Reciprocating compressor with auxiliary port

A reciprocating compressor comprising:

• a cylinder,
• a piston that reciprocates in said cylinder,
• a chamber defined by said piston and said cylinder,
• means for admitting low-pressure fluid to said chamber,
• means for discharging high-pressure fluid from said chamber,
• a flow path extending from a side of the piston that slides over said cylinder through said piston to said chamber,
• an auxiliary port that supplies fluid at an intermediate pressure between that of said high-pressure fluid and that of said low-pressure fluid and is located in a wall of said cylinder so that said auxiliary port is intermittently connected to said chamber through said flow path through the piston during an upper portion of the piston stroke and is covered by said piston for a lower portion of the piston stroke, and
• a check valve that prevents flow away from said chamber and is located in series with said auxiliary port when the port is connected to said chamber so that, as the piston moves during its down stroke, the piston uncovers said auxiliary port to allow intermediate-pressure fluid to enter said chamber then the piston blocks said auxiliary port to stop the flow of intermediate-pressure fluid at which time the downward motion of the piston further lowers the pressure in said chamber and allows low-pressure fluid to enter the chamber through said means for admitting low-pressure fluid and when said piston then moves upward during its compression stroke, said check valve prevents flow of fluid away from said chamber through said auxiliary port.