Abstract: A compressor comprises a cylinder block having cylinder bores formed radially spaced from and circumferentially distributed equidistantly about the cylinder longitudinal axis. Pistons are slidably received in the respective bores for reciprocation therein executing alternately suction and discharge strokes. The compressor also has a discharge valve assembly for controlling discharge of a compressed fluid from each of the bores into a discharge chamber, which assembly is axially movable between a first position in which the assembly is abutted against an end wall of the block and a second position in which the assembly is spaced from the end wall of the block to define a narrow space therebetween to interconnect the bores with each other. When the assembly is pushed toward the second position by the pressure of the compressed fluid during initial running of the compressor, bypass channels interconnect the cylinder with the discharge chamber.