The figure demonstrates the vacuum clutch mechanism. This type of clutch employs the present vacuum while in the motor manifold to operate the clutch. The vacuum clutch is made of a reservoir, non-return valve, vacuum cylinder with piston, and solenoid valve.  Normally area the flat facet on the clutch plate https://dallasfhgda.livebloggs.com/39382813/clutch-plate-for-dummies