What causes cavitation in a pump?

• A. Vapor bubbles form due to low suction pressure or high discharge pressure, collapsing and causing damage.
• B. Air leaks into the system.
• C. Excessive motor speed.
• D. Damaged impeller.

Answer: (A)

Cavitation happens when the liquid inside the pump experiences a drop in pressure below its vapor pressure, causing tiny vapor bubbles to form. This most often occurs on the suction side when there isn’t enough net positive suction head (NPSH available) or when discharge pressure is very high. As the fluid moves to areas of higher pressure inside the impeller, these bubbles collapse violently, sending shock waves that erode surfaces, create loud noise, and reduce pump performance.

So the fundamental cause is the formation and violent collapse of vapor bubbles due to a pressure drop sufficient to vaporize the liquid. Air leaks can introduce bubbles but aren’t the root cavitation mechanism; excessive motor speed or a damaged impeller can worsen symptoms or indicate other issues, but cavitation itself is driven by the pressure drop and vaporization.