Komatsu PC210-6 Excavator Boom and Arm Movement Issue

[MikePhua]

The Komatsu PC210-6 is a robust mid-sized excavator widely respected for its powerful engine, efficient hydraulics, and versatile capabilities in various agricultural, construction, and earthmoving tasks. Recently, some operators have encountered an unusual problem where moving the arm in while simultaneously raising the boom causes the boom movement to stop or stall unexpectedly. Understanding and resolving this issue is critical to maintaining productivity and machine reliability.
Technical Background

• The PC210-6 features a Komatsu SAA6D107E-3 six-cylinder diesel engine delivering about 165 horsepower, designed in EPA Tier 4 Final compliant standards.
  
• Its hydraulic system uses a closed-center, load-sensing design with variable displacement pumps controlling boom, arm, bucket, and swing functions independently but coordinating simultaneously.
  
• Boom cylinders measure about 5.1 inches in bore and 52.5 inches in stroke, while the arm cylinder is 5.3 inches in bore and 58.7 inches in stroke, providing powerful, smooth lifting and digging forces.
  

Problem Description

• When operators command simultaneous arm-in (curl) and boom-up (raise) movements, the boom will sometimes stop moving entirely after initial motion.
  
• Prior to this symptom, the machine operated normally without interlocking or stalling during multifunctional hydraulic operations.
  
• The stall typically occurs mid-motion and can last until controls are released or repositioned.
  

Potential Causes

• Hydraulic Flow Restriction: Load-sensing systems allocate hydraulic flow based on demand. Excess simultaneous demands can lead to pressure drops or priority conflicts, restricting one actuator’s flow.
  
• Valve or Servo Malfunction: Internal spool valves or servos controlling flow to the boom cylinder may be sticking or malfunctioning, failing to maintain consistent flow under combined load conditions.
  
• Pressure Relief Issues: Faulty relief valves may activate prematurely, diverting flow from the boom under certain combined function stresses.
  
• Hydraulic Fluid Condition: Contaminated or low hydraulic fluid can cause sluggish response or valve sticking, exacerbating flow issues.
  
• Pump Wear or Fault: The variable displacement pump may be unable to maintain stable flow at lower engine RPM or under concurrent multi-circuit demands.
  

Troubleshooting Recommendations

• Inspect hydraulic fluid condition, level, and cleanliness; perform a fluid change if contaminated.
  
• Test hydraulic pressure at boom and arm circuits using pressure gauges to detect significant drops or spiking.
  
• Examine boom control valve and servo for wear, damage, and free movement; clean or replace components as necessary.
  
• Review hydraulic pump performance through diagnostic tools or service centers; adjust or repair pump components if flow limitations are detected.
  
• Consult with Komatsu service manuals for testing procedures and hydraulic circuit schematics.
  

Glossary

• Load-Sensing Hydraulic System: A system that adjusts pump output based on cylinder demand, improving efficiency but requiring precise regulation.
  
• Spool Valve: A control valve directing hydraulic fluid flow to actuators.
  
• Pressure Relief Valve: A valve that diverts excess hydraulic pressure to prevent system damage.
  
• Variable Displacement Pump: A pump capable of changing output flow to match system demand.
  
• Hydraulic Servo: A pneumatic or hydraulic actuator controlling valve spool movement.
  

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The complicated interaction of hydraulic flow demands during simultaneous boom and arm movement can cause flow restrictions or control valve malfunctions on the Komatsu PC210-6, leading to boom stalling. Addressing this issue involves systematic inspection and maintenance of the hydraulic system, cleaning or replacing valves, and ensuring pump efficiency, ultimately restoring smooth, coordinated multifunction machine operation.