Control system for helical screw compressor

A helical screw compressor and control system comprising in combination:

• a helical screw gas compressor operably connected to deliver compressed gas to a service line and characterized by a casing having a pair of parallel intersecting bores, a gas inlet port, and a gas discharge port, a pair of intermeshing screw rotors disposed in said bores, auxiliary ports opening into said casing for bypassing a portion of the gas throughput of said compressor, and a rotary valve for opening and closing said ports to regulate the gas throughput capacity of said compressor;
• an actuator for rotating said rotary valve;
• an inlet throttling valve including actuator means for controlling the movement of said throttling valve to modulate the flow of inlet gas to said compressor;
• a check valve interposed in said service line downstream of said compressor for preventing the backflow of compressed gas from said service line to said discharge port and a blowdown valve in communication with a compressor discharge conduit means between said check valve and said discharge port and operable to open for venting said discharge conduit means between said check valve and said discharge port;
• control means responsive to a first pressure condition in said service line for causing said rotary valve to regulate the gas throughput of said compressor from a full capacity operating condition to a first reduced capacity operating condition;
• further control means responsive to a second pressure condition in said service line for causing said inlet throttling valve to modulate the flow of gas to said compressor to further reduce the gas throughput of said compressor;
• and,
• pressure sensing means responsive to sensing a third pressure condition in said service line which is greater than said second pressure condition for effecting the operation of said blowdown valve to open.

A helical screw compressor and control system comprising in combination:

• a helical screw gas compressor operably connected to deliver compressed gas to a service line and characterized by a casing having a pair of parallel intersecting bores, a gas inlet port, and a gas discharge port, a pair of intermeshing screw rotors disposed in said bores and forming variable volume chambers, a capacity control valve operable to vary the effective displacement volume of said chambers to regulate the gas throughput capacity of said compressor;
• an actuator for moving said capacity control valve;
• an inlet throttling valve including actuator means for controlling the movement of said throttling valve to modulate the flow of inlet gas to said compressor;
• control means responsive to a first pressure condition in said service line for causing said capacity control valve to regulate the gas throughput of said compressor from a full capacity operating condition to a first reduced capacity operating condition;
• further control means responsive to a second pressure condition in said service line for causing said inlet throttling valve to modulate the flow of gas to said compressor to further reduce the gas throughput of said compressor;
• a check valve interposed in said service line downstream of said compressor for preventing the backflow of compressed gas from said service line to said discharge port and a blowdown valve in communication with a compressor discharge conduit means between said check valve and said discharge port and operable to open for venting said discharge conduit means between said check valve and said discharge port;
• and,
• pressure sensing means responsive to sensing a third pressure condition in said service line which is greater than said second pressure condition for effecting the operation of said blowdown to open.