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How to Add Oil to Hydraulic Cylinders

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When pressure is added to an operational hydraulic system, fluids are compressed and forced through hoses until they reach the hydraulic cylinder. The pressure of the fluid causes the hydraulic ram to rise which, in turn, usually lifts or extends another component. Oil is the most commonly-used hydraulic fluid because it can withstand high temperatures and will not cause corrosion on working machinery. Over time, hydraulic oil can become thin and dirty. For machinery that is in use on a daily basis, the oil should be changed approximately every six months.

Turn off the hydraulic machinery by the isolator and activate the pressure relief valve until the gauge display reads zero. This will drain the cylinder of fluids. Locate the oil holding tank and remove the lid bolts with a hexagonal wrench. Inspect the hydraulic oil and estimate how much is in the tank. Prepare enough empty 25 liter drums to hold the waste oil and plug in the fluid removal pump. The extraction hose should be placed into the waste oil and the output hose should be tucked into one of the empty 25 liter drums.

Activate the fluid removal pump and begin filling the 25 liter drums with waste oil. Continue to switch drums as they become full until all of the oil in a holding tank has been removed. Replace all of the lids on the drums and ensure they are secured tightly. Arrange for waste collection and put the fluid removal pump away.

Take a roll of general-purpose cloth and wipe the inside of the holding tank clean. Keep the working area free of drips and splashes by placing waste cloth into a garbage bag as soon as it has been used. Carry out a full visual inspection of the tank to ensure all oil deposits and traces of sludge have been completely removed. If high levels of sludge are present, it may be necessary to flush the system first before adding new hydraulic oil.

Prepare enough new drums of hydraulic oil to reach the full level mark on the inside of the holding tank. Remove the lids from each drum individually and pour oil into the holding tank, taking care not to cause excessive splashing or air bubbles. Continue adding drums of hydraulic oil until the holding tank has reached the maximum level line.

Place the lid back onto the oil holding tank and tighten down the bolts using the hexagonal wrench. Activate the hydraulic hand pump until pressure appears on the gauge. Turn on the isolator and return the hydraulic machinery to service. Run several working cycles to ensure the machinery is running correctly.


Hydraulic oil changes in heavy machinery should only be carried out by experienced personnel.

  • Hydraulic oil changes in heavy machinery should only be carried out by experienced personnel.

Based in the United Kingdom, Paul Miceli has been a professional writer since 2006. He has been published online by Ideate Media and Promiga and has a proven track record of producing informational articles and sales copy. Miceli is educated to U.K. "A-level" standard, continues to work as a paint sprayer and has more than 25 years of automotive body repair experience.