Hydraulic flow matching is the most technically critical aspect of specifying an excavator flail mower. Get it right and the attachment performs at full capacity with long service life. Get it wrong and you will have slow rotor speed, poor cut quality, overheating hydraulic oil, premature motor failure — or all four simultaneously. This guide explains exactly how hydraulic flow works in a flail mower system, how to find your excavator's output specification, and how to match it correctly to the right attachment.
The Hydraulic Circuit: How Flow Drives the Rotor
An excavator flail mower uses the machine's auxiliary hydraulic circuit to drive a hydraulic motor mounted on the attachment body. The motor converts hydraulic flow (volume per unit time, measured in litres per minute — L/min) and pressure (measured in bar) into rotational torque and speed at the rotor shaft.
The relationship between flow, pressure and motor output follows a straightforward formula: power (kW) = flow (L/min) × pressure (bar) ÷ 600. A motor receiving 100 L/min at 250 bar is receiving approximately 41.7 kW of hydraulic power. The motor's mechanical efficiency (typically 85–92%) determines how much of that power reaches the rotor shaft.
Rotor speed is determined by flow rate and motor displacement. A motor with 125cc/rev displacement receiving 100 L/min will rotate at approximately 800 rpm. The same motor receiving 80 L/min will rotate at 640 rpm — 20% slower, with proportionally reduced cutting performance.
Finding Your Excavator's Hydraulic Specification
The auxiliary hydraulic flow specification is in your excavator's operator manual, typically in the "Technical Specifications" or "Hydraulic System" section. Look for "auxiliary hydraulic flow", "attachment circuit flow" or "second auxiliary circuit". The figure will be expressed in L/min (litres per minute) or GPM (US gallons per minute; multiply by 3.785 to convert to L/min).
You also need the maximum auxiliary circuit pressure, expressed in bar or PSI (divide PSI by 14.5 to convert to bar). This is the relief valve setting for the auxiliary circuit — the maximum pressure the circuit will sustain before the relief valve opens.
| Excavator Weight Class | Auxiliary Flow (L/min) / Max Pressure (bar) |
|---|---|
| 1.5–3 tonne (mini) | 20–40 L/min / 180–220 bar |
| 3–6 tonne (mini) | 30–60 L/min / 200–250 bar |
| 6–10 tonne | 50–80 L/min / 220–280 bar |
| 10–15 tonne | 70–110 L/min / 250–300 bar |
| 15–22 tonne | 90–140 L/min / 250–320 bar |
| 22–35 tonne | 120–180 L/min / 280–350 bar |
| 35–50 tonne | 150–220 L/min / 300–380 bar |
These are typical ranges only. Always verify your specific machine's specification from the operator manual or manufacturer. Significant variation exists between models and years within the same weight class.
Matching Flow to the Flail Mower
Every PANDA FORCE flail mower has a specified minimum and maximum flow range. The attachment must receive at least the minimum flow to reach operating rotor speed. It must not receive more than the maximum flow, which would overspeed the motor and cause seal failure.
The ideal operating point is 80–90% of the attachment's maximum rated flow. This provides full rotor speed with a safety margin against flow variation under load.
| Model / Working Width | Flow Range / Max Pressure / Excavator Class |
|---|---|
| PF-MEF-400 — 400mm | 20–40 L/min / 180–220 bar / 1.5–3 t |
| PF-MEF-600 — 600mm | 30–55 L/min / 180–240 bar / 3–6 t |
| PF-EFM-600 — 600mm | 40–60 L/min / 180–250 bar / 5–8 t |
| PF-EFM-800 — 800mm | 50–80 L/min / 180–280 bar / 6–12 t |
| PF-EFM-1000 — 1,000mm | 60–100 L/min / 200–300 bar / 8–15 t |
| PF-EFM-1200 — 1,200mm | 80–120 L/min / 200–320 bar / 10–20 t |
| PF-EFM-1500 — 1,500mm | 100–150 L/min / 220–340 bar / 14–25 t |
| PF-EFM-2000 — 2,000mm | 140–180 L/min / 250–350 bar / 20–35 t |
| PF-HDF-1500 — 1,500mm | 120–160 L/min / 280–380 bar / 20–40 t |
| PF-HDF-2000 — 2,000mm | 160–220 L/min / 300–380 bar / 30–50 t |
What Happens When Flow Is Too Low
Insufficient hydraulic flow is the most common cause of poor flail mower performance. The symptoms are: slow rotor speed (audible as a lower pitch), poor cut quality with vegetation wrapping around the rotor, excessive vibration as the rotor struggles to maintain speed under load, and overheating of the hydraulic motor.
Operating continuously with insufficient flow causes the motor to work at high torque and low speed, which increases internal leakage and heat generation. Over time, this degrades motor seals and reduces efficiency further — a progressive failure mode that is often misdiagnosed as a motor fault rather than a flow problem.
If your flail mower is cutting poorly and the rotor sounds slow, check hydraulic flow before assuming the motor is faulty. A flow meter test takes 15 minutes and can save an unnecessary motor replacement.
What Happens When Flow Is Too High
Excessive flow overspeeds the hydraulic motor beyond its rated rpm. This causes: motor bearing failure from centrifugal loads, seal failure from high internal pressure, rotor imbalance from blade centrifugal forces exceeding design limits, and potential structural failure of the rotor drum.
Overspeed failure is typically sudden and catastrophic rather than gradual. It is prevented by ensuring the excavator's auxiliary circuit relief valve is set at or below the flail mower's maximum rated pressure, and that the flow rate does not exceed the motor's maximum rated displacement.
Flow Adjustment and Control
Most modern excavators allow the auxiliary hydraulic flow rate to be adjusted via the machine's control system. This is typically accessed through the monitor display under "attachment settings" or "auxiliary flow". Setting the flow to match the flail mower's rated range is the first step in commissioning a new attachment.
Some excavators have a fixed auxiliary flow rate that cannot be adjusted. In this case, you must select a flail mower whose flow range encompasses the excavator's fixed output. If the excavator's flow is too high for any suitable working width, a flow control valve can be installed in the hydraulic circuit to limit flow to the attachment.
Frequently Asked Questions
My excavator has two auxiliary circuits. Which one should I use?
Use the circuit with the higher flow rate — typically the first auxiliary (AUX1) circuit. The second auxiliary circuit is usually lower flow and intended for tilt rotators or secondary functions. Check both circuits' flow specifications in the operator manual and use the one that best matches your flail mower's requirements.
Can I combine two auxiliary circuits to get more flow?
Some excavators support "combined flow" or "high-flow" mode that merges two circuits for higher total flow. This is typically used for high-flow attachments like large forestry mulchers. Check your excavator's manual for combined flow capability and the resulting flow rate before specifying a high-flow flail mower.
Summary
Hydraulic flow matching is not complicated, but it requires accurate data and careful cross-referencing. Obtain your excavator's auxiliary flow and pressure specification from the operator manual, match it to the flail mower's rated range, and set the machine's auxiliary flow control to the correct value during commissioning. This single step prevents the majority of flail mower performance problems and premature failures.
Need Help Matching Your Excavator to the Right Model?
Provide your excavator make, model and auxiliary hydraulic specification. Our technical team will confirm the correct PANDA FORCE model and flow settings.