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How do I calculate impeller size?

shup0739 (Mechanical)

(OP)

14 Mar 03 10:28

Currently I have a pump with an 11" impeller at a discharge pres of 22psi and 112GPM.

I'd like to know how much will the flow and/or pressure will change if I trim or increase my impeller size.

is there a formula for this ?

thank u

insideman (Mechanical) · Answer 1 · 2003-03-14 11:54:33

Flow may not change. Pressure will be proportional to diameter squared.

d23 (Petroleum) · Answer 2 · 2003-03-14 13:35:15

shup0739

For general terms the pump affinity laws apply to impeller size or rotating speed.

FYI:
22 PSI at 112 GPM sounds low for an 11 inch impeller. Hope this is a slow running pump.

Kawartha (Mechanical) · Answer 3 · 2003-03-14 13:44:22

shup0739,

As suggested by D23 use the affinity laws to provide a rough appoximation of the effect of changing impeller size.

Q1/Q2=D1/D2
Hd1/Hd2=(D1/D2)squared
HP1/HP2=(D1/D2)cubed.

You can expect this formula to give you accuracy within 10 to 30%.

hero123 (Petroleum) · Answer 4 · 2003-03-18 02:21:35

Affinity laws are the best equations to calculate and estimte the changes, however these are constant efficiency equations. But when there is a change in impellar size, efficiency does change and hence these equations may not predict the changes very accurately, however they definitely give a close estimate.

hope this helps.

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