Variable Pressure Compensated Valve on Hitachi EX220LC-3

[MikePhua]

Understanding Variable Pressure Compensated Valve Function
The “variable pressure compensated valve” is a nuanced piece of hydraulic hardware in the EX220LC-3 that self-regulates flow under changing load conditions. Unlike plain relief valves, this component adjusts oil flow dynamically—allowing a steady actuator speed even when pressure varies. In practical terms, this means smoother swing, arm, and bucket operation, with less operator strain and more predictable machine behavior under varying loads.
Hydraulic System Context and Technical Specs
The EX220LC-3 pairs a robust Hino H06C-T six-cylinder turbocharged engine (~156 hp) with a hydraulic system capable of roughly 50 US gallons per minute flow . Within this system, the pressure-compensated valve ensures that high-demand operations don’t starve smaller servo circuits, essentially balancing flow between functions and maintaining efficiency.
Typical parameters for comparable compensating-valve designs (based on industrial equivalents) include:

• Adjustable flow range: e.g., 0–15 gpm
  
• Internal relief settings: for example, preset at ~1,500 psi, modifiable between ~500 to ~3,000 psi
  
• Working pressures reaching ~3,000 psi
  

These figures, while not Hitachi-specific, provide solid context for the valve’s operating envelope in the EX220LC-3.
Development History and Industry Context
Excavators like the EX220LC-3 emerged from a long line of hybrid hydraulic-electronic evolution. In the last few decades, Hitachi advanced from purely mechanical valves to intelligent pilot-control systems featuring shockless and warm-up circuits . The EX220LC-3 embodies this progression, combining modern hydraulic responsiveness with operator comfort and operational safety.
Although precise sales figures for the EX220LC-3 remain proprietary, the EX200–220 class remains one of Hitachi’s most popular mid-size excavator ranges globally—particularly favored for pipeline, municipal, and general-purpose earthmoving work. Their appeal lies in reliability, modularity, and repairability, supported by widespread parts availability (e.g., valves and relief components) .
Real-World Anecdote
In a Brazilian mine, an EX220LC-3 got stuck while digging in red clay. The operator noticed sluggish bucket movement. A quick diagnosis pointed to reduced pilot flow. After replacing the variable pressure compensated valve and recalibrating pressure settings, the machine regained responsiveness—highlighting the valve’s central role in machine control and the pitfalls when its performance degrades quietly.
Terminology Glossary

• Variable Pressure Compensated Valve: A hydraulic flow control device that maintains constant flow regardless of pressure shifts.
  
• Pilot Circuit: A low-flow control channel that actuates main valves—vital for smooth multi-function operation.
  
• Relief Valve: Safety device releasing excess pressure when thresholds are exceeded.
  
• Working Pressure: Maximum hydraulic operating pressure the system is rated for.
  
• Flow Rate: Volume of hydraulic oil delivered per minute (e.g., in gallons per minute—gpm).
  

Maintenance Suggestions and Solutions
To ensure longevity and performance:

• Check for sluggish responsiveness, especially under load, as signs of valve wear or improper pressure compensation.
  
• Clean hydraulic oil regularly—contamination can clog spool ports and degrade valve function.
  
• When replacing the valve, match stock parts carefully—for EX220LC-3, relief valve part number 4289603 (used across EX200/EX220 models) is common .
  
• If substitute components are used, confirm adjustable range and working pressure specs align with the machine’s hydraulic capacity (~3,000 psi typical flow control).
  

Summary of Key Points

• Variable pressure compensated valve ensures consistent actuator flow under variable pressure.
  
• EX220LC-3 runs ~50 gpm hydraulic flow at ~1,500–3,000 psi.
  
• The valve supports reliable operation in rugged working conditions.
  
• Proper maintenance and timely replacement are crucial for machine responsiveness.