How to Clean Hydraulic Oil

Updated July 19, 2017

Hydraulic oil in pressurised control systems rely on fluid pressures to actuate and control moving parts consistently. These systems require the use of clean hydraulic oil to increase reliability during the life of the equipment. In the heavy-equipment industry, hydraulic fluids move the pistons that lift, carry and manipulate heavyweight materials. To lower the cost of replacing old hydraulic oil for new, companies have been searching for economical ways of cleaning and recycling hydraulic fluids to be recycled. How to clean hydraulic oil is not a simple process, nor is it something easily accomplished. Per the United States government, the way to clean hydraulic oil is through a method of aerating and filtering old oil to remove water and contaminants that have built up within used hydraulic fluids.

Drain used hydraulic fluid from a fluid control system that has been used for a time period that under normal circumstances would leave the fluids contaminated. Store the used hydraulic oil in a clearly marked container or oil drum to be recycled. Take a sample of the oil to be analysed and place it in a clean receptacle.

Send your hydraulic oil sample to Exxon Mobil Corp for its Signum Oil Analysis. Follow the link provided below this article in the Resources section to find a link directly to Exxon Mobil's Signum Oil Analysis service. Test your sample of hydraulic oil to confirm it can be recycled. Test results will show you how contaminated your sample is and what contaminants are present. Use these results to customise the cleaning process and to be sure the recycled hydraulic oil will perform as well as new, clean hydraulic oil.

Raise the barrel of used hydraulic oil above the ground at least 5 feet. Attach a hose from the bottom of your used hydraulic drum into the inlet of a hydraulic cleaning system. This system involves a rotating disc, a pressurised container and a filter. A system such as this will follow the "Pall" design and works the best for cleaning hydraulic oil.

Place the outlet hose of the Pall filtration system into a clean recycled hydraulic oil container to receive the filtered and cleaned hydraulic oil after it has been processed by the Pall recycling unit. Open the hose valve to allow the old hydraulic oil to enter the recycling unit. Turn on the pressurised air and let the system work. As the recycled fluid exits, adjust the flow of oil going into the recycling system enters the systems at the same pressure as it is leaving the hydraulic recycler.

Watch the Pall system to ensure it is working correctly. When the oil enters the cleaning system, it falls onto a spinning disc. This creates a large surface space for the oil, which will separate the oil from any water that contaminates the hydraulic fluid. At the same time it is separating the water from the oil, pressurised air (12 times ambient) will evaporate the water that is being separated from the oil on the spinning disc. As the oil spreads outward on the spinning disc, it will fall off of the disc and drain into a filter that captures and separates contaminants such as metals, dirt and silicon down to three microns from the water-free hydraulic oil.

Sample and have analysed the recycled hydraulic oil by Exxon Mobil's Signum Analysis to confirm the recycled hydraulic oil is ready for use again in any system that utilises pressurised hydraulic oils to activate moving parts in systems that rely on fluid control for operation. After confirming the recycled hydraulic oil is clean enough for the systems you use, return the hydraulic oil to service when needed.


Use heated air to assist the evaporation of water contaminating hydraulic oil. Recycle hydraulic oil in fluid control systems that do not demand the highest-quality hydraulic oil. Increase reliability of your hydraulic systems by knowing when and where it is safe to use recycled hydraulic oil.


Without properly flushing hydraulic systems and attaching filters on critical hydraulic equipment, you can cause catastrophic damage. Even after recycling hydraulic oil, you need to replace filters and flush hydraulic lines free from remaining contaminants within the hydraulic system of any fluid-control equipment.

Things You'll Need

  • Hydraulic oil
  • Test sample
  • Centrifuge (spinning disc)
  • Filter (3 micron)
  • Air (pressurised)
  • Fluid tank
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About the Author

Francis Walsh has been working as a freelance writer since 2003. He has contributed to websites such as Shave, Autogeek and Torque & Chromeas, as well as provided content for private clients. Walsh has worked as a performance part-packer and classic car show promoter, now serving as crew chief for Nitrousfitz Racing.