Gas actuated slide valve in a screw compressor

A refrigeration screw compressor, having a suction and discharge port, comprising:

• a housing, said housing defining a working chamber in flow communication with said suction and said discharge ports of said compressor;
• a male rotor disposed in said working chamber;
• a female rotor disposed in said working chamber in meshing engagement with said male rotor, rotation of said male and said female rotors operating to compress a gaseous working fluid within said working chamber from a suction to a discharge pressure;
• a capacity control slide valve, said slide valve having an actuating piston;
• a first conduit which communicates refrigerant gas from one of a first and a second source of refrigerant gas, the source from which said refrigerant gas is communicated being at a pressure sufficient to move said slide valve in a direction which loads said compressor;
• and
• a second conduit for selectively venting refrigerant gas communicated to said actuating piston to a location in said compressor where the pressure is less than discharge pressure so as to move said slide valve in a direction which unloads said compressor.

A refrigeration system comprising:

• an oil separator;
• a condenser;
• a metering valve;
• an evaporator;
• and
• a screw compressor, said screw compressor compressing, in operation, a gaseous working fluid from a suction to a discharge pressure in a working chamber which is in flow communication with a suction and a discharge port, said compressor having a slide valve actuated by gaseous working fluid sourced from said working chamber when the pressure of refrigerant gas in said working chamber exceeds the pressure of working fluid downstream of said discharge port, but in or upstream of said oil separator, whenever said compressor is in operation.

A refrigeration system comprising:

• an oil separator;
• a condenser;
• a metering valve;
• an evaporator;
• and
• a screw compressor, said screw compressor compressing, in operation, a gaseous working fluid from a suction to a discharge pressure in a working chamber which is flow communication with a suction and a discharge port, said compressor having a slide valve actuated by gaseous working fluid which is selectively sourced from the one of at least two locations within said refrigeration system which is at higher pressure.

A method of controlling the position of a slide valve in a refrigeration screw compressor which compresses a gaseous working medium from a suction to a discharge pressure in a working chamber having a suction and a discharge port, comprising the steps of:

• supplying said gaseous working fluid to said compressor at a suction pressure;
• compressing said gaseous working fluid in the working chamber of said compressor;
• discharging said gaseous working fluid from said working chamber of said compressor through said discharge port;
• and
• controlling the position of the slide valve, so as to load said compressor, using said gaseous working fluid, said gaseous working fluid being sourced from the working chamber of said compressor.

A method of controlling the position of a slide valve in a refrigeration screw compressor which compresses a gaseous working medium from a suction to a discharge pressure in a working chamber having a suction and a discharge port, comprising the steps of:

• supplying said gaseous working fluid to said compressor at a suction pressure;
• compressing said gaseous working fluid in the working chamber of said compressor;
• discharging said gaseous working fluid from said working chamber of said compressor through said discharge port;
• and
• controlling the position of said slide valve so as to load said compressor by the use of gaseous working fluid sourced from one of two locations, one of said locations being downstream of said discharge port and the other of said two locations being upstream of said discharge port and in said working chamber.