Cavitation in Pumps – Causes, Effects, and Prevention

Mohan Sundar / EV& Engineering 

What Is Cavitation in Pumps?

Cavitation is a phenomenon in which vapor bubbles form inside a liquid due to a sudden drop in pressure below the liquid’s vapor pressure. These bubbles later collapse violently when they move into higher-pressure regions inside the pump.

The collapse of these bubbles creates extremely powerful microscopic shock waves. Although the bubbles are tiny, repeated implosions continuously strike the internal metal surfaces of the pump at very high energy levels.

Over time, these repeated impacts damage the pump impeller, casing, seals, bearings, and other internal components.

Cavitation is most commonly seen in centrifugal pumps because of the pressure variations occurring inside the impeller.

Inside a pump, if pressure suddenly falls below the vapor pressure of the liquid:

• Tiny vapor-filled bubbles form
• These bubbles travel with fluid flow
• When pressure rises again, the bubbles collapse instantly
• The collapse creates shock waves
• Shock waves damage metal surfaces

This entire process is called cavitation

Step-by-Step Cavitation Process

The cavitation process generally occurs in the following sequence:

Stage 1 – Pressure Drop

As fluid enters the impeller eye, velocity increases and pressure decreases.

If pressure becomes lower than the vapor pressure of the liquid, vapor bubbles begin forming.

Stage 2 – Bubble Formation

Tiny cavities or vapor bubbles appear in low-pressure regions.

This usually occurs near the suction side of the impeller blades.

Stage 3 – Bubble Movement

The bubbles move along with the flowing liquid toward higher-pressure zones inside the pump.

Stage 4 – Bubble Collapse

When the bubbles enter high-pressure regions, they collapse violently within milliseconds.

This collapse produces localized shock waves and extremely high-pressure micro-jets.

Stage 5 – Surface Damage

Repeated bubble collapse attacks metal surfaces continuously.

This leads to:

• Pitting
• Surface erosion
• Cracking
• Material removal

Main Causes of Cavitation

Low Suction Pressure

Low suction pressure is one of the primary causes of cavitation.

If the pump does not receive sufficient liquid at the inlet, pressure drops drastically.

This may happen because of:

• Blocked suction strainers
• Long suction piping
• Small pipe diameter
• Excessive suction lift
• Closed suction valve
• Poor piping design

Insufficient NPSH

• Net Positive Suction Head (NPSH) is one of the most important concepts related to cavitation.

  There are two types:

• NPSH Available
• NPSH Required
• For safe pump operation:

  $NPS{H}_{Available}>NPS{H}_{Required}$

  If available NPSH becomes lower than required NPSH, cavitation begins.

High Liquid Temperature

• Hot liquids vaporize more easily because their vapor pressure is already high.

  This makes hot water pumps highly vulnerable to cavitation.

  As temperature increases:

• Vapor pressure increases
• Bubble formation becomes easier
• Cavitation risk rises

High Pump Speed

• Higher rotational speed increases fluid velocity and pressure drop.

  This can create low-pressure zones inside the impeller.

Operating Beyond Design Capacity

• Running pumps at very high flow rates creates unstable hydraulic conditions and internal turbulence.

  Air Leakage in Suction Line

• Air leaks disturb smooth liquid flow and create unstable pressure conditions.

  Common leak locations include:

• Flanges
• Gaskets
• Valve connections
• Pipe joints

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Types of Cavitation

Different types of cavitation can occur depending on operating conditions.

Suction Cavitation

This is the most common form of cavitation.

It occurs when the suction side cannot provide enough liquid to the pump.

The pump attempts to draw more liquid than available, creating low pressure.

Common Causes:

• Blocked suction line
• Low tank level
• High suction lift
• Restricted inlet flow

  Discharge Cavitation

  Discharge cavitation occurs when discharge pressure becomes excessively high.

  This creates internal recirculation inside the pump.

  Causes:

• Closed discharge valve
• System blockage
• Excessive back pressure

Vaporization Cavitation

Occurs mainly because of high liquid temperature.

Hot liquids require only small pressure reductions for vapor formation.

Internal Recirculation Cavitation

Occurs at very low flow conditions.

Fluid starts circulating internally inside the pump instead of flowing normally.

This creates turbulence and low-pressure zones.

Air Cavitation

Air entering the system behaves similarly to vapor bubbles.

It creates vibration, noise, unstable operation, and performance loss.

Parts Affected by Cavitation

Cavitation can damage nearly every major component inside the pump.

• Impeller Damage
• Pump Casing Damage
• Mechanical Seal Failure
• Shaft Damage
• Wear Ring Damage
• Reduced Pump Efficiency
• Pump Outlet Pressure Reduction
• Excessive Noise
• Increased Vibration
• Overheating
• Complete Pump Failure

Warning Signs of Cavitation

Operators should never ignore the following symptoms:

• Grinding noise
• Crackling sound
• Excessive vibration
• Reduced flow rate
• Low discharge pressure
• Pressure fluctuations
• Frequent seal failures
• Increased motor current
• Overheating
• Reduced efficiency

Early detection can save significant maintenance cost.

How to Detect Cavitation

• Sound Monitoring
• Vibration Analysis
• Pressure Monitoring
• Flow Monitoring
• Thermal Inspection
• Visual Inspection

How to Prevent Cavitation

Preventing cavitation is always better than repairing damaged pumps.

• Improve Suction Conditions
• Maintain Proper NPSH
• Always ensure: NPSHAvailable>NPSHRequired
• Reduce Fluid Temperature
• Avoid Excessive Pump Speed
• Eliminate Air Leakage
• Use Proper Pump Selection
• Install Booster Pumps
• Use Cavitation-Resistant Materials

Materials such as stainless steel improve erosion resistance.

How to Resolve Existing Cavitation Problems

If cavitation already exists:

• Inspect suction piping
• Remove blockages
• Reduce pump speed
• Increase suction pressure
• Replace damaged impellers
• Repair seals and bearings
• Recalculate system design
• Operate near design conditions

In severe cases, the entire piping system may require redesign.

The most common symptoms include noise, vibration, reduced flow, low discharge pressure, and efficiency loss. Components such as impellers, bearings, seals, shafts, and casings are highly vulnerable to cavitation damage.

Proper pump selection, maintaining adequate NPSH, improving suction conditions, operating near the Best Efficiency Point, and regular monitoring are essential for preventing cavitation.

Early detection and timely corrective action can significantly increase pump life, reduce maintenance cost, and improve overall system reliability.

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