Restoring Hydraulic Functionality in the Hitachi EX60URG After Pump Failure

[MikePhua]

The EX60URG and Hitachi’s Compact Excavator Lineage
The Hitachi EX60URG is a compact hydraulic excavator designed for precision work in confined spaces, particularly in urban and utility environments. Part of Hitachi’s EX series, the EX60URG was developed in the late 1990s and early 2000s, featuring a zero-tail swing design and a robust hydraulic system built around the Uchida piston pump. Hitachi Construction Machinery, founded in 1970, has long been a leader in hydraulic excavator innovation, with global sales exceeding hundreds of thousands of units across its compact and mid-size platforms.
The EX60URG typically weighs around 6 metric tons and is powered by a four-cylinder diesel engine. Its hydraulic system includes a main variable displacement piston pump and auxiliary gear pumps for pilot and blade functions. The machine’s modular design allows for relatively straightforward access to components, but diagnosing hydraulic faults can still be complex due to the interdependence of pilot pressure, valve actuation, and pump modulation.
Catastrophic Pump Failure and Rebuild Challenges
In one case, an EX60URG suffered a catastrophic failure of its Uchida main pump. The piston support ring fractured, causing internal damage to the swash plate, pistons, and other components. The pump was sent to a repair facility, but due to cost constraints, the unit was returned partially disassembled and missing undamaged parts. The operator sourced replacement components independently and rebuilt the pump manually.
This kind of failure is not uncommon in high-hour machines, especially when pilot filters are neglected or fluid contamination occurs. The swash plate in a variable displacement pump is critical for controlling flow rate and direction. Damage to this component can result in erratic pressure delivery and loss of function across multiple circuits.
Symptoms of Hydraulic Dysfunction After Reinstallation
After reinstalling the rebuilt pump, the EX60URG exhibited several hydraulic issues:

• The blade moved slowly with minimal force
  
• The swivel brake remained engaged, preventing cab rotation
  
• Travel motors failed to disengage brakes
  
• Boom and bucket functions worked intermittently or required “jagging” the levers
  
• No change in engine sound during operation, despite hydraulic demand
  
• Turbulence was observed in the hydraulic tank, indicating active flow
  

These symptoms suggest a combination of pilot pressure loss, relief valve malfunction, and possible gear pump failure.
Pilot Pressure and Swivel Brake Release
The swivel brake on the EX60URG is hydraulically released via pilot pressure. When the pilot filter becomes clogged—especially with gelatinous contaminants from degraded seals or fluid breakdown—pilot pressure drops, and the brake remains engaged. In this case, removing the clogged pilot filter allowed the brake to release and restored cab rotation.
Pilot pressure is typically generated by a gear pump and regulated through a pilot control valve. If the gear pump is damaged or the pilot circuit is obstructed, functions like blade movement and travel brake release will fail.
Relief Valve Malfunction and System Recovery
A field technician later diagnosed the main pressure relief valve as being stuck open. This valve protects the hydraulic system from overpressure by diverting excess flow back to the tank. When jammed open, it prevents the system from building sufficient pressure for actuator movement.
After flushing and resetting the relief valve, most functions returned to normal. However, the blade remained inoperative due to a faulty gear pump, which likely failed during the initial pump breakdown or was damaged by debris.
Relief valves can be tested by:

• Installing pressure gauges at key circuit points
  
• Observing pressure drop during actuation
  
• Removing and inspecting valve seats and springs
  
• Flushing valve bodies with clean hydraulic fluid
  

A Story from the Field
In Edinburgh, a model engineering society acquired an EX60URG to develop a miniature railway and park. After months of troubleshooting, they discovered that the pump failure had cascaded into multiple hydraulic faults. With limited budget and no dealer support, they rebuilt the pump in-house, sourced manuals, and constructed their own hydraulic schematic. The breakthrough came when a technician identified the relief valve issue, restoring nearly full functionality. The blade pump remained a challenge, but the machine was operational enough to continue site development.
Recommendations for Compact Excavator Hydraulic Recovery
To restore hydraulic function after major pump failure:

• Replace all filters, especially pilot and return filters
  
• Flush the system thoroughly to remove debris and gelled contaminants
  
• Inspect and test relief valves for proper operation
  
• Verify pilot pressure at control valves and brake actuators
  
• Rebuild or replace gear pumps if blade or pilot functions remain weak
  
• Use OEM-spec hydraulic fluid and monitor for temperature and contamination
  

For older machines, maintaining a parts manual and constructing a circuit diagram can greatly aid in troubleshooting. Many compact excavators share hydraulic architecture across models, allowing for cross-referencing and part substitution.
Conclusion
The Hitachi EX60URG, while compact and versatile, relies on a finely tuned hydraulic system that can be disrupted by pump failure and contamination. Restoring functionality requires a methodical approach—diagnosing pilot pressure, relief valve integrity, and gear pump performance. In the world of compact excavation, power is not just about horsepower—it’s about pressure, precision, and persistence. When the fluid flows true, the machine follows.