Cavitation is caused by which condition?

• A. Excess NPSH
• B. Low ambient temperature
• C. Lack of NPSH
• D. Overheating motor

Answer: (C)

Cavitation happens when the pressure in the liquid at the pump inlet falls below its vapor pressure, causing tiny vapor bubbles to form. In a pumping system this is most likely to occur when there isn’t enough suction head, i.e., the available Net Positive Suction Head (NPSH) is less than what the pump requires. When the liquid pressure drops to vapor-pressure levels, bubbles form and then collapse as they move to higher pressure regions, leading to noise, vibration, and potential damage. Excess NPSH would keep the liquid above its vapor pressure, preventing cavitation; low ambient temperature lowers vapor pressure but doesn’t create cavitation by itself in this context; overheating the motor isn’t the fluid condition causing cavitation. So the condition that causes cavitation is the lack of NPSH.