Adding a Third Hydraulic Function to the Komatsu WA320-3 Loader

[MikePhua]

The WA320-3 and Komatsu’s Wheel Loader Evolution
The Komatsu WA320-3 was introduced in the late 1990s as part of Komatsu’s third-generation wheel loader lineup. Designed for versatility in construction, aggregate handling, and municipal work, the WA320-3 featured a hydrostatic transmission, a robust Z-bar linkage, and a fuel-efficient diesel engine producing around 170 horsepower. With an operating weight of approximately 13,000 kg and a bucket capacity ranging from 2.5 to 3.2 cubic meters, it became a popular mid-size loader across North America and Europe.
Komatsu, founded in Japan in 1921, has long emphasized durability and operator comfort. The WA320-3 was built during a transitional period when hydraulic systems were becoming more modular, but electronic integration was still minimal—making it a favorite among mechanics who preferred analog diagnostics and straightforward valve blocks.
Hydraulic System Architecture Open vs Closed Center
Understanding the hydraulic system type is essential before modifying or expanding it. The WA320-3 uses an open-center hydraulic system for its loader functions. In an open-center system, hydraulic fluid flows continuously through the valve block when no functions are engaged. This design is simpler and more common in mid-size loaders, but it requires careful valve selection when adding new circuits.
However, the pilot control system—used to actuate the main valves—is closed center. This means pilot pressure is only generated when needed, and the system remains pressurized but idle when not in use. Mixing open and closed center components without proper isolation can lead to pressure loss, valve chatter, or system overheating.
Adding a Third Spool for Grapple or Auxiliary Function
The WA320-3 typically comes with a two-spool valve block controlling lift and tilt. To add a grapple rake or other hydraulic attachment, a third spool must be integrated. There are two main approaches:

• Stack-on valve: Add a third section to the existing valve block, maintaining factory-style integration.
  
• External auxiliary valve: Install a separate valve bank with its own control lever or pilot valve.
  

Stack-on valves are preferred for maintaining OEM ergonomics and minimizing cab clutter. However, they require sourcing compatible valve sections and may involve modifying the valve block housing.
Key considerations:

• Flow rate: The new valve must handle the loader’s hydraulic flow, typically 25–35 GPM.
  
• Pressure rating: Match the system’s relief pressure, usually around 3,000 psi.
  
• Pilot control: A pilot valve may be needed to actuate the new spool from the cab.
  
• Return path: Ensure the new valve has a proper return line to the tank.
  

Some aftermarket valves, such as those from Prince or Cross, may appear suitable but lack the flow capacity for loader-scale hydraulics. Always verify specifications before installation.
Manufacturer Support and Attachment Kits
In some cases, the manufacturer of the grapple rake or auxiliary attachment may offer a hydraulic kit tailored to the WA320-3. These kits often include:

• Valve block with matched flow and pressure specs
  
• Pilot control lever or joystick
  
• Mounting brackets and hardware
  
• Hoses and fittings pre-cut for the loader’s layout
  

Using a kit simplifies installation and ensures compatibility. It also reduces the risk of warranty issues or system damage due to mismatched components.
A Story from the Field
In Florida, an operator wanted to add a grapple rake to his WA320-3 for land clearing. After researching valve options, he found a Prince three-spool loader valve but was unsure about system compatibility. A local equipment appraiser confirmed the loader’s open-center architecture and advised against using a low-flow valve. Instead, the operator sourced a stack-on valve section from a salvage WA320 and installed it with a pilot lever mounted near the right armrest. The grapple function worked flawlessly, and the loader became a dual-purpose machine for both loading and debris handling.
Recommendations for Retrofit Projects
Before adding a third hydraulic function:

• Confirm system type (open vs closed center) using service documentation
  
• Measure flow and pressure requirements of the attachment
  
• Source valve components rated for loader-scale hydraulics
  
• Consult with a hydraulic technician or dealer for integration advice
  
• Test all functions under load before returning to full operation
  

For long-term reliability, use high-quality hoses with abrasion-resistant sleeves and secure all fittings with proper torque. Label new controls clearly to avoid operator confusion.
Conclusion
Adding a third hydraulic spool to the Komatsu WA320-3 loader is a practical upgrade that expands its versatility. With a clear understanding of the machine’s open-center system and pilot control architecture, operators can integrate grapple rakes or other attachments safely and effectively. In the world of heavy equipment, hydraulic flexibility is the key to doing more with less—and the right valve unlocks a whole new set of capabilities.