Abstract: A piston assembly includes an annular body defining a groove, with a ring disposed within the groove. The piston assembly includes a centering device disposed within the groove between an inner face of the ring and a root of the groove. The centering device centers the ring concentrically within the groove when the ring is in an uncompressed condition, prior to installation into a bore of an engine block, to prevent the inner face of the ring from moving radially outward beyond an outer edge of the groove when the ring is in the uncompressed condition.

Abstract: Force balanced (or nearly balanced) rings to eliminate (or greatly reduce) pressure caused force build up of the ring(s) against the cylinder wall. Especially important in high pressure engines and/or where increased depth ring/cylinder contact surface is used.

Abstract: A piston-ring arrangement for use in an internal combustion engine including a cylinder with a piston axially displaceable within the cylinder and at least one piston ring guided in the cylinder. The cylinder, piston and piston-ring are made of a ceramic material. The piston ring is formed of two circumferentially extending parts and is mounted in a groove in the circumferentially surface of the piston. The groove has a depth greater than the corresponding radial depth of the piston ring so that a spring element can be positioned between the base of the groove and the piston ring for biasing the piston ring radially outwardly. The spring element can be annular member with a corrugated shape or a multi-part ceramic member shaped to provide a biasing action.

Abstract: The pressure relief valve is debris resistant, self-cleaning, and self-actuating in a cryopump. It includes an o-ring carried by a valve member within a valve cylinder. In opening, the valve member moves away from an end port to open vent ports in the side of the valve cylinder while withdrawing the o-ring to a debris free and protected region of the valve. As the valve member is moved into the closed position in response to an atmospherical pressure differential, a wiper ring cleans debris from the inner surface of the valve cylinder. A taper is provided on the inner surface of the cylinder to release compression on the vacuum sealing o-ring upon opening and to compress the o-ring as the valve member moves to the closed position. The wiper ring is expansible in order to provide a wiping action along the entire taper and prevent debris from reaching the o-ring. The end of the valve cylinder opposite to the end port serves as a shock absorber as the valve is opened.

Abstract: An improved piston ring assembly, particularly for a Stirling engine, comprises a piston ring made from a TFE fluorocarbon such as Rulon which is disposed in a piston ring groove and is acted upon by an annular bi-metal element disposed between the groove and the ring. When the engine is cold, the bi-metal element urges the ring outwardly so that a flat radially outer surface of the ring is forced into face-to-face contact with the cylinder wall. When the engine has warmed up, the force of the element of the piston ring is relaxed and the thermal expansion of the piston ring maintains the outer surface of the ring in face-to-face contact with the cylinder wall.