What should be checked if cavitation is observed in a chilled water pump?

• A. Impeller size
• B. Bearing lubrication
• C. NPSH available vs required
• D. Motor RPM

Answer: (C)

Cavitation happens when the pressure at the pump’s suction drops to or below the liquid’s vapor pressure, causing bubbles that can damage the impeller. The essential check is the NPSH relationship: compare the NPSH available at the suction with the NPSH required by the pump at the operating flow. If the available head is not enough to meet the pump’s requirement, cavitation occurs.

For a chilled water pump, you’d look at the suction conditions: the supply pressure, suction elevation, and any losses in the suction piping. You want enough head so that the pressure at the pump inlet stays above the water’s vapor pressure. This may involve raising suction pressure, reducing suction line losses (cleaning strainers, removing restrictions, minimizing bends), or adjusting the system to lower the point of suction losses. If needed, you can select a pump with a lower NPSH requirement or move to a different operating point on the pump curve.

Other factors like impeller size, bearing lubrication, or motor RPM can affect performance and wear, but cavitation is fundamentally a matter of insufficient suction head relative to the pump’s NPSH requirement.