Scroll-type compressor for helium gas

A scroll-type compressor for helium gas comprising:

• a hermetic container for accommodating a motor-compressor unit constituted by an upper scroll compressor section and a lower electric motor section which are connected to each other through a main shaft rotatably supported by a frame;
• said scroll compressor section including stationary and orbiting scroll members each having an discoidal end plate and a spiral wrap protruding upright from said end plate, said scroll members being assembled together with said scroll wraps meshing with each other, said main shaft having an eccentric mechanism engaging with said orbiting scroll member so as to cause an orbiting movement of said orbiting scroll member with respect to said stationary scroll member while preventing said orbiting scroll member from rotating about its own axis, a suction port and a discharge port formed in a central portion and an outer peripheral portion of said end plate of said stationary scroll member, respectively, so that the orbiting movement of said scroll member causes a radially inward movement of closed compression spaces defined between said scroll members while progressively decreasing the volume of said compression chamber, whereby the helium gas sucked through said suction port is progressively compressed in said compression spaces and finally discharged from said discharge port into a space in said hermetic container so as to maintain a high discharge pressure in said space of said hermetic container, the compressed gas then being delivered to an outside of said compressor through a discharge pipe;
• an oil separator connected to said discharge pipe for separating an oil from said compressed gas;
• an oil cooler for cooling the oil separated in said oil separator and the oil stored in an bottom portion of said hermetic container;
• and an oil injection system including at least one oil injection port formed to open in a surface of said end plate of said stationary scroll member for injecting the oil cooled by said oil cooler into the helium gas under compression to cool said helium gas, and a oil injection pipe line connecting said oil cooler with said oil injection port for delivery of the cooled oil, and wherein a size of said oil injection port as measured in a direction of thickness of said scroll wrap is greater than the thickness of said scroll wrap of said orbiting scroll member.