A conveyor needs 30 rpm at the drive shaft. Its hydraulic motor delivers 600 rpm under load, so a 20:1 reduction looks right. But will the conveyor restart with material still on the belt? Choosing a hydraulic motor planetary gearbox requires two checks: whether the drive can deliver the required speed while running, and whether it can produce enough torque to start the load.
Start with the motor shaft, not the pump rating
The hydraulic motor converts flow and pressure into shaft rotation. The planetary gearbox reduces that speed and multiplies torque. For a fixed-displacement motor, flow chiefly determines running speed, while the pressure difference across the motor governs available torque. Pump flow can differ from the flow reaching the motor, particularly when several functions share a circuit. Use the motor manufacturer's performance curves at the flow, inlet pressure and return pressure expected at the machine.
Worked example: a conveyor running at 30 rpm
Suppose a motor delivers 120 N·m at 600 rpm at the intended operating point. The conveyor needs 2,000 N·m while running and 3,000 N·m to break away when loaded. Assume 94% running gearbox efficiency for this illustration. These are example inputs, not product ratings.
| Check | Calculation | What it tells us |
|---|---|---|
| Output speed | 600 rpm ÷ 20 | The drive reaches the required 30 rpm at the stated operating point. |
| Available running torque | 120 N·m × 20 × 0.94 | About 2,256 N·m is available. The gearbox must also be rated for the continuous load and duty. |
| Loaded restart | 3,000 N·m ÷ 20 | Even with no losses, the motor would need 150 N·m at startup. Its 120 N·m running figure cannot establish whether it will start the belt. |
Before accepting the 20:1 ratio, ask for the motor's guaranteed starting torque at the pressure difference available during restart. Check that torque through the gearbox using the supplier's starting-loss data, then verify the permitted peak output torque and number of starts. Increasing the ratio might help the restart, but it would also reduce belt speed unless the motor could run faster with the available flow.
Check the interfaces before ordering
A matching bolt circle is only one part of a motor adapter. Compare the pilot diameter, shaft projection, spline tooth form and engagement length on both drawings. Two flanges can bolt together while the spline bottoms out or engages too little of the hub. On the output side, show where the load acts: the same chain pull applied farther from the gearbox bearing produces a greater bending moment.
| Send the supplier | Ask them to confirm |
|---|---|
| Motor model, displacement, flow range and inlet/outlet pressures | Loaded running speed and starting torque at the actual operating points. |
| Loaded starts per hour, run time, reversals and ambient temperature | Continuous, cyclic and thermal capacity for this duty. |
| Motor interface drawing and mounting orientation | Adapter fit, spline engagement, lubrication arrangement and access to motor ports or case drain. |
| Output shaft drawing, sprocket pitch radius and chain forces | Permitted bearing loads at the actual overhang as well as shaft torque capacity. |
For a replacement drive, include the old nameplate and a dimensioned sketch, but also describe why the unit is being replaced. A conveyor that reaches line speed yet stalls on loaded starts calls for a torque review. One with repeated output-bearing failures calls for a closer look at chain pull, overhang and alignment. Send TOGINE the motor data and load cycle so the proposed ratio and interface can be checked against the machine.