How to Get Air Out of a Hydraulic System

Written by c.l. rease | 13/05/2017
How to Get Air Out of a Hydraulic System
Hydraulic systems use fluid pressure to operate. (Hydraulic pipes from an industrial vehicle image by JCVStock from

Air causes the pressure in a hydraulic system to drop. This causes a variety of problems, depending on the type of hydraulic system. When air enters a vehicle brake system, you will need to apply more pressure to the brake pedal to stop the vehicle. In contrast, a hydraulic jack will not lift any weight when air displaces fluid in the hydraulic cylinder. Bleeding the system removes air from the system and allows the system to function properly.

Fill the fluid reservoir to the full line with hydraulic fluid. Remove the fill screw if you are removing air from a hydraulic jack to add fluid directly to the hydraulic cylinder.

Pressurise the hydraulic system by extending the hydraulic cylinder. For example, press and hold the brake pedal of a vehicle if removing air from a brake system.

Open the bleeder valve located near the hydraulic cylinder with an adjustable wrench. Close the bleeder valve when no air flows from the valve. Repeat the procedure three to four times to remove all air from the system.

Fill the hydraulic system with hydraulic fluid after removing all air from the system. Install the fill screw if you removed it to fill the hydraulic system.

Test the system to ensure proper operation. Repeat the bleeder process if the system does not function correctly.

Things you need

  • Hydraulic fluid
  • Flathead screwdriver
  • Adjustable wrench
  • Clean rags

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