Cavitation in Hydraulic Systems: Causes, Mechanisms and Complete Engineering Solutions

Cavitation is one of the most destructive and costly problems in hydraulic systems. It can occur in pumps, valves, motors, suction lines, filters and almost any point where fluid flow is restricted or accelerated.

In this extensive guide, we will explain:

how cavitation forms,
why it is directly related to vacuum,
its causes and symptoms,
the physics behind bubble collapse,
the type of damage it creates,
and most importantly how to prevent it.

1. What Is Cavitation?

Cavitation is the formation of vapor cavities (bubbles) inside a hydraulic fluid when the local pressure falls below the fluid’s vapor pressure. Once these bubbles travel into a higher-pressure zone, they collapse violently.

This collapse creates micro-jets strong enough to damage metal surfaces.

Cavitation has three steps:

Local pressure drop
Vapor bubble formation
Bubble collapse (implosion)

These implosions generate concentrated shockwaves up to 1000 bar, causing erosion and pitting.

2. Why Cavitation Occurs: The Physical Condition

Two physical conditions must exist:

2.1 Pressure drops below vapor pressure

Hydraulic oil starts to vaporize when pressure falls near 0.02–0.05 bar abs (depending on temperature). Even a small vacuum is enough to initiate cavitation.

2.2 High flow velocity regions

According to Bernoulli’s principle:

higher velocity → lower pressure

Thus cavitation frequently appears at:

pump suction ports
clogged filters
narrow pipe sections
high rpm pump operation

3. Main Causes of Cavitation (Top 10 Real-World Causes)

3.1 Suction vacuum at pump inlet

This is the most common reason.

3.2 Undersized suction line

Higher velocity increases pressure loss.

3.3 Clogged suction filter

Suction filters are almost always responsible for severe cavitation.

3.4 Blocked tank breather

Tank forms vacuum → pump cannot draw oil.

3.5 Low oil level

Air enters the pump → bubbles form.

3.6 Oil too viscous (cold start)

Flow becomes restricted.

3.7 Excessive pump rpm

Pump outruns available inlet flow.

3.8 Long suction line

Friction loss increases.

3.9 Air ingestion

Microscopic air leaks in suction line.

3.10 High oil temperature

Low viscosity + higher vapor pressure → more cavitation.

4. Symptoms of Cavitation

Professionals can detect cavitation through the following signs:

metallic hammering noise
high-frequency whine
reduction in flow rate
excessive heating
foamy reservoir surface
pressure fluctuations
unstable valve operation

5. Damage Caused by Cavitation

Cavitation is extremely destructive:

5.1 Surface erosion

Bubble collapse creates micro-jets that impact metal surfaces with enormous force.

5.2 Pitting on pump components

Rotors, valve plates and bearings get crater-like damage.

5.3 Loss of volumetric efficiency

Pump cannot maintain rated output.

5.4 Heat generation

Energy loss → heat.

5.5 Catastrophic pump failure

Severe cavitation can destroy a pump in hours.

6. Engineering Solutions to Prevent Cavitation

Cavitation is preventable with proper system design.

6.1 Increase inlet pressure

shorten suction line
enlarge pipe diameter
avoid 90° elbows
remove or relocate suction filter
reduce flow velocity

6.2 Maintain correct tank level

Pump inlet must remain submerged.

6.3 Ensure free tank breathing

Replace clogged breathers.

6.4 Choose the right viscosity

Match ISO VG to operating conditions.

6.5 Reduce pump rpm

Stay within NPSH-required limits.

6.6 Eliminate air leaks

Seal fittings, flanges and connectors.

7. Diagnosing Cavitation (Professional Methods)

7.1 Suction pressure measurement

Using a vacuum gauge:

–0.1 to –0.3 bar g → warning
–0.3 to –0.6 bar g → high risk
–0.6 to –1.0 bar g → cavitation absolutely present

7.2 Thermal imaging

Local hotspots indicate cavitation zones.

7.3 Acoustic analysis

Frequency response reveals bubble collapse patterns.

8. Conclusion

Cavitation is the silent killer of hydraulic pumps.
It is caused by vacuum at the pump inlet and can be eliminated by proper suction design and pressure management.

Understanding cavitation is essential for:

troubleshooting
increasing equipment lifespan
preventing costly failures
improving hydraulic efficiency

This article is part of Sancoqhub’s engineering knowledge series designed to support technicians, engineers and system designers.