How to Bleed Hydraulic Lines

by Contributor

The performance of any hydraulic system relies heavily on the condition and maintenance of the pistons as well as the lines feeding them. Occasionally, these lines may need to be bled in order to obtain the perfect level of pressure and performance. Though most manufacturers feel that you should only use the rather expensive bleeding tools or kits supplied by their own companies, there is a cheaper and easier way to bleed your hydraulic lines.

Secure your hydraulic pump or machine on a level surface. If you are bleeding hydraulic lines from a car, you'll want to place the car on jacks in the garage or on the street, not in the driveway.

Remove all components of the machine that block your access to the bleed valves but are not part of the hydraulic system. For motor vehicles, this may include the wheels or oil pans.

Bleed the hydraulic lines from the line that is furthest from the master cylinder of the pump. Proceed to bleed the other lines in order until you reach the last hydraulic line.

Remove the fluid reservoir cap or plug. Place it in a clean, dry area where it will be easy to retrieve.

Prepare all your refill bottles at this point, so you will be prepared to replace the bled fluid at the appropriate time.

Attach clear, plastic tubing to the bleeder outlet screw. The tubing should be about 3 inches long and 1/8 inch in diameter. Create a tight fit, so there will be no leaks or air allowed into the cylinder.

Feed the other end of the tube into one of the empty soda bottles.

Pump the hydraulic piston control a few times to help initiate the flow. For example, if you are trying to bleed brake lines on your car, you should pump the brake a few times.

Open the bleeder-outlet screw while keeping pressure on the valve.

Close the outlet screw once the valve level can be pressed all the way down and there is no more pressure.

Bleed each line repeatedly until the hydraulic fluid comes out looking as much like the unused fluid as possible. Refill the reservoir as you bleed each line, never letting it run empty.


  • For easy clean up, smear some petroleum jelly on any surfaces you don't want damaged by the hydraulic fluid.
  • Use only the hydraulic fluid suggested by the manufacturer.


  • Improper disposing of hydraulic fluids is not only environmentally irresponsible, but it may also be illegal in your area. Take your used fluid to an auto-parts or machinery-maintenance shop for proper disposal.
  • Don't allow any of the hydraulic fluid to drip or spill on painted areas of your machinery, as this will result in bubbled or stripped paint. If you happen to spill some, wipe it up with a clean, wet cloth immediately.

Items you will need

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