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6 Steps For Flushing A Hydraulic System

There are times when flushing a hydraulic system is good for the machine. Sometimes, the system is flushed in order to change from one fluid to another.

However, you need to be very careful when changing out fluids, as some are not compatible with the machine in general, but the seals and O-rings may be more susceptible to damage or corrosion from the chemical components.

Regardless of your reasons for cleaning out the machine or changing your hydraulic cylinder parts, there are several steps that should be taken.


Step One


Start by draining the system completely, but when the fluid is at operating temperature. Look at all the lines, the cylinders, the reservoir, filter housing, and fluid accumulation.  Change out all the filters.


Step Two

Using a lint-free rag, carefully remove all of the sludge or deposits from the reservoir. There shouldn’t be any loosened or soft paint either.


Step Three

If you are going to be changing out for a different fluid, you need to flush the system with a lower viscosity fluid that will be close to the fluid that will be used. You need to stroke the valves often to make sure they are thoroughly flushed. Flushing should continue until one level beyond the target cleanliness levels for the system is reached.

Step Four

Take care to the drain any flushing fluid as hot and quickly as possible. Again, replace the filter and thoroughly inspect and clean the reservoir.

Step Five

Bleed and vent the pump after filling the system with about 75% of the new fluid. Run the pump with the bypass open for about 15 seconds before taking a pause for about 45 seconds. This will prime the pump. Do this several times before moving to step six.

Step Six

After priming the pump, let it run for about a minute with the pressure relief or bypass still open. Let it sit for another minute before closing the bypass and letting the pump operate normally for about five minutes. The relief valve should lift and confirm that it has been flushed well. Don’t operate the actuators yet.

Let the system rest for about five minutes before starting the pump and individually operating the actuators. This lets the fluid return to the reservoir so you can monitor it.


As you move through the restart, you will fill continue adding fluids until the system is full. Run the system at operating temperature for 30 minutes before stopping and replacing the filters. Check for contaminants. At this point, if everything is clear, you will notice if your flushing has been successful.

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