Hydraulic Diverter Valve Behavior on the Terex 82-20 CRT Carrier

[MikePhua]

The Terex 82-20 CRT and Its Transmission Configuration
The Terex 82-20 CRT carrier is a specialized platform often used in forestry and cable yarding operations, particularly in rugged terrain where mobility and hydraulic control are critical. Terex, originally founded in 1933 and known for its diverse range of heavy equipment, developed the 82-20 CRT to support high-torque applications with modular drivetrain setups. Many units are paired with West Coast Falcon yarders or similar winch systems, relying on a divorced-mount Allison transmission behind a Detroit Diesel 6V71 engine.
This configuration allows full use of all three transmission gears in both travel and yarding modes. The hydraulic system is powered via a PTO (power take-off) linked to the transmission, with pressure routed through control valves and diverter valves to switch between operational circuits.
Understanding the Diverter Valve Function
A hydraulic diverter valve is designed to redirect fluid flow between two or more circuits. In the case of the 82-20 CRT, the diverter valve determines whether hydraulic pressure is sent to the travel circuit or the yarding circuit. This is essential for switching operational modes without mechanical reconfiguration.
Key components include:

• Pilot pressure input to actuate the valve
  
• Internal spool or shuttle mechanism
  
• Return lines to reservoir
  
• Pressure relief and check valves
  

When functioning correctly, the diverter valve fully isolates one circuit while energizing the other. However, if the valve fails to close completely, residual pressure may leak into the inactive circuit, causing unintended movement or hydraulic drag.
Symptoms of Diverter Valve Malfunction
Operators may observe:

• Travel circuit partially active during yarding mode
  
• Hydraulic motors receiving pressure when idle
  
• Increased heat in hydraulic fluid due to bypass leakage
  
• Erratic control response or delayed actuation
  
• Audible hissing or vibration near the valve body
  

In one case from the Pacific Northwest, a yarder mounted on an 82-20 CRT began creeping forward during winch operation. Technicians traced the issue to a diverter valve that was not fully seating, allowing pressure bleed into the travel circuit.
Root Causes and Contributing Factors
Common reasons for diverter valve failure include:

• Contaminated hydraulic fluid causing spool sticking
  
• Worn seals or O-rings allowing internal leakage
  
• Misaligned pilot pressure or faulty solenoids
  
• Debris lodged in the valve body
  
• Incorrect valve sizing or installation
  

Older machines may suffer from degraded valve seats or corroded internal surfaces, especially if fluid maintenance has been inconsistent.
Inspection and Diagnostic Procedure
To assess diverter valve performance:

• Isolate hydraulic pressure and drain the system
  
• Remove valve body and inspect spool movement manually
  
• Check pilot pressure source and verify actuation timing
  
• Use a hydraulic flow meter to detect unintended flow paths
  
• Inspect seals, springs, and internal surfaces for wear
  

Some technicians install temporary pressure gauges on both circuits to monitor pressure behavior during mode switching. A pressure rise in the inactive circuit indicates valve leakage.
Repair and Replacement Strategy
If the valve is repairable:

• Clean all internal components with lint-free cloths and solvent
  
• Replace seals, springs, and worn spools
  
• Polish valve seats and reassemble with torque specs
  
• Flush hydraulic system and replace filters
  

If replacement is necessary:

• Match valve specifications to flow rate and pressure range
  
• Confirm compatibility with transmission PTO output
  
• Install with proper orientation and secure mounting
  
• Test under load and verify full isolation between circuits
  

In some cases, engineers opt for remote-mounted diverter valves with manual override to simplify troubleshooting and reduce heat exposure.
Field Anecdote and Practical Insight
In British Columbia, a logging crew operating a Falcon yarder on a Terex 82-20 CRT noticed inconsistent winch response during steep pulls. After investigating, they found the diverter valve was partially energized due to a faulty pilot solenoid. Replacing the solenoid and cleaning the valve restored full control. They later added a pilot pressure indicator light to the cab to monitor valve status during operation.
Preventive Measures and Long-Term Reliability
To maintain diverter valve performance:

• Change hydraulic fluid every 1,000 hours or annually
  
• Use fluid with anti-foaming and anti-corrosion additives
  
• Install magnetic filters to capture fine debris
  
• Inspect valve operation during seasonal service
  
• Monitor temperature and pressure trends with onboard diagnostics
  

Some operators retrofit their systems with electronic diverter valves and programmable logic controllers to automate mode switching and reduce human error.
Conclusion
The diverter valve on the Terex 82-20 CRT plays a critical role in managing hydraulic flow between travel and yarding circuits. When functioning properly, it ensures safe, efficient operation across modes. However, wear, contamination, and misalignment can lead to pressure bleed and control issues. With thorough diagnostics, proper maintenance, and thoughtful upgrades, operators can preserve system integrity and keep their machines performing reliably in demanding environments.