Replacing the Hydraulic Solenoid Valve on a Hitachi EX50URG Excavator

[MikePhua]

The EX50URG and Hitachi’s Compact Excavator Lineage
The Hitachi EX50URG is a compact hydraulic excavator designed for urban construction, trenching, and utility work. Produced in the late 1990s and early 2000s, it features a tight tail swing, offset boom capability, and a turbocharged Isuzu 3AD1 three-cylinder diesel engine. With an operating weight around 5 metric tons and a dig depth exceeding 3.5 meters, the EX50URG was built for maneuverability and precision in confined spaces.
Hitachi, a pioneer in hydraulic excavator development since the 1960s, has maintained a reputation for reliability and serviceability. The EX series was widely adopted across Asia-Pacific and Australia, with thousands of units sold into rental fleets and contractor operations. The EX50URG’s offset boom design allows for parallel digging along walls and foundations, making it a favorite in urban infrastructure projects.
Hydraulic Solenoid Valve Function and Failure Symptoms
The offset boom cylinder on the EX50URG is controlled by a hydraulic solenoid valve mounted on a three-port block. This valve regulates flow direction and pressure to the knuckle cylinder, enabling lateral boom movement. The solenoid coil energizes the valve spool, allowing hydraulic fluid to pass through the designated port.
Common failure symptoms include:

• Boom offset function not responding to joystick input
  
• Audible clicking from the coil but no hydraulic movement
  
• Coil overheating or insulation damage
  
• Valve spool seized or stuck in neutral position
  
• Exposed copper windings due to coil deterioration
  

In one case, the coil was so corroded that it tore apart during removal, revealing internal copper strands and rendering the valve inoperable.
Identifying and Replacing the Valve and Coil
The original coil was marked with the following specifications:

• Manufacturer: Sterling Hydraulics
  
• Voltage: 12VDC
  
• Power: 18W
  
• Model: CAS 012D
  
• Origin: Made in USA
  

However, no part number was visible on the coil or valve body. After consulting a component parts manual for the EX50URG, the correct part numbers were identified:

• Complete solenoid valve: 4253619
  
• Valve name code: 0397600
  
• Coil part number: 0397604
  

These identifiers are crucial when sourcing replacements, especially for machines operating outside Japan. In Australia, the operator contacted Rexroth Hydraulics, who supplied an equivalent valve for AUD $210. This highlights the importance of cross-referencing part numbers across manufacturers and regions.
Aftermarket Compatibility and Installation Tips
When OEM parts are unavailable or delayed, aftermarket equivalents can be used if specifications match. Key parameters to verify include:

• Voltage and wattage rating
  
• Coil diameter and mounting thread
  
• Valve spool configuration (normally open or closed)
  
• Port size and flow capacity
  
• Seal material compatibility with hydraulic fluid
  

Installation steps:

• Disconnect battery to prevent accidental energization
  
• Remove damaged coil and valve using appropriate wrenches
  
• Clean valve block mating surfaces and inspect for debris
  
• Install new valve and torque to manufacturer specs
  
• Connect coil wiring with heat-shrink terminals
  
• Test function with engine running and monitor for leaks
  

After installation, cycle the boom offset function several times to purge air and confirm smooth operation.
A Story from the Field
In Queensland, a technician working on an EX50URG encountered a seized solenoid valve while preparing the machine for trenching. With no part number visible, he relied on a parts manual and sourced a replacement from a hydraulic supplier. The new valve restored full boom offset control, and the operator paired it with a freshly fabricated 200 mm trenching bucket from a local manufacturer. The machine returned to service that weekend, completing a drainage job with improved precision.
Preventive Measures and Long-Term Reliability
To extend solenoid valve life:

• Inspect coil insulation annually for heat damage
  
• Use dielectric grease on connectors to prevent corrosion
  
• Avoid prolonged energization without hydraulic movement
  
• Replace damaged wiring harnesses promptly
  
• Keep valve block clean and free of hydraulic residue
  

For machines operating in humid or coastal environments, consider installing weatherproof coil covers or relocating exposed components away from splash zones.
Conclusion
Replacing the hydraulic solenoid valve on a Hitachi EX50URG excavator requires careful identification, sourcing, and installation. With the correct part numbers and attention to coil specifications, operators can restore offset boom functionality and maintain precision in tight workspaces. In compact excavators, every valve plays a role in shaping the job—and when the knuckle moves smoothly, the machine becomes an extension of the operator’s intent.