How to Bleed Hydraulic Lines

Because pressure is such a vital factor in the efficiency of a hydraulic system, the condition of its hydraulic lines can play an important role in the operation of the system. Although you usually can obtain commercial kits and tools that will make bleeding of these lines possible, these items are usually expensive. Rather than spending money unnecessarily, you can bleed these lines, yourself, if you have the necessary information, such as that which you'll find below.

Things you'll need:

  • Bottles
  • Plastic tubing
  • New hydraulic fluid

Step 1 - Choose the Best Work Environment

If you plan to work on a hydraulic pump or machine, choose a surface that is level. To bleed a vehicle's brake lines (which are hydraulic), position the vehicle on the flat surface of your garage, level concrete pad, or even a level street. Avoid working on a driveway surface which is usually sloping.

Step 2 - Provide Access to Bleed Valves.

If your machine, pump, or vehicle has components that interfere with your access to bleed valves, if it is possible, move or remove these components to give you better working room. For work on the hydraulic system of some vehicles, you may need to raise them to gain access to wheel wells or oil pans. Where you are working on the hydraulic systems of vehicles you need to raise, be sure to use jack stands to support the vehicle.

Step 3 - Bleed Your Hydraulic Lines

Begin by bleeding lines that are more remote from the hydraulic pump or master cylinder. Then, progress to lines closer to the pump or master cylinder until all lines have been bled. Finally, unscrew the drain plug or reservoir cap and set it aside in an area that is clean and will be accessible when you need to retrieve it. Collect clean, dry bottles that you'll drain your fluid into. You'll need to pour the fluid from these bottles back into the system when the time is right.

Step 4 - Attach Plastic Tubing

Locate the bleeder outlet screw, and fit plastic tubing over the screw. The tubing should be clear and should be 3 inches long and 1/8-inch in diameter. Fit the tube tightly over the screw, tight enough that there will be fluid leaks from the cylinder, and that no air will enter the cylinder. When one end of your tubing is secured onto the outlet screw, place the other end into one of your bottles.

Step 5 - Pump Fluid Out of the Lines

By pumping your hydraulic piston control, you will force hydraulic fluid out of the lines and into the bottle. To remove fluid from a vehicle's brake lines, you'll need to pump the brake pedal. Maintain pressure on the valve as you open the bleeder screw. When you are able to press the valve all the way down and all pressure is released, then you can screw the outlet screw closed. Use this procedure to bleed each line. When the hydraulic fluid looks like the new hydraulic fluid, your bleeding is finished. As you refill the reservoir while bleeding the individual lines, be sure you don't let it become empty. When finished, replace all components, including tightening of your drain plug.