An air winch uses a pneumatic motor to turn a rope drum, often through reduction gearing. Reducing drum speed increases available drum torque for a given motor torque, with losses in the transmission. Use the calculator to compare speed reduction and torque multiplication. Motor torque, rope radius, brakes and load ratings are not inputs, so it does not select a winch or establish lifting capacity.
Air Winch Interactive Calculator
Vary motor speed, gearbox ratio, and gearbox efficiency to see drum speed and torque multiplication for an air winch.
Equation Used
The entered motor speed is divided by total gear ratio to obtain drum rpm. Torque multiplication is that ratio multiplied by entered gearbox efficiency. This represents an enclosed reduction gearbox; air motors and gear arrangements vary between winches.
- Gear ratio is total motor-to-drum speed reduction.
- Torque multiplier is ideal ratio corrected by gearbox efficiency.
- Drum rpm follows the gear ratio; rope-layer radius changes line speed and pull, which are not outputs here.
From compressed air to drum rotation
A pneumatic motor converts energy from compressed air into rotary motion. An enclosed gearbox reduces that motor speed before the drum winds or pays out rope. Motor construction is not universal: commercial winch ranges include radial-piston and gear-type motors as well as other arrangements.
At a selected motor operating point, a larger reduction ratio gives lower drum rpm and a larger torque multiplier. Gearbox efficiency reduces transmitted torque and power; it does not change the tooth-count speed ratio in this calculation. Real motor speed depends on the motor, load and air supply rather than only a throttle position.
Main parts
- Air supply and control valve: deliver and regulate flow to the motor.
- Pneumatic motor: produces the input rotation.
- Reduction gearbox: trades speed for torque.
- Drum and bearings: support rotation and the rope load.
- Brake and load-control equipment: serve functions that gearing alone does not establish.
The animation illustrates these connections. It does not model air consumption, pressure-dependent torque, brake holding or the capacity of the rope, drum, mounting structure or rigging.
Choosing equipment for the job
Pneumatic winches are used in material handling, marine work and industrial installations where a suitable compressed-air supply is available. Air, electric and hydraulic drives each require equipment rated for the environment and task.
Pneumatic power alone does not establish hazardous-area approval, heat resistance, unlimited stall duty or suitability for lifting people. Personnel lifting needs equipment specifically intended and approved for that service; a ratio calculation or a blanket reduction of a material-winch rating is not a substitute.
For selection, use the exact manufacturer’s rated line pull and speed at the specified rope layer, air pressure and flow, together with brake, rope, installation and duty requirements. This calculator helps explain the transmission, not certify an installation.
Gearbox calculation and rope geometry
Let N be motor rpm, R the total reduction ratio, and η the entered Gear Eff. percentage divided by 100. Drum Speed = N/R. Torque Mult. = Rη. Speed Cut = 100(1 − 1/R) percent, and Gear Loss = 100 − Gear Eff. percent.
Gear Loss is the assumed fraction of mechanical input power lost in the gearbox at the modeled operating point. It is not whole-system compressor-to-rope efficiency. Absolute drum torque would require motor torque: Tdrum = TmotorRη.
With drum torque and an effective rope-centre radius r, ideal tangential line pull would be F = Tdrum/r. At constant drum rpm, rope speed would be 2Ï€rn per minute. A larger active rope radius therefore lowers pull for the same torque and raises line speed for the same rpm.
Those last quantities are explanatory relations, not calculator outputs. Rope layering, motor torque, reeving losses and braking are absent. Manufacturer ratings may specify different layers; do not assume a first-layer pull applies to the full drum or that a calculated force is a working-load rating.
Worked example: reduction and efficiency
Enter motor speed 2000 rpm, ratio 25:1 and Gear Eff. 90%. Drum Speed is 2000/25 = 80 rpm. Torque Mult. is 25 × 0.90 = 22.5. Speed Cut is 100(1 − 1/25) = 96%, and Gear Loss is 10%.
Changing ratio to 50:1 gives 40 rpm, a torque multiplier of 45 and a Speed Cut of 98%; assumed gearbox loss remains 10%. Changing efficiency to 80% at that ratio leaves drum speed at 40 rpm but lowers the torque multiplier to 40.
For a separate illustration, an assumed motor torque of 10 N·m with the original 25:1 and 90% settings would give 225 N·m at the drum. At an assumed rope-centre radius of 0.10 m, the simple tangential-force relation gives 2250 N. Neither added assumption is a calculator control or an equipment rating, and the result does not authorize a lift.
Air, electric and hydraulic drives
| Drive | Required supply | Data needed for selection |
|---|---|---|
| Pneumatic | Compressed air at the required inlet conditions. | Pressure, flow, motor curve, exhaust and air-treatment requirements. |
| Electric | Electrical supply and suitable controls. | Voltage, current, motor duty, protection and control requirements. |
| Hydraulic | Hydraulic power unit and circuit. | Pressure, flow, fluid, heat rejection and load-control requirements. |
All three need appropriate brakes, rope, drum, mounting and task-specific ratings. No drive type automatically provides a hazardous-area certification or an unlimited lifting duty.
Air-winch calculation questions
No. It gives drum rpm and relative torque multiplication. Actual line pull also requires motor torque and rope-centre radius; an approved rating additionally depends on the complete winch and installation.
The gear ratio fixes the relative shaft speeds. The entered efficiency reduces transmitted torque and power at that operating point. The model holds motor speed fixed rather than solving its response to load.
It is the percentage reduction from motor rpm to drum rpm. At ratio 25:1, drum speed is 4% of motor speed, so Speed Cut is 96%.
The effective rope-centre radius grows. At unchanged drum torque, tangential pull decreases; at unchanged drum rpm, line speed increases. Consult the manufacturer’s layer-specific ratings.
No. Manufacturers offer several air-motor types, including radial-piston and gear motors. This calculator only represents their motor-to-drum transmission ratio.
No. Suitability and any required certification apply to the particular equipment and environment. A compressed-air drive by itself does not establish approval.
No. A numerical derating does not establish personnel-lifting suitability. Use equipment specifically intended and approved for the application and follow its manufacturer’s instructions.
No. It does not test brakes or rope strength. Unexpected load movement requires the equipment’s prescribed safe response and inspection; the calculator is not a procedure for suspended-load testing or brake adjustment.
References and further reading
Ingersoll Rand air-winch range distinguishes motor types and material/personnel applications. Infinity air-winch specifications show why the rope layer and particular model matter when comparing capacity. Use the exact equipment manual for operation, inspection and installation.
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