US Patent 7555902 Tandem master cylinder with central valves

A tandem master cylinder (1) with central valves has ball-shaped valve members (25, 40) with leaf springs (26, 41) serving as valve springs. The ball-shaped valve members (25, 40) can be manufactured of a plastic material, coated with an elastomer. The size of the balls is preferably adjusted to the size of the pistons (4, 5) to allow a maximum flow while ensuring at the same time that the piston walls retain a thickness. The leaf springs (26, 41) have a bowl-shaped body (61), which is shaped like a partial sphere. To avoid an entrapment of brake fluid or a vacuum between the balls (25, 40) and the leaf springs (26, 41), respectively, a central hole (62) has been provided in the bowl-shaped body (61). The leaf springs (26, 41) are equipped with a plurality of tongue-shaped extremities (63) extending radially outward with end portions (64) bent toward the axial side on which the valve members (25, 40) are located.