To bleed new hydraulic lines, systematically release trapped air from the system, typically by opening bleed valves while operating the hydraulic function and observing the fluid until it runs clear and bubble-free.
Understanding the Need to Bleed
When new hydraulic lines, components, or fluid are introduced into a system, air can become trapped within the circuits. Air is compressible, unlike hydraulic fluid. Its presence can lead to spongy operation, reduced power, inconsistent movement, and potential damage to components over time. Bleeding is the process of removing this trapped air.
Preparation is Key
Before starting the bleeding process, gather the necessary supplies and take safety precautions:
- Safety First: Wear safety glasses and gloves. Hydraulic fluid can be under pressure and cause injury.
- Locate Bleed Points: Identify the bleed screws or valves on the hydraulic components (e.g., cylinders, pumps, control valves). Consult your equipment's service manual if needed.
- Collect Fluid: Have a container ready to catch expelled hydraulic fluid. Attach a clear tube to the bleed valve nipple (if available) and place the other end in the collection container, ideally submerged in a small amount of clean fluid to prevent air from being drawn back in.
- Check Fluid Level: Ensure the hydraulic reservoir is filled to the proper level. Bleeding will consume some fluid, so you may need to top it up during or after the process.
- Gather Tools: You'll likely need a wrench or socket to open and close the bleed valves.
The Bleeding Process
Bleeding is often a multi-step process that may require a helper to operate the hydraulic controls while you manage the bleed valves.
- Identify the Lowest Point: Start bleeding at the bleed point furthest from the pump and/or lowest in the system to allow air to rise and be expelled.
- Attach Collection Tube: Securely attach a clear plastic tube to the bleed valve nipple. Place the other end into your collection container, ensuring it stays submerged in fluid to create a seal.
- Open the Bleed Valve: Open the bleed valve by turning it counterclockwise until it is fully open.
- Operate the Hydraulic Function: Have your helper slowly operate the hydraulic function associated with the component you are bleeding (e.g., extend/retract a cylinder, cycle a motor). This pushes fluid and trapped air towards the bleed valve.
- Observe the Fluid: Allow the air to escape. You may notice bubbles in the fluid as the air escapes from the system. Watch the fluid flow through the clear tube into the container. Initially, it will likely contain many bubbles.
- Continue Until Clear: Leave the valve open until no more air is visible in the fluid. The fluid flow should become smooth and consistent, without any air pockets or bubbles.
- Close the Bleed Valve: Once the fluid runs clear, close the bleed valve by turning it clockwise. Do not overtighten.
- Repeat for Other Points: Move to the next bleed point and repeat steps 3-7. Continue this process for all bleed points in the system.
- Check Reservoir and Test: After bleeding all points, check the hydraulic fluid reservoir level and top up as needed. Slowly operate the hydraulic functions through their full range of motion several times to help work out any remaining small air pockets. Observe performance for smoothness.
Tips for Success
- Be Patient: Bleeding can take time, especially with complex systems or long lines.
- Work Slowly: Operating the hydraulic function slowly helps prevent churning the fluid and creating more air bubbles.
- Keep Reservoir Full: Never let the reservoir run dry during bleeding, as this will introduce more air.
- Listen: Sometimes you can hear air hissing out of the valve.
- Multiple Cycles: It may be necessary to cycle the hydraulic function and bleed valves multiple times to remove all air.
- Check Connections: Ensure all connections in the new lines are tight before and after bleeding to prevent air leaks.
