Affinity Law for Multi-Stage Pumps
Affinity Law for Multi-Stage Pumps
(OP)
I am evaluating a 10-stage Pacific pump originally purchased in 1957. The rated head at shutoff was 960-ft.
Twenty years later the client removed three stage. There is no pump curve for 7-stages. The engineer in 1977 estimated the 7-stage pump to be 440-ft at shutoff. Today I field verified the shutoff being with 10% of 440-ft.
I am not aware of any pump affinity laws regarding multiple stages. My current view is the original 10-stage pump would be 96-ft per stage. Removing 3-stages would reduce the head by [3*96]=288-ft resulting in 662-ft at shutoff.
My question: How can one predict going from 960-ft to 440-ft? I hope the question is not too dumb.
Twenty years later the client removed three stage. There is no pump curve for 7-stages. The engineer in 1977 estimated the 7-stage pump to be 440-ft at shutoff. Today I field verified the shutoff being with 10% of 440-ft.
I am not aware of any pump affinity laws regarding multiple stages. My current view is the original 10-stage pump would be 96-ft per stage. Removing 3-stages would reduce the head by [3*96]=288-ft resulting in 662-ft at shutoff.
My question: How can one predict going from 960-ft to 440-ft? I hope the question is not too dumb.





RE: Affinity Law for Multi-Stage Pumps
To achieve 440ft at the CV you will probably need 5 stages with a diameter trim on 1 or 2 stages.
As the head has reduced what about the flowrate? if there was any change to flow - then you need to draw a system curve and reselect the number of impellers and impleller diameters at the flow / head required.
RE: Affinity Law for Multi-Stage Pumps
rmw
RE: Affinity Law for Multi-Stage Pumps
RE: Affinity Law for Multi-Stage Pumps
The records are vauge and I guess some undocumented impellor trimming could have occurred.
The data is taken at shutoff - meaning the flow is not changed.
Artisi - You seem to confirm my 96-ft per stage analysis.
Meaning the affinity law for pressure rise per stage is proportional??
RE: Affinity Law for Multi-Stage Pumps
Johnny Pellin
RE: Affinity Law for Multi-Stage Pumps
Multistage pumps are also designed with stage configurations so that individual stages and especially the higher pressure stages oppose each other in order to balance the thrust forces. Therefore, it is difficult to imagine how they removed an odd number of stages and didn't over-thrust the shaft.
Something doesn't add up here unless the third stage was the double suction first stage that JC described.
That old pump must have been a beast to have survived this abuse (and most of those built back then were just that, beasts.)
rmw
RE: Affinity Law for Multi-Stage Pumps
If all impellers are equal (no double suction 1st stage, all same dia) then yes the head per stage calc is proportional.
There are losses associated with removing impellers depending on the type of pump and how they are removed. The engr in 1977 likely took these losses into account, though 200+ ft of losses is very high. Vertical pumps will typically leave the bowls empty, horiz. pumps will be fitted with de-stage pieces and sleeves to blank off volute passageways and balance thrust.
The affinity law is used to refigure pump performance from one speed to another... has the RPM of the pump changed as well?
Did you know that 76.4% of all statistics are made up...