Mechanical Component -Pumps

7/22/2019 Mechanical Component -Pumps

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I L L U S T R A T E D S O U R C E B O O K of M E C H A N I C A L C O M P O N E N T S

S E C T I O N 2 6PUMPSPumps: Majo r Classes an d Types 26-2How Pumps Wor k 26-5Centrifugal Pumps 26-6Rotary Pumps 26- 12Reciprocating Pumps 26- 13Pump Applications 26-17Pump Selection 26-23Other Considerations in Choosing Pumps 26-25Priming Pumps 26-26Find How Much Horsepower to Pipe Liquids 26-27


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26-2

Pumps.. .Major Classes and Typesne of mans oldest aids, the pump today ranks second only t o0 he electric motor as the most widely used industrialmachine. Anything that will flow is pumped-from highly volatile

ether to thick muds and sludges. moltem metals and liquids at1000F, or higher, pose few real problems for modern pumps.Though the origin of pumps is lost in antiquity, we do know thatcrude pumping devices provided water for ancient Egypt, China,India, Greece and Rome. Today the U S . alone draws more than200 billion gallons each day from its water resources and pumpsmove almost every drop. Of this total, an impressive80billion gal-lons is said to be industrys share.To meet these demands we find an almost confusingly large vari-ety of available pumps. They range from tiny adjustable displace-ment units to giants handling well over 100,000 gallons per

minute. Number of designs soars into th e hundreds, some differingin elements as small as packing glands, some in the entire princi-ple of operation.Its neither possible nor desirable to cover every variation i n a con-cise practice practical handbook or manual. Soweve made a high-ly selective choice of widely used industrial pumps of all classes andtypes - the pumps youre likely to run into in your work. Andweve stuck to units using mechanical means to move liquid fromone point to another, putting aside for a time such devices as ejec-tors, hydraulic rams, etc.So youll find the important facts about industrial pumping ineasy-to-read form in the following pages. Put them to workimproving the effectiveness of your pumping operations.

CUS S TYP IMPORTANT GENERAL FACTSThe majority of centrifugal pumps built in the U.S. today

Vo lu te are volute type. They are ovallable as horizontal orvertical pumps, single- or multistage for wide flow ranges

Diffuser-type centrifugals find many uses as multistagehigh-pressure units. Origina lly more sfficienl than volute-type pumps, today effiiiency of both types is about equot

Dif fuser

Mixed-flow cenlr ifugal pumps are ide al for low-headlarge-capacity applications. Usually vertical, they have@ a single-inlet impeller. Some horironlal units are builtM ixed- f l owAxial-flow ,units, aften ca lled p ropeller pumps. developrnoll 03 their head by lifting 4611 f vanes, ore wuallye ertical, ond best suited for low heads, large capacitiesAxial-f lowFor cleor liquids. turbine pumps, either horizontal orvertical, f i l l o need between other cenlrifugal and usualrotary designr.They ore low- to medium-capacity,high-head

Turbine orregenerat ive

Gear pumps consist of two or more gears [spur, single- ordouble-heticol teeth], while vene pumps hsve o series ofvanes, blader or buckets turned by o single ro to r . Thisrotary closs also include5 lobe or shuttle-block designs

Gear

Cam-and-plston rotaries, like mort types in th is clo~s,@ ore positive-displacement units, gi ving steady dischargeflow Along with screw-type pumps, and related designs,

@ they handle a wide range of nonabrasive viscous liquidsCam-and-piston

Screw

Old standbys far yeors, direct acting steam pumps now areavailable In many designs for hondling cold or hot water,011, and (1 wide range of industrial liquids of many types

Direct-acting

Power pumps ore dnven from outride Ihrough a cronk-shaft or other device Capacities range from very low tomedium flows, at pressures up to 15,000 PS or higher

Power

Crank.and-flywheel pumps are on e form of reciprocatingpower pump, IO derignoted to distinguish them from powerpumps using, for exomple, an eccentric os drive mechanism

Crank-f lywheel

Source: The following 25 pages are repr inted with permission of Power Magazine, The McGraw-Hill Companies


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Pumps 26-3

DEFINITIONSPUMPING i s t h e a d d i t i o n o f emrgy to o l l q u i d tomove i t f r o m one p o i n t t o a n o t ho rCENTRIFUGAL PUMPS e m p l o y n n t r i f u s a l forceto deve lop o pressure rim fo r nov lns o l i q u i dROTARY PUMPS UM gears, vones, piston:, scrawa,corns, segment:, etc, In o f l xod coring t o p r c d u us t wdy pos l t i va d isp lacam en t o f o l i q u i dRECIPROCATING PUMPS U M pir tons, p lunsen.d loph r wr ns or o t he r dev ica t o pos i t l ve ly d l r phco as iven vo lum e o f l i qu id du r ing aoch s t roke o f t heunitIMPELLER i s the rotat ing alemat in a anhlfusalpum p lh r ounh wh ich i lqu t d passas a n d b y nmnm ofw h i c h enway i s im par t ed t o t he l lqu ldCASING of o centr i fugal p u m p i s the housing sur-roundins the Impel ler . It contains t h e b w r l n g s forsuppor t ing the shaf t on wh ich tmwl le r mounhLIQUID PISTON OR PLUNGERof o rec iprorot ingpum p I s t he m ov ing m em ber t ha t con t ach th e i l q u l dan d imports enargy to i tSINGLE-STAGEcen t r i f uga l pum p l a one in wh icht o t al h w d it deve lopad by ona imwlierMULTISTAGE contrifupot pum p i s one hav ing t woor nor m impdlers oct lng In aorlu In one coslns

c lasses and types in use todayRotav

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The world of pumps can be extremely confusing to new-comers-and even to some oldtimers. Diagram, left, isdesigned to clear up much of the mystery a nd confusionsurrounding pump classes and types. You might call it y ourroad ma p to the world of pumps. Based on often-usedstandard classifications, it incorporates a number of usefulfacts that a re a big help in pump selection and application.

Three classes o f pumps find use today -centrifugal, rotaryand reciprocating. Note that these terms apply only to themechanics of moving the fluid, not to the service for whichthe pump is designed. This is important, because manypumps are built and sold for a specific service, and in thecomplex problem of finding which has the best design de-tai ls we may overlook the basic problems of class and type.

Each classification is further subdivided into a number ofdifferent types, diagram left. For example, under the rotaryclassification we have cam, screw, gear and vane pumps.Each is a particular type of rotary pump.To go one step further, let's take a brief look at a fuel-oilpump in wide use today. It is a rotary three-screw typeavailable with rotors of a number of different materials andfour means of balancing axial thrust.

The last two items are important details in pump appli-cation; first two are keys to classification of the unit. TheHydraulic Institute recommends that the standard classifi-cation be considered as applying to type only, leaving thebuilder to use the details he has developed or standardizedfor that type of pump. So in selecting a pump we oftenfind we must compare, detail for detail , a number of makes.Broad breakdown in diagram comes in handy then.

Ou r next consideration is a wide statement of the generalcharac terist ics of a given class of pumps. Table, above left,does just this for us.

For example, if we want to handle relatively small ca-

classesDacities of clean,

and typesclear liquids at high head, we can referio the table. In any problem of this type we must remember

that suction lift should not exceed recommended limit.Capacity in gallons per minute (gpm) determines pumpsize and influences classification. Nature of fluid is alsoinvolved, as is pump construction. Head is a big factor.

Table shows a reciprocating pump is suitable for thegeneral conditions we have in mind - mall capacity, highhead, clean, clear liquids. Then, depending on job needs,we may choose a piston or plunger type, direct-acting,crank-and-flywheel, or power type. It may be simplex,duplex, triplex, or have a larger number of cylinders.

Once we've settled these items we're ready t o stu dy valvedetails, materials, drives, etc. In general, you'll find thatpump details are greatly influenced by job requirements.Thus the particular arrangement of a centrifugal pump ma ydepend as much on piping, space and working conditionsas on any other existing factors. Drive chosen for the pumpmay be fixed by the pump speed, pla nt heat balance, powersupply available or cost of a particular fue l in the area.Bu t again, these are details, to be decided after we find apump suitable for the hydraulic conditions we must meet.And the key to meeting the hydraulic conditions is the rightclass and typeof pump.Where two or more different units meet hydraulic needs,we must go one step further a nd decide which pump is bestfor the installation. We may want or need low first cost,long life or maximum operating economy. Normally we donot find all in one package. So we must decide which ismost important and go ahead from there.Gett ing the right p ump is much like coming to a fork inthe road. Our map tells us which way to turn.Once on theright road all we need do is watch our route markers. Thenext 29 pages do just th at for you in the world of pumps.


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26-4

As a boy you probably whirledCENTRIFUGAL around your head a bucket on theend of a rope, jus t like the little guy

in the three sketches above. As you recall, the water stayedin the bucket just as long as you kept it turning at a fairspeed. The force that kept the water in the bucket is a t workin centrifugal pumps.

Imagine an impeller a t rest in water, above left. Thisis like the lads bucket before he starts whirling it. Nowrotate the impeller, middle sketch. Water will fly out frombetween the blades just as i t would squirt ou t of the whirl-ing b ~ k e tf it had a hole in the bottom.

The force causing the water to leave the impeller (o r thebucket) is centrifugal force and thats where pumps of thisclass get their name. They depend on centrifugal action eventhough details differ, as well see later.

Going back to the middle sketch, as the impeller throwsout liquid, inore rushes into the center where the lowestpressure exists, and where a suction pipe is normally fitted.This liquid too is thrown out , is followed by more, an d wehave the steady discharge characteristic of centrifugals.

Once the liquid is being thrown from the impeller we mustguide it to its destination. Otherwise weve accomplishedlittle more than make a big splash.

By putting the impeller in a casing we can change flowfrom haphazardly outward to controlled movement in thedirection we want. With vanes like those of the deepwellpump in the righthand sketch we can even turn the f lowupward. A casing, with or without vanes, acts somethinglike a hose attached to the bottom of the boys bucket.

The result is a workable pump for imparting energy toa liquid at one point to cause it to move to another.

Long of major importance in theRECIPROCATING pumping field, reciprocatingunits today are finding manynew uses, particularly in the fields of metering and pro-portioning, and where extremely high pressures are needed.

Direct-acting steam pumps, lop left, have two sets ofvalves in the liquid end. When the piston moves to the leftas shown, liquid is drawn in through the righthand set ofsuction valves and liquid previously drawn into the cylinderis discharged through the upper left set of discharge valves.This is a double-acting pump, liquid being discharged onevery stroke. The actual arrangement of the valves differsin various designs.

Power pumps, top right and lower left, have a number ofdifferent arrangements for suction and discharge valves.In these two single-acting units, liquid is drawn into thecylinder during one stroke of the plunger. On the nextstroke, the plunger forces liquid through the dischargevalves into the pump outlet.Radial-piston pumps, lower right, one of many relativelyrecent designs, have their pistons attached to an outer ringwhose center of rotation can be changed. Moving the ringto an eccentric position produces suction and dischargethrough valves in the center of the pump. Reversing thedirection of ring rotation reverses liquid flow. A large num -ber of other designs are discussed later.


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Pumps 26-5

Like reciprocating pumps but unlike cen-ROTARY trifugals, most rotary pumps are positive-displacement units -t ha t is a given quan-tity of liquid is discharged for each revolution of the shaft.Like the centrifugal pump, flow is usually steady, withoutlarge pressure pulsations.

Rotary gear pumps, above left, have two or more gears ina casing and during rotation the liquid fills the spaces be-tween the gear teeth on the suction side. From there it iscam ed around and squeezed out as the teeth mesh on theother side of the pump.

Sliding-vane rotary pumps, above center, are built in anumber of different designs. In the type shown, the vanesmove in and ou t of the rotor, which is set off-center in thecasing. When the rotor turns counterclockwise, liquid flowsinto the cavity formed by rotor bottom and casing wall.

As the rotor turns, it brings the next vane in to position totrap the liquid in the cavity. Further rotation forces theliquid around and out the discharge opening of the pump.The vanes a re held against the inner wall of the casing bycentrifugal force produced by rapid rotation of the rotor.Screw pumps, above right, draw the liquid into one orboth ends of the rotor or rotors, where it is trapped in thepockets formed by the threads. It is moved along to the dis-charge point much like a nu t on a thread. Screw-type rotarypumps may have one, tw o or three screws. When only asingle screw is used, liquid enters at one end, is dischargedat the other. The screw runs in a double-threaded helix.Clearance is an important factor in many rotary-pumpdesigns that are used today.Later, pp 88, well discuss the large number of other ro-tary-pump designs used fo r a variety of industria l services.

OTHER PUMPING PRINCIPLESSome of the most interesting recent design

developments are in pumps for process andnuclear-energy applications. To handle liquidmetals, for example, we now have electromag-netic pumps, in which electrical energy is ap-plied directly.Electromagnetic pumps include the Faradaytype for ac or dc power, the ac linear-inductiondesign (a modification of this is called the Ein-stein-Szilard pump) and the electromagneticcentrifugal. These, and other similar designs,represent new approaches to the problem ofmoving a liquid from one point t o another.Among older ideas for moving liquids thereare, of course, the familiar air lift, hydraulicrams, a nd the Humphrey pump. Here, however,we stick tu common mechanical methods.

HowPumpswork


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26-6

Q

SINGLE-STAGE general-purpose pump has horizontally spilt carlng, w ob r -~o l odswfflng boxor, cart-Iron double-suction caring. The Impeller 1. modo of bronxa

MULTISTAGE s l ngk u rc ? l on opposed-hn-poller pump for continuous heavy du t y

-A-HORIZONTAL TURBINE PUMP, slngle stage, i s so&-venting to prevent vapor binding.Units Ilk. this or0 bulk w l t h standard stuffing boxes, or with a mechnnlcal sen1

ENCLOSED-TYPE non-averload Imp eller onstainless-steel shoft for vacuum service

C e n t r i f u d rautnns- - I I-~Earlier we saw how modern pumps are classified and typed. Now we're readyto take a closer look at centrifugal pumps - he most widely used units.Illustrations on these tw o pages are a small sampling of today's designs. Studyshows that though all come under one broad classification. intended applicationis a major factor in impeller and casing design, materials used, and other me-chanical and hydraulic features. For hese reasons we find pump builders stress-ing ultimate use somewhat more than classification and type.Thus centrifugal pumps are termed boiler-feed, general-purpose, sump, deep-well, refinery (hot oil), condensate, vacuum (heating), process, sewage, trash,circulating, self-priming, sanitary, bait, booster, paper stock, chemical, fire, jet,sand, slurry, ash, glass, stoneware, submersible, tail-water, etc. In general, eachhas specific features of design and materials recommended by the builder forthe particular service. This makes selection and application easier.

Another suMivision grows out of broad structural features. Thus we findhorizontal and vertical units, close-coupled designs, single- and double-suctionimpellers, horizontally split casings and barrel casings, etc. Correct evaluationof all these variations is one of the big jobs in selecting a pump. SINGLE-STAGE pump WWsleeve booringsand mechanical MI for hot-wotor usms


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Pumps 26-7

NON-CLO(IOING PUMP8 2-bladed impei-Inr, boll beorlngs, removable suction cover

SUCTION SIDE of o single-rmge fir. pump, rompletc wlth motor ond fhtbrpr. RMIprand M n g s for t h i s servkn or. Inbo rnt oy torted before undnrwrlhn' approwl

MIXED-FLOW v.rtcol pump mor be eitherwater or oi l iubrlcated, depending en job

VEETICAL &Sgle-stnlmpelfer, ball a d


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26-8

VOLUTE converts veloc ity energ y of th eilquld Into s t a t i c pressure (read in psl)

Pump a c t i o nIn volute-type pumps the impellerdischarges into a progressively ex-panding spiral casing, proportioned togradually reduce liquid velocity. Thusvelocity energy is changed to pressurehead in the volute.

Stationary guide vanes surround therunner in a diffuser-type pump. Thesegradually expanding passages changethe direct ion of liquid flow and con-vert velocity energy to pressure head.

Liquid in a turbine pump is pickedup by the impeller's vanes and whirleda t a high velocity for nearly one revo-lution in an annular channel in whichthe impeller turns. Energy is added to

Spec i f i c speedSpecific speed is an index of pumptype, using the capacity and headobtained a t the point of maximumefficiency. It determines the generalprofile or shape of the impeller. Innumbers, specific speed is the rpm atwhich an impeller would run if re-duced in size to deliver 1 gpm againsta total head of 1 ft .Impellers for high heads usuallyhave low specific speed; impellers forlow heads have high specific speed.As diagram, r i gh t , shows, each im-peller design has a specific-speed rangefor which it is best adapted. Theseranges are approximate, without clear-cut divisions between them. Chartgives general relations between im-peller shape, efficiency and capacity.Suction limitations of differentpumps bear a relation to the specificspeed. The Hydraulic Institute pub-lishes charts giving recommended spe-cific speed limits for various cond;+ions.

DIFFUSER changes f low direction, aids In TURBINE pump adds energy to the liquidconverting volocity energy to pressure In a number of impulses during rotation

MIXED-FLOW units use bo% cont rl fu gal PROPELLER pump develops most of I t s headf o r ce and lift of vanes on the liqu id by propelling action of vanes on llquld

the liquid in a number of impulses, soit enters the discharge at high velocity.head partly by centrifugal force and

partly by the lift of the vanes on th eliquid. Propeller pumps develop mostMixed-flow pumps develop their of their head by the propelling or lift-ing action of the vanes on the liquid.

Specific speed, rD m

Centrifugal Mixed-Flow Propeller

SPECIFIC SPEED Is approximately related to Impeller shape and efficiency, as shownby these curves. Thoro Is no sharp dividing line between various impeller designs


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Pumps 26-9

Besides being classified according to specific speed, an im- or wall, on only one side. Closed impellers, C and D, havepeller is also typed a s to how the liquid enters, its vane shrouds on both sides to enclose liquid passages. Single ordetails, and use for which it is intended. end-suction units, C, have liquid inlet on one side; in

Open impellers, A, have vanes attached to a central hub double-suction type, D, liquid enters both sides. E, F an dwith relatively small shrouds. Semi-open, B, have a shroud, G are paper-stock, propeller and mixed-flow designs.

Centrifugal-pump casings may be split horizontally, A,vertically, B, or diagonally (a t an angle other than 90 deg).Horizontally split casings are also termed axially split.Both suction and discharge nozzles are normally in lowerhalf of casing; upper half lifts for easy inspection. Vertical-

ly split casings are also called radially split. Theyre usedin close-coupled or frame-mounted end-suction designs.

Barrel casings, C and D, are used on high-pressure dif-fuser and volute pumps. Inner casing fits in outer barrel.Discharge pressure acting on inner case provides seal.

To prevent costly wear of casing and impeller at the runningjoint, wearing rings, also called casing rings, are installed.Where these rings are removable, as they usually are, theycan be replaced at a fraction of the cost of a new impelleror pump casing that might otherwise be needed.

Seal A is a plain flat joint. Similar joint, B, has a flatring mounted on the pump casing. A t C the ring fits into acasing groove; impeller has a similar ring.

In designs D, E, and F, ings are fitted to both casing andimpeller. Form varies with pressure, service, etc.

Practically every type of bearing has been used in centrif-ugal pumps. Today, ball, sleeve and Kingsbury bearingsfind most common use. Many pumps are available withmore than one type of bearing to meet different needs.

Ball bearings, A, m a y be of single- or double-row type.

Spherical roller bearings are widely used for large shafts.Sleeve bearings, B and C, may be either horizontal or

vertical. In the latter, water is often the lubricant.Kingsbury thrust bearings, D, ind use in larger pumps.Design resembles that used in other rotating machinery.


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26- 10

Sleeves protect sh aft against corrosion,erosion and wear affecting its strength.Many forms are used on large pumpsbut on small ones sleeve is often left\ \ I off to cut hydraulic and stuffingboxlosses. Shaft is then made of a metalthat is sufficiently corrosion- and wear-resistant for satisfactory life.

Interstage sleeves guard multistagepump shafts. In some, long hub onimpeller replaces interstage sleeve.

These are used to prevent air leakageinto pump when running with a suc-tion lift and to dist ribute sealing liquiduniformly around annular space be-tween box core, shaft-sleeve surface.

Also called seal cages and watersealrings, they receive liquid under pres-sure from pump or independent source.

Grease sometimes serves as sealingmedium when clear liquid isnt avail-able or cant be used (sewage pumps).

Stuffing box stops air leaking into cas-ing when pressure is below atmospher-ic: holds leakage out of casing to aminimum when pressure is above.

Sketches show solid-packed box,which has no lantern rings: two injec-tion designs, which do. O n pumpshandling hot liquids, or having highstuffing-box pressures, box is oftenwater-jacket cooled. In some, coolantand pumped liquid mix.

Mechanical seals in wide variety servewhere leakage is objectionable. Theyalso find use where stuffing-boxes cantgive adequate leak protection.

Sealing surfaces are perpendicularto pump shaft and usually comprisetwo polished lubricated parts runningon each other. Though not guaranteedleakproof, leakage is usually nil.Outside type, A, is used where grittyliquids or leakage retained in stuffing

box would be undesirable. Inside. B,finds much use for volatile liquids.


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Pumps 26-11

t I

CAM-AND-PISTON EXTERNAL-GEAR INTERNAL-GEAR

TWO-LOBE THREE-LOBE

SINGLE-SCREW

SWINGING-VANE SL ID IW - VAN E Sk4WSE-S-

UNIVERSAL-JOINV CCENTRK IN Ru(IW CHAMMll ILEXIUL-TUBE


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26-12

so

Rotary pumpsRotary pumps, usually positive-dis-placement units, consist of a fixed cas-ing containing gears, vanes, pistons,cams, segments, screws, etc, operatingwith minimum clearance. Instead ofthrowing liquid as in a centrifugal,rotaries trap it, pushing it around theclosed casing, much like reciprocatingpumps. But unlike a piston pump, arotary discharges a smooth flow.

Fifteen designs, left, illustrate a fewof the devices chosen to move fluidsfrom one point to another. Oftenthought of as viscous-liquid pumps,rotaries are by no means confined tothis service alone. Theyll handle anyliquids from A to 2, f free of hardsolids. And ha rd solids can be handledif steam jacketing will melt them. ASwith centrifugals, materials and drivesvary with job, liquid, etc.Cam-and-piston pumps, also calledrotary-plunger type, consist of a n ec-centric with a slotted arm a t its top.Shaf t rotation causes eccentric to trapliquid in casing, discharges it throughslot t o outlet.

External-gear pumps are the sim-plest rotary type. Liquid first fills thespaces between gear teeth a s they sepa-rate on suction side, is then camedaround and squeezed out as the teethmesh. Gears may have spur, single-or double-helical teeth. Some designshave drilled idler to cut internal thrust.

Internalg ear pumps have one rotorwith internally cut teeth meshing withan externally cut gear idler. Crescent-shaped partition, to prevent liquidfrom passing back to suction side, mayormay not be used.lobular pumps resemble the gcar-type in action, have two or more rotorscut with two, three, four o r more lobeson each rotor, synchronized for posi-tive rotation by external gears.

Single-screw pumps have a spiraledrotor turning eccentrically in an inter-nal-helix st ato r or tiner. Rotor is metalwhile helix is hard or soft rubber.

Two- and three-screw pumps haveone or two dlers, respectively. Flow isbetween the screw threads along theaxis of the screws. Opposed screws maybe used to eliminate end thrust.

Swinging-vane pumps have a seriesof hinged vanes which swing out a s therotor turns, trapping liquid a nd forcingit ou t the discharge pipe.

Sliding-vane pumps use vanes thatare thrown against casing bore whenrotor turns. Liquid trapped betweentwo vanes is carried around a nd forcedou t the discharge.

Shuttle-block pump has a cylin-drical rotor turning in a concentriccasing. In the rotor is a shuffle blockand piston reciprocated by an eccen-trically located idler pin, producingsuction an d discharge.

Universal-/oint pump ha s a stubshaft in free end of rotor supportedin a bearing at about 30 deg with thehorizontal. Opposite end of rotor isfixed t o drive s haft. When rotor re-volves, four sets of flat surfaces openand close for a pumping action of fourdischarges per revolution.Eccentric i n flex ib le chamber pro-duces pumping action by squeezing theflexible member against p ump housingto force liquid ou t discharge.

Flexibbtube pump has a rubbertube squeezed by a compression ringon an adjustable ccccntric. Pumps ofthisdesign are built single- and 2-stage.

Characteristic curves, above left, fora typical rotary gear pump show theflat H-Q elation obtainable. Displace-ment of a rotary varies directly asspeed, except as capacity may be af-fected by viscosity and other factors.Thick liquids may limit pump capac-it y at higher speeds because they cantflow into casing fast enough.

Slip or loss in capacity throughclearances between the casing and ro-tating element, assuming a constantviscosity, varies as pressure increases.Fo r example, in above curves, capacitya t 0 discharge pressure is 108 gpm.But at 300 psi and same speed, capac-it y is 92 gpm. Difference is slip.

Power input to a rotary increaseswith liquid viscosity; efficiency de-creases. This is true, of course, withother classes of pumps. B ut since ro-taries find wide use for viscous liquids,it is wise to use the chart, above ri#tt,for sizing suction lines to prevent ex-cessive friction loss.


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Pumps 26-13

SINGLE-ACIING vertical-type power pumpha5 plnlon ahaft for driving crankshaft

INVERTED triptex vertical-piunger powerpump fo r high-pressure job applications

ROTARY-PLUNGER single-acting pump unlthas five or seven plungers in a circle

DIRt?CT-ACIING ho rimn tai duplex plston pump. Steam end i s at le*, liquid end i s atright. Platon-rod no ti on shifts steom vatve for admiralon and exhaust os the stoam

QUAORUPLEX horizontal-plunger power pump fo r h igh p reuures s motor driven throughpinion and gear. Each Scotch yoke drlvaa two plungers. Pump valves are the bolt type

Recb roca t i na numnsThe 13pumps on hese two pages arebut a few of the many reciprocatingtypes in regular use today. But youwill find shown here most of the majordesigns.Reciprocating pumps, unlike cen-trifugals, p 80, are more often classedaccording to type, rather than use.Perhaps this is because their ultimateuse is less clearly defined than forcentrifugal pumps. While certain ap-plications for this type, like fuel-oilpumping, are declining, others, likeboiler and chemical feeding, are rising.

Biggest recent developments are innon-geared higher speed power pumps

-bo th large and small units. Adjusta-ble displacement pumps, also calledmetering and proportioning or con-trolled-volume, are being improvedevery year to give wider capacityranges, greater accuracy, easier control.Power pumps, always of importancein the marine field for boiler feed arefinding some new berths in stationaryplants for the same service where loadsjustify them. And if pressures in super-pressure plants rise, it is likely thatpower-type reciprocating pumps willbe used for boiler feed. Of course,much depends on new developments inthe design of centrifugal pumps.


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26- 4

~~NTRO~ED-VO~UMElunger pump ha5 screw ad/ustment ofstroke ength. Change of crankpin positlonalters capacityof pump

MRERIWCP and propartlonlng pof coupling for adfusrlng stro

oil fo r actuatlon of diaphragm w s h o llquld handled of s th by means of variatlan of the crankpin posEtion

DIAPHRAGM pump with bo ll suction ond dirchorge valves Isbuiltwith stationary or movable base, i s motor driven through beam

DUPLEend w

HORIZONTAL SIMPLEX power pump i s driven by pinion gearedto crankshaft, has disk-type suction, discharge valves, air dome

HORpu

LEX o ~ ~ s l d ~ ~ ~ w p a e k e dar-vatve-typers shown am cmaehadtogether by the


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Pumps 26-15

A 11 C 0 E

Reciprocating-pump liquid ends are built in a large number of designsfor various liquids, service conditions and pressures. Shown above area few typical arrangements for modem pumps.

Die-acting steam pump, A, often has valve-plate liquid end withremovable discharge-valve decks. Cup-type packing for liquid pistonis also shown. Valvelpot type, B, has valve chambers closed by indi-vidual covers. Outside-pecked plunger pump, C , has its valves in pots-all packing leakage is external where it can be seen.Vertical power pump, D, .has plunger packing a t cylinder top, whilehorizontal triplex pump, E, has it in the usual location with valvesabove and below plunger. At F, valves are in step arrangement. An-other design for a vertical triplex pump appears a t G. Liquid-end designi s a function of pressure developed, liquid handled, capacity, dc .

Flat or 'D' slide valves find use forsteam pressures of 200 psi and lessBalanced piston valves are commonin large high-pressure pumps.

Ffat valve, A, is thrown by auxiliarypiston. Motion is regular and positive.Balanced-piston valve, 3, runs insleeve, has minimum friction, long life.C is another balanced-piston valve.

Typical steam-valve linkage,D, con-nects to rod. Steam-end design of ver-tical pumps resembles those shown.

A B

C b

Packing is any material used to con-trol leakage between a moving andstationary part in a pump. Flexible,and usually soft, it is expendable.Simple piston-rod stuffing box, A,has several rings of square packig.On small rods a single nut surroundsgland, instead of studs shown. Chevron W Wpacking, B, is often used.Sketch shows A 11 Cplunger of high-pressure pump. C isa iacketed stuffing box.piston packing- talc- many forms.Duck-packed piston, D, is for bronze-fitted general-service pump. Cup pack-ing , E , is standard for oil pumps. solidrubber rings, F, ar e also popular.


16/28

26-16

A B c DAs a general rule, stem-guided disk valves are used for low-pressurejobs, wing-guided (flat- or bevel-faced) for moderate pressures, andbevel-faced wing for high pressures. But much depends on liquid, etc.

Flat disk, A, has inclined ribs in seat to direct liquid so it rotates diskslightly at each stroke. Ball valve, B, often finds use where free open-ing for thick liquid is desired. Cage guides ball during its rise and fall.Seat is circular and completely open. Wing-guided valve, C, or thickgritty liquids, can be fitted with renewable rubber inserts for wings.Another design, D, for high-pressure clear liquids, has renewable seats.Low-pressure valve, E, and high-pressure valve, F, or thick liquidsare alloy-steel with synthetic inserts for all ordinary services. Specialmaterials are used where corrosive liquids are to be handled. Double-ported ring-type valves, G, p 92, are popular in large power pumps.

A 6 C

Suction and discharge cushion cham-bers smooth liquid flow. Dischargechamber, A, is often built as part ofpump while suction chamber may bepar t of pump or in adjacent piping.Pressure alleviators, B and C, induse with high-pressure power pumpsto absorb shock from sudden stoppingof liquid. They usually consist of aspring-loaded plunger operating in ashtffngbox. Liquid does not escapefrom piping system during surges.

There seems no end to devices forvarying capacity of small reciprocat-ing pumps. A few appear on pp 90-91.For large power pumps, however, notso many variations exist perhaps be-cause of the lesser number of designs.Suction-valve unloader, A, gives aquick but gradual reduction in liquiddelivery from full to zero flow in notmore than one-half revolution ofpump. It increases liquid delivery insame way, i s pneumatically actuated.

Stroke-transformer, B, can automa-tically or manually vary plunger mo-tion from zero to maximum stroke.Output is infinitely controllable.


17/28

Pumps 26- 17

The modem double-case barrel-type centrifugal pump i s today's answer forpressures approaching 6000 psi and temperatures to 1000 F. In t he common2600-psi ange, units of this type run at about 3600 rpm, have up to 12 stages.'The first superpressure plant uses two pumps of this type in series, withheaters between. Note how vertically split inner assemblv i s housed in casing.

Medium- and ~ i ~ ~ m ~ r e s s u r eoiler feedHorizontal split-case diffuser-type pumps with about six stages are commonfor 3600-rpm duty at pressures to 1600 psi. Some thinking today sees theseunits applied up to 2500 psi, but that is in the future. Design shown s 6-stagewth back-to-back impellers in groups of two f o r better hydraulic balance. Abig advantage of this type of pump is easy removal of top for maintenance.

Pump upplicutiof7sAny attempt to list every possible application of pumps isalmost certain to run aground because editors, being human,might overlook important jobs like pumping goldfish, ap-ples, oranges, eggs and beer.So these tw o pages, and the following four, give a nec-essarily selective cross section of pump classes and typeson the job. There lies the ultimate goal of pump designersand builders-a product th at performs a given service a tthe best over-all cost with minimum operating and main-tenance needs. To secure these results the pump must besuited to the job, installed correctly, operated and main-tained as the builder recommends. For now, let's take aquick look a t application.

Pump class, type, drive and materials are among themajor factors in unit selection. While generalizations are

often dangerous, studies of a large number of moderninstallations show that industrial and service establishmentsthroughout tbe U.S. se centrifugals for about 60% oftheir jobs, reciprocating for about 227& rotary for about12% and deepwell for about 6%. About 86% of the cen-trifugals have motor-drive, 44% of reciprocating, 96% ofrotary and 95% of deepwell. Steam engines, turbines andinternal-combustion engines drive about 13% of the cen-trifugals. Steam is outstanding for reciprocating units,driving almost half of those in use.

While these statistics are helpful from an over-all view-point, they serve merely as a guide to what industry isdoing today. For help with a specific installation, the textand illustrations on these six pages will lead you throughthe maze of classes and types toward a sound answer.


18/28

26-18

Power reciprocating for boiler feedAt pressures over about 250 psi where load is variable, power reciprocatingpumps find application. They are also used for desuperheater feed in thispressure range. Vertical quintuplex units like that above are popular in feedservice because they are easy t o control automatically in stepless straight-linefashion from 0 to 1 0 0 ~ o f rated capacity. Use is now on the upswing.

low-pressure boiler feedDirect-acting pumps, with or without receiver, find use in smaller low-pressureboiler installations. Simple, rugged and economical, they give outstandingservice. Though not always classed as feed pumps, centrifugal condensationsets, r igh t , are extremely popular in heating and similar installations. Com-pact and efficient, they handle wide temperature, pressure, capacity ranges.

Fuel oilScrew and gear pumps are the modern units for fuel-oil pumping but direct-acting steam pumps still do the job in some plants. Screw pump shownhandles up to 80 gpm at continuous pressures of 275 psig, intermittent to 325psig. Pumps of this type find many other uses besides fuel-oil pumping,including lubrication, booster, circulating, governing and elevator jobs.


19/28

Pumps 26- 19

Heater drains, condensateHandling condensate from hotwells, heater drains and other sources mayimpose severe operating conditions on a pump. In condenser service, suctionhead is low, liquid is near the boiling point, suction seal is a minimum andload changes wide. Usual centrifugal condensate pumps have one to fourstages, special sealing and balancing features. Uni t shown is single-stage.---Cooling waterWhether tremendous, like the 55,000-gpm unit at left, or tiny as those on asmall a ir conditioner, cooling-water pumps have some common traits. Theyare usual ly single-stage, standard-fitted, split-case. In th e larger capacitiesthey are often horizontal units, though many vertical designs are also used,both large and small. Their duty is seldom severe; operation is trouble-free.

Handl ing ash, abrasive solidsIn contrast to cooling-water service, handling abrasive solids of any kindimposes many special problems on a pump. Rubber-lined units with specialseals, as shown, are one good answer for ashes, sand, etc. Other designsinclude packingless types, flat-blade impellers and special arrangements forsuction inlet. While the pump is important, so are other system details.


20/28

26-20

General purposeThis term applies to all classes of pumps, but centrifugal designscategory perhaps outnumber al l others. Usual meaning of term is 6to handle clear cool liquids at ambient or moderate temperaturessingle-stage. these units may be split-case, and are standard-fittedequally good for a number of services. Some handle liquids with

in thisI pump. Oftenpumpssolids,

General process workIn recent years engineers have developed special process-pump designs fea-turing accessibility, good efficiency and long life. Some designs are availableas pa rt of a s tandard line whereas others are made up to suit the particularservice conditions for a specific job. As these illustrations show, ease ofmaintenance is a prime consideration: complete disassembly is simple.

Chemical processOutwardly resembling the general process pump, units designed for chemicalservice may differ markedly in materials. stuffing boxes, seals, etc. Usual aimis to produce a single pump line that comes as close as possible to being ableto serve all process needs in the chemical industry. Usual units are horizontal,with radially split casings. They can handle a wide range of chemical liquids.


21/28

Pumps 26-21

Chemical feedRequiring easy adjustment of capacity, chemical-feed pumps are buil t in alarge number of different designs. Unit shown has its reciprocating pumpingelements arranged for accessibility. Suction and discharge valves are balltype.

Well-water supply

c

Water , like gold, is where you find it. Often this is deep in the earth. So wefind many designs for this service. Veepwell pump, A, often called a turbinepump, is a multi-stage diffuser unit. Jet pumps, B, bypass a portion of theirdischarge t o an ejector nozzle at the suction screen where it helps improveflow into pump. Submersible, C, has motor in well. D i s plunger pump.


22/28

26-22

Sewage and sumpCentrifugal pumps for sewage usua!ly have special non-clogging impellersand a casing that is easily opened for unit inspection, above right. Sumppumps, left and extreme right, may be portable or permanent, depending onneeds of the installation. Impeller is almost always the non-clogging type toprevent solids from catching in it. Automatic control is practically universal.

New and special servicesDeveloped in '30s for hot-water circulation, and later refined for chemicaland nuclear-power jobs, canned pumps are now strongly bidding for industrialjobs where leak-free service and minimum maintenance are essential. Unit Ais fractional hp, goes right in pipe. B has axial air-gap motor, is built in10-hp and smaller sizes. C is chemical unit, D one for nuclear-energy service.

~ i ~ h - p ~ e s s u r eervicesWhere quick starts, compact installation and steam drive are desirable, asin certain boiler-feed applications, petroleum refining, etc. the high-pressureturbine-driven type shown above has many uses. It consists of a single-stageimpeller near one end of the shaft ; at the other end is a velocity-staged turbinewheel. Single shaft produces a compact unit easy to install and operate.


23/28

Pumps 26-23

Typical piping hookups

Et-. Static suction lift- -A

heodB

for pumpsn

serving industrial loadslbfol heod

C D E

Pump selection 5 steps foSelecting a pump is much like buying a hat-you have threemajor decisions to make. These are size, type and bes t buy.But of course choosing a pump can be a far more complexproblem, especially where unusual or difficult liquid con-ditions are met. Steps outlined below have proven suitablefor typical general-purpose,process and similar applications.Selection of other types - oiler-feed, condensate-return,hydraulic-system, etc. - sually involves analysis of factorsnot directly related to the pump itself. For example, youmight have to compute several plant heat balances beforeyou can make a firm decision on boiler-feed pump type,capacity, drive, etc., best for the existing conditions. Someof these factors were discussed earlie r; others are too com-plex for coverage here.

1Trying to pick a pum p without a sketch of the system layoutis like a miner trying to work without his lamp. Youre inthe dark from start to finish. Base sketch on actual job,as planned. Show all piping, fittings, valves, equipment,etc. Mark length of pipe runs of sketch. Be sure to includeall vertical lifts. Where piping is complex, an isometricsketch is often extremely helpful.

Sketch layout (see diagrams abov e)

2 Determine capacity (see Table I)Job conditions fix capacity required. For example, maximumsteam flow from the exhaust of a turbine, along with steamcondit ions, determines, the minimum amount of coolingwater at a given temperature. Seasonal changes, safetyfactor desired, etc., influence actual capacity chosen. Wheredemand is unknown and must be estimated, Table I is a bighelp in indicating typical ranges to be expected. It doesnot, however, give exact values because there can be widevariations from one installation to another. Except for

small pumps and those for metering and proportioning,capacity is expressed in gallons per minute (gpm).

3Diagrams above show various heads in typical pumpingsystems. Definitions, facing page, will help you understandthe meanings of various terms. If a pump handles 500 gpmof water thrcmgh 86 f t of 6411. suction pipe, diagram aboveright, and there is one medium-radius elbow having aresistance equal to 14 f t of st raight pipe. total equivalentlength of suction pipe is 86 4- 14=100 ft. Friction loss fromTable I1 is 1.7 f t of water per 100 f t of pipe. Velocity head isalmost 0.5 f t and static suction lift is 8 ft . Hence, suctionlift is 8 + 1.7 + 0.5 = 10.2 ft . Discharge head is foundin a similar way, using discharge pipe size, length of runsand fittings in the line. Tota l head is the sum of suctionlift and discharge head. Where we have a static suctionhead, as in the second hookup from the left, we subtractsuction head from discharge head to obtain the total head.Always have pump manufacturer check your head calcu-lations. Then youll be certain the pump is suitable.

Figure total head (se e Tables II,111)

4 Study liquid conditionsUp to this point weve determined but two requirementsour pump must meet - head and capacity. Now we cometo characteristics of the liquid and their effect on pumpselection. Liquid heavier than water (specific gravitygreater than 1) takes more horsepower to be moved fromone point to another; lighter liquids require less power.Liquid temperature and vapor pressure fix the net positivesuction head needed for satisfactory operation. Unless youare thoroughly experienced with this phase of pum p selec-tion, it is best to have the manufacturer check suction condi-tions. Viscosity of liquid affec ts horsepower, head and


24/28

24-24

DEFINITIONSSTATIC SUCTION L I F T i s v e r t i c d dir lance, f l,from SUPPIYe v e l l o pump renlerline; pump aboveSYPPIY.STATiC SUCTION HEAD: some 01 s I o t i < wcl ionl i f l , b v l pump i s below supply level.STATIC DISCHARGE HEAD i s verlieal dir lonce, It .from pump csnlerline Io point of free delivery.TOTAL STATIC HEAD i s vertical dir lonre. It , f r o ms ~ p p l y e v e l l o di irharge l e v e l .FRlCTiON HEAD i s ~ W S S W ~ , in II of l iquid,needed l o overcome rosislonce o f pipe, f ill ings.SUCTION LiFT is s lo l i c wc l i o n haod piUI w t l i o nfri head ond v a l o c i l y head.TOTAL HEAD i i sum of f w t i o n l i f l and dischorsehaod. Where lhere i s w t l i o n heod, t o l d hemd i sdif f erence between dischorse and w c l i o n heads.NOTE: Soma enciinaeri use d r n o m k wc l ion lifl,dynamic dischorse head ond to101 d y n a m i c headinslead of te rms above. While the word d ynam ichsipr O X C ~ ~ S Sde o o f m o i ion . ie. head whenl iqu id i s f lowing. lh e simpler terms are favored.

results

I: TYPICAL WATER REQUIREMENTSUsuol b u i l d i n g s ' I C i t i es o n d t o w n s

F i x t u r e C o l d ,Wof e r . ~ l o r e l lush valveWolsr . r lore l f lush l ankU r i n o l i , f lush valveUrinalr. f lush lankLavotorierShower. A.in. headShower, &in. ond largerNeedle ba lhShompoo rproyB o t h r , l v bKitchen r inkPont ry r ink, ordinaryPont ry r ink, I o i g e b ibbSlop s inksWash f r aysLaundry t r o yGarden-hose bibb

9 P mA510301033

63015A26636i o

H o t . 9 P m000033630154266360

P o p u lo t i o n l o t o l * * , g p m1000 8002000 12003000 15004000 1700:ooo 20006000 22008000 27009000 290010.000 310020,000 5100AO.000 87005o:ooo 11,000

60,000 13.000100.000 19,000150,000 28,000180.000 33,000200,000 37,000'Appror imole m a x i m u m f l o w f rom fixtures: l o "To ta l includes w o t e r fo r domestic lupplyobloin m a x i m u m prebobfe f l o w , mu l t l p ~ y and f i re prolsct ion. Where city or l o w n i sm a x i m u m possible l l o v by a vm ge ticlor prademinonlly indurlr iol. o grealer f low wi l lbored on ~ ) r e v i o ~ ixperience. probably be required.

capacity, as well as class of pump chosen. Here, again, yourbest bet is the manufacturer. Liquid pH influences pumpmaterials, p 85,while solids affect mechanical construction.

5 Choose class and t ypeStudying the laycut, like trying on a hat, tells us what size(capacity and head) pump we need. This furnishes our firstlead as to what class of pump is suitable. For example,where high-head small-capacity service is required, tablep 77 , shows that a reciprocating pump would probably besuitable. Reviewing the liquid characteristics furnishesanother clue to class because exceptionally severe conditionsmay rule out one or another right at the star t. Sound eco-nomics dictates choosing the pump that provides the lowestcost per gallon pumped over the useful life of the unit .Operating factors deserving recognition when deciding onclass include type of service (continuous or intermittent),running-speed preferences (high-speed pumps often costless), future load expected and its effect on pump head, pos-sibility of parallel or series hookup, and many otherspeculiar to a given job. These factors deserve as much studyas head and capacity; they're just as important.Once you know class and type you're ready to check thesein a rating table, p 104, or a rating chart as on p 87 . As youcan see, the table lists pump capacity, head, horsepower,etc. Where required capacity and head, or both, falls betweentwo tabulated values, it is usual practice to choose a pumpto meet the next larger condition where this is not too farfrom the existing job conditions. Otherwise, another make ortype of pump may have to be used.One important fact to keep in mind is that mnny largepumps are custom-built for a given plant or application.Under these conditions the pump manufacturer performsmost of the steps listed above, basing his design on infor-mation supplied by the engineer on the job.

11: PIPE FRICTION LOSS FOR WATER( W r o u g h t - i r o n o r s t e el S c h e d u l e 40 p i p e i n g o o d c o n d it i o n )

D i a , F l o w ,i n . s p m2 502 1002 1502 2002 300A 2004 300A 5004 10004 20006 20 06 5006 IO006 20006 40008 5008 10008 20008 A0008 8000

10 IO00IO 300010 500010 750010 10.00012 200012 5000I 2 10,00012 15.00012 20.000

F r i c t i o n 105r,f t o f w a t e re l o c i t y , V e l o c i t y h e o d ,

f t p er r e c f t o f w o t e r p e r 100 f t p i p e4.78 0.355 4.679.56 I .42 17.414.3 3.20 38.019.1 5.68 66.328.7 12.8 1465.OA 0.395 2.277.56 0.888 4.8912.6 2.47 13.025.2 9.87 50.250.4 39.5 1962.225.551 1 . 122.244.A3.216.4112.825.751.33.9311.819.629.539.35.7314.328.7.!" 0

21.3

0.07670.A791.927.6730.70.1600.6392.5610.210.90.2402.165.9913.514.00.51 13.1912.828.751.1

0.299I .666.1723.893.10.4241.565.8622.688.60.4974.0010.824.042.20.7764.4717.438.468.1

111: RESISTANCE OF FITTINGS A N D VALVES( L e n g t h o f r t r o i g h t p i p e , f t , g i v i n g e q u i v o l e n t r e s i s t a n c e )

P i p e S t d M e d - L o n g - 45- l e e G a t e G l o b e S w i n gs i z e, e l l r a d r a d d e g v a l v e , v a l v e , c h e ck ,in . e l l el l e l l o p e n o p e n o p e n1 2.7 2.3 1.7 1.3 5.8 0.6 27 6.72 5.5 4.6 3.5 2.5 11.0 1.2 57 133 8.1 6.8 5.1 3 .8 17.0 1.7 85 20A i I . 0 9.1 7.0 5.0 22 2.3 110 275 lA.0 12.0 8.9 6.1 27 2.9 140 336 16.0 14.0 11.0 7.7 33 3.5 160 408 21 18.0 1A.O 10.0 43 A.5 220 5310 26 22 17.0 13.0 56 5 . 7 290 6712 32 26 1u.J 15.0 66 6. 7 340 80

14 36 31 23 l I . O 76 8.0 390 9316 42 35 27 19.0 8, 9 . 0 4 3 0 10 718 A6 40 30 21 100 E.? 50 0 12020 52 A3 3A 23 110 2.0 56 0 13 424 63 53 40 20 140 14.0 580 16036 PA 7 9 60 A3 200 20.0 ' O C O 110


25/28

Pumps

---

E,:ek -.p0 -00

. ! -

--

26-25

11001000900

I-800.,P-' 7 O O g-6002u1

- 5 0 0%- 4 O O i3002200100

Typical cent r i fugal -pump r at ing tableT d o l hood , f!

Size Gp m IO I5 20 25 301000..8 1060-1.0 1150-1.21070.1.2 1150.1.5 1210-1.712F0.2.1 1360-2.4

150 760.53 850- .78 950.1 1030-1 2 1100-I1170.1.9 1190-2.3 1260-2.61400-3.6

3cL {:! 870-1.2 950-1.6 1000-1.9 1100-2.4 1170-2.81 2 0 0 4 . 1 1230-3.7 1290-4.11490-5.8400 750-1.3 850.1.8 940-2.4 1040.3 1120.3.74c ( 6 6 1080.4 1170-4.6 1210-5.51400-8.4

617-.21 707-.03 778-.A0 865-.5168 0- 37 760..49 865-.63 900-.76856-.78 916-.94 980-1.1

950-1.1 1010-1.4 1100-1.7 1170-2

1W 690-.63 800-.95 910-1.3 1010-1.6 1110-2.05

820..93 850-1 I 930-1.35 990.1.6970-1.8 1040~2.1 1080.2.3

Exornple: 1080.4 indicates pump speed is I O B O rpm;actuol input required to operote pump is 4 hp .

Other considerations in choosing pumpsOur previous two pages outline usual steps in choosing apump for typical industrial services. There are cases, how-ever, where selection is better made by the pump builder.

Estimating data sheets, above right, are available frommanufacturers to aid you in making a complete statementof conditions a new pump must meet. When sending suchan estimate to a manufacturer it is wise to include a clearfree-hand sketch of the installation.While the sheet shown is for a centrifugal pump, formsfor reciprocating and rotary estimates resemble this closely.Having the manufacturer select your pump insures gettingthe right unit, providedyou supply the information he needs.Net positive suction head is often listed on estimate sheets

and must be entered to give a complete picture of pumpingconditions. This term gives pressure available or required toforce a given flow, gpm, into the impeller, cylinder or casingof a pump. For uniformity, npsh is stated as feet of liquidequivalent to required pressure in psi over and above vaporpressure of liquid at pumping temperature.Every pump has its individual required npsh character-istics which the manufacturer can plot on a performancecurve. Npsh at any point on the curve is head in feet ofliquid pumped equivalent to pressure in psi required toforce liquid into the pump. Values shown by pump manu-facturer are based on tests and are regularly corrected tothe centerline of the pump.As engineer in charge of plant services you must locatethe pump and design the suction piping so available npshis equal to or greater than npsh required by pump. Curves,right, give vapor pressure of water at different tempera-tures. They also give conversion factors for changing flowfrom Ib per hour to gpm. Both are useful in planning.

Pipe sizes for lines where flow demand is likely t o changeor resistance may increase over a period of years require 5careful study. If sized only o n basis of today's demands orresistance, we may find that what was once an economicalinstal lation becomes a money-waster.Complete Analysis. Though not all jobs warrant it, apiping system can be completely analyzed for present andfuture operations by using pump characteristic and system-head curves like those on p 86. But instead of plotting onesystem-head curve, a series, one for each operating mndi-tion, is plotted. Study of these will show jus t what we mayexpect from a given pump today, tomorrow, and five ormore years from now. This is a job for the engineer in theplant and it deserves more attention than it usually receives.

2.00.70 2.10.75 2 2

&8Q 2.30.85 2A0.90 2 50.95 2.6I .o 2.7

2.8

a

100 200 300 400 500Te m p e r a tu r e , F150 250 350 450 550


26/28

....

OO'JBLE VO' IJTE rnrircolntcr l iquid-vapor A IR SfPARATOR and ? w e d l i t h a r g e p a r hmixturr $UV'PO prlme, separates vapor in pump give pr im ing action in t h i s unit

SLOTS in impel ler vanes permit olr to beentrained by prlming l lquM in th is pmnp

suction and discharge, liquid being circulated from dis-charge to suction on prime. Automatic valves or hydraulicaction stop circulation after pump primes. Some pumpscirculate liauid continuously.

priming pumpsPositive-displacement pumps - eciprocating and rotary -are self-priming for total suction lifts to about 28 ft . whenin good condition. But with long suction lines, high l i f t sor other abnormal conditions, they must be primed.

Centrifugal pumps are not self-priming; on a suction liftthey mus t be primed. Either special self-priming units maybe used or auxiliary priming equipment may be installed.Illustrations at top of this page show six modem self-priming units. Designs vary from one maker to another,

but a liquid reservoir of some type on the discharge iscommon. It holds priming liquid and serves as an airseparator. Other desians have a liauid reservoir on both

Auxiliary equipment for pump priming includes ejectors,vacuum pumps, etc., used in hookups like those sketched.

With a flooded suction, A, opur casing air-vent petcocksand then slowly open suction gate valve. Incoming liquidpushes air from casing. Bypass around discharge checkvalve, E , permits using liquid in discharge line. Foot valve,C, holds water in suction line, is augmented by auxiliarysupply. Separate pump, D, draws air from casing for prim-ing. Or an ejector, E, does same job. Priming tank, F, oldssupply of liquid large enough to establish flow throughpump on starting. Vacuum pumps, G and H, re manuallyand automaticallv controlled to mime the main numu.


27/28

Pumps 26-27

Find How Much Horsepowerto Pipe Liquids ICharts give answers for flow from 50 to 100,000 gpm for pipe-roughnessratios of 0.02 to smooth.DouglasC . Greenwood

Th e charts o n thesc two pages will make it easicr todesign pumps and othcr cquipmcnt for handling liquidflowing in pipes.First, it is often helpful to know the theoreticalhorsepowcr rcqiiired to raise the liquid to various heads.

This is obtainccl from th c horsepowcr-gpm charts. T he yare plotted for a IO-ft head of watcr: F or oth er hcads,multiply hp by HA0 whcre H is the reviscd head; fo rother liquids, multiply by the corresponding specificgravity.

Horsepower

Hp-gpm Chart . . .shows how much hp isrequired to pump wateragainst a IO-it head.Full-pipe flow i s assumed.

Horsepower


28/28

26-28

SYMBOLSG =f l ow rate, gpm R = Reynold's number w =fluid density, Ib per cu ft= 0.0833 Vd/vV =velocity, fpsd = pipe dia, in.

HI =head loss, f t1=lengt h of pipe, ft

r = elative roughness of pipe = c/dc = effective height of roughness partic le, in.

P = pressure, psi f = r iction factor Y = inematic viscosity, ft2/sec

Next, for practical results friction losses must beaccounted for. These vary and should be known foreach individual case.Muc h uscd in liquid-flow calculations is th c Darcyformula6LV*='d32.16

which can be modified, if velocity is in gpm, toLG2

d 5HI 0.0312J- 11or for head loss in psi units

Practical values of f vary from about 0.01 to 0.06depending on pipe smoothness and dia. For laminarflow, f = 64.4/R. The flow chart gives f for variousvalues of R and pipe roughness. Values E fo r variouspipes arc: 0.00006 in. for smooth drawn tubing; 0.0018in. for wrought iron; 0.01 in . for cast iron. Curvcs forrelative roughness values of 0.0005 to 0.01 are plotted.Most of these lie in the transition zone between laminarflow and complete turbulence.

Fluid-flow Chart . . .gives f r ic t ion fo r var ious pipe condi t ions and va lues of Reynold 's Number .

0.05

0.04

.cL

c0 0.03Y-

r0u.-c._IlL

0.02

0.0 I

03 I I I l l l l I I I I l l l l l I I I 1 I I l l 110 10,000 I00,000 I,000,000

Documents

Mechanical Component -Pumps