How do I calculate impeller size?

[shup0739]

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]

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

 

[d23]

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]

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]

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.