Pressure setting means for a multistage type piston compressor

A multistage piston compressor comprising:

• a housing;
• a suction chamber located in the housing, wherein the pressure in the suction chamber is a suction pressure;
• a discharge chamber located in the housing, wherein the pressure in the discharge chamber is a discharge pressure;
• a rotary shaft supported in the housing;
• a plurality of bores formed in the housing at predetermined angular intervals about the axis of the shaft;
• a valve plate located in the housing, wherein the valve plate includes a suction port and a discharge port corresponding to each bore;
• a piston housed in each bore, wherein each piston reciprocates and compresses a refrigerant when the shaft is rotated;
• compression chambers defined in each bore between a rear end of the associated piston and the valve ate, wherein the compression chambers include a first compression chamber and a second compression chamber;
• an intermediate chamber connecting the discharge port of the first compression chamber to the suction port of the second compression chamber, wherein the refrigerant is compressed in stages and flows from the first compression chamber to the second compression chamber through the intermediate chamber;
• a crank chamber formed within the housing, wherein each piston has a front end opposite to the rear end and exposed in the crank chamber, and
• a passage for connecting the intermediate chamber with the crank chamber such that the pressure of the intermediate chamber is applied to the crank chamber and acts on the front ends of the postions, herein the pressure of the intermediate chamber is between the suction pressure and the discharge pressure.