Affinity laws for trimming of impellers.

Q = flow rate  H = head  P = power  N = speed  D = diameter

Characteristics of a pump with impellers with different diameters
Curves of a pump with reduced impellers

Head curves for impellers with different diameters  510, 460, 410 mm. 

IMPORTANT. Trimmed impeller usually has less efficiency than a full size impeller.

Te BEP moves toward the less flow.

IMPORTANT. NPSH rises. It necessary to take into account when you decide to trim an impeller. 

When trimming of an impeller is applied?

Trimming of an impeller is used to adapt a pump curve to a system curve so that to provide the efficient pump operation.

Energy savings at an impeller cutting

When the  pump with impeller 510 mm is selected the duty point will be on the cross of H-Q curve and System curve

with a flow1540 m3/h, but requered flow is 1000 m3/h. 

In addition, the pump consumes extra power and overloads a motor.  

To meet system requirements, a control valve is used.  Operating point shifts to a  flow 1000 m3/h.

But control valve throttle a pump head what cause the Energy loss.

The difference in shaft power is 120 kW.

The saving potential is very substantial.

The difference in NPSH between fullsize and trimmed impeller is 0.5 m.

The difference is necessary to take into account.