How Do You Bleed Air From Hydraulic Lines?

A hydraulic system passes hydraulic fluid through lines from the component that creates the pressure (the master cylinder) to the output components or pistons that transfer the pressure to perform the required task. Examples of the hydraulic system include motor vehicle hydraulic brakes, lifting arms of excavators and motor vehicle power steering systems. Air in the hydraulic system makes the system work inefficiently or to cease functioning. Procedures for bleeding hydraulic systems vary depending on the machinery. Consult the operation manual for your vehicle or equipment for specific instructions.

Instructions

1

Remove panels and wheels from the vehicle or machinery to gain access to the bleeding valve of the hydraulic output component. Use lifts, blocks and other safety devices if you remove the wheels.

2

Attach the hose of the bleeding kit to the bleeding valve of the output component or piston.

3

Top up the hydraulic fluid reservoir to its maximum level.

4

Loosen the bleeding valve about a quarter turn to a half turn.

5

Action the vacuum pump on the bleeding kit to draw the fluid from the reservoir, through the hydraulic line and output component into the bleeding container. Open the bleeding valve more if you encounter strong resistance in drawing the fluid.

6

Tighten the bleeding valve to avoid pumping air back into the system when you return the pump to the original position.

7

Repeat Steps 4 to 6 until at least a half cup of fluid has bled through the system. Top up the hydraulic reservoir as you work to ensure it does not drop below its low mark.

8

Test the system by compressing the brake pedal several times. If it feels spongy or offers little resistance, bleed the line some more.