Control means for gas compressor having dual slide valves

Abstract

A rotary screw gas compressor for a refrigeration system comprises a motor-driven single main rotor having helical grooves and mounted for rotation in a rotor bore in the compressor housing and a pair of star-shaped gate rotors rotatably mounted in the housing and engageable with the helical grooves to define a plurality of compression chambers. A suction slide valve member is slidably positionable (between full load and unload positions) to control where low pressure uncompressed refrigerant gas from a suction port is admitted to the compression chambers to thereby function as a suction bypass to control compressor capacity. A discharge slide valve member is slidably positionable (between minimum and adjusted volume ratio positions) to control where high pressure compressed refrigerant gas is expelled from the compression chambers to a discharge port to thereby control the volume ratio and thereby the input power to the compressor. Both slide valve members are disposed in side-by-side sliding relationship in a common recess in the compressor housing which extends alongside and communicates with the rotor bore and each has a face which is complementary to and confronts the main rotor surface in sliding sealed relationship. The slide valve members are independently movable by separate piston-cylinder type hydraulic actuators. A control system responsive to compressor capacity and volume ratio operates the actuators to position the slide valve members to cause the compressor to operate at a predetermined capacity and minimum power input. The control system includes sensing devices to detect the position of the slide valve members.