Troubleshooting Hydraulic and Electrical Controls on the Komatsu Dresser 220-5

[MikePhua]

The Komatsu Dresser 220-5 Excavator
The Komatsu Dresser 220-5 is a mid-sized hydraulic excavator born from a joint venture between Komatsu Ltd. of Japan and Dresser Industries of the United States during the late 1980s. This collaboration aimed to expand Komatsu’s footprint in North America while leveraging Dresser’s distribution network and market familiarity. The 220-5 model was part of a broader series that combined Komatsu’s engineering with Dresser’s rugged design ethos, resulting in machines that were particularly popular in infrastructure development and quarry operations.
Equipped with a Komatsu S6D125 diesel engine producing approximately 150–170 horsepower, the 220-5 featured a fully hydraulic control system, a two-speed travel function, and a robust undercarriage suited for demanding terrain. Though exact sales figures are hard to pin down, thousands of units were distributed across North America and Southeast Asia, with many still in operation today due to their mechanical simplicity and rebuild-friendly architecture.
Terminology Annotation

• Valve Spool: A cylindrical component inside a hydraulic valve that directs fluid flow based on its position.
  
• Pressure Transducer: An electronic sensor that converts hydraulic pressure into an electrical signal for monitoring or control.
  
• PPC Manifold: Pilot Pressure Control manifold, which distributes low-pressure pilot signals to actuate main hydraulic valves.
  
• Auto Decel Mode: A feature that reduces engine RPM automatically when hydraulic demand drops, improving fuel efficiency.
  
• Arm Half Flow Valve: Also known as the arm throttle valve, it modulates hydraulic flow to the arm circuit for smoother operation.
  

Electrical Devices on Valve Spools
On the Komatsu Dresser 220-5, several electrical components are mounted atop the hydraulic valve spools. These are pressure transducers that feed real-time data to the onboard control computer. Their primary role is to assist in automatic shifting between high and low travel speeds and to trigger engine deceleration when hydraulic demand subsides.
This system was part of Komatsu’s early efforts to integrate electronic control into hydraulic systems, a precursor to today’s fully digital excavator platforms. The transducers monitor pilot pressure and send signals to the ECU (Electronic Control Unit), which then adjusts engine RPM or travel speed accordingly.
Locating the Arm Half Flow Valve
The arm half flow valve is typically mounted on the main control valve block, which contains multiple spools for boom, stick, bucket, and travel functions. On the 220-5, this block is located beneath the operator’s cab or adjacent to the hydraulic pump compartment. Identifying the correct spool—whether for boom, stick, or travel—requires tracing labeled hydraulic lines and referencing the machine’s hydraulic schematic.
In one field case, a technician traced a weak and slow arm movement to a stuck spool in the arm circuit. After disassembling the valve and cleaning debris from the spool bore, performance returned to normal. This highlights the importance of regular hydraulic fluid filtration and periodic valve inspection.
Symptoms of a Stuck Spool
When a spool in the hydraulic valve is stuck or partially obstructed, the following symptoms may appear:

• Sluggish or weak movement in the corresponding function (e.g., arm or boom)
  
• Delayed response to joystick input
  
• Increased engine load without corresponding hydraulic output
  
• Audible strain from the pump or relief valve activation
  

These issues can often be traced to contamination, wear, or internal scoring of the spool surface. In older machines like the 220-5, spool sticking is a common issue due to aging seals and fluid degradation.
The Role of Pressure Switches in Auto Deceleration
The pressure switches mounted on the PPC manifold serve a dual purpose. First, they detect when hydraulic demand drops—such as when the operator pauses between movements. Second, they signal the ECU to initiate auto deceleration, reducing fuel consumption and noise.
This feature was considered advanced for its time and contributed to the 220-5’s reputation for fuel efficiency. Komatsu even developed a diagnostic “Tee tool” that could be inserted between the machine harness and computer to monitor pressure signals in real time. Though rare today, these tools were standard in dealer service kits during the 1990s.
Circuit Complexity and Troubleshooting Advice
The 220-5’s electrical and hydraulic systems are intertwined, making diagnostics challenging without proper documentation. Technicians often face dozens of circuits and connectors, many of which lack modern labeling. To simplify troubleshooting:

• Use color-coded wiring diagrams and hydraulic schematics
  
• Label each connector during disassembly
  
• Test pressure transducers with a multimeter and hydraulic gauge
  
• Clean all electrical contacts with dielectric cleaner
  
• Replace brittle or cracked harnesses with heat-resistant replacements
  

Field Anecdote and Lessons Learned
In 2018, a Vietnamese contractor operating a 220-5 near Ho Chi Minh City reported intermittent arm weakness. After weeks of trial-and-error, the issue was traced to a faulty pressure transducer that was sending erratic signals to the ECU. Replacing the sensor restored normal function, and the contractor began a preventive replacement program for all PPC-mounted sensors across his fleet.
Suggested Maintenance Intervals
To keep the Komatsu Dresser 220-5 in optimal condition:

• Hydraulic fluid: Replace every 1,000 hours or annually
  
• Filters: Inspect every 250 hours, replace every 500 hours
  
• Electrical connectors: Inspect quarterly, especially in humid climates
  
• Valve spools: Clean and inspect during major service intervals
  
• Pressure sensors: Test annually or when symptoms arise
  

Conclusion
The Komatsu Dresser 220-5 remains a testament to durable design and transitional technology. Its blend of hydraulic muscle and early electronic control offers valuable lessons in maintenance and diagnostics. Understanding the role of pressure transducers, spool valves, and auto deceleration circuits is key to keeping these machines productive. With proper care and informed troubleshooting, the 220-5 can continue serving in excavation and earthmoving roles well beyond its original design life.