Bobcat X325 Auxiliary Hydraulic Pressure Adjustment and Thumb Compatibility

[MikePhua]

The X325 and Its Hydraulic Architecture
The Bobcat X325 compact excavator was introduced in the late 1990s as part of Bobcat’s push into the mini-excavator market. With an operating weight of approximately 6,000 lbs and a 27-horsepower liquid-cooled diesel engine, the X325 was designed for trenching, grading, and light demolition. Its hydraulic system is open-center, gear-pump driven, and supports both single-acting and double-acting auxiliary functions.
The auxiliary hydraulic circuit is routed through a dedicated spool in the main valve bank, allowing operators to run attachments such as thumbs, augers, and compact grapples. However, pressure regulation for the auxiliary line is not always straightforward, especially when retrofitting attachments that require lower operating pressure than the system’s default relief setting.
Understanding Relief Valve Behavior
The X325’s hydraulic system includes:

• Main relief valve: Protects the system from overpressure, typically set around 2,550 psi
  
• Work port relief valves: Installed on boom and bucket circuits to protect against shock loads
  
• Auxiliary spool: May or may not include a dedicated port relief valve depending on factory configuration
  

In many cases, the auxiliary spool piggybacks off the adjacent bucket spool’s relief valve, especially when the two share a common return path. This means that unless a separate port relief is installed, the auxiliary line may default to the main system pressure.
A technician in Alberta discovered that his X325’s auxiliary spool lacked a dedicated relief valve. The thumb attachment he installed was rated for 2,250 psi, so he had to retrofit a port relief valve into the valve bank to prevent overpressure damage.
Adjustment Procedure and Tools Required
To adjust auxiliary pressure:

• Locate the auxiliary spool in the valve bank
  
• Identify whether a port relief valve is installed (look for a hex plug or set screw with jam nut)
  
• If present, connect a 5,000 psi pressure gauge to the base port of the thumb cylinder
  
• Activate the auxiliary function and observe pressure
  
• Turn the relief valve set screw counterclockwise to reduce pressure (typically 1/8 turn increments)
  
• Lock the jam nut and recheck pressure
  

Recommended tools:

• 5,000 psi hydraulic gauge with quick coupler
  
• 3/4" wrench or socket for jam nut
  
• Allen key or flathead for set screw
  
• Sharpie or paint marker for reference indexing
  

In one retrofit in Wisconsin, a contractor marked the set screw with a paint dot before adjustment. This allowed him to track changes and return to baseline if needed. After two 1/8 turns, the pressure dropped from 2,550 psi to 2,200 psi—within the thumb’s safe operating range.
Thumb Cylinder Compatibility and Pressure Limits
Hydraulic thumbs are typically rated for 2,000–2,500 psi. Exceeding this can cause:

• Seal blowout
  
• Rod bending
  
• Mounting bracket fatigue
  
• Hose rupture
  

Before installation:

• Verify cylinder pressure rating
  
• Check flow requirements (X325 delivers ~10 GPM)
  
• Confirm base port orientation (shaft vs. non-shaft end)
  
• Use rated hoses and fittings
  

A landscaper in Maine installed a thumb rated for 2,000 psi without adjusting the relief. After two weeks, the cylinder began leaking at the rod seal. He later installed a port relief valve and replaced the cylinder with a higher-rated model.
Factory vs. Field Configuration
Not all X325 units come with auxiliary port reliefs installed. Some were shipped with blank plugs in the valve bank, requiring aftermarket installation. Bobcat service literature notes that auxiliary reliefs are optional and must be ordered separately or installed during setup.
Signs your machine lacks a dedicated auxiliary relief:

• No set screw or jam nut on aux spool
  
• No pressure drop when cylinder stalls
  
• Thumb operates with excessive force or speed
  
• Relief only occurs at main valve setting
  

In one case from Texas, a technician confirmed the absence of a port relief by tracing the hydraulic schematic and inspecting the valve body. He installed a relief cartridge rated for 2,200 psi and restored safe operation.
Conclusion
Adjusting auxiliary hydraulic pressure on the Bobcat X325 requires understanding the valve bank layout, relief valve behavior, and attachment compatibility. Whether installing a thumb or running a hydraulic broom, proper pressure regulation ensures safe, efficient operation and protects components from damage. With a few tools and careful observation, operators can fine-tune their machines to match the demands of modern attachments—extending the life of both the excavator and the tools it powers.