How (and When) to Go About Bleeding a Hydraulic Jack

Hydraulic jacks need to be bled on certain occasions if they are to work to their peak capacity. If the tool has been in heavy use for some time, has spent any time on its side or has recently been transported over any substantial distance, odds are good that at least a few air bubbles have gotten into the fluid system.

The presence of even small amounts of air in a hydraulic jack’s operating fluid can degrade performance noticeably. This is because air can be compressed and expanded – 2 things you do not want your hydraulic fluid to do. Worse, it can prevent the proper flow of fluid in the system. This air can limit the maximum weight the hydraulic jack can lift, or cause it to let the load down slightly after it has been lifted – either of which can be anything from annoying to deadly depending on what you are lifting.

Luckily, bleeding a hydraulic jack of air is fairly simple.

Read your hydraulic jack’s manual. Always read the manual.

Familiarising yourself with the user manual, and especially with its specific bleeding procedures. It will let you now if any special tools are needed, or any unusual procedures. If the manual for your hydraulic jack contradicts this guide, the manual is probably correct!

Remove the hydraulic jack from any equipment (engine hoist, etc) that it may be attached to.

This is both for the sake of safety and to make it easier to access the jack itself. Check the manuals for any associated equipment for the procedures to do this safely.

Open your hydraulic jack’s bleed valve

This is normally accomplished by turning the pump handle counter-clockwise while the ram is in its lowest position.

Remove the fluid fill plug.

This will usually be found on the side of the hydraulic jack, towards the centre. This can usually be done with just a flathead screwdriver.

Cycle the hydraulic jack.

Insert the pumping handle into the jack’s handle socket and give it between 10 and 20 strokes, unless the manual gives a different figure. This should cycle the fluid through the system, fetching any air to the bleeder valve, and out through the oil fill hole.

Top up the fluid in the jack

Check the fluid level, and add more according to the procedures in the hydraulic jack’s manual if necessary.

Replace the fluid fill plug.

This prevents oil contamination, spillage or the introduction of more air into the hydraulic jack’s fluid system.

Close the release valve again.

This returns the hydraulic jack to its normal working configuration.

Extend the jack

Use the pumping handle to raise the hydraulic jack to its maximum extension. This lets you ensure that the jack is working normally.

Note – If the jack’s ram does not extend, you may have to repeat these procedures with the jack upside down or in its side to allow any air in the ram chamber to escape.

Return the hydraulic jack to normal use.

Bleeding a hydraulic jack normally leaves it free of air bubbles and operating normally. You can return it to its engine hoist or any other equipment now.

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