Start with line pull, not motor displacement
For a first screening, required drum torque equals line pull multiplied by effective drum radius: drum torque = line pull × effective drum radius. Effective radius is not always the bare-drum radius. It includes the drum core, half the rope diameter and rope already wound on the drum.
State rated and maximum pull separately. If the customer only knows the mass to be moved, that is useful input but not automatically the required line pull.
Rope layers change both pull and speed
As rope builds on the drum, the effective radius increases. With the same available drum torque, line pull decreases on outer layers; at the same drum rpm, rope speed increases. A statement such as “10 kN winch” is incomplete unless it identifies the rope layer or effective drum diameter.
Provide drum core diameter, rope diameter, usable drum width, required rope length and the layer on which rated pull must be achieved. If minimum pull matters near a full drum, use the outer-layer radius in the calculation.
Convert line speed into drum and motor speed
Required line speed determines drum speed, then the gearbox ratio sets motor speed. Use the effective radius that applies to the stated speed condition because line speed changes as the drum fills. Separate loaded speed, no-load return speed and any low-speed inching requirement.
The chosen motor must remain inside its verified speed range at every required operating point, not only during no-load recovery.
Match motor torque to differential pressure and flow
Motor output torque depends on displacement, pressure differential and mechanical efficiency. Useful differential pressure is inlet pressure minus return pressure and circuit losses; it is not automatically the pump relief setting. Calculate continuous and peak duty separately, then check the selected model data for pressure, starting behavior, speed and back-pressure limits.
Pressure and flow must be separate values with units. Record working pressure, peak pressure and available flow at working pressure. Confirm that the pump can provide the required pressure and flow at the same time.
Choose the motor structure for the duty
Radial piston motors are a common starting point for heavy winches that start under load, operate at very low speed or see frequent reversing and shock. Orbital motors can be practical for compact auxiliary winches and light-to-medium intermittent pulling where packaging and simplicity are priorities.
This is a starting framework, not a blanket rule. Final selection depends on the specific model’s starting torque, continuous torque, minimum stable speed, pressure, speed, case-drain arrangement and mechanical interface.
Treat motor, gearbox, brake and valve block as one system
The planetary gearbox converts motor speed and torque to the drum; the brake provides mechanical holding; and the valve block manages load control, relief, anti-cavitation, brake release and speed-change functions. These components must be checked against the same duty.
A brake is not a substitute for a correctly designed load-control circuit. For overrunning or suspended loads, the responsible machine designer must confirm the brake concept, counterbalance behavior, emergency condition and applicable safety requirements.
Worked example from a JST winch catalog
The JSJ series catalog shows how pull, motor and gearbox are matched in practice. Model JSJ2.5-5-70-10-ZP-1 is rated for 5 kN single-line pull on the first drum layer and is fitted with a JNM05-75 motor and a C2.5 planetary gearbox with ratio 5. The 10 kN model in the same frame, JSJ2.5-10-70-10-ZP-1, keeps the same gearbox and ratio but moves to a JNM05-130 motor, the larger displacement supplying the higher drum torque.
Two points follow. First, at a fixed drum and gearbox, higher pull is met by more motor displacement, which then needs more flow for the same line speed. Second, the catalog pull is a first-layer value: on outer layers the same winch pulls less and winds faster, as explained in first layer vs full drum line pull. In the model code, Z means the winch has a brake and P means it has a counterbalance valve. See the full table on the JSJ hydraulic winch page.
Common winch motor sizing mistakes
- Sizing at relief pressure. The motor only sees the differential pressure left after return pressure and losses.
- Ignoring return back-pressure and case drain. High return pressure reduces torque and can affect the brake release and motor seals; check the case-drain arrangement for the chosen motor.
- Quoting pull without a rope layer. A first-layer rating and a full-drum rating can differ greatly.
- Treating the brake as load control. The brake holds the load at rest; lowering speed is controlled by the counterbalance circuit. Slipping or dragging brakes are covered in hydraulic winch brake slipping troubleshooting.
- Checking only no-load speed. Loaded line speed sets the flow the pump must deliver at working pressure.
Information needed for a practical review
- Winch purpose and duty cycle
- Rated and maximum line pull, including rope layer
- Drum dimensions, rope diameter and rope capacity
- Loaded and no-load line speed
- Working pressure, peak pressure and available flow with units
- Return conditions, brake and valve functions
- Mounting space, shaft, ports, drawings or photographs
A reliable drive is selected backward from the rope and drum, not forward from a familiar motor code. Final model and safety-related functions must be confirmed for the actual machine before ordering.
FAQ
What size hydraulic motor do I need for a winch?
Work backward from the rope: drum torque = line pull × effective drum radius on the layer where rated pull is required, then divide by the gearbox ratio and efficiency to get motor torque. The displacement that delivers that torque at your usable differential pressure is the starting size; then check speed and flow at the required line speed.
Can a winch motor be selected from the pump relief pressure?
No. Useful differential pressure is inlet pressure minus return pressure and circuit losses. Sizing at the relief setting overstates available torque, and the winch may stall under load.
Do I need a brake on a hydraulic winch motor?
For lifting or any load that can drive the drum back, a mechanical holding brake is normally specified, together with a load-control valve. In the JSJ model code, Z means with brake and P means with counterbalance valve. The machine designer must confirm the brake and load-holding concept.
Which JST motors are used on winches?
The JSJ hydraulic winch series is driven by JNM and JHM radial piston motors through a planetary gearbox. QJM motors are also available with a brake option. Orbital BM motors can suit compact, light-duty auxiliary winches.
Why does my winch pull less on the outer layers?
Rope builds up on the drum and increases the effective radius. With the same drum torque, line pull falls and rope speed rises on outer layers, so rated pull must always be quoted with its rope layer.
Technical information is provided for preliminary selection. Confirm the selected model, installation and application requirements before ordering.