Pneumatic Engine

A 2 cylinder pneumatic motor powered by compressed air only.

A 2 cylinder pneumatic motor powered by compressed air only.
This ‘just for fun project’, with no practical use, got quite some attention on YouTube.


  • Operating pressure: 3-8 bar
  • Torque: 50-90 Nm at 6 bar
  • Rotation speed: depends strongly on load and limits of air supply


To get a rough idea of how much torque the motor provides and especially how stable it will run, i made some calculations.
The produced Torque depending on the crank angle is described by this very simplified function:
M(α) = 8bar * 1800mm² * 48mm * ( |sin(α)| + |sin(α+90)| )

Problems / Neglected aspects with this simplified approach:

  • Different cylinder forces when extending and retracting (due to different effective surface area)
  • Friction losses
  • Pressure is not constant when there is movement

Torque graph
Torque vs Angle graph at 8 bar.

Because double acting cylinders are used and the chosen 90 degree offset between the two cranks, this motor runs quite smoothly and there are no torque gaps at any angle.

Torque graph at different pressures
Torque vs Angle at different pressures (4 bar, 6 bar, 8 bar).



  • 2x Compressed Air Cylinder
  • 2x Bistable 5/2-Way-Valve controlled by air pressure
  • 4x 3/2-Way-Valve with Roller
  • 1x Pressure regulating Valve


  • 5x 20 mm bearing block
  • Wodden baseplate
  • Custom crank
  • Custom timing-rings for actuating the valves

image Layout of all components used