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Mechanics Corner: Cancer of the system

Jim Schlund Published on 21 May 2010

Cavitation is called the cancer of the hydraulic system. Like cancer in humans, it can be a silent killer of your system by eating away at the hydraulic pump and other parts of the system.

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What is cavitation?

Hydraulic pumps run into problems when there is the lack of oil to the inlet side of the pump. The pump is gravity-fed. Your machinery has a vent, often in the oil cap where you pour in the oil. If the flow is restricted or the air is not allowed to create the required displacement because the vent is closed, oil can’t reach the pump. When the oil isn’t reaching the pump, it creates a void. Some call it low pressure, absence of pressure or a vacuum.

Cavitation occurs when bubbles form on the surface of the system in low pressure. When the pressure changes suddenly to a high pressure, the bubbles implode. The force of these bubble implosions cause pitting in the metal where the bubbles were attached and small pieces of metal break off. The hole gets larger as the bubbles continue to stick to the gap. Because the pump is after the filter, debris or chunks of metal that come off because of cavitation will travel up the lines and hoses, plugging couplers and damaging the system. Cavitation will create holes in the housing of your hydraulic pump, which causes leaks and more pressure problems.

Cavitation doesn’t always have an audible sound, but if you can hear sporadic popping or thumping when using the hydraulic system, you may need to check it out.

Why does cavitation occur?

Cavitation becomes a problem when farmers use too heavy of oil, the wrong oil or don’t change the oil. There are conditioners and additives in most hydraulic oils that can prevent cavitation. Those additives will break down over time and under excessive heat, so your oil needs to be changed before those conditioners are depleted. Testing your oil will help you know when to change it.

Another major factor in causing cavitation is a clogged filter. The filter is on the inlet side, and when it is clogged the oil can’t get to the pump, creating the vacuum needed for cavitation.

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Tractors and equipment are in and around dirt and mud all the time, so the cap on your oil reservoir can easily get plugged up, closing the airway into the reservoir. Without the air pressure, flow is restricted and a low-pressure vacuum created – textbook elements of cavitation.

Cold weather can also add to the likelihood of cavitation. Cold oil is more prone to cavitation because the oil is thicker and won’t flow to the pump as well as when it is warmed up.

How to avoid it

  1. Change your oil when it needs to be changed. Testing your oil to know when to change it by keeping the proper amount of additives will help take care of most cavitation problems. Also make sure you use the proper oil for your equipment as stated in your owner’s manual.
  2. Change your filter every 200 to 250 hours or as outlined in the owner’s manual. You should be changing your filter more often than you change your oil. I change my filter two or three times between oil changes. Keeping the filter clear will help the oil to flow the way it should.
  3. If the vent for your system is on the oil cap, make sure it is clean. Remove the cap and wash it off with a solvent and blow it out with a compressor. This will help keep the atmospheric pressure in the oil reservoir in balance. During dusty conditions, the cap can get plugged up quickly. You may need to check it daily to make sure the air isn’t being restricted. Check your owner’s manual to locate the vent on your hydraulic system.
  4. Let your equipment run for five minutes before getting after the task at hand. This will warm up the oil and improve flow when you start using the hydraulic system.

Mechanic’s tip:

Want to know more about what’s going on in your equipment? Next time you change your hydraulic filter, cut it open. You will always find some dirt, steel, copper and brake fibers. If you find a lot of any of these materials in your filter, you may have a problem coming that should be addressed. For example, if you find a lot of dirt in the filter, the operator might not be cleaning off the couplers before putting them in or someone left the cap off the reservoir. Brass could signal a thrust washer is breaking down. If you find a lot of black or brown fuzzy fibers, there could be some problems with your brakes or clutch. PD

Jim Schlund
  • Jim Schlund

  • Retired Diesel
  • Mechanics Professor
  • College of Southern Idaho

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