U-cup seal for pistons

Claim 1

A U-cup seal for a piston and cylinder assembly comprising an annular ring of resilient material having in cross section four walls, an inner wall, an outer wall and sidewalls, one of the sidewalls being substantially flat, the inner wall being of arcuate shape extending inwardly toward the center of the ring, the junction of the one sidewall and the inner wall being on a point, the other sidewall having an inwardly extending annular groove therein, the junction between the inner wall and the other sidewall being rounded into the configuration of a half O-ring, said rounded configuration forming an inner annular flange, the outer wall having a substantially flat portion for more than half its width from the one sidewall to the other sidewall with the rest of the outer wall adjacent the other sidewall having an outwardly inclined portion from the flat portion, the junction of the inclined portion with the other sidewall being on a point and forming an outer annular flange, the flanges being on opposite sides of the annular groove, the inner annular flange extending outwardly from the ring a greater extent than the outer annular flange, the inner diameter of the ring being smaller than the outer diameter of the base of a ring-receiving groove in the piston, whereby when the ring is seated in the piston groove the ring is distoRted so that the inner wall is substantially flattened with the inner annular flange forming a seal with the adjacent corner of the piston groove and the tension placed on the ring by the distortion thereof causes the outer annular flange to extend outwardly into a wiping contact with the inner wall of the cylinder and when pressure is applied to the inwardly extending annular groove in the other sidewall the inner and outer flanges are caused to extend in opposite direction to further seal the surfaces being contacted thereby.