Flow cavitation is primarily caused by what condition?

• A. Cavitation due to high ambient temperature
• B. Cavitation caused by insufficient NPSH
• C. Cavitation due to excessive flow
• D. Cavitation due to high viscosity

Answer: (B)

Cavitation happens when the liquid pressure drops below its vapor pressure, causing bubbles to form and then violently collapse. In a pump, the crucial factor is the suction pressure available. If the available Net Positive Suction Head (NPSHA) is not enough to meet the pump’s required NPSH (NPSHr), the pressure at the inlet falls low enough for the liquid to flash into vapor as flow rises. Those vapor bubbles form at the impeller eye and collapse downstream, creating noise, vibration, and potential damage. So, the primary condition is insufficient NPSH.

Temperature can influence cavitation risk because warmer liquid has a higher vapor pressure, reducing the margin before cavitation occurs, but without enough suction head, cavitation will still happen. Excessive flow can contribute by lowering suction pressure, but the root cause remains the insufficient suction head relative to the liquid’s vapor pressure. High viscosity changes flow characteristics but does not by itself cause cavitation.