In a centrifugal pump, Why is the suction line diameter usually larger than the discharge line diameter?

1. To Reduce Friction Losses in Suction

a.  A larger suction pipe means slower fluid velocity.

Lower velocity = less friction loss in the pipe.

b. This helps maintain higher pressure at the pump suction.

Less friction = higher NPSHa (Net Positive Suction Head Available), which helps prevent cavitation.

2. To Maintain NPSHa Above NPSHr

a. Cavitation occurs if pressure at the suction drops below vapor pressure.

b. A large diameter reduces pressure drop, helping to keep suction pressure above vapor pressure.

c. This is especially critical in high-flow or hot fluid systems.

3. Discharge Side Can Handle Higher Pressure

a. On the discharge side, the fluid is already pressurized by the pump.

b. Higher pressure = smaller pipe can be used, and the fluid can still flow efficiently.

c. Slightly higher velocity on discharge is acceptable (and sometimes even desirable)