12 stage centrifugal pump

[impeller1]

Good day,

I just need confirmation on something. I have a 12 stage horizontal centrifugal pump. I have recorded values of flow, suction pressure, discharge pressure and speed. I'd like to work out the flow and differential head values to the rated speed. I've applied the affinity laws:

N1/N2 = Q1/Q2

(N1/N2)^2 = H1/H2

Are these laws applicable to a 12 stage pump??? The points I'm getting don't seem to line up properly on the performance curve. Is there a variation to the laws? The actual speed is within 7% of the rated speed

Thanks

 

[NGLENGR]

They should be, assuming the fluid gravity is correct. In my world, the pumps are tested on water (sg = 1.0) and we run them on ethane, propane, and other light hydrocarbons. You'll need to correct for that.

There's also the possibility that you pump has some significant internal wear, if the performance is severely degraded.

http://www.engineeringtoolbox.com/affinity-laws-d_408.html

 

[Artisi]

Same law. But are your tested figure correct, always very suspect when taken in the field unless extreme care has been taken using cerified gauges, correct tapping and measuring points etc.

 

[rmw]

With 12 perfect impellers, no recirculation, and no other losses, your affinity laws would be additive. However, with that many stages you have ample opportunities for internal recirculation, stage mis-matches due to impeller wear or style differences (all impellers might not be the same). You didn't state the condition of this pump; new, used, rebuilt, but even a brand new pump right out of the box has some losses around each set of impeller wear rings as well as other inter-stage losses that area additive too.

rmw