Master cylinder having double structured seal ring

摘要

A main object of the present invention is to provide a technique capable of improving the assembling performance of a double seal ring. According to the first embodiment of the invention, on the piston 31 side to which a seal ring is attached, there are provided a ring retaining portion 300 having an outside diameter L0 and for retaining a double seal ring 51, a first land portion 310 adjacent to the ring retaining portion 300 and having an outside diameter L1 (where L1>L0), and a second land portion 320 adjacent to an opposite side of the ring retaining portion 300 to the first land portion 310 and having an outside diameter L2 (where L2<L1). The outside diameter L2 of the second land portion 320 is set to be equal to or smaller than an inside diameter of the outer peripheral resin ring 55, and one side surface of the outer peripheral resin ring 55 on the side of the second land portion 320 is supported by a retainer ring 80 retained by the piston 31. According to the second embodiment of the invention, the piston 32 itself is provided with a tapered portion 280 having a function as an attachment tool. The tapered portion 280 is gradually enlarged in outside diameter from the insert end portion X for attaching the seal ring towards the attachment groove 2300. The outside diameter of the tapered portion 280 at the insert end portion X is set to be smaller than the inside diameter of the resin ring 55.