Patent GB-1270087-A (GB)
Title: Rotary compressor control system
IPC: F04C28/24
Filed: 1970-04-13
Abstract: 1,270,087. Rotary compressors. WORTHINGTON CORP. April 13, 1970 [April 24, 1969], No.17460/70. Heading F1F. A rotary motor-driven compressor control system comprising compressor suction control means 92, Fig.3, operable to load and unload the compressor 90, an oil/air tank 104 connected to compressor discharge, an air storage tank 110 connected through a demister 106 and a non- return valve 114 with the oil/air tank and control means operatively associated with the air storage tank to operate the suction control means to unload the compressor and to start and stop the compressor motor in response to the pressure in the air storage tank, includes bleed means operatively associated with the oil/air tank and operable in response to the compressor unloading operation of the said control means to bleed the oil/air tank at a predetermined rate and means operatively associated with the oil/air tank and the compressor motor respectively and responsive to the pressure in the oil/air tank to prevent the stopping of the compressor motor by the control means until the pressure in the oil/air tank has been reduced to a predetermined value to prevent the immediate re-starting of the compressor against a high-pressure load in the oil/air tank. The control means comprise a pressure switch PS-B mounted on the air storage tank 110 and operatively associated with switches 140, 144, 154, 156, 158 and 172, Fig.4, in an electric circuit having a two position selector switch 166 movable to a start/stop position 174 or a constant speed position 164. The means associated with the oil/air tank and the motor comprises a pressure switch PS-C mounted on the oil/air tank and operatively associated with a switch 178 wired in parallel with the switch 172. With the selector switch 166 moved to its start/stop position 174 and on the pressure in the air storage tank reaching a predetermined value the switch 140 is broken to de-energize a solenoid 142 of a threeway solenoid-actuated valve 118 to connect line 122 to line 120 to supply a pressure signal to close a closure disc 94 of the suction control means 92 and at the same time supply a pressure signal to a line 130 to actuate a bleed valve 126 to connect a line 128 with a line 132 having a restriction 133 and an air injection line 134 having a non-return valve 136. Conversely when the solenoid 142 is energized the lines 122, 130 are vented to atmosphere through a port 124 to reopen the control means 92 and re-load the compressor and close the bleed valve 126. The switch 172 connected to operate a motor starter 64 is also broken but at this stage the starter motor and hence the motor driving the compressor are not stopped since power is supplied thereto through the unbroken switch 178 under control of the pressure switch PS-C. At this stage however the oil/air tank is vented to atmosphere through restricted line 132, control means 92 and an inlet filter 100. When the pressure in the oil/air tank is reduced to a predetermined value the pressure switch PS-C breaks the switch 178 to stop the motor. During the time that this pressure reduction is taking place air is being recirculated through the compressor via the injection line 134 to keep the compressor lubricated. When the compressor re-starts on a fall in pressure in the air storage tank 110 it will do so against a very lowpressure in the oil/air tank 104. Switch 144 controls motor starter interlock means, switches 154, 156 motor overload safety devices and switch 158 is associated with a temperature-responsive switch 108 to sense the temperature of the discharged air. With the selector switch 166 moved to its constant speed position, as may be required, e.g., by excessive number of re-starts of the compressor motor during the day despite the 2 to 2¢ minute delay by the restricted bleed line 132, the operation is substantially as described above except that the motor is not stopped. In a modification the fixed restriction 133 is replaced by a variable restriction comprising a spring-loaded valve member 196, Fig.7, having a restricted orifice 202. When the pressure in the oil/air tank is high the valve opens to bleed the tank rapidly until a lower value of pressure is reached, whence the valve closes and bleeding takes place slowly through the orifice 202. For a description of a second embodiment of the invention, Fig. 5 (not shown) reference should be made to the Specification.