Gas compressors

A refrigeration system including a positive displacement single stage rotary compressor with means providing a plurality of suction and compression chambers;

• means for injecting a single fluid only, that being the refrigerant gas in a liquid state, into an intermediate position on the compression side;
• a gas feedback circuit from the output of the compression side to said intermediate position, said circuit including means for liquifying gas from said output, means for positively ensuring that the supply of liquid is provided substantially only when the compressor is in operation and ceases when the compressor stops, a temperature sensor between said output and the liquifying means, and a valve responsive to said sensor between the liquifying means and said intermediate position, the sensor having a closed chamber containing fluid that is substantially directly influenced by the superheated gas from said output whereby it exerts a pressure directly related to the superheat temperature on a control member of said valve, and the valve having adjustment means whereby the valve can be set to maintain a desired degree of superheat of gas discharged from said output;
• a motor for driving the compressor, directly coupled thereto;
• means including a pump driven by and directly coupled to the motor for distributing a liquid coolant over said motor;
• and a heat exchanger in contact with the motor coolant through which gas in a liquid state is passed before being injected into said compressor, thereby to cool the coolant.