How to Bleed Air from a Hydraulic System

[MikePhua]

Hydraulic systems are a crucial part of heavy machinery, and maintaining their proper function is essential for optimal performance. However, air can sometimes enter the hydraulic system, leading to reduced performance and potentially damaging components. This article will explain how to effectively bleed air from the hydraulic system to ensure smooth operation.
Why Air Gets into Hydraulic Systems
Air can enter the hydraulic system for several reasons:

1. Low Hydraulic Oil Level: When the oil level in the reservoir is too low, air can easily enter the system.
   
2. Worn or Damaged Seals: Aging or damaged seals can allow air to enter through leakage points in the system.
   
3. Loose or Damaged Hydraulic Lines: Loose connections or damaged hoses can allow air to enter the hydraulic system.
   
4. Hydraulic Pump Issues: Air can enter the system if the hydraulic pump is drawing in air or if there are issues with the pump’s intake.
   

Signs of Air in the Hydraulic System
If air has entered the hydraulic system, it typically manifests in the following symptoms:

1. Sluggish or Unstable Operation: The hydraulic components may operate slowly or in an erratic manner, causing instability.
   
2. Increased Hydraulic Oil Temperature: Air generates friction within the hydraulic oil, which can cause the temperature to rise.
   
3. Fluctuating Hydraulic Pressure: The pressure in the system may become unstable, affecting the operation of the hydraulic components.
   

How to Bleed Air from the Hydraulic System

1. Check the Hydraulic Oil Level
   Make sure the hydraulic oil level is within the manufacturer’s recommended range. If the oil level is too low, top up with the correct type of hydraulic oil.
   
2. Inspect and Replace Seals
   Regularly check seals in the hydraulic system, especially at the pump, valves, and hose connections. If any seals are worn or damaged, replace them promptly to prevent air leaks.
   
3. Inspect Hydraulic Line Connections
   Examine the hydraulic line connections for any looseness or damage. Ensure that all connections are tight to prevent air from entering the system.
   
4. Use Bleed Valves to Release Air
   Many hydraulic systems come equipped with bleed valves to release air. Here’s how to use them:
   • Locate the bleed valve, typically found near the hydraulic pump or cylinder.
     
   • Use an appropriate tool to loosen the valve and let the trapped air escape.
     
   • Start the machine and apply pressure gradually, observing whether the system returns to normal operation.
     
   • Tighten the valve securely after the air has been purged.
     
5. Operate the Hydraulic System
   Without any obvious leaks, operate the hydraulic system slightly by raising or lowering the boom or manipulating the hydraulic controls. This helps to expel any remaining air from the system.
   
6. Check the Hydraulic Pump Intake
   Inspect the pump’s intake areas, such as the intake filter or suction lines, for air leaks. If the pump is drawing in air, it will need to be repaired or replaced.
   

Post-Bleeding System Checks
After bleeding the system, perform the following checks:

1. Observe the Hydraulic System’s Response
   Ensure that the hydraulic system is operating correctly, with smooth and responsive movements. There should be no noticeable delays or jerky actions.
   
2. Monitor the Hydraulic Oil Temperature
   After running the system for a while, check the hydraulic oil temperature to ensure it has returned to normal operating levels.
   
3. Regularly Inspect the Hydraulic System
   Continually inspect the oil level, lines, seals, and other components to ensure no new air leaks develop in the system.
   

Conclusion
Air in the hydraulic system can cause significant performance issues and affect the overall efficiency of the equipment. By checking the hydraulic oil level, inspecting seals and hydraulic lines, and using bleed valves or operating the system, you can effectively remove air from the system. Regular maintenance and inspection of the hydraulic system are key to keeping your equipment running smoothly and avoiding issues caused by air buildup.