GB612408A - Pressure operated power apparatus - Google Patents

Abstract

612,408. Fluid-pressure servo motor-control systems. GORDON & CO., Ltd., J. (Hagan Corporation.). March 21, 1944, No. 5231. [Class 135] A pressure-operated power unit comprises an operating member, an actuating diaphragm 1 for moving the operating member in one direction, a return diaphragm 2 for moving the operating member in the other direction and subject to a constant pressure pre-set to suit the load conditions, and means for regulating the pressure applied to the actuating diaphragm responsive to a variable condition to be controlled and responsive to movement of the operating member to maintain it in the requisite position against the prevailing load. Figs. 1 and 2 show the apparatus applied to the control of an outlet damper 96 so as to maintain the pressure within the combustion chamber of a boiler furnace constant. Two coaxial diaphragms 1, 2, having the same effective area are connected by a post 3 and mounted respectively in casings 5, 12 integral with a frame 6. The post 3 is connected to an operating lever 20 by links 28 on either'side of the post 3. These links are connected at their upper ends to the post 3 by a pin 29 and at their lower ends to the bifurcated end of the lever 20 by trunnions 30. The bifurcated end of the lever 20 is fixed to a pin 21 mounted in a bearing 22 on the frame 6. The outer end of the lever 20 is adjustably connected with the damper 96 by one of a series of holes. The chamber 18 below the diaphragm 2 is subject to a constant but adjustable fluid loading pressure by means of a regulator 83, whilst the chamber 19 above the diaphragm 1 is subject to an opposing control pressure regulated by a relay valve arrangement 32, Fig. 5. The latter has a housing 33 containing a diaphragm 34 closing a chamber 35 to which a further control pressure is admitted through an opening 37. The diaphragm 34 is loaded by a compression spring 531 acting on a flanged socket 52 and is arranged to operate a valve sleeve 44 working in a housing 38. The sleeve 44 carries a retainer 45 with an exhaust port 47 and a threaded lug 50. A tension spring 48 secured to the lugs 50 surrounds a clamping bolt 51 and maintains a link 53 in engagement with the lug 50 and the bolt 51. The valve sleeve 44 co-operates with the end of a rod 41 carrying an inlet valve 42 controlling the inlet from a constant pressure supply by a pipe 40. A spring 71 aids the valve 42 to close. The control chamber 19 is connected with the housing 38 by a pipe 73. The spring 53<1> also abuts a threaded socket 54 adjustable in a trunnion ring 55 carried by a bifurcated arm 56. An arm 62 carried by the same pin 59 as the arm 56 has a cam follower 64 riding on a cam 63 carried by the pin 21 so as to turn with the lever 20. After a control operation the lever 20 acts through the cam 63, the arm 62 and the spring 53<1> to restore the pilot valve arrangement 42, 44 to its neutral position in which the inlet valve 42 is closed and the sleeve 44 seats on the end of the rod 41. The regulator 83, Fig. 1, comprises a diaphragm 89 to one side 84 of which a constant fluid pressure is admitted by a pipe 85 and on the other side of which is a chamber 90 in free communication with the chamber 18 by a pipe 88. Fluid at constant pressure is admitted to the chamber 90 under the control of a valve 86 operated by the diaphragm 89. A spring 92 adjusted by a knob 95 may assist or oppose the fluid pressure loading of the diaphragm 89 in the chamber 84. A control pressure is admitted to the chamber 35 through a pipe 101, Fig. 2, and the opening 37 under the control of a regulator 97. The latter comprises a diaphragm 98 subject on its under side to the pressure in the combustion space of the furnace and connected to a valve 99 which vents the pressure in the pipe 101 when the pressure in the combustion space rises and increases the pressure in the pipe 101 when the combustion chamber pressure falls, the relay 32 and the diaphragm regulating apparatus ultimately opening the damper 96 in the one case and closing it in the other so that the combustion chamber pressure is maintained substantially constant.