Hydraulic flow matching is the most technically critical aspect of selecting an excavator flail mower. Get it wrong and you will have a poorly performing attachment, potential hydraulic system damage, or both. This guide explains hydraulic flow and pressure requirements in plain language — no engineering degree required.
What Is Hydraulic Flow Rate and Why Does It Matter?
Hydraulic flow rate (measured in litres per minute, L/min) is the volume of hydraulic oil that your excavator's auxiliary circuit delivers to the attachment per minute. The flail mower's hydraulic motor converts this flow into rotational speed (RPM) at the rotor.
If the flow rate is too low, the rotor will not reach its designed operating speed. The result is poor cutting performance — the flails do not have enough tip speed to cut effectively, and the motor may stall on dense vegetation.
If the flow rate is too high, the motor will overspeed. This causes excessive heat, accelerated wear and potential motor failure. Most flail mowers have a maximum flow rating that must not be exceeded.
What Is Operating Pressure and How Does It Relate to Flow?
Operating pressure (measured in bar) is the hydraulic pressure at which the circuit operates. Pressure determines the torque output of the hydraulic motor — higher pressure means more torque, which means more cutting force.
Flow and pressure work together: flow determines rotor speed, pressure determines cutting force. A flail mower needs both adequate flow (for speed) and adequate pressure (for torque) to perform correctly.
Most excavator auxiliary circuits have a pressure relief valve set between 180 and 380 bar. The flail mower's motor must be rated for the circuit pressure. If the motor's maximum pressure rating is lower than the circuit relief valve setting, the motor can be damaged.
Always check both flow rate AND operating pressure when specifying a flail mower. A motor rated for 250 bar connected to a 350 bar circuit will fail prematurely.
How to Find Your Excavator's Hydraulic Specifications
The auxiliary hydraulic flow rate and pressure are listed in your excavator's operator manual or technical specification sheet. Look for "auxiliary hydraulic flow" or "attachment hydraulic flow" in the specifications section.
If you cannot find the specifications in the manual, contact the excavator manufacturer or dealer with your machine's model number and serial number. They can provide the exact auxiliary circuit specifications.
Note that some excavators have multiple auxiliary circuits with different flow rates (standard flow and high flow). Confirm which circuit you are connecting to.
| Excavator Size | Typical Auxiliary Flow Range |
|---|---|
| 1.5–3 tonnes | 20–35 L/min |
| 3–6 tonnes | 30–55 L/min |
| 6–12 tonnes | 50–90 L/min |
| 12–20 tonnes | 80–140 L/min |
| 20–35 tonnes | 120–200 L/min |
| 35+ tonnes | 160–280 L/min |
What Happens When Flow Is Too Low?
- Rotor does not reach operating speed — cutting performance is poor
- Motor stalls on dense vegetation — operator must make multiple passes
- Increased vibration as rotor speed fluctuates under load
- Overheating as the motor works harder to maintain speed
- Accelerated wear on blades and rotor components
What Happens When Flow Is Too High?
- Motor overspeeds — exceeds its rated RPM
- Excessive heat generation in the motor
- Accelerated wear on motor seals and internal components
- Risk of motor failure and hydraulic oil contamination
- Increased vibration from rotor imbalance at excessive speed
Flow Control and Adjustment
Most modern excavators allow the auxiliary hydraulic flow rate to be adjusted through the machine's control system. This allows you to set the flow to match the flail mower's requirements precisely.
If your excavator's maximum auxiliary flow exceeds the flail mower's maximum rating, set the flow to the attachment's maximum. If the excavator's flow is below the minimum requirement, the attachment is not compatible with that machine.
Some flail mowers include an integrated flow control valve that limits the maximum flow to the motor regardless of the excavator's output. This provides additional protection against overspeeding.
Summary
Hydraulic flow matching is not complicated once you understand the principles. Find your excavator's auxiliary flow rate, check it against the flail mower's requirements, and confirm the operating pressure is within the motor's rating. If you are unsure, the PANDA FORCE technical team can check compatibility for any excavator make and model.
Check Hydraulic Compatibility for Your Excavator
Send us your excavator make, model and weight and we will confirm which PANDA FORCE models are compatible and recommend the optimal specification.