Designing a Rotating Grab Circuit for the JCB JS220: Hydraulic Integration and Control Strategies

[MikePhua]

Introduction
The JCB JS220 excavator, a mid-sized machine known for its versatility and robust hydraulic system, is often retrofitted with specialized attachments such as selector grabs. While the machine typically includes two-way hammer lines for grab actuation, integrating a rotation function requires additional hydraulic and electrical modifications. This article explores the technical challenges of adding a rotating grab circuit, clarifies key terminology, and offers practical solutions based on field experience and engineering principles.
Understanding the Hydraulic System
The JS220 features a load-sensing hydraulic system with multiple pumps and a valve chest designed to prioritize flow based on demand. The system is optimized for standard functions—boom, arm, bucket, and travel—but can be adapted for auxiliary circuits with careful planning.
Key hydraulic components relevant to this modification:

• Main hydraulic pump with load-sensing capability
  
• Valve chest with service ports and pressure taps
  
• Hammer lines (two-way) for grab open/close
  
• Solenoid valves for directional control
  
• Joystick buttons for operator input
  

Terminology Clarified

• Load-Sensing System: A hydraulic configuration that adjusts pump output based on the pressure and flow requirements of active functions.
  
• Dead-Heading: A condition where hydraulic flow is blocked, causing pressure to build up—often used to load the pump artificially.
  
• Solenoid Valve: An electrically actuated valve that directs hydraulic flow based on control signals.
  
• Selector Grab: A multi-function attachment used for sorting and handling materials, often requiring both opening/closing and rotation capabilities.
  

Challenges in Adding a Rotation Circuit

• No Dedicated Rotation Lines
  The JS220 typically lacks factory-installed lines for rotation, requiring custom plumbing and control integration.
  
• Pump Feed Dependency
  Tapping into the pump directly may only provide pressure when another service is dead-headed, leading to unreliable rotation performance.
  
• Load-Sensing Activation
  To ensure consistent pressure, the circuit must trigger the pump to stroke up—usually via a load-sensing signal or pressure tap in the valve chest.
  

Field Anecdote: Irish-Australian Fitter’s Retrofit
A fitter working between Ireland and Australia sought to install a rotating selector grab on a 2006 JS220. He planned to use a two-way solenoid valve controlled by joystick buttons but struggled to find a reliable pressure feed. He considered tapping the top of the pump but realized it would only work when another function was dead-headed. Eventually, he learned of a plug in the valve chest that could provide a load-sensed feed—allowing the pump to respond dynamically to rotation demands.
Historical Perspective: Evolution of Auxiliary Circuits
In earlier excavator models, auxiliary circuits were often hard-plumbed with manual valves. Modern machines like the JS220 use electronic controls and load-sensing hydraulics, offering greater efficiency but requiring more sophisticated integration. The shift reflects broader trends in construction equipment—where modular attachments and operator ergonomics drive design.
Case Study: UK Retrofit with Additional Circuit Kit
A technician in Lincoln, UK, retrofitted a JS220 using an auxiliary circuit kit designed for hammer and rotation functions. He installed a solenoid valve block near the boom base, wired to joystick buttons, and tapped into a pressure port in the valve chest. The system included a load-sensing line to ensure the pump responded to rotation demands. After testing, the grab rotated smoothly under full load, with no need to dead-head other functions.
Best Practices for Retrofit Design

• Identify a pressure tap in the valve chest that responds to load-sensing
  
• Use a two-way solenoid valve rated for expected flow and pressure
  
• Wire joystick buttons through the machine’s control harness or auxiliary switch panel
  
• Install check valves to prevent backflow and protect the solenoid
  
• Test under load to verify pump response and rotation speed
  

Recommended Tools and Techniques

• Hydraulic schematic for valve chest layout
  
• Multimeter for electrical continuity and voltage checks
  
• Pressure gauge for verifying feed line performance
  
• Hose crimper and flare tools for custom plumbing
  
• Service manual for joystick wiring and control logic
  

Conclusion
Adding a rotating grab circuit to the JCB JS220 requires a blend of hydraulic insight and electrical finesse. By understanding the machine’s load-sensing architecture and identifying appropriate pressure sources, operators can achieve reliable rotation without compromising existing functions. As attachments become more specialized, retrofit strategies like these ensure older machines remain competitive and adaptable in modern job sites. In hydraulic design, the key is not just pressure—but precision.