Hydraulic Oil Replacement in Excavators

An excavator's hydraulic oil tank typically contains half of the hydraulic oil required for the entire hydraulic system, with the remaining half distributed across the hydraulic pump, motor, multi-way valve, hydraulic cylinders, and various pipelines. When changing the hydraulic oil, merely replacing the oil in the tank without addressing the entire hydraulic system results in a mere mixture of old and new oil. Combining different hydraulic oil brands can further lead to oil degradation.

Preparation for Hydraulic Oil Replacement:

  1. Procure the Necessary Equipment:

    • Purchase hydraulic oil for the entire excavator hydraulic system (2.5 times the volume of the hydraulic oil tank), filters, cleaning oil, 3 kg of flour, ropes, plugs for sealing hydraulic lines, a pump, and various-sized empty oil drums.
    • Prepare a fully functional excavator.
  2. Cleaning the Hydraulic Oil Tank:

    • Drain all hydraulic oil from the tank and remove the hydraulic filter.
    • Disconnect the pipeline between the pump and the tank, allowing the oil to drain from the pipeline.
    • Clean the hydraulic oil tank and pipelines using cleaning oil. Wipe the interior of the tank with medical gauze.
    • Apply a mixture of flour and oil to the tank's interior, especially corners and around the filter housing. Thoroughly clean the tank and filter housing.
    • Replace the hydraulic filter and secure the cover.
  3. Flushing the Hydraulic Piston Pump:

    • Open the upper and lower oil drain ports of the hydraulic piston pump, drain the hydraulic oil, and close the lower drain port.
    • Flush the pump with cleaning oil through the upper drain port until clean oil flows out.
    • Seal the lower drain port and fill the pump with clean hydraulic oil.
  4. Replace Pump Inlet Seal (O-ring):

    • Replace the seal at the pump's inlet.
    • Connect the hydraulic oil tank to the pump's supply pipeline, and fill the tank with clean hydraulic oil through the hydraulic filter port.

Changing Oil in Hydraulic Cylinders:

  1. Change Hydraulic Oil in Boom Cylinder:

    • Elevate the excavator's boom to its highest position, ensuring the engine is off.
    • Disconnect the oil pipes from both ends of the boom cylinder.
    • Use a rope to secure the boom of the excavator.
    • Drain the oil from the cylinder, and reconnect the pipes after changing the oil.
  2. Change Hydraulic Oil in Arm Cylinder:

    • Raise the boom to its highest position, ensuring the engine is off.
    • Disconnect the oil pipes from both ends of the arm cylinder.
    • Secure the arm using a rope.
    • Drain the oil from the cylinder, and reconnect the pipes after changing the oil.
  3. Change Hydraulic Oil in Bucket Cylinder:

    • Disconnect the oil pipe from the bucket cylinder on the back of the boom.
    • Seal the disconnected end with a plug.
    • Drain the oil from the cylinder, and reconnect the pipe after changing the oil.

Changing Oil in Swing Motor System:

  1. Changing Oil in Swing Motor:
    • Disconnect one of the oil pipes between the multi-way valve and the swing motor.
    • Seal the disconnected end.
    • Use a suitable container to collect oil from the swing motor.
    • Start the engine and slowly rotate the excavator. When clean oil flows out, immediately turn off the engine.
    • Reconnect the disconnected oil pipe.

Changing Oil in Travel Motor Systems:

  1. Changing Oil in Left and Right Travel Motors:
    • Lift one side of the excavator's track using the boom.
    • Remove the side cover of the travel motor.
    • Disconnect any oil pipe from the travel motor.
    • Seal the disconnected end and collect the oil.
    • Start the engine and operate the excavator in the supported direction until clean oil flows out.
    • Turn off the engine and reconnect the oil pipe.
    • Repeat the process for the other side.

Considerations for Oil Change:

  1. Adherence to Procedure:

    • Strictly follow the designated steps for changing oil in the hydraulic oil tank, piston pump, hydraulic cylinders, and motor systems. Any deviation may result in operational errors.
  2. Quality of Hydraulic Oil:

    • Choose hydraulic oil that meets the quality standards of the American Society of Engineers. Using certified hydraulic oil ensures stability in viscosity between 40°C and 100°C.
  3. Viscosity Requirements:

    • Depending on the excavator's usage hours, a combination of N46HL and N68HL anti-wear hydraulic oils may be suitable. For excavators with over 15,000 operating hours, using N68HL hydraulic oil is recommended.
  4. Oil Lifespan:

    • The lifespan of hydraulic oil is approximately 4,000 to 6,000 hours or around two years. Environmental factors, such as temperature fluctuations, can lead to water condensation in the oil tank, contributing to oil degradation.
  5. Hydraulic Filter Selection:

    • Choose hydraulic filters with a 10μm50% filtration precision, pressure range of 1.4–3.5MPa, and a rated flow rate of 40–400L/min. Recommended replacement intervals are around 500 hours.
  6. Sealing of Disconnected Oil Pipes:

    • Ensure the replacement of seals (O-rings) on all disconnected oil pipes. Apply thread sealant on the thread surface during reconnection to prevent leaks.

In conclusion, proper preparation and adherence to specific procedures are essential for effective hydraulic oil replacement in excavators. Careful consideration of oil quality, viscosity requirements, and regular maintenance of hydraulic filters contribute to prolonged excavator performance and lifespan.

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