Piston type compressor having arcuately shaped fluid port

A piston type compressor comprising:

• a housing having cylinder bores, and fluid ports in communication with the cylinder bores;
• pistons reciprocatingly arranged in said cylinder bores;
• a drive shaft rotatably supported by said housing;
• a transmission mechanism operatively coupled to said drive shaft and said pistons for converting rotation of said drive shaft into reciprocal movement of the pistons;
• valves to open and close the fluid ports, each said valve having a longitudinal direction, a proximal end and a distal end on the opposite side of the proximal end;
• and
• wherein a middle line is provided which passes through a middle point of a maximum length of each said fluid port in the longitudinal direction of each said valve, extends transversely with respect to said fluid port and perpendicularly crosses a reference line extending in the longitudinal direction of said valve, said middle line dividing said fluid port into a first section positioned on the side of the proximal end of said valve and a second section positioned on the side of said distal end of said valve, an area of said second section being greater than an area of said first section.