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Design Manual 2008

FIGURE 5-26’ AIRVAC VALVE PIT

FIBERGLASS 3-PIECE PIT

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Design Manual 2008

B. COMPONENTS COMMON TO BOTH PIT TYPES

3” ValveThe AIRVAC valve is vacuum operated on opening and spring assisted onclosing. System vacuum ensures positive valve seating. The valve has a 3-inch full-port opening, is made of glass filled polypropylene, and has a stainlesssteel shaft, delrin bearing and elastomer seals.

The valve is equipped with a rolling diaphragm-type vacuum operator and iscapable of overcoming all sealing forces; and of opening using vacuum from thedownstream side of the valve. All materials of the valve are chemically resistantto normal domestic sewage constituents and gases.

The AIRVAC 3” valve and controller combination requires 5 in. Hg vacuum foroperation and to avoid low air-to-liquid ratios. The lower the vacuum level, theless differential (atmospheric pressure to line vacuum) exists. This equates toless air entering the system resulting in lower line velocities and sluggish flowcharacteristics.

Valve capacity: Chapter 6 contains a detailed discussion of the 30 gpm ratedcapacity of the AIRVAC 3" valve and when that capacity is possible. It is veryimportant to note that the rated capacity of the valve is not to be confusedwith the recommended design capacity of the valve pits.

To ensure proper air-to-liquid ratios, AIRVAC recommends a maximum peakflow of 3 gpm be used for all valve pits serving residential customers. Buffertanks may be sized using higher design capacities. Table 5-1 shows therecommended maximum # of connections for the various pit types.

Size: Many states do not have vacuum sewer regulations. Some of those thatdo, apply concepts of the Ten State Standards that advocate the ability to passa 3” solid through any part of a sewage collection and treatment system. Inaddition, some plumbing codes have provisions that to prohibit restrictions less

than 3” downstream of any toilet.

To be consistent with industry standards, AIRVAC’s vacuum valve wasdesigned to be a full-port 3” valve capable of passing a 3” solid while matchingthe outside diameter of 3” PVC SDR pipe.

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Design Manual 2008

Pressure loss through the interface valve: The driving force in a vacuumsystem is the pressure differential that exists between atmosphere and vacuumin the system. This differential occurs when the valve opens. As a result, theonly place to impart energy in a vacuum system is at the valve itself. Any lossthrough the valve further depletes this energy resulting in less available fortransport within the pipeline. This is especially critical considering that this lossoccurs at every valve and during each valve cycle.

The flow coefficient (Cv factor) is that flow rate in gpm which would yield a headloss of 1 psi. The AIRVAC valve is produced with an internal geometry thatkeeps friction loss to an absolute minimum, having a Cv factor of 268.

ControllerThe controller/sensor is the key component of the valve. The device relies onthree forces for its operation: pressure, vacuum, and atmosphere. As thesewage level rises in the sump, it compresses air in the sensor tube. This

pressure initiates the opening of the valve by overcoming spring tension in thecontroller and activates a three-way valve. Once opened, the three-way valveallows the controller/sensor to take vacuum from the downstream side of thevalve and apply it to the actuator chamber to fully open the valve. Thecontroller/sensor is capable of maintaining the valve fully open for a fixed periodof time, which is adjustable over a range of 3 to 10 seconds. After the presettime period has elapsed, atmospheric air is admitted to the actuator chamberpermitting spring assisted closing of the valve.

The AIRVAC vacuum valve controller is chemically resistant to sewage andsewage gases and is capable of operating when submerged in water. It was

designed to give consistent timing as set by the system operator. The AIRVACvalve pit was also designed so that a very repeatable, specific amount of liquidis withdrawn on each cycle (10 gallons). With a consistent amount of air and aspecific amount of liquid, the air-to-liquid ratio is kept consistent.

In-sump breatherThe controller requires a source of atmospheric air to the actuator chamberpermitting spring assisted closing of the vacuum valve. Without this air, thevalve would remain in the open position. The in-sump breather usesatmospheric air from the sump and its associated 4” gravity building sewer and4” air intake (or the optional 6” dedicated air-terminal). The in-sump breather is

designed to protect the controller from unwanted liquid during system shut-downs and restarts. It also prevents sump pressure from forcing the valve toopen during low vacuum conditions and provides positive sump ventingregardless of traps in the gravity service line.

Note: Conceptually the in-sump breather provides the same function for bothstyles of valve pits; however, in the 1-piece pit the in-sump breather iscombined with the 2” sensor line as a single unit.

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Design Manual 2008

Flexible Service LateralThe contractor must be careful when making the connection between the valvepit and the vacuum main. The difficulty arises when the contractor must connecttwo fixed points at different locations/elevations with rigid, solvent-welded pipe.Many times this requires multiple fittings, some of which may be deflectedbeyond an acceptable range. In certain cases, this can result in either avacuum leak, or worse, a line break caused by overstressing of the joint.

The AIRVAC Flexible Service Lateral, which uses 3" flexible PVC hose,eliminates this problem. Connections at both ends of the flexible service lateralare the same as with PVC pipe. The use of a flexible service lateral virtuallyeliminates stress-related leaks caused by poor workmanship or groundsettlement.

FIGURE 5-3: AIRVAC FLEXIBLE SERVICE LATERAL

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Design Manual 2008

Stub-OutTo minimize the risk of damage to the fiberglass valve pit during homeownerconnection to the system, a stub-out pipe of sufficient length, typically 6 ft. fromthe valve pit, is recommended. The orientation of the valve pit as it relates tothe house and the wye connection varies according to the number ofconnections to the pit (see Figure 5-4).

If the building sewer piping network does not have a cleanout within it, oneshould be placed outside and close to the home. Some agencies prefer havinga cleanout at the dividing line to establish the point at which the agency’smaintenance begins. This typically would be at the end of the stub-out pipe.

5' MIN.

SERVING 2 HOUSES

45°

SERVING 1 HOUSE

6' MIN. LENGTH GRAVITYSERVICE LATERAL WITH

GLUED CAP

5 ' M I N

.

RIGHT-OF-WAY

PRIVATE YARD

FLOW

VACUUM MAIN

VALVE PIT

ASSEMBLY

45°

FIGURE 5-4: TYPICAL CONFIGURATIONSFOR GRAVITY CONNECTIONS

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Design Manual 2008

Valve pit covers: traffic ratedCast iron covers and frames, designed for H-20 traffic loading, are typicallyused for all valve pit installations. For traffic-rated covers, the frame weight isgenerally 90 lbs. and the lid weight about 100 lbs.

AIRVAC recommends that concrete collars be used for all AIRVAC valve pitslocated in traffic areas. The actual design of the concrete collar is theresponsibility of the Design Engineer. In addition, the Design Engineer’s mustclearly define “traffic areas” on their construction drawings and/or specifications.

Unless otherwise specified, the words “AIRVAC SEWER” in 1” tall lettering willbe used on the cover.

Contact AIRVAC’s engineering department for a list of vendors that supplytraffic-rated frames and covers that match AIRVAC’s valve pits.

Valve pit covers: non-traffic ratedWhen a lighter lid is desired, as in non-traffic situations, a lightweight aluminumor cast iron lid may be used. These lids should clearly be marked "Non-Traffic".

For consistency reasons, AIRVAC does not recommend the use of non-trafficcovers if there are only a few isolated cases in the project where a non-traffic lidcan used.

Contact AIRVAC’s engineering department for a list of vendors that supply non-

traffic rated frames and covers that match AIRVAC’s valve pits.

Valve pit covers-pick holes & sealsThe type of lid used varies according to which AIRVAC valve pit (1-piece or 3-piece) is used:

• Covers for the 1-piece pit have a concealed pick hole and elastomerseals.

• Covers for the 3-piece pit have an open pick hole and no elastomer

seals.

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Design Manual 2008

C. VALVE PIT COMPONENTS: PE 1-PIECE PITS

Figure 5-5 shows the AIRVAC PE 1-piece valve pit assembly.

FIGURE 5-5VALVE PIT COMPONENTS

PE 1-PIECE PIT

INTEGRAL ANTI-

BUOYANCYCOLLAR

SUCTION PIPE

IN-SUMPBREATHER/

SENSOR PIPE

1-PIECE PIT

3" VALVE

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Design Manual 2008

1-Piece PitThe 1-piece pit is manufactured by the rotational molding process using PE withan integral upper valve chamber, lower collection sump and anti-buoyancycollar. The wall thickness of the entire unit is ½” in order to be suitable for H-20traffic loading.

The upper chamber houses the vacuum valve, controller and in-sump breatherwith a 36” inside diameter at the bottom and is conically shaped to allow fitting a26 ¾” frame with a 23 ½” diameter clear opening cast iron cover. The upperchamber includes a 3” vacuum service lateral pipe support with rubber o-ringseal to insure proper pipe alignment with the valve/suction pipe. Both the 5’and 6.5’ deep pit have an upper chamber depth of 30”.

The lower chamber contains 4 stabilizing embosses to support the valve pit andis designed to allow up to (4) houses to be connected with either 4” or 6”pressure rated Sch 40, SDR 21 or SDR 26 PVC pipe. Elastomer connections

are used for the entry of the building sewer. Holes for the building sewers arefield cut at the position directed by the engineer. The 5’ deep pit has a lowercollection sump depth of 30” and a capacity of 57 gallons, while the 6.5’ deeppit has a lower collection sump depth of 48” and a capacity of 115 gal.

In-Sump Breather/Sensor PipeThe 2” sensor pipe is incorporated into the sump-breather and the unit has atwist lock mechanism to mate with the hole that connects the upper and lowerchambers.

Suction PipeThe 3” suction pipe is PE and also has a twist lock mechanism to mate with thehole that connects the upper and lower chambers.

Integral Anti-Buoyancy CollarsThe AIRVAC 1-piece valve pit has a factory installed integral PE anti-buoyancycollar.

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Design Manual 2008

D. VALVE PIT COMPONENTS: FIBERGLASS 3-PIECE PITS

Figure 5-6 shows the AIRVAC fiberglass 3-piece valve pit assembly. The 3major pieces are the valve pit cone, the pit bottom and the sump.

FIGURE 5-6VALVE PIT COMPONENTSFIBERGLASS 3-PIECE PIT

3" VALVE

STUB-OUT

ANTI-BUOYANCYCOLLAR

PIT BOTTOM

IN-SUMPBREATHER

SENSOR PIPESUMP

SUCTON PIPE

VALVE PITCONE

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Design Manual 2008

Valve Pit ConeThe valve pit cone houses the vacuum valve, controller and in-sump breather.It is fabricated with filament-wound fiberglass with a wall thickness of 3/16" inorder to be suitable for H-20 traffic loading. The valve pit is 36" in diameter atthe bottom and is conically shaped to allow the fitting of a 23 ½" diameter clearopening cast iron frame and cover at the top. Depths are normally 42". One 3"diameter opening, with an elastomer seal, is pre-cut to accept the 3" vacuumservice line.

Pit BottomThe pit bottom is made from the reaction injection molding process (RIM) usingheavy duty liquid molding resin polymer. The pit bottom has a nominalthickness of .320”, with .500” reinforcing ribs.

The pit bottom is provided with holes pre-cut for the 3" suction line, 4"cleanout/sensor line (later sealed by grommets), the in-sump breather and 16

stainless steel sump-securing bolts. A factory supplied elastomer o-ringprovides a watertight seal between the pit bottom and the sump. The pit bottomhas a lip that allows the valve pit to fit perfectly centered on top of the sump/pitbottom. While groundwater can enter the valve pit cone area, the seal betweenthe pit bottom and sump prevents any extraneous water from entering thesump.

SumpThe sump has a wall thickness of 3/16" and is designed for H-20 traffic loadingwith 2 ft. of cover. Elastomer connections are used for the entry of the building

sewer. Holes for the building sewers are field cut at the position directed by theengineer. The sumps employed thus far have two different heights: 30" and54". Both are 18" in diameter at the bottom and 36" in diameter at the top, withthe smaller size having a capacity of 55 gallons and the larger one 100 gallons.

In-Sump BreatherThe controller requires a source of atmospheric air to the actuator chamberpermitting spring assisted closing of the vacuum valve. Without this air, thevalve would remain in the open position.

The in-sump breather uses atmospheric air from the sump and its associated 4”gravity building sewer and 4” air intake (or the optional 6” dedicated air-terminal). The in-sump breather is designed to protect the controller fromunwanted liquid during system shut-downs and restarts. It also prevents sumppressure from forcing the valve to open during low vacuum conditions andprovides positive sump venting regardless of traps in the gravity service line.

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Design Manual 2008

Suction & Sensor PipesBoth the 3” suction pipe and the 2” sensor pipe are Sch 40 PVC and areinstalled through grommets in the pit bottom.

Anti-Buoyancy Collars AIRVAC fiberglass anti-buoyancy collars are sometimes used on the fiberglassvalve pit settings (see Fig 5-7). The designer should perform buoyancycalculations to see if they are necessary. These collars fit around the taperedvalve pit and rely on soil burden to keep the pit from floating.

53" NOMINAL

5 3 " N O M I N A L

36" DIAMETER

(+/- 1/8")

5" RADIUS

4 CORNERS

VALVE PIT

COMPACTED

SELECT FILL

COMPACTED

GRANULAR FILL

1/2" THICK

FRP RESIN

TOP VIEW ELEVATION VIEW

FIGURE 5-7: AIRVAC ANTI-BUOYANCY COLLAR

Anti-buoyancy collars consisted of mass concrete rings are not recommended.These concrete rings required care be taken during the valve pit installation aspoor bedding and backfill could lead to settlement problems. Settlement of theconcrete ring most likely will coincide with damage to the building sewer and/orthe pit itself.

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Design Manual 2008

E. BUILDING SEWER (House to Pit)

Building SewerThe term building sewer refers to the gravity flow pipe extending from the hometo the valve pit setting. This includes the pipe in private property as well as inthe public right-of-way (i.e. – the stub-out). In many cases, state or localauthorities regulate installations of building sewers.

For residential service, the building sewer should be 4" and slope continuouslydownward at a rate of not less than 0.25-in/ft (2-percent grade). Line size forcommercial users will depend on the amount of flow and local coderequirements.

AIRVAC recommends that pressure rated pipe be used for the building sewer.There are two reasons for this. First, the pipe OD must match the valve pit inletgrommet to prevent the entrance of I/I in to the valve pit sump. Second, thebuilding sewer may be exposed to high vacuum at times. Under normalconditions, these vacuum levels would be low (5-10 in. Hg) and would occur for

just a short duration (the 3-5 second valve cycle). However, should the air-intake be blocked and the vacuum valve fail in the open position at the sametime, the building sewer could see the full system vacuum of 20 in. of Hg.

AIRVAC also recommends that pressure rated fittings be used for the stub-outpipe portion of the building sewer that is located in the public right-of-way.

Table 5-2 shows AIRVAC’s recommendations. These recommendations

assume that the pipe is also in compliance with all applicable codes.

4” Air Intake An air intake, consisting of 4" PVC pipe, fittings and a screen (Figure 5-8), isrequired for each building sewer. Its purpose is to provide a sufficient amountof air to enter into the service line and vacuum main to act as the driving forcebehind the liquid that is evacuated from the sump.

The house vent may not be used in place of an air intake. While it may providethe necessary air, its location could result in the house plumbing traps being

evacuated during a valve cycle. For this reason, the air intake must be locateddownstream of the last house plumbing trap.

The use of a check valve within the air intake mechanism itself is notrecommended as this will result in problems with the traps inside the house.

Most plumbing-code enforcement entities require the air intake to be locatedagainst a permanent structure, such as the house or a wall.

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Design Manual 2008

FIGURE 5-8: 4” AIR INTAKE

FIGURE 5-9: OPTIONAL 6” DEDICATED AIR-TERMINAL

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Design Manual 2008

Optional 6” Dedicated Air-Terminal As an alternative to requiring each house to have a 4” air-intake on theirbuilding sewer, the AIRVAC’s molded 6” Dedicated Air Terminal (DAT) may beused at each valve pit instead. The DAT was designed to look like other utilityboxes/structures typically seen in rights-of-way. Testing indicates that using the6” DAT results in a much more effective method of air induction than using thecombined air/sewage method associated with the 4” air intakes. Otheradvantages include:

1) The DAT’s use eliminates the need for the unsightly 4” air-intake in thehomeowner’s gravity piping that is located either next to the house or inthe middle of the yard.

2) Eliminates the possibility of vacuum emptying home plumbing traps.

3) Allows the valve pit to be put into service before any home gravity

laterals are installed (see NOTE). This also relieves the fear of possiblepit implosion that could occur when a valve is installed without thehomeowner’s 4” air-intake in place.

4) Provides a mounting point for future valve pit options such as valveCycle Counter, Alarm Monitoring Systems, or valve breather.

5) Allows for the use of a normally-opened backwater valve preventiondevice on home gravity laterals without the design or installationrestrictions associated with normally closed backwater valves used onvacuum systems.

6) Eliminates any adverse effects on the valve operation associated withimproper gravity lateral installations (improper fall, belly in piping).

7) Prevents municipalities from becoming involved with problem diagnosisrelating to improper gravity lateral installations. As long as the valve pitfunctions properly, any other problem is the homeowner’s responsibility.

If a Dedicated Air Terminal (DAT) is used, one of the 4 sump openings must bereserved for that purpose. The manifolding of a building sewer to the DAT

outside the sump is not permitted. This reduces the possible number ofconnections to the valve pit from 4 to 3.

After the vacuum system has been installed and passed the final test the AIRVAC Valves may be installed and put into service. The system vacuummust be maintained in service once the valves are installed. This is the onlyapproved method of valve installation before home gravity connectioninstallation that retains the AIRVAC product warranty.

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Design Manual 2008

Proper Time to Install the Vacuum ValveUnless the optional 6” Dedicated Air Terminal is used, the AIRVAC vacuumvalve should be installed only after the homeowner has connected thebuilding sewer to the stub-out at the valve pit. (See Figures 5-10 & 5-11) andthe 4” air intake is in place. The normal sequence of events is as follows:

• Contractor installs lines and pits

• Contractor conducts final 4 hour test on lines & station

• Contractor flushes vacuum mains

• The system is accepted by the operating entity

• Homeowner’s plumber installs building sewer and the 4” air intake

• Operating entity installs the vacuum valve

Potential Problems if Valve is installed During ConstructionThe desire to have a complete system has led some design engineers torequire the system installation Contractor to actually install the AIRVAC vacuumvalve during the construction period. AIRVAC does not recommend thisprocedure as this can result in some very serious problems as described below:

Pit collapse/implosion: Cycling the AIRVAC valve without the homeowner’slateral and 4” air intake installed can cause bottom sump to implode. This wouldrequire the pit to be re-excavated and replaced. This not only is costly, butfinger-pointing on who is to blame will surely ensue.

Homeowner may illegally hook-up early: Knowing that a complete system isavailable, the homeowner could connect to the valve pit without the Owner’sknowledge. This action would preclude the Owner from doing the normalinspection of the homeowner’s gravity lateral, air intake, etc. Again, this couldlead to some serious problems such as I&I, water in the controller, etc.

Valve may be improperly installed: It is conceivable that the Contractor mayconnect hoses to the wrong port, fail to tighten all hose clamps, fail to adjust thecontroller timing properly, etc. Any of these could severely affect the operationof the system.

Valve timing may be improper (timing is site specific): The timing of thevalves is a major concern. Each valve needs to be adjusted differentlyaccording to its location within the system. AIRVAC believes that it is expectingtoo much for the Contractor to know how to balance the system by properlytiming each valve. The Contractor cannot be expected to be a vacuum expert.The valve should be properly installed and timed by someone who has beentrained to do so…either the system operator or AIRVAC personnel.

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Design Manual 2008

FIGURE 5-10: VALVE PIT INSTALLATIONPRIOR TO HOME HOOK-UP

FIGURE 5-11: VALVE PIT INSTALLATION AFTER HOME HOOK-UP

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Design Manual 2008

Backwater ValvesSome entities prefer the use of backwater valves on the homeowner's buildingsewer in order to provide sewage backup protection for houses that share avalve pit. This is especially true when the houses are at different elevations.

For the typical “normally closed” type backwater valve, positioning is critical. Ifnot installed between the home and the gravity air intake pipe, the AIRVACvalve will not operate.

AIRVAC recommends backwater valves that are designed to be “normallyopened”. Positioning is not an issue for this type of valve and they have provento have superior performance when used in a vacuum system.

In any case, AIRVAC should be consulted before such a device is installed.

Grease TrapsState and local codes typically require grease traps for restaurants, hotels orany other establishment that serves meals. These are simple devices, usuallyplaced in the kitchen floor that are designed to provide retention time for greaseto cool and solidify so that it can be removed before it enters the sewer system.

Grease that is allowed to enter and solidify in a valve pit can cause problemswith the operation of the valve. The most common problem would be greasethat enters the sensor pipe and later accumulates between the surgesuppressor and controller. Grease in this area would not allow the free flow ofair necessary for valve closure. The result would be a valve that does not

close.

In general, grease is rarely a problem with the standard AIRVAC valve pit. It ismore likely to be a problem in a buffer tanks as these are used to serve the typeof commercial establishments where grease can be a problem.

AIRVAC recommends that the sewer authority require all customers to followcodes regarding the installation of grease traps.

Connection via a Pump

AIRVAC does not recommend connecting a grinder pump or lift station directlyto an AIRVAC valve pit. Instead, a transitional manhole should be used as aninterface between pressure and vacuum. As an option, a buffer tank can beused for this transition.

If there is no other practical way to serve a customer other than connecting apump directly to an AIRVAC valve pit, please contact AIRVAC’s EngineeringDepartment for guidance.

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Valve Pits5 - 21

D. DO’S AND DON’TS

Table 5-3

Do’s and Don’ts: Valve Pits

DON’T DO THIS: DO THIS:

Connect more than 4 homes to a single valvepit

Use a 2:1 ratio as a standard and carefullyanalyze where service to 3 or 4 homes is

feasible

Exceed a peak flow rate of 3 gpm for a singlevalve pit

Limit peak flow to 3 gpm for a single valve pitUse buffer tanks for higher flows

Allow infiltration in the homeowner’s buildingsewer

Ensure building sewer meets specification andis inspected by the local authority

Connect any home or other establishmentswith storm systems attached

Ensure no downspouts, sump pumps, cisternsor other storm water receptacle are connected

Use non-pressure pipe & fittings for stub-outsor building sewers

Use pressure rated pipe & fittings for stub-outsand building sewers as shown on Table 5-2

Allow bellies in the building sewer which couldfill with liquid and block off air

Inspect the building sewer prior to pipe burialto ensure no bellies exist

Combine sewage and air by manifolding abuilding sewer to the 6” Dedicated Air-

Terminal

Use the 6” Dedicated Air-Terminal as an “air-only” device

Allow installation of the 3” interface valve untilthe 4” air intake is in place

Install 4” air intake prior to the valveinstallation

Connect a grinder pump directly to an AIRVACvalve pit

Use a transitional manhole as an interfacebetween pressure & vacuum



Design Manual 2008

CHAPTER 6BUFFER TANKS

A. DESCRIPTION

Buffer tanks are designed with a small operating sump in the lower portion. Additional emergency sewage storage is provided above the sump. Theoperating sump is to be configured 18” in diameter with a depth of 12”. In nocase should a buffer tank be constructed without one such sump per valve.

It is very important that all joints and connections be watertight to eliminateground-water infiltration. Equally important is the need for a well-designed pipesupport system, since these tanks are open from top to bottom. The supporthardware should be of stainless steel and/or plastic.

For all buffer tanks, above ground venting of the AIRVAC valve must beinstalled to insure proper venting in the event that the buffer tank becomes filledwith sewage. AIRVAC recommends the use of its 6” dedicated air-terminal forthis purpose. In addition, AIRVAC recommends the use of an external, flexiblebreather rather than the in-sump breather that is used for other valve pits.

Figure 6-1 shows a typical single buffer tank arrangement, which may be usedto accept high sewage flows from schools, apartments, nursing homes, orconventional sanitary pump stations. Dual valve buffer tanks may also be usedfor higher flows (Figure 6-2). A prefabricated buffer tank made of a compositematerial in lieu of concrete is also available (contact AIRVAC for details).

B. WHEN & WHERE USED

Buffer tanks are typically used for schools, apartments, nursing homes, andother large-volume users. Their use should be limited to users where service at only one or two locations is possible (e.g.: a commercial user) and when noother option is available. Stated another way, buffer tanks should not beused where individual valve pits could otherwise be utilized.

A system with nothing but high-flow inputs is not recommended, although it ispossible to have a limited amount of high-flow inputs (buffer tanks) into avacuum system. Much depends on the location of the buffer tank itself, thelength of travel to the vacuum station, the amount of lift in the system, and howmany other buffer tanks there are in close proximity. In general, the closer tothe station, the fewer lifts to overcome, and the fewer other buffer tanks thatexist, the less likely it is that the buffer tank will have an adverse effect on thesystem operation.

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FIGURE 6-1: SINGLE BUFFER TANK

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Design Manual 2008

FIGURE 6-2: DUAL BUFFER TANK

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C. EFFECT ON SYSTEM HYDRAULICS

Efficient flow within a vacuum system relies on partial liquid and partial airinputs at controlled rates. This is normally accomplished by uniform distributionof valve pits through a service area with each valve pit attached to no more thanfour (4) homes. This allows relatively small liquid flow followed by a volume ofair for propulsion of liquid. In this manner, a uniform system air-to-liquid ratio ismaintained thereby maximizing available vacuum throughout the system.

By contrast, buffer tanks with valves that cycle frequently can sometimescontribute larger volumes of the liquid, but with the same amount of air. Thiscan lead to irregular air to liquid ratios, inefficient vacuum pump performanceand sluggish system operation. For these reasons, buffer tanks should only beutilized under the following conditions:

• Buffer tanks should be limited to users where service at only one ortwo locations is possible (e.g.,: a commercial user).

• Buffer tanks should not be used where individual valve pits couldotherwise be utilized.

• Buffer tanks should not be placed at line extremities withoutcontacting AIRVAC.

• Single buffer tanks are to be connected to a 6” or larger vacuummain.

• Dual buffer tanks are to be connected to an 8” or larger vacuum main.

D. BUFFER TANK SIZING

The AIRVAC 3-inch valve is capable of admitting 30 gpm of liquid, assumingsufficient vacuum levels exist at the valve location . This capacity isachieved when the valve cycles 3 times in a minute, with each cycledischarging 10 gallons as described in the following paragraph.

The length of one complete valve cycle is about 6-8 seconds, consisting of 2-3seconds for the liquid, followed by 4-5 seconds of air. During this time, vacuumlevels at the valve location temporarily drop as energy is used to admit thesewage into the main line. The valve rests before the next cycle begins, whichoccurs when another 10 gallons accumulates in the sump. Vacuum recoveryoccurs during the valve-closed time as the vacuum level in the main is restored.Typically a rest period of 10-15 seconds is needed to allow vacuum to berestored to normal levels.

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When vacuum levels decrease there is a corresponding decrease in the valvecapacity. This is due to the lower pressure differential that exists which resultsin less available energy and hence slower evacuation times.

A low vacuum condition can occur when a larger than usual amount of flowenters the main, followed by a relatively small amount of air, resulting in a low

air-to-liquid ratio. This could occur, for example, at a buffer tank where highdischarge rates are common and where repeated firing of the valve over shortperiods of time may not allow sufficient vacuum recovery. The net result wouldbe progressively decreasing pressure differentials and lower evacuation rates.

The net result is that large flows and high valve discharge capacity are typicallynot compatible. Buffer tanks require high discharge rates; however, this higherrate may result in water-logging which would result in a lower evacuationcapacity of the next valve cycle.

Considering the previous discussion, a lower evacuation rate of 15 gpm is

recommended for buffer tank sizing. This lower rate assists proper vacuumrecovery and provides a safety factor of sorts.

Table 6-1 shows the recommended design capacities as well as the maximumallowable design flow rates to use for buffer tanks.

TABLE 6-1

Recommended Design Flow RatesFor Buffer Tanks

Buffer Tank TypeRecommended

Design Peak Flow (gpm)(as a general rule)

Absolute MaximumPeak Flow (gpm)(case by case) *

Single Buffer tank 3.1 - 15.0 gpm 30 gpm

Dual Buffer tank 15.1 - 30.0 gpm 60 gpm

Consult AIRVAC > 30.0 gpm > 60 gpm

* Depending on static and friction loss, the overall amount of peak flow entering thesystem through buffer tanks and the exact location of the buffer tank, it may be possibleto size a particular buffer tank with the upper limits shown in this column. Consult

AIRVAC’s Engineering Department for guidance and approval.

For flow inputs greater than 30 gpm, please consult AIRVAC. Assumingsystem hydraulics allow, it may be possible to use a splitter manhole, which willevenly split and divert the flow to two or more dual valve buffer tanks (seeFigure 6-3).

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FIGURE 6-3: TWO DUAL BUFFER TANKSWITH SPLITTER MANHOLE

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E. LIMITATIONS ON USE

Maximum flow contributed by buffer tanksTo minimize the possibility of system water-logging, AIRVAC recommends theuse of buffer tanks be limited as follows:

• 25% rule: No more than 25% of the total peak flow of the entire systemshould enter through buffer tanks.

• 50% rule: No more than 50% of the total peak flow of a single vacuummain (i.e. – single flow path) should enter through buffer tanks.

• On a case by case basis: Depending on static and friction loss and theexact location of the buffer tank, it may be possible to exceed the 25%

and 50% limits shown above. Consult AIRVAC’s EngineeringDepartment for guidance and approval.

Maximum flow at a single locationThe positioning of a buffer tank(s) within the collection system has an impact onsystem hydraulics. In general, the greater the distance from the vacuum stationthe buffer tank is positioned and the higher the static loss that must beovercome, the larger the negative effect becomes on the overall transportcapabilities of the system.

There are no hard and fast rules regarding this issue, however please consult AIRVAC’s Engineering Department for guidance on the placement of buffertanks.

Buffer tanks fed by a pumpWhen a lift station or grinder pump discharges to a buffer tank, the conventionalpeak flow figures for the customers served by the pump should not be used.Rather, the rated discharge capacity of the pump should be used to sizethe buffer tank. Consult AIRVAC for guidance on input values for friction loss.

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F. SITUATIONS TO AVOID

Accepting flow from an existing gravity sewerPerhaps no one single factor has resulted in more problems with vacuumsystems than excessive flow from an existing gravity system entering a vacuumsystem via buffer tank(s).

There have been several isolated cases of severe system problems caused byexcessive flow that entered from existing gravity systems. In the most extremecase, a system could be totally out of operation resulting in house backups.Obviously this is a situation AIRVAC wants to avoid.

One problem is that it is difficult to accurately predict the flow that can beexpected from existing gravity systems. With new construction, one canaccurately predict average and peak flow rates and design the vacuum mainsand vacuum station accordingly. However, with an existing system, anotherelement is introduced into the equation: I&I. In these cases, AIRVAC’sexperience is that the consultant usually does one of the following duringdesign:

• I&I is either not considered or is understated. If it actually occurs whenthe system is on-line, the system does not function properly because it isundersized. Result: During normal flow periods the system works fine,but during rain events it may experience problems.

• In an effort to anticipate I&I, the designer overstates its magnitude.Larger vacuum mains, a larger collection tank and larger and possiblymore vacuum pumps are used. If I&I is not of the magnitude anticipated,the system may not function properly during normal operation because itis oversized (flow transport is sluggish, problems occur at the vacuumstation, etc.). Result: System may work fine during rain events, butsystem operation may be inefficient during normal periods. Additionally,there are significant additional costs, both capital and O&M, associatedwith the larger system components.

Obviously, neither of the above situations is acceptable. Should it be possibleto accurately predict I&I, it may be that this flow can be considered in a vacuumsystem. However, before AIRVAC will consider this, an analysis of theexisting gravity system must be done. As a minimum, this would includehaving flow records that identify the magnitude of flow that can be expectedduring normal periods as well as rain events (minimum 1 year of flow data).Even then, should there be a large difference between normal daily flow andflow during rain events, AIRVAC would recommend against accepting this flow.

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Overuse of Buffer tanksSome of the earliest systems tried using larger flow inputs (300 gallons at atime). Hydraulic studies of these systems showed very poor vacuum transportcharacteristics due to low air/liquid ratio. This phenomenon is called “water-logging”. The vacuum main ends up with too much liquid and not enough air,which is the driving force, and vacuum levels are choked-off at the extremeends. For these reasons, the AIRVAC design calls for small flow inputs (10gallons) with a sufficient amount of air following at the end of each valve cycle.

There is no problem in using buffer tanks on a limited basis. However, AIRVACdoes not recommend using buffer tanks on a widespread basis. The earlierdiscussions of this chapter provide guidelines on the limited use of buffer tanks.(See “Limitations on Use”).

Allowing more than 30 gpm to a buffer tankThe AIRVAC valve typically will not cycle more than 3 times in 1 minute, witheach cycle being 10 gallons. It is possible for one cycle to be greater than 10gallons, as long as the incoming flow rate is sufficient to keep pressure on thecontroller’s sensor, which will allow the valve to stay open. So, at 40 gpm, 3cycles will still occur, but each one at 13.3 gallons instead of 10. Since theamount of air that follows each cycle does not change, a lower air to liquid ratiowill result (same air/more liquid) and eventual waterlogging is likely.

G. POTENTIAL ADVERSE IMPACTS

There are three negative aspects associated with the use of buffer tanks thatthe designer should consider:

• Unlike the regular AIRVAC valve pit where the lower sewage sump iscompletely enclosed and separated from the top portion where the valveresides, a buffer tank simply has an AIRVAC valve mounted in amanhole. This means the operator is exposed to raw sewage shouldmaintenance on the valve be required.

• Rather than the system being completely sealed, a system with buffertanks will have points open to the atmosphere, which can result inpossible odor problems.

• Just like manholes in a gravity system, buffer tanks may be the source ofunwanted infiltration/inflow.

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Buffer Tanks6 - 10

H. DO’S AND DON’TS

Table 6 –2

Do’s and Don’ts: Buffer Tanks

DON’T DO THIS: DO THIS:

Use an in-sump breather for a buffer tank Use an external breather and a 6” dedicatedair-terminal for all buffer tanks

Allow more than 25% of peak flow to enter thesystem via buffer tanks w /out AIRVAC’s

approval

Limit peak flow entering system via buffertanks to 25%, Consult AIRVAC to request

higher limit on a case by case basis.

Allow more than 50% of peak flow to enter anysingle flow path via buffer tanks w /out

AIRVAC’s approval

Limit peak flow entering any flow path viabuffer tanks to 50%. Consult AIRVAC to

request higher limit on a case by case basis

Use buffer tanks when individual valve pitscould otherwise be used

Use buffer tanks for larger flows only whenservice is possible at just one or two locations

Use buffer tanks at line extremities Contact AIRVAC if service at line extremitiesis necessary

Exceed recommended capacity of single anddual buffer tanks w/out AIRVAC’s approval

Use SBT for peak flows up to 15 gpmand DBT for peak flows up to 30 gpm

Consult AIRVAC to request higher capacitieson a case by case basis

Size a buffer tank using conventional peakflow figures when the buffer tank is connected

to a lift station or grinder pump

Use the rated discharge capacity of the pumpto size the buffer tank.

Connect a buffer tank to an undersizedvacuum main

Use a minimum 6” main for a SBT and aminimum 8” main for a DBT

Design a system that accepts flow from anexisting gravity sewer via buffer tanks without

first consulting AIRVAC

Serve by other means unless gravity flow andI&I can be accurately predicted



Design Manual 2008

CHAPTER 7

PREFABRICATED VACUUM STATION SKIDS

A. GENERAL

AIRVAC provides complete vacuum station skid packages. The skid-mountedmechanical and electrical plant is assembled, tested and painted at our

AIRVAC production facility in Rochester, IN prior to shipment to the job site. Atthe job site, the skid is lifted into the building and connected to the incomingvacuum mains and the outgoing force main.

The AIRVAC prefabricated vacuum station is a result of our nearly 30 years ofexperience in the vacuum sewer industry. The equipment brands used, thematerials and the various configurations are all a product of this experience.Various fail-safe features are incorporated into the skid design making the

complete package operator friendly and reliable. Because of these features,the vast majority of vacuum stations in operation in the U.S. use AIRVACprefabricated skids. Should a custom-designed vacuum station be desired,contact the AIRVAC Engineering Department for guidance.

B. POSSIBLE SKID CONFIGURATIONS

Using the formulas in Chapter 3, the design engineer can calculate the size ofthe vacuum tank, the quantity and size of the vacuum pumps and the capacity

and head requirements of the sewage pumps. With this information, the skidmodel that most closely meets the sizing requirements can be selected.

AIRVAC skid models are identified using the following designations.

Prefabricated Vacuum Station Skids

SKID MODEL DESIGNATIONS

Model 3 D - 45 Vacuum Pump Type (capacity)

A 117 cfm *Collection tank size/100 B 170 cfm

Vacuum Pump Type (size) C 305 cfm

# of Vacuum Pumps D 455 cfm

* Used for special applications only

Tables 7-1 and 7-2 that follow can be used to make a preliminary selection ofthe skid model that best suits the application. To use these tables, select thePeak flow and the appropriate ‘A” factor to determine the number and capacity

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of the vacuum pumps required. Then, a check must be made to insure that themaximum pipe volume has not been exceeded. If it has, either larger vacuumpumps or additional vacuum pumps of the same capacity are required.

The collection tank volume and the maximum pipe volume figures shown inTables 7-1 and 7-2 are based on a peak factor of 3.50. If a lower peak factor isused, a slightly larger collection tank volume is required and slightly less pipevolume can be tolerated. Conversely if a higher peak factor is used, a slightlysmaller collection tank can be used and slightly more pipe volume can betolerated. In any case, detailed vacuum station calculations as described inChapter 3 should be performed before making the final skid modeldetermination.

Table 7 - 1

Skid model - Preliminary selection

When 2 vacuum pumps are usedCollection Tank Vol Vacuum Pump Capacity Required (cfm)

Peak based on 3.50 Peak based on Peak Q & longest line (Lmax)MaxPipe

Vacuum Q Calculated Rounded Lmax 7000' 10000' 12000' >12000' Vol

Pumps (gpm) (gal) (gal) A 7 8 9 11 (gal)

50 676 1,000 47 53 60 74

75 813 1,000 70 80 90 110 15,200

100 951 1,000 94 107 120 147

2 -170 cfm 125 1,089 1,000 117 134 150 184

2B 150 1,227 1,500 140 160 180 221 28,300

175 1,364 1,500 164 187 211 257

200 1,502 1,500 187 214 241 294

225 1,640 2,000 211 241 271 331

2 - 305 cfm 250 1,778 2,000 234 267 301 368 42,200

2C 275 1,915 2,000 257 294 331 404

300 2,053 2,000 281 321 361 441

325 2,191 2,500 304 348 391

350 2,329 2,500 328 374 421

2 - 455 cfm 375 2,466 2,500 351 401 451

2D 400 2,604 3,000 374 428

425 2,742 3,000 398 455

450 2,880 3,000 421

AIRVAC standard skids; others by special request

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Design Manual 2008

Table 7 - 3

Available AIRVAC skidsTANK SIZE

(gal)2 VACUUM

PUMPS3 VACUUM

PUMPS4 VACUUM

PUMPS

1000 gal 2B-10

2B-15 3B-151500 gal 2C-15 3C-15

2B-20* 3B-202000 gal 2C-20 3C-20

2B-25* 3B-25

2500 gal 2C-25* 3C-252D-25

3000 gal 2C-30* 3C-302D-30

3500 gal 2C-35* 3C-35

4000 gal 2C-40* 3C-40

4500 gal 2D-45* 3D-45

5000 gal 2D-50* 3D-50

5500 gal 2D-55* 3D-55

6000 gal 3D-60* 4D-60

6500 gal 4D-65

7000 gal 4D-70

AIRVAC standard skid; others by special request

* Normally not available but can be if additional vacuumpumps are to be added in the future




Design Manual 2008

C. MODIFICATIONS TO THE STANDARD AIRVAC SKID

Minor modificationsEach project has requirements that may require slight modifications to thestandard skid arrangement. Some examples are:

• Skids can be oriented to face either right or left (i.e. – mirror images areavailable).

• The collection tank nozzles will vary according to the number of vacuummains and their associated diameters.

• Sewage pump capacity and head conditions may result in spacing andconfiguration changes.

Major modificationsStandard equipment used in an AIRVAC skid is shown on Table 7-4. Optionalequipment is available; however, these are major modifications that will requireadditional design and fabrication time by AIRVAC. Also, it is not unusual foroptional equipment to add 25-50% to the cost of the vacuum station skid.

Table 7-4

Standard Equipment used on an AIRVAC skid

EQUIPMENT STANDARD OPTIONAL

Vacuum Pumps Rotary vane (Busch) n/a

Sewage Pumps Horizontal, non-clogcentrifugal (various mfg’s)

Vertical pumps(various mfg’s)

Collection Tank Carbon Steel w/epoxycoatings

Stainless Steel orFiberglass

Control logic Relay logic PLC(Allen Bradley)

Contact AIRVAC’s Engineering Department for a complete, detailed list ofstandard skid components and available upgrades.




Design Manual 2008

D. VACUUM STATION EQUIPMENT CONFIGURATIONS

The vacuum station equipment can be configured in many different ways.Some common configurations are shown on Table 7-5.

Table 7-5

Typical skid configurations

Configuration Description

#1Vacuum Pumps, sewage pumps, control panel &

collection tank all on a single skid

#2Vacuum Pumps, sewage pumps & control panelon a single skid; collection tank separate (floor

mounted)

#3Vacuum pumps and control panel on skid #1;

sewage pumps on skid #2; collection tankseparate (floor mounted)

Contact AIRVAC’s Engineering Department for sample drawings of these skidarrangements.

Configuration 1: all equipment on a single skid (smaller skid models)In this configuration, all of the equipment is located on a single skid. Thecontrol panel is typically mounted next to the collection tank.

This is typically used only for the smaller sized skids (i.e. - only 2 vacuum

pumps and when the collection tank is 2000 gallons or smaller) and whenprotection from flood is not an issue.

Typical skid sizes are 8’ wide with the length varying between 14’ and 26’ long.The building footprint is usually the skid dimensions plus 4 feet on all sides.




Design Manual 2008


Configuration 2: all equipment on 1 floor (larger skid models)This configuration also has all equipment located on the same floor, but doesnot have the collection tank located on the skid.

This is typically used for the larger stations (>2000 gallon collection tank) thathave more than 2 vacuum pumps. The control panel is mounted on themechanical equipment skid.

Typical skid sizes are 7’ wide with the length varying between 17’ and 27’ long.The building footprint is usually the skid dimensions plus 4 feet on all sides.

Configuration 3: split-level design (all skid model sizes)This is a split-level design, with either a full or partial basement. This is usedwhen protection from flood is an issue.

In this configuration, the vacuum pumps and controls are located on the topfloor above flood level and the collection tank and sewage pumps are located inthe basement.

The vacuum pump and control panel are located on a single skid, the sewagepumps are on another skid and the collection tank is mounted on the floor.

The vacuum pump skid is usually 6’-6” wide and the length can run between 16’and 24’ long. The sewage pump skid is usually 7’ wide and the length can runbetween 3’ and 8’. The building footprint is usually the skid dimensions plus 4

feet on all sides. Space for steps and step landings must also be considered.



Design Manual 2008

AIRVAC Services8 - 1

CHAPTER 8

AIRVAC SERVICES

A. THE TEAM APPROACH

AIRVAC believes in the team approach where we assist the engineer,contractor and owner in all aspects of the project. Below are examples ofthe level of support AIRVAC provides during all phases of a project.

Table 8-1

AIRVAC Services

PROJECT PHASE AIRVAC SERVICE

Planning Preliminary system layout

Design Detailed design assistance

Construction Field Services/daily testing

Start-up System start up – lines & station

Home hook-up Plumbers class/valve installation

Initial operation Initial system operation

Operator training Operator training at factory/on-site

After-market Technical support/operation services

These services are described in more detail on the following pages.



Design Manual 2008


B. PRELIMINARY SYSTEM LAYOUT

Upon receipt of some basic project information, AIRVAC engineers will assistconsulting engineers with the preparation of a preliminary system layout as wellas a budget estimate.

System layout/preliminary design/Technical information A preliminary system layout will be provided, including vacuum main sizing.Preliminary sizing of the vacuum pumps, sewage pumps and the collection tankwill be made. The estimated quantities of the various system components willbe identified. A Technical Report will be provided that summarizes the designassumptions, line and station sizing, the valve pit quantities required and otherthe project specific information.

Cost information A budget estimate will be provided that includes an estimate of both capitalcosts as well as the annual Operation & Maintenance costs.

C. DETAILED DESIGN ASSISTANCE

When a consulting engineer commences the detailed system design, an AIRVAC engineer will be available for design assistance ranging fromengineering training to hands on design work. An AIRVAC engineer will also

review the completed design to verify the aspects of the design that relate to the AIRVAC system.

Line profiling assistance AIRVAC can provide assistance with vacuum main profiling. Typically thisincludes assistance with profiling the most critical vacuum main. AIRVAC willreview the line profiles when completed and do a hydraulic analysis of bothstatic loss and friction loss.

Plan and Profile sheetsEach design firm has their own style and ideas on how much detail to includeon the plan and profile drawings. Information that typically is included in otherutility design work should be included in vacuum sewer plans as well. Inaddition, there are certain vacuum-specific items that need to be shown as well.Table 8-2 shows some of the critical vacuum-specific items that AIRVACencourages designers to include when preparing the P&P sheets.



Design Manual 2008


Table 8-2

Key features to include on the Plan & Profile sheets

ITEM WHY IS THIS NEEDED?GENERAL

Horizontal & vertical scale (Ex: 1” = 50’; 1” = 5’) Design review, bidding & construction purposes

Bar scale Plans are sometimes reduced for printing

PLAN VIEW

Flow arrow To clearly indicate direction of flow

Length, size & type of pipe (Ex: 320 lf- 8” SDR 21 PVC) For review, bidding & construction purposes

Pipe termination

Branch line connection

Division valves

For bidding & construction purposes

To clearly indicate the use of wye fittings


Houses/lots to be served To indicate which houses/lots share a pit

Slab or basement elevation (Ex: El 110.25) For pit depth determination

Valve pit location and callouts

Valve pit designation (Ex: VP – A23) For construction purposes & maintenance records

Valve pit type & depth (Ex: 3030WT) To establish product quantities

Valve pit rim elevation (Ex: El 103.50) Combined with slab elevation & pit type this will beused to determine if the pit is deep enough to servethe intended house(s)

Valve pit stub-outs To determine pit orientation & stub-out lengths

PROFILE VIEW

Flow arrow To clearly indicate direction of flow

Valve pit locations To insure they are not too close to the top of a lift

Pipe length, size, type & slope(Ex: 320 lf-8” SDR 21 PVC @0.20%)

For review, bidding & construction purposes

Pipe termination

Division valves

Inverts - top & bottom of lifts



To indicate lift heights

Inverts - change in pipe slope For construction purposes

Inverts – branch to main connection To insure sufficient ‘over the top’ spacing



Design Manual 2008


There are many different ways to graphically present the items shown in Table8-2. For example, some firms like to repeat plan view information on the profileview to act as a cross-check. Others prefer not to do this as changes made inone view during the design may inadvertently be missed in the other viewresulting in conflicting information. Each method has its pros and cons.

AIRVAC has no preference on how the information is presented, but rather ismore concerned on what information is actually included on the plan & profilesheets. As a general guideline, the designer should consider the followingwhen deciding on the format used for the plan & profile sheets:

• Bid-ability and constructability. Is there sufficient detail for bidders tofairly price the job and for contractors to properly construct the system?

• AIRVAC review. Is there sufficient information to allow AIRVACengineers to review for the design for compliance with the guidelinescontained in this manual, and to allow for a hydraulic review to becompleted (static & friction loss)?

• Regulatory agency review. Is there sufficient information to allow aregulatory agency to review for compliance with rules and regulations?

• Owner and operator use. Is there sufficient information to serve as basisfor the as-built drawings and for future maintenance records?

Station skid drawingsDetailed drawings of the various skid arrangements are available from AIRVAC.Typical drawings include:

• Plan & section: skid assembly

• Control panel layout

• Power distribution

• Vacuum/sewage pump controls

• Electrical wiring

•

Alarm/level controls• Point to point wiring

Contact AIRVAC’s Engineering Department for assistance with skid drawings.



Design Manual 2008


Standard details AIRVAC maintains an excellent inventory of standard detail drawings. Thesedetails are periodically updated to include new products, product changes, etc.Contact AIRVAC’s Engineering Department for a copy of the latest standarddetails.

Sample Specifications AIRVAC can provide detailed specifications using the ConstructionSpecifications Institute (CSI) format for the vacuum-related aspects of a project,including:

• Valve & valve pit equipment Specifications

• Pre-Fabricated Vacuum Station Specification with Electrical

• Custom Constructed Vacuum Station Specification with Electrical

Contact AIRVAC’s Engineering Department for format and availability.

Use of AIRVAC-supplied drawings & documents Any AIRVAC drawing or other documents provided by AIRVAC during thedesign phase are done so with the understanding that they can be used in thefinal construction documents only if AIRVAC is chosen as the vacuum systemsupplier.

DISCLAIMER: AIRVAC is not an engineering firm, and cannot and does not provideengineering services. AIRVAC reviews the design, plans, and specifications for a project onlyfor their compatibility with AIRVAC's vacuum products, and accepts no responsibility for theoverall project design. Any information provided to project engineers is provided solely to assistthe engineer in designing and engineering and maintaining an overall system that can utilize

AIRVAC vacuum products.



Design Manual 2008


D. CONSTRUCTION FIELD SERVICES

A correct installation is vital to the ultimate success of a vacuum system.

AIRVAC can provide skilled field representatives to advise and assistcontractors and consulting engineers with the construction of AIRVAC systems.

In most first-time vacuum projects, AIRVAC provides a Field Representative tobe present during the entire construction period. For repeat clients, or forprojects where a consulting firm with vacuum experience is involved, AIRVACcan also provide part time field services.

E. SYSTEM START-UP

AIRVAC technicians can assist with the critical stage of system start-up. Start-up is usually conducted in two phases: the vacuum station and the collectionsystem.

The AIRVAC Technician conducts all of the tasks related to the vacuum stationstart-up. The Contractor, with AIRVAC’s help, does the collection system start-up task.

Table 8-3

Start-up Services

VACUUM STATION COLLECTION SYSTEM

Vacuum & sewage pump tests Review As-built drawings

Electrical review Final 4-hr vacuum test

Level control tests Flush ends of lines

Final Vacuum test Open & clean collection tank

Place system in automatic mode Place system in automatic mode

Prepare Start-up Report Prepare Start-up Report



Design Manual 2008


F. HOME HOOKUP & VALVE INSTALLATION

Along with system start-up, this is one of the most critical stages of the entireproject. Even a well-designed and constructed system can experienceoperational difficulties early on if the following activities are not carried out.

Public EducationTo ease homeowner fears, AIRVAC can participate in various public educationendeavors, including participation in public meetings, conducting tours ofexisting systems and participation in Owner sponsored workshops.

Plumbers Class AIRVAC has found it to be very advantageous to conduct training classes withlocal plumbers who will be doing the home hook-ups. In some cases, the

Owner will require the local plumbers to attend the AIRVAC class to becomecertified to install the homeowner’s gravity line and connect it to the vacuumvalve pit.

Home hook-up inspection & valve installation AIRVAC can provide the Owner with inspection assistance regarding thehomeowner gravity line connections to the valve pits as well as actualinstallation of the AIRVAC 3” valve. Specifically, AIRVAC will:

• Provide inspection of the homeowner gravity line in conjunction with

County plumbing inspectors. AIRVAC will help to insure that all airintakes are in the proper locations, that sufficient slope exists on allpiping and that the homeowner makes a proper connection to the Ownersupplied gravity stub leading to the valve pit.

• Install the 3” AIRVAC interface valve in each valve pit after thehomeowner plumbing inspections are completed and approved by thelocal plumbing inspectors and the Owner.

G. INITIAL SYSTEM OPERATION

When a system first goes on line, the system hydraulics will change with everyvalve that is installed. To help the Owner during this critical time, AIRVAC canassist them during the early stages of system operation.



Design Manual 2008


H. OPERATOR TRAINING

Training of the system operators is an important part of any sewage scheme. AIRVAC provides excellent operator training to ensure optimal system

operation.

Factory training - Operator’s school AIRVAC offers a 1-week operator training school conducted at the AIRVACfactory. Training is provided on the following topics:

• AIRVAC valve operation and overhaul.

• Troubleshooting procedures; faults are set up in the AIRVAC rig forthe trainees to locate and rectify.

• Collection station maintenance.

• Record keeping.

• Installation of AIRVAC valves, valve pits, holding tanks, servicelaterals and sewers (most owners make minor additions to thesystem).

On-site training AIRVAC can also perform on-site training. This hands-on training would includetroubleshooting tips, assistance with setting valves and the controller timing,and making adjustments to the vacuum station and vacuum valves to mirror thechanging system hydraulics.

Arrangements for other such training sessions can be made with the AIRVACService Department.

AIRVAC Test RigThe AIRVAC glass pipe test and demonstration rig is located in Rochester,Indiana. Engineers and clients are welcome to view the rig but are requested totelephone AIRVAC for an appointment.

All aspects of the AIRVAC system, including an operating clear valve, aredemonstrated.



Design Manual 2008


I. AFTER-MARKET SERVICES

Technical support from the AIRVAC Engineering and Service departmentsprovide any necessary support to assist the owner in providing timelyinformation and solutions to problems.

24/7 Technical support AIRVAC provides on-site technical support to the owner during systemoperation and in emergency situations as required. With our toll free 800#,service assistance is available 24 hours a day, 7 days a week.

Problem Simulation AIRVAC maintains a complete vacuum system at our factory that can be usedto simulate field conditions and onsite problems to help solve owner problems

or suggest solutions.

Annual System Evaluation & Tune-up An AIRVAC technician will cycle and re-time all AIRVAC valves, conductexterior leak tests on each controller and visually inspect each valve pit. Thetechnician will visit each vacuum station to perform various equipment tests.

Contract MaintenanceIn some cases, AIRVAC can provide the operation and maintenance functions

for the owner for an annual fee. This service would include normal day-to-daymaintenance, preventive maintenance, service calls and emergency callouts.

Response to natural disasters and emergencies AIRVAC has been involved several times with the Federal EmergencyManagement Agency (FEMA) reacting to damage from floods, tornadoes andhurricanes. We understand and work within the FEMA guidelines to restoreservice as quickly as possible.

AIRVAC will contact the system operator prior to offer standby assistance.

Field personnel can be dispatched to help restore the system, if requested.

Spare parts AIRVAC maintains an inventory of spare parts at our Rochester, IN facility.This includes every single part and piece that makes up our products. With thisinventory, the owner can expect spare parts within 24 hours of their request.



Design Manual 2008

Af ter-market Services24/7 Technical support

Annual System Evaluation & Tune-upContract MaintenanceProblem simulationResponse to natural disasters & emergenciesSpare parts

8-98-98-98-98-98-9

Backwater valves 5-20

Buffer TanksDescriptionDos’ & Don’tsEffect on system hydraulicsSizingWhen & where usedLimitations on use

Potential adverse impactsSituations to avoid

6-16-106-46-46-16-7

6-96-8

Building sewerBuilding sewer4” air-intake6” dedicated air-terminal

Collection TankMaterialsSizing

5-145-145-16

3-23-2

ControllerDescription 5-5

Construct ion Field Services 8-6

Conversion factors 3-12

Electronic Air Admission Control (EAAC) 4-27

Electrical Panel

Motor control centerMotor control panelRelay logic vs. PLC

3-133-133-14

Fault Monitoring SystemDescription 3-17

Index1



Design Manual 2008

FiguresFig 1-1: Typical layoutFig 1-2: Vacuum main during period of no flowFig 1-3: Typical back-surgeFig 1-4: Typical vacuum station schematicFig 1-5: Vacuum vs. gravity: excavationFig 1-6: Vacuum vs. gravity: profilesFig 3-1: NPSHa diagramFig 3-2: Station calculation sheetFig 3-3: Level control probe diagramFig 4-1: Lift detailFig 4-2: Profiling before a series of liftsFig 4-3: Downhill transportFig 4-4: Uphill transportFig 4-5: Level transportFig 4-6: Service lateral with liftsFig 4-7: Friction loss calculation sheet

Fig 4-8: Vacuum lift capabilityFig 4-9: Static loss determinationFig 4-10: Pipe volume calculation sheetFig 5-1: 6.5’ PE 1-piece pitFig 5-2: 6’ fiberglass 3-piece pitFig 5-3: AIRVAC flexible service lateralFig 5-4: Typical configuration for gravity connectionsFig 5-5: Valve pit components PE 1-piece pitFig 5-6: Valve pit components fiberglass 3-piece pitFig 5-7: AIRVAC anti-buoyancy collarFig 5-8: 4” Air-intake diagram

Fig 5-9: Optional 6” Dedicated air terminalFig 5-10: Valve pit prior to home hookupFig 5-11: Valve pit after home hookupFig 6-1: Single buffer tankFig 6-2: Dual buffer tankFig 6-3: 2 Dual buffer tanks with splitter manhole

1-21-41-41-71-101-103-73-103-144-24-84-94-104-104-124-224-23

4-244-285-25-35-65-75-95-115-135-165-16

5-195-196-26-36-6

Flexible service lateral 5-6

Flow determination Average daily flowPeak flowPeaking factorsInfiltration

2-12-22-12-3

Index2



Design Manual 2008

FrictionChartsLoss calculationsLoss limits

4-154-144-26

Gauge taps 4-3

Grease traps 5-20

Homeowner Issues Air-intakeBackwater valvesBuilding sewerHome Hookup & valve installationGrease trapsOptional 6” dedicated air terminalProper time to install valve

5-145-205-148-75-205-175-18

Horizontal Directional Drill ing (HDD) 4-4

In-sump breatherDescription

Level controls

5-5

3-14Lifts

Lift detailLoss calculationsLoss limitsRecommended lift heightsSlope between liftsWhen lifts are required in the service lateral

4-24-244-264-244-114-11

Location tape 4-2

LossesDue to friction

Due to lifts (static loss)

4-14

4-23

Prefabricated vacuum station skids AIRVAC standard skid modelsModifications to the standard AIRVAC skidSkid model designationsVacuum station equipment configurations

7-47-57-17-6

Index3



Design Manual 2008

Preliminary System LayoutCost informationSystem layout/preliminary designTechnical information

8-28-28-2

Operator Training AIRVAC test rigFactory training-Operator’s schoolOn-site training

8-88-88-8

Sewage pumpsMaterialsNPSH calculationsPump capacityTDH calculation

3-43-53-43-5

Static lossesObservations from in-house hydraulic studiesRecommended static loss limitsStatic loss calculations

4-254-264-24

System Start-upInitial system operationStart-up proceduresWhen to install the vacuum valve

8-78-65-18

Index4



Design Manual 2008

TablesTable 2-1: Peak factorsTable 3-1: Vacuum station component sizingTable 3-2: Values of Vo for different peak factorsTable 3-3: Discharge pump NSPH calculations/nomenclatureTable 3-4: A” factorTable 3-5: Do’s and Don’ts: Vacuum Station DesignTable 4-1: Directional drill guidelinesTable 4-2: Maximum flow for various pipe sizesTable 4-3: Maximum line length for various pipe sizesTable 4-4: Main line design parametersTable 4-5: Guidelines for determining line slopesTable 4-6: Slope between liftsTable 4-7: Service lateral design parametersTable 4-8: PVC pipe sizes & related AIRVAC design informationTable 4-9: Friction tables: 4”

Table 4-10: Friction tables: 6”Table 4-11: Friction tables: 8”Table 4-12: Friction tables: 10”Table 4-13: Recommended lift heightsTable 4-14: Static & friction loss design guidelinesTable 4-15: Pipe volume per linear foot for various pipe sizesTable 4-16: Do’s and Don’ts: Vacuum Piping DesignTable 5-1; AIRVAC Valve pit typesTable 5-2: Recm’d pipe types for stub-outs & building sewersTable 5-3: Do’s and Don’ts: Valve PitsTable 6-1: Recm’d max design flow rates for buffer tanks

Table 6-2: Do’s and Don’ts: Buffer tanksTable 7-1: Skid model- preliminary selection (2 VP’s)Table 7-2: Skid model – preliminary selection (3 or 4 VP’s)Table 7-3: Available AIRVAC skidsTable 7-4: Standard equipment used on an AIRVAC skidTable 7-5: Typical skid configurationsTable 8-1: AIRVAC servicesTable 8-2: Key features on Plan & Profile sheetsTable 8-3: Start-up services

2-23-13-33-63-93-204-44-64-74-84-94-114-114-144-15

4-164-184-204-244-264-274-315-15-155-216-5

6-107-27-37-47-57-68-18-38-6

Vacuum Chart Recorder

Description 3-16

Vacuum GaugesDescription 3-16

Index5



Design Manual 2008

Vacuum MainsCleanouts/access pointsConstruction issuesDo’s & Don’tsFittingsGasketsInstallation Tolerances – Directional drillingInstallation Tolerances – Open cutIsolation valvesLine connectionsLine lengthsLine sizingLocation tapePiping materialsPipe volume

Profile changes (lifts)Slope between liftsSlope on vacuum mainsSystem layout guidelines

4-34-14-314-14-34-44-34-34-134-74-64-24-14-27

4-24-114-94-5

Vacuum Main testsDaily testFinal test

4-44-5

Vacuum PumpMaterials

Pump-down time (‘t’)Sizing: based on flow & A/L ratioSizing: based on pipe volume

3-8

3-93-83-9

Vacuum StationsBio-mass sizingComponent sizingDo’s and Don’tsEqualizing linesHeatLevel controls

NoiseOdor controlStandby generatorStation pipingStation sump valve

3-193-13-203-163-183-14

3-183-183-183-163-17

Index6



Design Manual 2008

Vacuum Station CalculationsCalculation sheetsHs (static head)Hf (friction head)Hv (vacuum head)NPSHa (Net Positive Suction Head available)NPSHr (Net Positive Suction Head required)Qmax (peak flow)Qa (average flow)Qmin (minimum flow)Qdp (discharge pump capacity)Qvp (vacuum pump capacity)“t” (system pump-down timeTDH (Total Dynamic Head)Vo (collection tank operating volume)

Vct (collection tank volume)Vp (piping system volume)

3-103-63-63-63-53-62-22-22-23-43-83-93-53-2

3-24-28

Vacuum systems Advantages-Construction Advantages-Operation (general) Advantages-Operation (hurricane prone areas) ApplicationsGeneral descriptionHistoryMajor system components

System layout guidelinesVacuum pipingValve pitVacuum stationWhere used

1-91-111-111-91-11-11-5

4-51-61-51-71-9

Index7



Design Manual 2008

Index8

Vacuum System Hydraulics Air to Liquid ratioBack-surgeSaw-tooth profileSummary of vacuum main design fundamentals

1-31-41-34-29

Vacuum ValveDescriptionValve capacity

5-45-4

Valve PitsDo’s and Don’ts – valve pitsFlexible service lateralIn-sump breatherPit covers

Pit sharingPit typesShipping & handlingStub-outs

5-215-65-55-8

5-25-15-85-7

Valve Pits – PE, 1-piece pits1-piece pitsIn-sump breather/sensor pipeSuction pipeIntegral anti-buoyancy collar

5-95-105-105-10

Valve Pits – fiberglass, 3-piece pits3-piece pitsValve pit conePit bottomSumpIn-sump breatherSuction & sensor pipes

Anti-buoyancy collar

5-115-125-125-125-125-135-13



Documents

AIRVAC Design Manual.2008