Sealing device

Claim 1

A sealing device for ensuring fluid tightness between a piston having an annular piston ring groove on its outer surface and a cylinder into which said piston is slidably fitted, wherein the sealing device essentially comprises an annular endless resilient seal ring made of a resilient sheet-like material and having in its unmounted condition an inner diameter smaller than the outer diameter of said annular piston ring groove, one of the opposite surfaces of said resilient seal ring being fitted is said piston ring groove in a facing manner with respect to the bottom surface of the groove, the inner peripheral part of the resilient seal ring constituting an embracing portion adapted to embrace the piston ring groove while the outer peripheral part of the same is projected outward beyond the outer surface of said piston in its mounted position and constitutes a seal lip in resilient contact with the inner wall of the cylinder bore, and said piston ring groove is formed with an annular relief groove at one end thereof opposite to the rear face of said outer peripheral part of said seal ring, said relief groove having a depth larger than that of said piston ring groove, for allowing free deformation of said seal lip in the radial direction, said piston ring groove being further formed with an annular engagement groove at the other end thereof having a depth thereof larger than that of said ring groove and receiving an innermost peripheral edge of the inner peripheral part of said resilient seal ring.