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How to Deal with the Knocking Noise Coming from Your Hydraulic System

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Hydraulic systems generally work very well if they have the proper maintenance. Still, problems can arise, especially if your system has some age on it. One problem you may be having is hearing an abnormal noise. If so, the below information should help you get rid of it so your system will start working good again.


The noise you are hearing from your hydraulic system may be caused by aeration.  Aeration is caused by air that contaminates the hydraulic fluid. When the air gets in the fluid, your system will start making a knocking noise as it is compressing and decompression, as it is circulating through the hydraulic system. Some other symptoms you may be having is erratic actuator movement and the fluid foaming.

Air enters into the system through the pump inlet. Because of this, you need to keep the pump intake lines clean and in good condition. All fittings and clamps should also always be tight. Look at the intake lines to see if they have any small holes in them. If so, you need to replace them.  It would be a good idea to go ahead and replace all the old intake lines.


Cavitation means the pump is not able to pump properly to bring in a full charge of oil. When the pump cavitates, this increases the noise level, and the front bearing and shaft will feel very hot. There are also other signs that you are having a cavitation problem. For example, the oil will look milky, the pump will have problems building up to full pressure, and the cylinders will move erratically.

To help with this problem, clean the pump suction strainer even if it looks clean. Clean it with a solvent and then use an air hose to dry it. There may be varnish in the wire mesh. If so, this restricts oil flow, which can cause a knocking noise.

You should also check the pump inlet plumbing to make sure it is not clogged. Make sure the hoses are not collapsed. Look at the air breather that is located on top of the reservoir to see if they are clogged up with dirt or lint.

If your hydraulic seal is still making noise, or you do not know how to do any of the things listed above, hire a technician to come to your company to repair it for you. They can also do maintenance while they are there to ensure everything is working properly.