GB759734A - System for unloading gas compressors - Google Patents

Abstract

759,734. Fluid-pressure servomotor control systems. COOPER-BESSEMER CORPORATION. Nov. 26, 1954 [Dec. 15, 1953], No. 34312/54. Class 135. The volume of the clearance space and hence the output of a gas compressor 10 having an inlet 12 and an outlet 13 to a tank 32 is regulated by a piston 15 in a cylinder 14 forming an. extension of the compressor cylinder, the position of the piston being determined by an hydraulic servomotor 18, the flow of liquid to and from the opposite ends of which is controlled by a pilot valve 22. The position of the piston 31 of the pilot valve is dependent on the pressure on a spring-loaded diaphragm 34 forming one wall of a chamber 35 connected to the compressed gas tank 32. The servomotor is connected by flexible pipes 20, 21 to ports 20a, 21a in the pilot valve which is formed with recesses 23, 25 connected to a return pipe 26 to a liquid tank, and a recess 24 connected to the discharge pipe 29 of a pump 27. The pressure to be maintained in the tank 32 is set by a lever 48 coacting with .a scale- 50 and pivoted to a slide 47 and connected by a link 49 to the body of the pilot valve 22, the arrangement being such that when the pressure in the tank reaches the set value the piston is in the valve closed position shown. A fall of pressure in the tank results in displacement of the piston 31 to the right, thus allowing pressure-liquid to flow through the pipe 21 to the servomotor 18, the piston of which moves to the right, thus reducing the clearance space of the compressor cylinder and increasing the pressure of the gas discharged to the tank 32. The increased pressure returns the pilot valve piston 31 to its valve closed position. A rise of pressure in the tank results in increasing the clearance space and reducing the pressure of the gas discharged to the tank. In the event of failure of the hydraulic pressure, a pressure-responsive device 39, e.g. a bellows, closes a normally open switch 39 and energizes a solenoid 43 which closes interconnected valves 45 in the pipes 20, 21 so as to lock the servomotor in the position it occupies at the moment of failure. To permit manual operation of the pilot valve piston 31, the piston rod 33 is disconnected from the diaphragm 3, 4, and a follow-up is provided between the servomotor and the piston 31 by a pivoted lever 52, one end of which is connected to a sleeve 51 adapted to be secured by a screw 51a to the rod 33.