Caterpillar 320CL Auxiliary Hydraulics Setup and Optimization

[MikePhua]

The 320CL and Caterpillar’s Excavator Legacy
The Caterpillar 320CL hydraulic excavator was introduced in the early 2000s as part of the C-series lineup, building on the success of the 320B and 320C models. Designed for mid-size earthmoving, demolition, and utility trenching, the 320CL featured improved fuel efficiency, enhanced operator comfort, and refined hydraulic control. With an operating weight of approximately 44,000 lbs and a dig depth exceeding 22 feet, it became one of Caterpillar’s best-selling excavators globally.
Caterpillar, founded in 1925, has long dominated the hydraulic excavator market. The 320 series alone has sold hundreds of thousands of units worldwide, with the CL variant offering upgraded electronics and compatibility with a wider range of attachments—including those requiring auxiliary hydraulics.
Understanding Auxiliary Hydraulic Systems
Auxiliary hydraulics refer to additional hydraulic circuits beyond the standard boom, arm, and bucket functions. These circuits allow the excavator to power attachments such as:

• Hydraulic hammers
  
• Grapples
  
• Thumbs
  
• Tilt buckets
  
• Compactors
  
• Shears
  

The system typically includes:

• Control valve section or diverter valve
  
• Hydraulic lines routed along the boom and stick
  
• Quick couplers or flat-face connectors
  
• Pilot control switches or foot pedals
  
• Flow control valves and pressure relief settings
  

In the 320CL, auxiliary hydraulics were often installed as factory options or retrofitted by dealers. The system is powered by the main hydraulic pump, with flow diverted through solenoid valves or manual selectors depending on configuration.
Common Retrofit Challenges and Solutions
Retrofitting auxiliary hydraulics on a 320CL can present several challenges:

• Valve Block Compatibility
  • Some machines lack the extra spool in the main control valve
    
  • Solution: Install an add-on valve stack or diverter valve with pilot control
    
• Electrical Integration
  • Wiring harness may not include connectors for auxiliary solenoids
    
  • Solution: Use aftermarket switch kits with relay and fuse protection
    
• Line Routing and Protection
  • Boom and stick may lack factory brackets for hose clamps
    
  • Solution: Weld or bolt custom brackets and use spiral wrap for abrasion resistance
    
• Flow and Pressure Matching
  

• Attachments may require specific flow rates (e.g., 30–40 GPM for hammers)
  
• Solution: Install inline flow restrictors or adjustable valves to match specs
  

A contractor in Alberta retrofitted his 320CL with a hydraulic thumb using a diverter valve and foot pedal control. After adjusting the flow with a needle valve and reinforcing the hose brackets, the system operated smoothly under load.
Control Options and Operator Interface
Auxiliary hydraulics can be controlled in several ways:

• Foot Pedal
  • Common for thumbs and hammers
    
  • Allows variable flow based on pedal pressure
    
• Joystick Button
  • Integrated into the right-hand joystick
    
  • Ideal for grapples and tilt buckets requiring intermittent actuation
    
• Toggle Switch Panel
  • Mounted on the console
    
  • Used for solenoid activation or flow direction control
    
• Proportional Control Dial
  

• Adjusts flow rate electronically
  
• Useful for attachments sensitive to speed or torque
  

Operators often prefer joystick integration for ergonomics and responsiveness. A fleet manager in Texas upgraded his 320CL with joystick thumb control and reported improved precision during demolition sorting.
Maintenance and Inspection Protocols
Auxiliary hydraulic systems require regular inspection to prevent leaks, contamination, and performance loss:

• Inspect hoses and fittings weekly for wear or abrasion
  
• Clean quick couplers before each attachment change
  
• Check solenoid function and wiring continuity monthly
  
• Monitor hydraulic fluid temperature and pressure during operation
  
• Replace filters every 500 hours or sooner in dusty environments
  
• Test flow rate annually using a flow meter and pressure gauge
  

A technician in Florida diagnosed sluggish grapple movement by testing flow at the coupler and discovering a partially blocked inline filter. After replacement, the attachment regained full speed and torque.
Attachment Compatibility and Setup Tips
When connecting attachments to the 320CL:

• Verify coupler type and size (usually ¾-inch flat-face)
  
• Match flow and pressure requirements to machine specs
  
• Use pressure relief valves to protect attachment seals
  
• Install case drain line if required by motorized tools
  
• Label hoses and connectors to prevent cross-connection
  
• Warm up hydraulic fluid before operating in cold climates
  

A restorer in Chile added a case drain line to his compactor setup after noticing seal leakage. The modification extended motor life and improved vibration control.
Conclusion and Recommendations
Auxiliary hydraulics transform the Caterpillar 320CL into a multi-purpose tool carrier capable of handling a wide range of attachments. Whether factory-installed or retrofitted, a well-designed system enhances productivity and versatility.
Recommendations include:

• Use OEM or high-quality aftermarket components for reliability
  
• Integrate controls ergonomically to reduce operator fatigue
  
• Match flow and pressure to attachment specs using adjustable valves
  
• Maintain clean connections and inspect hoses regularly
  
• Document hydraulic modifications and service intervals for future reference
  

With proper setup and care, the 320CL’s auxiliary hydraulics become a gateway to expanded capabilities—ready to hammer, grab, compact, and shape the jobsite with precision and power.