Presentation on Dew Ate Ring

8/7/2019 Presentation on Dew Ate Ring

1/58

CONSTRUCTION DEWATERING

EQUIPMENTS:

1


2/58

DEWATERING SYSTEM: The control of groundwater is one of the most common and

complicated problems encountered on a construction site.

Construction dewatering can become a costly issue ifoverlooked during project planning. In most contracts,dewatering is the responsibility of the contractor. Thecontractor selects the dewatering method and is responsiblefor its design and operation.

The purpose of construction dewatering is to control thesurface and subsurface hydrologic environment in such a wayas to permit the structure to be constructed in the dry.

Dewatering means the separation of water from the soil, or

perhaps taking the water out of the particular constructionproblem completely.

construction dewatering, which involves temporarily loweringthe ground water table to permit excavation and constructionwithin a relatively dry environment, is rarely a problem.

The geology, ground water conditions, and type of excavation

all influence the selection of dewatering technology.

2


3/58

INTRODUCTION : DEWATERING SYSTEM:

Dewatering system used in construction

technology uses following types of equipments for

the purpose of dewatering.

1. Various types of pumps-conventional method2. Well Point systems-advance method

3. Deep wells-advance method

3


4/58

INTRODUCTION:

Most projects require the use of one or more waterpumps at various stages during the period ofconstruction.

Construction pumps must frequently perform under

severe conditions , such as those resulting fromvariations in the pumping head or from handlingwater that is muddy, sandy, and trashy, or highlycorrosive.

Knowing the importance of pumping, Contractors

Pump Bureau publishes pump standards. The most satisfactory solution for the pumping

problem may be a single all-purpose pump, or in othersituations it may be better to use several types andsizes of pumps, to permit operational flexibility andeconomy.

4


5/58

CONTINUED..

Pumps are used extensively on construction

projects for such operations as:

1. Removing water from pits, tunnels, and other

excavations.2. Dewatering cofferdams.

3. Furnishing water for jetting and sluicing.

4. Furnishing water for many types of utility

services.5. Lowering the water table for excavations.

6. Foundation grouting

5


6/58

CONTINUED..

The factors that should be considered in selecting

pumps for construction applications include:

1. Dependability.

2. Availability of repair parts.3. Simplicity to permit easy repairs.

4. Economical installation and operation.

5. Operating power requirements.

6


7/58

Dimensional terminology for pumping operations7


8/58

TERMINOLOGIES:

The important terms which are used in describing pumpsand pumping operations as follows:

Capacity:

i. The total volume of liquid a pump can move in a givenamount of time.

ii. Expressed in gallons per minute (gpm) or gallons perhour (gph).

Discharge head:

i. The sum of the static discharge head plus the head lossesof the discharge line.

Discharge hose:

i. The hose used to carry the liquid from the discharge sideof the pump.

Impeller :

i. The rotating vanes within the pump housing which aredriven by the drive shaft.

ii. The vanes create a partial vacuum drawing the fluidthrough the pump.

8


9/58

CONTINUED..

self-priming:

i. The ability of a pump to separate air from a liquid andcreate a partial vacuum in the pump.

ii. This causes the liquid to flow to the impeller and on

through the pump. Static discharge head:

i. The vertical distance from the centerline of the pumpimpeller to the point of discharge.

Static suction lift:

i. The vertical distance from the centerline of the pumpimpeller to the surface of the liquid to be pumped.

ii. Suction capability is limited by atmospheric pressure.Therefore, max. practical suction lift is 25 ft.

iii. Decreasing the suction lift will increase that can bepumped.

9


10/58

CONTINUED..

Strainer :

i. A cover matched to the size of the pump

ii. Attached to the end of the suction hose that permitssolids of only a certain size to enter the pump body.

Suction head:

i. The sum of the static suction lift plus the suction linehead losses.

Suction hose:

i. The hose connected to the suction side of the pump.

ii. Suction hose is made of heavy rubber or plastic tubing

with a reinforced wall to prevent it from collapsing. Total head:

i. The suction head plus the discharge head.

Volute:

i. The housing in which the pumps impeller rotates

ii. It has channels cast into the metal to direct the flow ofliquid in a given direction.

10


11/58

CLASSIFICATION OF PUMPS:

The pumps commonly used on construction projects can be

classified as :

1. Displacement

Reciprocating (piston)

Diaphragm

2. Centrifugal

Conventional

Self-planning

Self-priming trash Submersible

Multistage

11


12/58

RECIPROCATING PUMP:

Single piston reciprocating pump

single acting reciprocating pump

double acting reciprocating pump

12


13/58

RECIPROCATING PUMPS:

Sub type of displacement pumps.

Operates as a result of the movement of a piston inside acylinder.

Classification:

a. Double acting pump: regardless of the direction of

movement of the piston, water is forced out of one end anddrawn into the other end of the cylinder.

b. Single acting pump: water is pumped during a pistonmovement in one direction only.

c. Duplex double or duplex single acting: depending upon no.of cylinders mounted side by side a duplex for two, triplex

for three etc. Capacity depends on the speed at which pump is operated

and independent of the head.

The max. head depends on :

a) The strength of the component parts of the pump.

b) The power available to operate the pump.13


14/58

CONTINUED.

The volume of the water pumped in one stroke willequal the area of the cylinder times the length of thestroke, less a small deduction for slippage through thevalves or past the piston, usually about 3 to 5 %.

The volume pumped in gallons per minute by simplexdouble-acting pump can be expressed as:

Q = c( d2 l n /4 231)

where

Q = capacity of a pump in gpm

c = one-slip allowance; varies from 0.95 to 0.97

d = diameter of cylinders in inches

l = length of stroke in inches

n = number of strokes per minute 14


15/58

CONTINUED.

The volume pumped per minute by a multiplex double-acting pump will be:

Q = N c ( d2 l n/4 231)

where N = no. of cylinders in the pump.

The energy required to operate a pump will be:

W = w Q h/ e

where

W = energy in foot-pounds per minute

w = weight of 1 gal of water in pounds

h = total pumping head, in feet, including

friction loss in pipee = efficiency of pump, expressed decimally

The horsepower required by the pump will be:

P = W/33000 = w Q h/33000 e15


16/58

ADVANTAGES:

I. Able to pump at a uniform rate against varying

heads.

II. Increasing speed can increase their capacity.

III. Reasonably high efficiency regardless of thehead and speed

IV. Usually self-priming.

16


17/58

DISADVANTAGES:

I. Heavy weight and large size for given capacity.

II. Possibility of valve trouble (pumping water

containing abrasive solids).

III. Pulsating flow of water.IV. Danger of damaging a pump when operating

against a high head.

17


18/58

DIAPHRAGM PUMP:

Section through diaphragm pump

The central portion of

flexible diaphragm is

alternately raised and

lowered by the pump

rod that is connected to

walking beam. This

action draws water

into and discharges it

from the pump.

18


19/58

DIAPHRAGM PUMPS:

Also a positive displacement type.

As this type of pump will handle clear water or

water containing large quantities of mud, sand,

sludge, and trash, it is popular as constructionpump.

It is suitable for use on jobs where the quantity of

water varies considerably, as it will diligently

continue pumping air and water mixtures.

The accessible diaphragm may be changed easily.

Size and capacity ratings are decided by The

Contractors Pump Bureau.19


20/58

CENTRIFUGAL PUMPS: Contains a rotation element called impeller.

It is the function of centrifugal pump to give the water thenecessary velocity as it leaves the impeller.

Principle :

consider, a drop of water at height h above a surface. If adrop of water is permitted to fall freely, it will strike thesurface with a velocity given by equation:

v2(out)-v2(in)= 2ghv2= 2gh

where,

v= velocity in feet per second.

g= acceleration due to gravity.

h= height of fall in feet. In actual practice the maximum possible head for the

increased speed will be less than 400 ft. The reduction iscaused by increased losses in the pump due to friction.

20


21/58

This figure showshow pressure

decreases in jet as

the velocity while

the reverse occurs

in a diffuser which

slows water down

and increases the

pressure.

21


22/58

CONVENTIONAL PUMPS: CONTINUED. The efficiencies of these

pumps may be as highas 75%,

Because of their highefficiency factors, theywill pump a greatervolume with lower fuelconsumption ascompared to other pumptypes. The effect thatincreasing speed or thediameter of an impellerhas on performance ofthe pump.

A centrifugal pump maybe equipped with eitheran open or enclosedimpeller. There arevarious types ofimpeller available nowa days:

22


23/58

TYPES OF CENTRIFUGAL PUMP: A smooth or gradual change is essential, any sudden change

would create a great deal of turbulence which dissipate energyinstead of increasing pressure. There are two main methods ofdoing this, and one unusual method.

Diagram A shows the most common, which is the "volutecentrifugal" pump, generally known more simply just as a

"centrifugal" pump. Here a spiral casing with an outer snail-shell-shaped channel of gradually increasing cross section draws theoutput from the impeller tangentially, and smoothly slows itdown. This allows the water to leave tangentially through thedischarge pipe at. reduced velocity, and increased pressure.

Diagram B shows the other main alternative, which is the so-called "turbine centrifugal" or "turbine pump", where a set ofsmoothly expanding diffuser channels, serve to slow the water

down and raise its pressure in the same way. In the type Ofturbine pump illustrated, the diffuser channels also deflect thewater into a less tangential and more radial path to allow it toflow smoothly into the annular constant cross-section channelsurrounding the diffuser ring, from whore it discharges at the top.

23


24/58

CONTINUED.

Diagram. C shows the third, lesser known type of centrifugal pumpwhich is usually called a "regenerative pump", but is also sometimescalled a "side-chamber pump" or ever, (wrongly) a "turbine pump".Here an impeller with many radial blades turns in a rectangularsectioned annulus; the blades accelerate the water by creating twostrong rotating vortexes which partially interact with the impelleraround the rim of the pump for about three-quarters of a revolution;energy is steadily added to the two vortexes each time water passesthrough the impeller.

When the water leaves the annulus it passes through a diffuserwhich converts its velocity back into pressure. Regenerative pumpsare mentioned mainly for completeness; because they have very

close internal clearances they are vulnerable to any suspended grit ordirt and are therefore only normally used with clean water (or otherfluids) in situations where their unique characteristics areadvantageous. They are generally inappropriate for irrigation duties.Their main advantage is a better capability of delivering water to ahigher head than other types of single-stage centrifugal pump. 24


25/58

CONTINUED.

Types of centrifugal pumps

25


26/58

CENTRIFUGAL PUMP INSTALLATIONS:

Surface mounted centrifugal pump installations26


27/58

CONTINUED.

27


28/58

SERIES AND PARALLEL OPERATION OF

CENTRIFUGAL PUMP:

Where a higher head is needed than can be achieved with a single

pump, two can be connected in series and similarly if a greater output

is needed, two centrifugal pumps can be connected in parallel.

It is clear that series connection of pumps has no effect on efficiency or

discharge but doubles the effective head. Parallel operation does not

however normally double the discharge compared to a single pump,

because the extra flow usually causes a slight increase in total head

(due to pipe friction), which will move the operating point enough to

prevent obtaining double the flow of a single pump.

28


29/58

CENTRIFUGAL PUMPS

It contains an impeller which

imparts water in pump, a

velocity to flow it against

considerable pressure from

the pump. Potential energy is converted

to kinetic energy.

Principle : V = ( 2gh )

OR h = V2 / 2g

29


30/58

Impeller may be open or enclosed.

Enclosed impeller = higherefficiency.

Open impeller = handles watercontaining trash.

Power, P = wQh / 33000e Efficiency of these pumps ~ 75 % .

So it will pump a greater volumewith lower fuel consumption ascompared to other pumps.

It passes spherical solids 1/4th thesize of suction opening. They passupto 10% by volume of mud, silt &sand.

30


31/58

This type of pumps are more

suitable for use of construction

projects.

A check valve on the suction sideof pump permits the chamber to

be filled with water prior to

starting of the pump.

As temp. of water increases

above 60 0F, maximum suctionlift of pump decreases.

SELF-PRIMING CENTRIFUGAL PUMPS

31


32/58

It is a pump which will clear

its passages of air if it

becomes air bound andresume delivery of the

pumpage without outside

attention.

To accomplish this, a charge ofliquid sufficient to prime the

pump must be retained in the

casing or in an accessory

priming chamber.

32


33/58


34/58


35/58

Since a construction pump frequently is operated

under varying heads, it is desirable to select a pump

with relatively flat head capacity & horsepower curveseven though efficiency may be sacrificed.

Since it gives use of electric motor providing adequate

power over wide pumping range

35


36/58

The Contractors Pump Bureau publishes pump

standards for several types of pumps, including self-

priming centrifugal pumps.

36


37/58

Minimum standards of capacities for Pumps.

37


38/58

MULTISTAGE CENTRIFUGAL PUMPS

More than one impeller.

Water discharged from one impeller flows into

the suction of another.

Suitable for pumping against high heads orpressure.

Used to supply water for jetting.

38


39/58

SUBMERSIBLE PUMPS

It is electric motor

operated pump useful in

dewatering tunnels,

foundation pits, trenches.

No suction lift limitation.

No noise problem.

Pump made up of

Aluminium or Iron is best.

39


40/58

TYPES

1. Small fractional horsepower size pumps : for

minor nuisance dewatering applications.

y Typically, 1/4, 1/3 , 1/2 hp units.

2. Large horsepower unit : useful for moving largevolumes and/or high head conditions.

y Power is 1 hp or more.

40


41/58


42/58

PERFORMANCE CURVE FOR SUBMERSIBLE

PUMPS

42


43/58

FACTORS AFFECTING SELECTION OF PUMP The most satisfactory pumping equipment will be

combination of pump & pipe that will provide the

required service for the least total cost.

1. Rate at which water is pumped.

2. Height of lift from existing water surface to point of

discharge.

3. Pressure head at discharge, if any.

4. Variations in water level at suction or discharge.

5. Altitude of the project.

6. Height of pump above water surface to be pumped.43


44/58

DEWATERING METHODS

Deep wells

Well point system

44


45/58


46/58

WELL POINT SYSTEM

Need for well point system:-

Presence of ground water above the depth ofexcavation.

Problems in excavating in sand and gravel.

Lowering the piezometric level of ground.

Problems in construction operation.

46


47/58

COMPONENTS OF WELL POINT

SYSTEM

Well point

Riser pipe

Header pipe

Centrifugal pump

47


48/58

Function of well point.

Function of riser pipe.

Function of header pipe.

48


49/58

FUNCTIONS OF COMPONENTS

49


50/58

MULTIPLE RISER SYSTEM

50


51/58

Type of soil where it can be used.

Permeable soil such as sand or gravel.

Permeable soils.

Problems in clayey soil.

51


52/58

The well point consists of a slotted or

perforated pipe which is covered with a

screen mesh.

At the foot of this pipe is an orifice whichpermits jetting of the pipe into the ground

during installation.

A well-point dewatering system consists of

a series of closely placed small diameter

wells installed to shallow depths

52


53/58

. These wells are connected to a pipe or

header that surrounds the excavation and

is attached to a vacuum pump.

Several risers are then connected todischarge ground water in the header

which is finally diverted to sump.

53


54/58

The construction steps in the well point system

are:

1. the well points are jetted into the ground;

2. the annular void is filled with filter media;

3. the well points are connected to a header pipeby means of a riser;

4. the header pipe is connected to suction pumps

for pumping

54


55/58


56/58

The normal range of well point spacing is from 3

to 12 feet. The well point depth is based on

adequate information on the soil conditions.

Recommended well point depth under the

following conditions:

(a) In uniform soil, place top of screen 3-5 ft

(minimum) below sub grade

(b) with clay at or above the grade, place top of

screen 6 in. above top of clay, and

(c) with deep coarse layer below grade, place

screen in coarse layer.56


57/58

Single pump or multiple pumps may be used,depending on availability of equipment and jobconditions.

If multiple pumps are used, they should be spaced

along the header, or they can be grouped into onesingle pump station.

In a single pump station only one discharge line isused, but in this case large header pipes are used tobring the water to the central pump station without

excessive friction. Redundant or standby pumps must be provided,

installed and be ready to operate in case ofmalfunction of the regular pumps

57


58/58

For high volume pumping a suction manifold

may be used, which reduces the water velocity

in the header line at the pump. The manifold

also causes smooth flow in the critical approach

to the pump entrance, reducing cavitations,

which will increase the capacity of the pump.

Header lines are sized to keep friction at

acceptable levels. Valves are used to facilitate

installation, repair and removal.

58

Documents

Presentation on Dew Ate Ring