moves from its top dead center to its bottom dead center the compression chambers 16a to 16f are communicated with the outlet 23b of the suction passage 23 through the suction ports 11a to 11f as the rotary valve 21 is rotated therefore the refrigerant gas within the suction chamber 3b passes through the suction passage 23 and the suction ports 11a to 11f and flows into the compression chambers 16a to 16f in fig3 the piston 17 within the compression chamber 16a is at the top dead center while the piston 17 within the compression chamber 16d is at the bottom dead center the drive shaft 4 rotates in the direction indicated by arrow r a capture groove 24 is formed in the front end face 21c of the rotary valve 21 the capture groove 24 is arranged on the opposite side of the suction passage 23 from the suction passage 23 the capture groove 24 is provided with an inlet groove 24a an outlet groove 24b and a bypass groove 24c as shown in fig2 and 3 the inlet and outlet grooves 24a and 24b extend in the radial direction of the rotary valve 21 and are spaced about a half circumference apart the bypass groove 24c extends along the circumferential direction of the rotary valve 21 so that the inlet groove 24a and the outlet groove 24b are connected at their inner ends the inlet and outlet grooves 24a and 24b are communicated in sequence with the suction ports 11a to 11f as the rotary valve 21 is rotated as shown in fig3 the inlet groove 24a extends in the circumferential direction of the rotary valve 21 by an angle u03b8 1 with respect to the center axis of the rotary.