The Silent Pump Killer: Understanding Cavitation in Hydraulic Systems

If you’ve ever stood next to a hydraulic power unit and heard a sound like marbles being shaken in a metal can, you weren't hearing mechanical parts hitting each other. You were hearing the sound of liquid boiling at room temperature and then exploding—a phenomenon known as cavitation.

Cavitation is one of the most common causes of hydraulic pump failure, yet it remains widely misunderstood. In this post, we’ll break down what it is, why it happens, and how your reservoir design plays a critical role in preventing it.

What is Cavitation?

In simple terms, cavitation is the formation and subsequent collapse of vapor bubbles within a flowing liquid.

In a hydraulic system, this happens when the pressure at the pump inlet drops below the vapor pressure of the hydraulic fluid. When the pressure is low enough, the oil literally "boils," turning from a liquid into a gas.

$$P_{inlet} < P_{vapor}$$

As these vapor bubbles travel from the low-pressure suction side to the high-pressure discharge side of the pump, they implode violently. This implosion releases a concentrated micro-jet of fluid that can strike metal surfaces at supersonic speeds, pitting the metal and eventually destroying the pump.

The Role of the Reservoir: Suction Head

One of the most effective ways to prevent cavitation is to ensure the pump has a "healthy" inlet. This is where your reservoir size and oil level come into play.

As you can see in the interactive simulation below, the suction head (the height of the oil above the pump inlet) acts as a gravity-fed "pusher."

Large Reservoir/High Oil Level: The weight of the oil creates positive pressure at the inlet, keeping the fluid well above its boiling point.
Small Reservoir/Low Oil Level: The pump has to "struggle" to pull the oil up. This creates a vacuum-like effect. If that vacuum is strong enough, cavitation begins.

Interactive Demo: Watch Cavitation in Action

Use the buttons below to toggle between a healthy system and a cavitating system. Note how the low oil level in the "Small Reservoir" mode triggers a warning and causes the pump to vibrate (shake) as bubbles form in the suction line.

Hydraulic Reservoir — Cavitation Demo

Select a reservoir size above to see what happens.

How to Spot and Stop Cavitation

Aside from the "marbles in a can" noise, look for these red flags:

Vibration: Unusual shaking of the pump housing or suction lines.
Heat: Cavitation generates localized heat that can degrade oil quickly.
Erratic Actuator Movement: As vapor bubbles compress (unlike liquid oil), your cylinders or motors may lose precision.

Prevention Checklist:

Keep it Full: Ensure the reservoir stays between the MIN and MAX lines on the sight glass.
Check the Breather: A clogged reservoir breather creates a vacuum inside the tank, making it harder for the pump to draw oil.
Clean the Suction Strainer: A dirty filter in the suction line is the #1 cause of "suction starvation."
Size Matters: Ensure your reservoir is sized correctly for the pump's flow rate—standard practice is usually 3 to 5 times the pump's GPM (Gallons Per Minute) output.