IMPELLER DIAMETER VS PUMP FLOW I003-1
If your pump is pumping too much flow, you can change the impeller diameter and then apply the affinity laws for centrifugal pumps. You may want to do this to operate closer to the pumpвЂ™s best efficiency point (BEP)
To predict the new flow:
The confusion comes when we decide to use a smaller pump with the same diameter impeller and speed. The new flow in that case becomes:
What happened? Why do we have to cube the ratio this time?
The reason is that when we went to the smaller pump design, the entire pump casing dimensions changed in proportion to the new impeller diameter. In the first example only one dimension changed.
The pump flow rate responded to this three dimensional change.