Everybody likes a quiet pump – it just does its job and doesn’t break down often. Although a noisy pump is often attributed to cavitation, not every abnormal noise suggests a pump is suffering from this problem. Failing bearings, flow turbulence, recirculation, and even a machine’s mechanical or electrical geometry can generate noise.

When it comes to hydraulic pumps, it pays to know what different noises mean. With practice you can learn to distinguish between the normal operating sounds and the signs that something is wrong.

Excessive or erratic hydraulic pump noise is a symptom of malfunction that could cause damage or accelerated wear if not addressed quickly and correctly. While it’s always alarming to hear strange noises emitted from your pump, determining which noises are related to different faults can indicate the root of your problem and provide the opportunity to repair the equipment before major damage occurs. 

1. Aeration

Aeration occurs when air contaminates the hydraulic fluid. Air in the hydraulic fluid makes an alarming banging or knocking noise when it compresses and decompresses, as it circulates through the system. The whining noise caused by air leaks is similar to cavitation, but is more erratic in nature due to the uneven distribution of the air in the hydraulic system.

Air usually enters the hydraulic system through the pump’s inlet. For this reason, it is important to make sure pump intake lines are in good condition and all clamps and fittings are tight. You could also check the fluid level in the reservoir, and if low fill to the correct level. In some systems air can enter the pump through its shaft seal, so checking the condition of the pump shaft seal would also be recommended.

2. Cavitation

A loud whining or screeching noise (or, in extreme conditions, a severe rattling sound) can be indicative of cavitation. Cavitation results in the erosion of metal components. The resulting metal debris in the system accelerates the wear of components located down the stream. In some cases, cavitation can lead to mechanical failure of different components.

Cavitation occurs when demand for hydraulic fluid is not being met. While cavitation can occur just about anywhere within a hydraulic circuit, it commonly occurs at the pump. Other areas where cavitation may occur include fluid line blockages, blocked fluid filters, overly high oil viscosity and excessive pump rotation speed. 

3. Relief valve settings

A whistling sound or erratic hissing often suggests that a relief valve is improperly adjusted or stuck open.  A good rule of thumb is if it doesn't sound right, it probably isn't. Slamming of actuators, stalls and excessive heat generation are the early symptoms of problems with these valves.

4. Directional valves spool shift

For the most part, directional valves should create no more than a faint "click" on very quiet machines. If you can hear a directional valve spool shift, chances are there could be a problem. 

If the pilot chokes are improperly adjusted on a two-stage directional valve, it will audibly slam when it shifts. The spool can easily be damaged, and sudden movement of the valve spool causes shock throughout the machine, meaning the weaker points of the system will suffer. In this instance the pilot choke will need to be adjusted for smooth shifting of the spool and improved component longevity.

5. Cylinders binding or slipping

Likewise, cylinders should also move with almost no noise. If a cylinder is creating noise, it may be binding or slipping.  A bent rod will wear seals and slippage degrades the performance of the machine, sending contaminants from the resulting worn out seals to other components.  A noisy cylinder should be investigated as soon as possible.

6. Other mechanical malfunctions:

Grinding sounds, whirring, roaring, rattling or general noisy operation all suggest some type of mechanical malfunction. In particular, grinding, scraping or rough running is an indication of serious internal wear. 

In such cases, the pump should be disassembled, inspected and overhauled by a trained technician. Worn components may be replaced, and in some instances, machining work performed to restore the pump surfaces. 

Is sound alone enough to troubleshoot?

Noise issues provide just one indication of what might be wrong with your hydraulic equipment. There are several other troubleshooting methods necessary to identify what is wrong with your pump, including monitoring for heat problems, pressure problems and flow problems. 

While sound alone will not diagnose the problem with your machine, listening to the sounds it makes can pay off in large dividends by catching problems early before they lead to costly component failures and unscheduled downtime of hydraulic equipment. 

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