Resolving Hydraulic Power Loss in the Komatsu PC220 Excavator

[MikePhua]

The PC220 and Its Hydraulic Architecture
The Komatsu PC220 series has long been a staple in mid-size excavator fleets worldwide. Introduced in the late 1980s and refined through multiple generations, the PC220LC-3 and later PC220-7 models were designed for versatility in earthmoving, trenching, demolition, and forestry. With operating weights around 23–24 tons and powered by Komatsu’s S6D105 or SAA6D102E engines, these machines rely heavily on a dual-pump hydraulic system to drive boom, arm, bucket, swing, and travel functions.
The hydraulic system is load-sensing, meaning it adjusts flow and pressure based on demand. It includes two variable displacement piston pumps, a main control valve bank, pilot circuits, relief valves, and flow-divide logic to optimize performance. When this system begins to lose power intermittently—especially after warm-up—it can be difficult to isolate the root cause without a methodical approach.
Symptoms of Progressive Hydraulic Weakness
Operators often report:

• Loss of travel power on one track
  
• Sluggish stick or boom movement
  
• Normal performance during cold start, followed by degradation after 20–30 minutes
  
• Pressure readings within spec during static tests
  
• No fault codes or alarms from the onboard system
  

This pattern suggests a thermal or flow-related issue rather than a catastrophic failure. The machine may perform well until hydraulic oil reaches operating temperature, at which point internal leakage or valve instability begins to affect flow distribution.
Pump Splitting and Flow Divide Behavior
The PC220’s hydraulic system uses a flow-divide valve to split output from the two pumps depending on operational mode. During travel or simultaneous functions, the system merges flow for maximum output. When stationary or performing single functions, the pumps may operate independently.
In diagnostic mode, technicians often manually separate pump flows to test individual performance. If one pump shows a drop in unload pressure while the other remains stable, it may indicate:

• Internal leakage in the valve bank
  
• Weak pilot signal to the flow-divide valve
  
• Thermal expansion affecting spool clearance
  
• Pressure compensation drift due to worn seals
  

A field mechanic in Rajasthan once discovered that a PC220LC-7 lost stick power only when traveling. By isolating pump flows and testing under load, he traced the issue to a cracked internal bore in the main valve block—visible only after teardown.
Unloading Pressure and Valve Bank Integrity
Unloading pressure refers to the pressure at which a pump diverts flow back to tank when not needed. While not directly tied to operational output, abnormal unload pressure can signal internal bypassing or spool misalignment.
If the front pump’s unload pressure drops significantly after warm-up, but main relief pressures remain stable, consider:

• Internal leakage within the flow-divide or merge valve
  
• Warped valve plates due to heat cycling
  
• Pilot valve malfunction affecting spool centering
  
• Contaminants causing spool stiction or delayed response
  

In one case, a contractor in Malaysia found that breaker operation in non-designated modes caused shock loading in the valve bank. Over time, this led to micro-fractures and internal leakage, degrading system performance even during bucket work.
Breaker Use and Hydraulic Shock Absorption
Hydraulic breakers impose intense pressure spikes on the system. If operated outside the designated B-mode or without proper gas charge, they can damage valve internals and seals. The breaker’s accumulator acts as a cushion, absorbing shock and preventing pressure waves from reaching the control valve.
Best practices include:

• Always operate breakers in B-mode or equivalent
  
• Check nitrogen gas charge monthly
  
• Inspect return lines for backpressure
  
• Use flow restrictors if needed to prevent overspeeding
  
• Replace damaged quick couplers and seals promptly
  

A fleet manager in Turkey reported multiple PC220 units losing hydraulic power after prolonged breaker use. Post-repair analysis revealed that the valve banks had internal scoring and bypass paths caused by repeated shock loads.
Preventive Measures and Diagnostic Strategy
To maintain hydraulic integrity:

• Replace hydraulic filters every 500 hours
  
• Flush system and change fluid every 2,000 hours or annually
  
• Use Komatsu-recommended hydraulic oil (e.g., HO46-HM)
  
• Log pressure readings under load and compare across functions
  
• Inspect pilot pressure lines for leaks or kinks
  
• Monitor temperature rise during operation and compare to baseline
  

When diagnosing:

• Separate pump flows and test each under load
  
• Stall individual functions (e.g., left track, stick) and record pressure
  
• Use infrared thermography to detect hot spots in valve bank
  
• Check pilot valve response time and spool centering
  
• Inspect relief valves for chatter or delayed opening
  

A Story from the Field
In 2018, a quarry operator in South Africa faced recurring hydraulic fade on a PC220-7. The machine worked flawlessly for 15 minutes, then lost travel power and stick responsiveness. After replacing pumps, pilot valves, and filters with no improvement, a teardown revealed a hairline crack in the flow-divide spool housing. The crack expanded with heat, causing internal bypass. A replacement valve block resolved the issue, and the machine returned to full duty.
Conclusion
Hydraulic problems in the Komatsu PC220 series often stem from subtle internal failures that emerge under thermal load. By understanding the system’s flow-divide logic, monitoring unload pressure behavior, and respecting breaker operation protocols, technicians can isolate and resolve performance loss. In the world of high-pressure iron, precision diagnostics and preventive care are the keys to uptime.