Patent GB-696392-A (GB)
Title: Improvements in or relating to fluid-operated control systems
Inventor: BILYEU GERALD IVAN
Filed: 1951-04-30
Abstract: 696,392. Fluid-pressure servomotor-control systems. FOXBORO CO. April 30, 1951, No. 10091/51. Class 135 In a fluid-pressure servomotor apparatus controlled by a plurality of interdependent variables, each variable controls a unit comprising a bleedtype pilot valve and a follow-up bellows, and the follow-up bellows and the fluid-actuated output motor are supplied in parallel from the same circuit. In an embodiment, a variable pressure is applied to a spiral hollow tube 69 and the subsequent movement of the tube is applied through an arm 70, link 71, a bell crank 78, link 74, floating bell crank 75, link 77, and a floating lever 64 to actuate an arm 66 carrying a spring-loaded plate 50. The latter acts as a baffle plate controlling the bleed from an outlet nozzle 51 of a conduit 52 supplied with air under pressure from a conduit 55 past a restriction 58. The modulated pressure so obtained in conduit 52 is applied to a diaphragm 53 which actuates interconnected supply and exhaust valves 56 controlling a diaphragm motor 83 connected to a valve 84. The pressure applied to the diaphragm is also fed through a conduit 57 to a spring-loaded bellows 59, and the latter acts on a lever 62 which is connected to floating lever 64 whereby the baffle plate 50 will be returned to its normal position. A spring-loaded bellows 90 acting in opposition to bellows 59 and, along with a capacity 94, supplied with pressure fluid from conduit 57 past a restriction 93 gives an integral action to the control. The datum point of the apparatus is set by a knob 81 which rotates a pivoted follower arm 79, and, through a link, moves an arm 73 which carries the pivot shaft of bell crank 75 and is itself pivoted to bell crank 78. In this embodiment. the outlet pressure of a pump is applied to the measuring element 69 and the input pressure is applied to a measuring element 69a of a similar control unit, the conduits 52, 52a containing the modulated pressures from the two units being connected in parallel to the control chamber diaphragm 53. A rise in pressure in element 69 causes a rise in pressure in diaphragm motor 83, but, in the case of the other unit, the bleed valve 50a, 51a is so rotated on its base plate that a reverse action takes place i.e. a rise in pressure in element 69a causes a decrease in pressure in diaphragm motor 83. Valve 84 controls the supply of motive fluid to the motor driving the pump. It will be seen that whichever unit is producing the lowest air bleed resistance will take over control of the relay 53, 56 and motor 83. The apparatus may be applied to the actuation of a valve controlling the supply of energy to an oven heater where the two input variables are the temperatures of the oven and the heater, respectively. In a modification in which there are three interdependent controlling variables, each control unit includes a relay valve structure 53, 56; and two further similar relay valve structures connected in series between the relay 53, 56 of the first control unit and the final output motor are provided. These additional relay valves are controlled, respectively, by the outputs of the second and third units, and it is the final pressure applied to the output motor that is fed back to the follow-up bellows in each unit. Specifications 591,270, 670,419 and U.S.A. Specification 1,897,135 are referred to.