Which condition commonly causes cavitation in pump systems?

• A. Excessively high NPSH available
• B. Insufficient NPSH available
• C. High discharge pressure
• D. Water with dissolved minerals

Answer: (B)

Cavitation happens when the pressure at the pump’s suction side drops below the liquid’s vapor pressure, causing bubbles to form. The amount of pressure head available at suction (NPSH available) must exceed what the pump requires (NPSH required) to prevent this. When available NPSH is insufficient, the liquid begins to vaporize in the eye of the impeller, bubbles form, and as they travel to higher-pressure areas they collapse violently, creating noise, vibration, and potential damage to the pump.

So the condition that commonly causes cavitation is insufficient NPSH available. Excessively high NPSH available would actually reduce the risk of cavitation, and while high discharge pressure can push the pump toward needing more NPSH, the immediate, common cause is not having enough suction head. Water with dissolved minerals leads to scaling, which is a different issue and not the typical cause of cavitation. To mitigate, increase NPSH available by boosting suction pressure, reducing suction losses, increasing water temperature control, or lowering pump speed, among other adjustments.