Running a Low Flow Brush Cutter on a High Flow Machine

[MikePhua]

Hydraulic Flow Basics
Hydraulic flow measured in gallons per minute (GPM) determines how much fluid the hydraulic pump delivers to attachments like brush cutters. Attachments specify a recommended flow range to operate optimally. Skid steer and compact equipment often come with either standard (low) flow auxiliaries, usually between 11-20 GPM, or high flow systems delivering 25-40+ GPM for more powerful implements.
Scenario: Low Flow Cutter with High Flow Machine
A Case 1845C equipped with a factory high flow auxiliary providing up to 30 GPM is used with a brush cutter designed for 20 GPM. An operator wonders if adapting hoses to connect the cutter to the high flow system and controlling engine throttle to maintain about 20 GPM will cause problems.
Key Considerations

• Flow Rate Control: Controlling engine RPM and flow restrictors helps prevent overdriving a low flow brush cutter with excessive fluid volume.
  
• Power Balance: Even at half throttle, a high flow machine delivers sufficient power for many attachments without performance losses.
  
• Wear and Fuel Consumption: Running an attachment designed for 20 GPM wide open on a low flow machine may create stress but increases responsiveness. On high flow machines, throttling back reduces fuel consumption.
  
• Hydraulic Motor Matching: Brush cutter motors designed for lower flow rates can experience inefficiency or damage if consistently fed higher flows without regulation.
  
• System Pressure: Pressure must also meet the minimum to achieve correct torque and cutting speed.
  

Advantages of Using High Flow Machines

• Faster spin-up times and better resistance to blade slowdown when cutting dense materials.
  
• Ability to handle more demanding vegetation or terrain by adjusting flow output.
  
• Reduced wait time for blade recovery after stalling.
  

Design Differences Between Low and High Flow Cutters

• Low flow cutters often have lighter components or fewer blades to match flow capacities.
  
• High flow models have larger hydraulic motors and heavier-duty parts for commercial use.
  

Recommendations

• Adapt hose fittings carefully ensuring no leaks or restrictions.
  
• Use throttle or flow controls to maintain safe operating flow near the cutter’s rating.
  
• Monitor attachment temperature and performance to detect over or under supply issues.
  
• Consult manufacturers for specific motor and flow compatibility details.
  

Glossary

• Hydraulic Flow (GPM): The volume of hydraulic fluid delivered per minute.
  
• Throttle Control: Engine speed regulation impacting hydraulic pump output.
  
• Hydraulic Motor: Converts fluid flow pressure into mechanical rotation.
  
• Flow Restrictor: Device limiting fluid flow to protect hydraulic components.
  
• Spin-up Time: Time taken for cutter blades to reach operational speed after start.
  

Conclusion
Running a low flow brush cutter on a high flow machine is feasible with appropriate flow and throttle management to avoid damaging the attachment. Operators gain improved blade responsiveness and reduce fuel use by matching hydraulic output closely to the cutter’s specifications. Awareness of system pressures, motor compatibility, and flow regulation ensures longevity and efficiency for both the attachment and the host machine.