What is important to prevent cavitation in pumps?

• A. Pump horsepower
• B. Fluid viscosity
• C. Net Positive Suction Head (NPSH)
• D. Pipe diameter

Answer: (C)

Cavitation happens when the pressure at the pump suction falls to or below the liquid’s vapor pressure, causing bubbles that collapse and damage the impeller. The crucial way to prevent this is to ensure there is enough suction head to keep the fluid above its vapor pressure at the pump inlet. This is captured by Net Positive Suction Head: you compare the suction head available (NPSH available) with the suction head required by the pump (NPSH required). When NPSH available is greater than NPSH required, cavitation is avoided.

NPSH available depends on conditions in the suction system—atmospheric pressure, the vertical lift, static head, and friction losses in the suction piping. NPSH required is determined by the pump design. In practice, you design the system to have NPSHa > NPSHr, and you can increase NPSHa by raising suction pressure or level, shortening or reducing losses in the suction line, or cooling the liquid to lower its vapor pressure.

The other options don’t directly guarantee cavitation prevention. Pump horsepower relates to overall power, pipe diameter affects flow and friction but not the fundamental suction pressure, and viscosity affects flow resistance but isn’t the primary control for avoiding cavitation.