Pump Suction — Consequences of Insufficient NPSH If the pump’s Net Positive Suction Head (NPSH) requirement is not satisfied in operation, what will occur?

Introduction:
NPSH ensures that the absolute pressure at a pump’s suction stays above the vapor pressure of the liquid, preventing vapor bubble formation. Failing to meet NPSH leads directly to cavitation, which damages components and degrades performance.

Given Data / Assumptions:

• Liquid: water at operating temperature.
• Known pump NPSH required (NPSHr) from manufacturer curves.
• Available NPSH (NPSHa) falls below NPSHr.

Concept / Approach:
When NPSHa < NPSHr, the local pressure at the impeller eye drops below vapor pressure. Vapor bubbles form and subsequently collapse in higher-pressure regions, causing pitting, vibration, noise, and sudden efficiency loss—classic symptoms of cavitation.

Step-by-Step Solution:
Assess suction conditions to compute NPSHa.Compare to NPSHr: if NPSHa < NPSHr → cavitation inception.Expect performance issues: head breakdown and noise.

Verification / Alternative check:
Observation: a drop in head–capacity curve at high flows and “gravel” sound indicates cavitation.

Why Other Options Are Wrong:
no flow: pumps may still deliver some flow; the primary issue is vapor formation.efficiency will be low / excessive power: these can occur secondary to cavitation; the root cause/outcome is cavitation itself.

Common Pitfalls:
Confusing suction recirculation or air entrainment with cavitation; NPSH specifically addresses vapor pressure margin.

Final Answer:
cavitation will be formed