Caterpillar E120B Auxiliary Hydraulic Line Setup Guide

[MikePhua]

The Caterpillar E120B excavator is a versatile machine designed with a primary hydraulic system to power its boom, arm, bucket, and swing functions. However, many operators seek to expand this capability with auxiliary hydraulic lines to run attachments such as hydraulic thumbs, grapples, or breakers. Setting up the auxiliary hydraulic line on the E120B requires understanding the machine’s hydraulic system layout, available ports, and control integration.
Understanding the Hydraulic System
The E120B uses an open-center hydraulic system derived from tandem axial piston pumps that feed primary functions and auxiliary circuits. The machine’s hydraulic valves and control system are designed to balance flow, pressure, and response for smooth multitasking.
The standard machine configuration may not include factory-installed auxiliary hydraulic hookups, but the system includes provisions for adding these lines.
Auxiliary Hydraulic Line Installation

• Hydraulic Ports: Identify auxiliary hydraulic ports on the side of the main control valve or in the pump circuit. These ports typically have capped fittings or plugs.
  
• Control Valve Integration: Auxiliary functions require connection to pilot controls or toggle switches inside the operator’s cab, allowing the operator to control flow and direction.
  
• Hydraulic Hoses: Use high-pressure hoses rated for excavator applications, routed safely from the valve block to the attachment mount.
  
• Quick Couplers: Employ quick-release hydraulic couplers for easy attachment connection and disconnection, minimizing downtime.
  
• Flow and Pressure Requirements: Auxiliary lines must be sized and connected to supply adequate hydraulic flow (typically 10-15 GPM) and pressure to operate supplemental equipment effectively.
  

Control Pattern Considerations
The E120B features pilot-operated joystick controls that can be configured for different control patterns. For auxiliary hydraulic functions, operators often use dedicated switches or modify control joysticks with pattern changes to include thumb or grapple control.
Steps to ensure seamless operation:

• Ensure pilot flow matches auxiliary circuit needs.
  
• Modify or retrofit control valves if necessary to support proportional control.
  
• Use manufacturer documentation or dealer support to correctly identify and adjust pilot circuit connections.
  

Safety and Maintenance

• Confirm all connections are tight and leak-free to prevent hydraulic fluid loss.
  
• Use recommended hydraulic fluid types and maintain cleanliness to protect pump and valve components.
  
• Route hoses away from pinch points, moving parts, or heat sources to extend service life.
  
• Periodically inspect quick couplers for wear and replace seals as needed.
  
• Train operators on auxiliary function operation to avoid equipment damage or safety hazards.
  

Technical Terms Explained

• Auxiliary Hydraulic Line: Additional hydraulic circuit used to power attachments beyond the machine’s primary functions.
  
• Pilot Control: Low-pressure hydraulic circuit controlling main valve operation.
  
• Quick Coupler: A coupling device enabling fast connection and disconnection of hydraulic lines.
  
• Open-Center System: Hydraulic system where fluid flows continuously at low pressure when valves are in neutral.
  
• Proportional Control: Hydraulic valve control method allowing variable flow and pressure responsive to operator input.
  
• Flow Rate (GPM): Gallons per minute measurement indicating hydraulic fluid volume moving through the system.
  

A User Experience
One E120B owner shared their experience retrofitting auxiliary lines for a hydraulic thumb after purchasing the machine without such hookups. They sourced appropriate hoses and fittings from a dealer and reconfigured the pilot control valves to enable auxiliary operation. After installation, the machine handled thumb control smoothly, enhancing excavation precision and material handling capabilities significantly.
Summary
Adding auxiliary hydraulic lines to the Caterpillar E120B excavator expands its operational flexibility by allowing attachments like hydraulic thumbs and breakers. Successful setup involves identifying and tapping into the machine’s hydraulic system ports, integrating control circuits, and maintaining proper flow and pressure specifications. Proper installation, alignment with control patterns, and thorough maintenance ensure reliable and safe auxiliary hydraulic function, increasing the productivity and versatility of the E120B in diverse construction tasks.