On centrifugal pumps, if it is ever necessary to reduce pump flow temporarily, do so by

• A. Throttling the discharge
• B. Throttling the suction line
• C. Both A and B
• D. None of the above

Answer: (A)

In a centrifugal pump, flow is controlled mainly by how much resistance the pump has to overcome in the discharge path. To reduce flow temporarily, you increase resistance on the discharge side by throttling the discharge valve. This lowers the pump’s operating point on its head–flow curve, yielding less flow while keeping the suction conditions favorable.

Throttling the suction line is not advisable because it lowers the pressure at the pump inlet, reducing available NPSH and increasing the risk of cavitation, air entrainment, and unstable operation. That’s why adjusting the discharge valve is the appropriate method to reduce flow.