Hitachi EX120-3 Hydraulic System Change – A Comprehensive Guide

[MikePhua]

Introduction
The Hitachi EX120-3 is a robust and efficient mini-excavator commonly used in construction, landscaping, and excavation projects. Its hydraulic system is essential for powering various functions, such as the arm, boom, bucket, and swing motors. Over time, the hydraulic components may degrade, and maintenance or complete system changes may be necessary. This article provides a step-by-step guide on how to change the hydraulic system on the Hitachi EX120-3 excavator, including essential tips and best practices.
Why Change the Hydraulic System?
Hydraulic systems in excavators like the Hitachi EX120-3 are crucial for providing the power required for lifting, digging, and maneuvering the machine. Common reasons for changing the hydraulic system or specific components include:

• Hydraulic fluid contamination: If the fluid becomes dirty or contaminated, it can cause damage to various components of the hydraulic system.
  
• Loss of hydraulic power: If the pump or valves are worn or malfunctioning, the hydraulic system may lose pressure, reducing performance.
  
• Leaks and damaged hoses: Over time, hoses, seals, and fittings can wear out, leading to leaks and inefficiencies.
  

Symptoms of Hydraulic System Failure

1. Sluggish Hydraulic Response
   • The hydraulic functions, such as arm or bucket movement, become slow or unresponsive.
     
2. Engine Overload
   • The engine may struggle or strain when using the hydraulic system, indicating a potential issue with the pump or fluid pressure.
     
3. Fluid Leaks
   • Visible leaks around the hydraulic hoses, cylinders, or pump.
     
4. Unusual Noise
   • Whining or grinding noises from the hydraulic components suggest internal damage or wear.
     

Tools and Equipment Needed
Before starting the hydraulic system change, ensure you have the following tools:

• Wrenches and sockets
  
• Hydraulic fluid (matching the machine’s specifications)
  
• New hydraulic pump, hoses, and filters (if necessary)
  
• Torque wrench
  
• Fluid drain pan
  
• Cleaning materials (rags, brushes, etc.)
  
• Safety gloves and glasses
  

Step-by-Step Guide to Changing the Hydraulic System

1. Preparation and Safety
   • Step 1: Park the excavator on level ground, ensuring it’s stable and secure. Turn off the engine and remove the key to prevent accidental starts.
     
   • Step 2: Disconnect the battery to prevent electrical mishaps while working on the hydraulic system.
     
2. Drain the Hydraulic Fluid
   • Step 1: Locate the hydraulic fluid reservoir and the drain plug. Position a suitable container under the drain plug to collect the old fluid.
     
   • Step 2: Open the drain plug and allow the fluid to drain completely. This may take some time, depending on the amount of fluid in the system.
     
   • Step 3: Once drained, dispose of the hydraulic fluid according to local environmental regulations.
     
3. Remove the Old Hydraulic Pump (If Replacing)
   • Step 1: The hydraulic pump is usually located near the engine or at the rear of the excavator. Disconnect any hoses and fittings connected to the pump.
     
   • Step 2: Remove the mounting bolts securing the pump in place. Be cautious as hydraulic pumps can be heavy. Use a lifting device if necessary to remove the pump safely.
     
   • Step 3: Inspect the pump for signs of wear or damage. If it is faulty, replace it with a new one that meets the machine’s specifications.
     
4. Inspect and Replace Hydraulic Hoses
   • Step 1: Examine all hydraulic hoses for cracks, leaks, or damage. If any hoses are worn or damaged, replace them.
     
   • Step 2: Clean the hydraulic connections and ensure they are free from dirt or debris before installing new hoses.
     
   • Step 3: Reinstall the new hoses securely, tightening all connections properly to avoid leaks.
     
5. Change Hydraulic Filters
   • Step 1: Locate the hydraulic filters. These are typically found near the pump or on the side of the hydraulic tank.
     
   • Step 2: Remove the old filters and replace them with new ones. Be sure to use OEM filters that match the system's specifications.
     
   • Step 3: Apply a thin layer of hydraulic fluid to the O-rings of the new filters to ensure a good seal.
     
6. Refill Hydraulic Fluid
   • Step 1: Once the pump, hoses, and filters are in place, refill the hydraulic system with fresh, clean hydraulic fluid. Use the type of fluid specified by Hitachi for the EX120-3.
     
   • Step 2: Check the fluid level, ensuring it is at the recommended level. You may need to add more fluid once the system is operating.
     
7. Bleed the Hydraulic System
   • Step 1: To ensure that air does not remain trapped in the hydraulic lines, operate the hydraulic functions (such as the arm, boom, and bucket) for several minutes.
     
   • Step 2: Keep the engine running at idle speed and cycle the hydraulic controls to allow the fluid to circulate and expel any trapped air.
     
8. Test the System
   • Step 1: After filling the system and bleeding the lines, test the hydraulic system by moving all hydraulic functions.
     
   • Step 2: Check for smooth movement, proper response, and no signs of sluggishness or hesitation.
     
   • Step 3: Observe the system for any fluid leaks around the hoses, pump, or other components. Tighten any connections as needed.
     
9. Final Check and Cleanup
   • Step 1: After confirming that the system is working properly, recheck the hydraulic fluid level and top up if necessary.
     
   • Step 2: Clean any spilled fluid around the pump, hoses, and connections to maintain a safe working environment.
     
   • Step 3: Dispose of any waste materials, including old hydraulic fluid, filters, and damaged parts, according to local disposal guidelines.
     

Preventive Maintenance Tips for Hydraulic System

1. Regular Fluid Changes
   • Change the hydraulic fluid at regular intervals as recommended by the manufacturer to keep the system clean and prevent contamination.
     
2. Inspection of Hoses and Fittings
   • Routinely inspect hydraulic hoses for signs of wear, cracks, or leaks. Replace damaged hoses immediately to avoid fluid loss.
     
3. Monitor Fluid Quality
   • Keep an eye on the condition of the hydraulic fluid. If it becomes dirty or contaminated, change it promptly to prevent damage to the pump and other components.
     
4. Filter Replacement
   • Replace hydraulic filters regularly to maintain fluid cleanliness and prevent blockages that can impair pump performance.
     

Conclusion
Replacing or changing the hydraulic system on the Hitachi EX120-3 excavator can be a straightforward process if done properly. Regular maintenance and addressing issues like fluid contamination, pump failure, or leaking hoses are key to ensuring the longevity of the machine. By following the steps in this guide, operators can successfully perform hydraulic system maintenance, restore performance, and prevent costly repairs down the line.