The figure displays the vacuum clutch system. This type of clutch works by using the prevailing vacuum from the engine manifold to operate the clutch. The vacuum clutch is made of a reservoir, non-return valve, vacuum cylinder with piston, and solenoid valve.  Always put the flat side on the clutch https://clutch-plate20752.techionblog.com/33049115/the-smart-trick-of-clutch-kereta-that-no-one-is-discussing