In a centrifugal pump, destructive cavitation occurs when:
Options:
(A) Absolute pressure at the impeller eye falls to or below the vapor pressure of the pumped liquid ($p_{\text{eye}} \le p_v$)
(B) The delivery valve is fully closed
(C) Pump speed falls below $500\text{ rpm}$
(D) The pump is primed with pure water
Answer Key:
A
Step-by-Step Solution & Explanation
Cavitation occurs when local static pressure at the lowest pressure zone (the pump impeller eye) drops to the saturation vapor pressure of the liquid ($p_v$) at the operating temperature. Vapor bubbles form instantly and are subsequently carried into high-pressure regions of the impeller vanes, where they collapse violently, generating pitting, extreme noise, vibration, and severe mechanical erosion. To prevent cavitation, $NPSH_a > NPSH_r$. Option A is correct.