VACUUM CLUTCH

The vacuum clutch is operated by the vacuum existing in the engine manifold. Fig shows the mechanism of a vacuum clutch. It consists of a vacuum cylinder with piston, solenoid operated valve, reservoir and a non-return valve. The reservoir is connected to the engine manifold through a non return valve. Vacuum cylinder is connected to the reservoir through solenoid operated valve. The solenoid is operated from the battery and the circuit incorporates a switch which is placed in the gear lever. The switch is operated when the driver holds the lever to change gears.

When the throttle is wide opened, the pressure in the inlet manifold decreases due to which the non-return valve closes, isolating the reservoir from the manifold. Thus a vacuum exists in the reservoir all the time.In the normal operation, the switch in the gear lever remains off, the solenoid operated valve remains in its bottom position. In this positions the atmospheric pressure acts on both the side of the vacuum cylinder, because the vacuum cylinder is open, so also atmosphere though a vent. When the driver holds the lever to change the gear, the switch is closed; energizing the solenoid which pulls the valve up. This connects one side of vacuum cylinder to the reservoir. Due to the difference of pressure on the vacuum cylinder piston, it moves. This movement of the piston is transmitted by a linkage to the clutch, causing it to disengage. When the driver is not operating the gear lever, the switch is open and the clutch remains engaged due to the force of springs.