What is Cavitation?

Cavitation is a destructive phenomenon that occurs in pumps when the liquid pressure drops below its vapor pressure, causing the formation and sudden collapse of vapor bubbles (cavities) in the fluid. This collapse generates intense shockwaves that damage pump components, reduce efficiency, and lead to premature failure.

How Cavitation Occurs

Pressure Drop:
When fluid enters the pump impeller, local pressure can fall below the liquid’s vapor pressure (often due to high speed or restricted flow).

Bubble Formation:
Low pressure causes liquid to vaporize, forming tiny bubbles.

Bubble Collapse:
Bubbles implode violently when they reach high-pressure zones (e.g., near the impeller blades), releasing energy that erodes metal surfaces.

Signs of Cavitation

Noise: A distinct “crackling” or “marbles-in-a-can” sound.
Vibration: Unusual shaking due to uneven fluid flow.
Performance Loss: Reduced flow rate and pressure.
Physical Damage: Pitted impellers, worn seals, or eroded volutes.

Effects of Cavitation

1. Mechanical Damage:
Pitting and erosion on impellers, shafts, and casings.

2. Efficiency Loss:
Bubbles disrupt flow, reducing pump performance by 10–30%.

3. Costly Downtime:
Premature bearing/seal failures require unplanned maintenance.

How to Prevent Cavitation

1. Ensure Adequate NPSH:
– NPSHₐ (Available) must exceed NPSHᵣ (Required) by at least 1–2 m.Increase suction tank elevation or reduce pipe friction.

2. Optimize Pump Operation:
– A pump’s “best efficiency point” (BEP) or “sweet spot” is a combination of head and flow rate at which it will perform at its highest level of energy efficiency and longevity. Avoid running pumps at extreme ends of the curve (far left or right of BEP).