PM2560 Pump Selection

8/7/2019 PM2560 Pump Selection

1/39

PM2560 Pump Selection


2/39

Ca lcula tion procedure for pump

selectionHere is a step-by-step procedure for choosingthe cl a ss, type, c a pa city, drive, a nd m a teri a lsfor a pump th a t will be used in a n industri a lsystem


3/39

1 st step .. Sketch the proposed l a yout

Use a single line di a gra m Show a ll of the piping, fittings, v a lves, a nd

equipment ( a s well a s other units)


4/39


5/39

2nd step continued

For this feed r a te, a pply your contingencyf a ctor or s a fety f a ctor

Typica l f a ctors a re in the r a nge of 1 0% (ca n bea s high a s 50% depending on the a pplic a tion)For ex a mple, required flow r a te = 450 GPM

Sa fety f a ctor a bout 1 0% or 45 GPM Flow r a te for pump selection = 450+45 = 495 GPM Round it up a bout 500 GPM or gre a ter


6/39

3 rd Step .. Ca lcula te tot a l he a d on thepump

Ca lcula te the tot a l sta tic he a d (pump loc a tion withrespect to suction a nd disch a rge)

Ca lcula te the he a d loss due to frictionCa lcula te the tot a l length of the str a ight pipeCa lcula te the equiv a lent length of the bends, v a lves,fittings etc.Ca lcula te the entr a nce a nd exit equiv a lent lengthNow c a lcula te the he a d loss using D a rcy s equ a tion


7/39

4 th step .. An a lyze the liquid conditions

Need the complete d a ta on the liquid being pumped Na me a nd chemic a l formul a Ma ximum a nd minimum pumping temper a ture

Corresponding v

apor pressures

at those temper

atures

Specific gr a vity Viscosity a t the pumping temper a ture Fla sh point Ignition temper a ture Unusu a l tendencies (fo a ming, cryst a lliza tion etc.) Solids content (size a nd type) Va ria tion in chemic a l a na lysis


8/39

5 th Step Select the C la ss a nd type of pump

Three cl a sses of pumps centrifug a l, rot a ry,

reciproc a ting Descriptor only

for the mech a nicsof MOVING THELIQUID (not theservice for whichthe pump w a sdesigned)


9/39

5 th step continued


10/39

Also consider oper a ting f a ctors for the pump Type of service? (continuous or intermittent?)

Opera

ting speed preferences? Future lo a d incre a se? Ma inten a nce f a cilities a va ila ble? Possible p a ra llel or series hookups?


11/39

Once you h a ve selected your type of pumpconsult a ra ting t a ble or r a ting ch a rt from a m a nuf a cturerWhen hydr a ulic requirements f a ll betweentwo pump models, pick the bigger


12/39

Pump R a ting Ta ble

ModelNa me


13/39

Exa mple R a ting Cha rt from a Ma nuf a cturer


14/39

Other d a ta

Other pump d a ta included inm a nuf a cturer sengineeringinform a tionincludech a ra cteristiccurves for v a riousdia meter impellersin the s a me c a sing


15/39

Other d a ta continued

Ma nuf a cturer m a y a lso provide a va ria ble-speed to he a d-c a pa city curve for a SPEC IFIC impeller


16/39

Next step EVALUATE THE PUMP!

C heck the specific speed of the centrifug a lpump

To do this we need to determine the specificspeed a nd suction specific speed Motors c a n oper a te a t different RPM Ta bul a te the oper a ting speed a nd how it effects

the specific speed a nd suction specific speed

head total H H NQ

N S

!

!

75.0

5.0

head suction positivenet PS PS S

!

!

75.0

5.0


17/39

Exa mple

A single-suction centrifug a l pump is driven bya 60-Hz a c motor. The pump delivers 1 0,000ga l/min of w a ter a t a 1 00-ft ( 3 0.5-m) he a d.The a va ila ble net positive suction he a d is 3 2 ftof w a ter. Wh a t is the best oper a ting speed forthis pump if the pump oper a tes a t its best

efficiency point?


18/39

Altern a ting-current motors c a n oper a te a t a va riety of speeds, depending on the numberof poles. Assume th a t the motor driving thispump might oper a te a t 870, 11 60, 1 750, or3 500 r/min. Ca lcula te specific speed a ndsuction speed for the v a rious RPM


19/39

Using a ta ble of specific speeds fordifferent types of pumps


20/39

Once you h a ve the specific speed


21/39


22/39

B a sic Principles

The he a d required to pump a fluid betweentwo points in a piping system c a n beca lcula ted by re a rra nging B ernoulli's l a w:

We did this a lre a dy for the l a st ex a mple


23/39

Equa tion indic a tes Hp = 0, then the piping is inequilibrium a nd no pump energy is needed toobt a in the desired flow.

If Hp < 0, this me a ns th a t the system is not inequilibrium a nd flow will incre a se,

ca using Hf to incre a se until Hp = 0 a nd equilibrium isest a blished.

If incre a sed flow is not desir a ble, a restriction must bepla ced in the pipe to c a use a n a rtifici a lly high frictiondrop.


24/39

In Most Pumping Systems

The difference in velocity he a d ca n be ignoredIf the l a st equ a tion shows th a t the he a d required forthe pump is 0, then piping is in equilibrium a nd nopump energy is neededIf the he a d required for the pump is less than zero ,th a t me a ns th a t the system is not in equilibrium a ndflow will incre a se c a using friction he a d to incre a seuntil pump he a d is zero


25/39

Pumps c a n only pump liquids not v a pours Liquids should not be v a porized during the

oper a tion of a pump

Rise in temper a ture a nd f a ll in pressureinduces v a poriz a tionNPSH a s a me a sure to prevent liquid

va

poriza

tionNPSHr is a function of pump designNPSHa incre a ses a s ca pa city incre a ses


26/39

Ca vita tion

Ea ch pump requires a cert a in minimumpressure a t its suction fl a nge

Ensure th a t no vapor is flashed between thepump suction a nd the cylinder or entr a nce to theimpeller v a ne

If a lower pressure is supplied, v a pour could

be freed by the liquid in the form of sm a llbubbles th a t would then c ollapse


27/39

Ca vita tion

The implosion cre a ted when v a por is fl a shedresults in c avitation

Noise, vibr a tion, gre a tly incre a sed we a r, a ndreduced pressure or throughput c a pa city a re sideeffects

To stop a product from v a porizing or boiling a tthe low pressure side of the pump the NPSHA(net positive suction he a d a va ila ble) must beequ a l to or gre a ter th a n the NPSHR (netpositive suction he a d required).


28/39

Net Positive Suction He a d

Definition of NPSH is the net pressure abovethe v a pour pressure of the liquid beingpumped!When a liquid s pressure drops below itsva pour pressure, g a s if flashed!We c a n a void c a vita tion by a ssuring th a t theliquid s pressure does not drop below itsva pour pressure a nywhere through the pump


29/39

NPSH

Minimum pressure required a t the pumpfla nge is expressed in feet of liquid c a lledNPSHSpecified by the m a nuf a cturerWhen w a ter or hydroc a rbons a re flowing, it ispossible to rec a lcula te the REDU C ED NPSHrequirement


30/39

NPSH ca n be c a lcula ted by:


31/39


32/39

Va por pressure of your product .Look a t the v a por pressure ch a rt

You will h a ve to convert the pressure to he a d.If you use the a bsolute pressure shown on theleft side of the ch a rt, you c a n use the a boveformul a


33/39

NPSHr

You h a ve to be a ble to re a d a pump curve tolea rn the N.P.S.H. required for your pump.

pump curve -- loca

te the va

lues for hea

d,ca pa city, best efficiency point ( B .E.P.),efficiency, net positive suction he a d (NPSH),a nd horse power required


34/39

NPSHr

pump curve is supplied by the pumpm a nuf a cturer.curve is going to show you the Net Positive

Suction He a d (NPSH) required for your pump a t a given c a pa city.Ea ch pump is different so m a ke sure you h a ve thecorrect pump curve a nd use the numbers for theimpeller di a meter on your pump.Keep in mind th a t this NPSH required w a s forcold, fresh w a ter.


35/39

EXAMPLE


36/39


37/39


38/39

NPSH required comes from the pumpm a nuf a cturer!


39/39

Summ a ry

We c a n c a lcula te the tot a l sta tic he a d of the systemWe c a n c a lcula te the tot a l friction a l losses when thefluid is moving this requires c a lcula tion of the

equiva

lent lengthUsing the a bove we c a n c a lcula te the tot a l he a d on thepumpHOWEVER, to eva lua te a system, we must ensure th a tNPSHa is gre a ter th a n NPSHrNPSHa is ca lcula tedNPSHr comes from the m a nuf a cturer

Documents

PM2560 Pump Selection