How It Works: Spring Engaged Friction Clutch

Mach III spring applied clutches transmit rotary motion from a shaft which rotates constantly to a shaft that is only required to rotate intermittently.  This type of clutch remains constantly engaged in the absence of air pressure.


  • The DRIVE HUB slides over the SHAFT. The drive hub includes a keyway which corresponds to the keyseat in the SHAFT. When a KEY is in place, the two members are connected. The clutch is locked onto the SHAFT with SET SCREWS.
  • Either the SHAFT on which the clutch is mounted or another shaft connected to the SLEEVE (by means of sprockets and roller chain, pulleys and belt, or a coupling) can be the input source.
  • Through-shaft mounted clutches such as the one shown must be connected to an ANTI-ROTATION RESTRAINT. Otherwise, drag in the bearings that connect the CYLINDER/PISTON assembly to the DRIVE HUB would cause them to rotate.
  • Lugs (tabs) on the outside diameter of the FRICTION DISCS fit into corresponding slots in the SLEEVE. The inside diameter of the DRIVE DISCS are connected to the DRIVE HUB via gear teeth or other drive geometries.
  • The SLEEVE includes a precision machined pilot onto which a sprocket, pulley, sheave, coupling or adapter can be attached.
  • The clutch is capable of rotation in both clockwise and counterclockwise directions.


  • ENGAGEMENT SPRINGS located in the CYLINDER apply a constant, fixed amount of force to the PISTON which, in turn, applies force to the FRICTION DISCS and DRIVE DISCS.
  • The SEPARATOR SPRINGS located between the FRICTION DISCS and DRIVE DISCS collapse from the force, allowing full contact between the faces of the discs.
  • The amount of torque transmitted is fixed by the force applied by the ENGAGEMENT SPRINGS.
  • The FRICTION DISCS and DRIVE DISCS remain in contact and stationary until compressed air is supplied.
  • The maximum recommended air pressure to release most Spring Engaged Mach III products is 90 PSI.


  • Compressed air supplied to the clutch through the AIR INLET moves the PISTON assembly backward which collapses the ENGAGEMENT SPRINGS.
  • As the ENGAGEMENT SPRINGS collapse, force is removed from the PISTON, allowing the SEPARATOR SPRINGS to push the FRICTION DISCS and DRIVE DISCS apart.
  • Once adequate air pressure is applied and the discs are fully separated, the clutch is fully disengaged.
  • Timing for full disengagement is short but depending upon the cycle rate of the application, it is sometimes advisable to install a quick exhaust port to allow the air to exit the clutch more quickly.

Note that disengagement only assures that torque is no longer transmitted. If the machine component that the clutch energizes must remain stationary when the clutch is disengaged, a clutch-brake combination should be considered.