Adding Dual-Acting Auxiliary Hydraulics to a Komatsu PC40-7

[MikePhua]

Why Auxiliary Hydraulics Matter on Compact Excavators
The Komatsu PC40-7 is a compact excavator built for versatility in tight spaces, often used in residential construction, landscaping, and utility trenching. While its base configuration handles digging and grading well, many attachments—such as hydraulic thumbs, vibratory plate compactors, and tilt buckets—require dual-acting auxiliary hydraulics. Without this circuit, the machine’s functionality is limited to basic excavation tasks.
Adding a dual-acting auxiliary hydraulic circuit transforms the PC40-7 into a multi-tool platform, capable of gripping, compacting, and manipulating materials with precision. For private owners and small contractors, this upgrade can dramatically improve productivity without investing in a larger machine.
Understanding Dual-Acting Hydraulics
A dual-acting hydraulic circuit provides pressurized flow in both directions—extending and retracting a cylinder or powering a motor forward and reverse. This is essential for attachments like:

• Hydraulic thumbs (grip and release)
  
• Plate compactors (vibration and directional control)
  
• Tilt buckets (left/right tilt)
  
• Augers with reverse function
  

Unlike single-acting systems, which rely on gravity or spring return, dual-acting systems require two hydraulic lines and a control valve capable of switching flow direction.
Evaluating the PC40-7’s Existing Configuration
The PC40-7 often comes without factory-installed auxiliary hydraulics, especially in older or gray-market units. However, it typically includes a boom swing foot pedal and a valve block with unused ports. These can be repurposed or expanded to support auxiliary functions.
Key components to inspect:

• Valve block: Look for blanked-off ports or auxiliary sections
  
• Pilot controls: Determine if joystick buttons or foot pedals are available for control
  
• Hydraulic pump: Confirm flow capacity and pressure ratings
  
• Return line: Ensure a low-pressure return path is available for motor-type attachments
  

In some cases, the boom swing circuit can be tapped using a diverter valve, allowing the operator to switch between swing and auxiliary functions. This is a cost-effective solution but may limit simultaneous operation.
Installation Strategy and Component Selection
To add a dual-acting auxiliary circuit, the following components are typically required:

• Hydraulic control valve (2-way or proportional)
  
• Solenoid diverter valve (if repurposing an existing circuit)
  
• Hydraulic hoses and quick couplers
  
• Electrical switch or joystick button for control
  
• Mounting brackets and hose clamps
  
• Return filter and reservoir check (if high-flow attachments are used)
  

Installation steps:

• Mount the control valve near the main valve block or under the cab
  
• Route hoses along the boom and stick using protective sleeves
  
• Install quick couplers at the stick end for easy attachment changes
  
• Wire the solenoid to a switch or joystick button for operator control
  
• Test flow and pressure with a gauge before connecting attachments
  

Some aftermarket suppliers offer complete kits tailored to specific excavator models. These kits include pre-cut hoses, matched fittings, and wiring harnesses, simplifying installation for owners without hydraulic experience.
Cost and Supplier Insights
Aftermarket kits for compact excavators range from $2,000 to $8,000 depending on complexity and brand. For example, a thumb circuit kit for a 16-ton excavator was quoted at $7,800, excluding the thumb itself. Smaller machines like the PC40-7 typically fall on the lower end of that range.
Recommended suppliers include:

• Hydraulic Circuit Technology (HCT Kits)
  
• Dealers specializing in Komatsu retrofits
  
• Fabricators who support gray-market machines
  

Before purchasing, confirm compatibility with your machine’s serial number and hydraulic specs. Some kits are designed for newer models and may require adaptation.
Field Experience and Practical Tips
One owner who added a hydraulic thumb to his PC40-7 noted that the installation was straightforward once the diverter valve was sourced. He repurposed the boom swing pedal and added a toggle switch to control flow direction. The thumb worked flawlessly, and the machine became far more useful for clearing brush and loading debris.
Another operator emphasized the importance of shielding hoses with spiral wrap and securing them with steel clamps. On compact machines, hose movement during boom articulation can lead to abrasion and premature failure.
Recommendations for Long-Term Reliability
To ensure the auxiliary circuit performs reliably:

• Use high-quality hydraulic hose rated for at least 3,000 psi
  
• Install a pressure relief valve to protect attachments
  
• Flush the system before connecting new components
  
• Label hoses and switches for easy identification
  
• Schedule regular inspections for leaks and wear
  

If using motorized attachments like compactors, consider adding a case drain line to prevent seal damage from backpressure.
Conclusion
Adding dual-acting auxiliary hydraulics to a Komatsu PC40-7 is a practical upgrade that unlocks a wide range of attachment capabilities. With careful planning, the right components, and attention to hydraulic routing, even older machines can be retrofitted for modern tasks. Whether you're compacting trenches or gripping logs, this enhancement turns a basic excavator into a versatile jobsite tool—ready to tackle more than just digging.