Piston and rider ring combination for horizontal reciprocating compressors

Claim 1

In a device having a nonlubricated reciprocating piston with an annular groove carrying a rider ring made of a material having a large coefficient of expansion relative to the piston material, the improvement comprising: a. an annular radially extending projection in said groove; b. an annular, radially extending recess in said rider ring into which said Projection extends; c. a first set of clearances between the side surfaces of said rider ring and the side surfaces of said annular groove; d. a second set of clearances between the projection and the side surfaces of said recess; and e. one of said sets of clearances being set initially at substantially zero at ambient temperature and the other set of clearances being set to meet the amount of thermal expansion of said rider ring to an operating temperature substantially different from ambient to cause the other set of clearances to reach substantially zero at said operating temperature; whereby axial movement of the rider ring is prevented regardless of low or high temperature operation of said compressor relative to ambient temperature