Cavitation Causes and How to Avoid It
Cavitation occurs when the pressure in the hydraulic oil drops below its vapour pressure and vapour bubbles form that blast away metal as they collapse. The problem usually starts on the suction side of the pump: a line that is too narrow, a clogged filter or oil that is too viscous. This guide covers causes, symptoms and effective countermeasures step by step.
View hydraulics basicsWhat is cavitation and why is it harmful?
Cavitation is the formation and sudden collapse of vapour or gas bubbles in the hydraulic oil. When the local pressure drops below the vapour pressure of the fluid, the oil boils and forms bubbles. As pressure rises again, these bubbles collapse with high energy and create pressure spikes that erode metal from the pump and valves. The result is material pitting, noise and a rapid loss of performance.
Which causes lead to cavitation?
Most cases begin on the suction side of the pump, where pressure is already low. Excessive flow velocity, clogged filters and the wrong viscosity push the pressure further below the critical limit. A tank mounted too low or a cold, thick fluid at start-up also encourage the problem.
- Keep the suction line short and generously sized.
- Hold the flow velocity in the suction line below 1.0 m/s.
- Avoid cold starts with thick oil, pre-warm the system.
- Place the tank high enough and fit a breather filter.
How do I spot cavitation in operation?
Cavitation almost always announces itself by sound. A harsh, rattling or gravel-like noise from the pump is the clearest sign. Add to that pressure fluctuations, milky foamy oil and, over time, visible pitting on the pump housing and control edges. Reacting early prevents costly follow-on damage.
How do I prevent cavitation for good?
Prevention starts on the suction side: short, wide lines, clean filters and the right viscosity. A vacuum of more than -0.8 bar on the suction side is considered critical and should be eased with larger nominal sizes or a boost pump. Regular servicing of filter and oil keeps the system stable for the long run.
- Check and replace suction and return filters at service intervals.
- Fit a boost pump where the suction head is high.
- Choose oil to the maker's spec and operating temperature.
- Keep the tank breather filter clean so no vacuum builds up.
Frequently asked questions
What does cavitation sound like at the hydraulic pump?
It is typically a harsh rattle or gravel-like noise, as if pebbles were running through the pump. The sound rises with speed and load. It is the clearest early warning sign and should be investigated at once.
What is the difference between cavitation and aeration?
In cavitation the oil itself boils because of too low a pressure. In aeration real outside air is drawn in through leaks. Both create bubbles and noise, but aeration is fixed by sealing the suction side.
Which viscosity helps prevent cavitation?
A viscosity matched to the operating temperature, such as ISO VG 46, allows easy intake. Oil that is too thick, for example at cold start, raises suction resistance. Bring the system up to operating temperature before full load.
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