Gas injection system for screw compressor

In a refrigeration cycle including a screw compressor provided with a slide valve means for controlling a compression capacity of said screw compressor, an economizer means disposed in a refrigerant liquid passage for subcooling said refrigerant liquid by the refrigerant of a reduced pressure, and a refrigerant gas injection line through which the refrigerant gas generated in said economizer means is injected into the compression chamber of said screw compressor in a compression phase of the screw compressor, a refrigerant gas injection system comprising:

• a pressure switch operative in response to the pressure in a cylinder forming an actuator for actuating said slide valve means;
• a gas injection solenoid valve provided in said refrigerant gas injection line and adapted to be opened and closed in response to an output signal from said pressure switch;
• an oil supply passage means for supplying pressurized oil into a cylinder chamber defined on a top of a piston disposed in said cylinder;
• an oil supply solenoid valve disposed in said oil supply passage, said oil supply solenoid valve being adapted to close said oil supply passage means when said screw compressor is operating at a full capacity or at a load level and to open said oil supply passage when said screw compressor is operating in an unloaded state;
• an oil passage means through which said cylinder chamber on a top of said piston is communicated with a suction side of said screw compressor;
• a low-pressure equalizer solenoid valve provided in said oil passage and adapted to be respectively closed and opened when said oil supply solenoid valve is opened and closed;
• and
• an equalizer passage through which a back chamber on an opposite side of said piston to said cylinder chamber is communicated with the suction side of said screw compressor.

In a refrigeration cycle having a screw compressor provided with a slide valve means for controlling a compression capacity of said screw compressor, an economizer means disposed in a refrigerant liquid passage for subcooling said refrigerant liquid by the refrigerant of a reduced pressure, and a refrigerant gas injection line through which the refrigerant gas generated in said economizer means is injected into the compression chamber of said screw compressor in a compression phase, a refrigerant gas injection system comprising:

• an oily supply passage means for supplying pressurized oil into a cylinder chamber defined on a top of a piston in a cylinder forming an actuator for actuating said slide valve;
• an oil passage means for providing a communication between said oil supply passage means and a suction side of said screw compressor;
• an oil supply solenoid valve disposed in said oil passage means, said oil supply solenoid valve being adapted to open said oil passage means when said screw compressor is operating at full capacity or at a load level and to close said oil passage means when said screw compressor is operating in an unloaded state;
• an unloading oil passage means for providing a communication between a interior of said cylinder substantially at a mid point of a stroke of said piston and the suction side of said screw compressor;
• an unload solenoid valve disposed in said unloading oil passage and adapted to be respectively closed and opened when said oil supply solenoid valve is opened and closed;
• an equalizer passage means through which a back chamber on an opposite side of said piston to said cylinder chamber is communicated with the suction side of said screw compressor;
• and
• a gas injection solenoid valve disposed in said refrigerant gas injection line and adapted for operating in relation to an operation of an oil supply means for supplying the pressurized oil in such a manner so as to open when said screw compressor is operating at a full load level and to close when the screw compressor is operating in the unloaded state.