Hydraulic Release of Single Hydraulic Circuit for Caterpillar 311D LRR Excavator

Introduction

This article details the procedure for releasing the hydraulic pressure from a single hydraulic circuit in the Caterpillar 311D LRR excavator.

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WARNING!

Hot hydraulic oil or high hydraulic pressure can cause serious injury. The hydraulic system retains pressure even after the engine is shut down. Failing to release this pressure before performing repairs can lead to severe injury.

Precautions

• When removing hydraulic system components or lines, ensure all moving parts are lowered to the ground and hydraulic oil is cold.
• Remove components only when the engine is stopped and the filler cap is cool enough to touch.
• Have suitable containers ready to collect fluids before opening or dismantling parts.
• Use tools and consumables listed in Caterpillar’s special publication NENG 2500, “Caterpillar Dealers Tool Catalog”.
• Dispose of all fluids in accordance with local regulations.

Steps to Relieve Hydraulic Pressure

1. Park the Machine:
   • Ensure the machine is on level ground.
     
2. Extend Bucket Cylinder:
   • Fully extend the bucket cylinder connecting rod.
   • Position the bucket parallel to the ground.
   • Lower the boom until the bucket is level with the ground (see Figure 1).
3. Stop the Engine:
   • Turn off the engine.
4. Turn Engine Start Switch to “ON”:
   • Do not start the engine.
5. Unlock Hydraulic Start Lever:
   • Place the hydraulic start lever in the unlocked position.
6. Move Joystick or Pedal:
   • Move only the joystick or pedal for the hydraulic circuit being repaired to the full position. This relieves pressure in the individual hydraulic circuit and the pilot hydraulic circuit.
   • If the hydraulic circuit requires the operating switch to be actuated, actuate the corresponding switch.
7. Lock Hydraulic Start Control Lever:
   • Place the hydraulic start control lever in the locked position.
8. Turn Engine Start Switch to “OFF”:
   • Turn off the engine start switch.
9. Loosen Hydraulic Tank Filler Plug:
   • Slowly loosen the hydraulic tank filler plug to relieve pressure in the hydraulic tank.
   • Keep the filler plug loose for at least 45 seconds to allow pressure to dissipate.
10. Tighten Hydraulic Tank Filler Plug:
    • Tighten the filler plug to the specified torque.
11. Relieve Pressure in Hydraulic Circuit:
    • The pressure in the individual hydraulic circuit is now relieved, allowing lines and components to be isolated or removed safely.

By following these steps, you ensure safe and effective pressure release from the hydraulic system of the Caterpillar 311D LRR excavator, preventing potential injuries and equipment damage.