736,731. Fluid - pressure servomotor - control systems. BAILEY METERS & CONTROLS, Ltd. May 22, 1953 [May 22, 1952], No. 14514/53. Class 135. A fluid pressure relay comprises a first fluid pressure responsive means such as the bellows 71 responsive to the fluid pressure between a fluid pressure source and a pressure controlling means including a baffle element 28 and a nozzle element 32, one of which is adjustable by a control element, valve means 80, 82 operated by the first fluid pressureresponsive means to establish a fluid output pressure and adapted to be closed when the fluid pressure applied to the first fluid pressureresponsive means has a predetermined value, and second fluid pressure responsive means such as the bellows 50 adapted under the influence of the output pressure to move the other element of the pressure controlling device whereby the output pressure is stabilized at a value corresponding to the position of the first of the elements. In Fig. 1, the fluid pressure relay is embodied in a pressure transmitter 1 sensitive to variations in pressure in a pipe 2 and adapted to transmit a loading pressure to a diaphragmactuated valve 3 in a conduit 4 which forms part of the system including the pipe 2. The pressure in the pipe 2 acts on a Bourdon tube 9, Fig. 2, anchored to a fixed block 7. The free end 10 of the Bourdon tube is connected to a pointer 13 mounted on a fixed pivot 14 and movable over a scale 16. A U-shaped arm 21 is fastened to the head 19 of the pointer 13 and a link 22 connects the free end of the arm 21 to a baffle arm 23 having a leaf-spring pivot 24. The angular movement of the arm 23 relative to that of the pointer 13 may be adjusted by a screw 26. The arm 23 carries a baffle element 28 normally spring-urged against a stop 29. The nozzle element 32 which co-operates with the baffle 28 is adjustably mounted on an arm 39, Fig. 4, similar to the arm 23 and having a leaf-spring pivot 40. The free end of the arm 39 is connected to a pointer 35 also mounted on the pivot 14 and movable over the scale 16. The arm 39 has an extension 43 to which is adjustably anchored one end of a tension spring 45, the other end of which is connected to a fixed bracket 48. The free end of a bellows 50 also engages the extension 43, and the spring 45 tends to move the nozzle 32 towards the baffle 28 against the pressure within the bellows 50. The latter is anchored to the bracket 48 and its interior is connected by a pipe 54 to the relay 55. The nozzle 32 is connected to the relay 55 by a pipe 51. Fig. 5 shows the relay 55 diagrammatically. It comprises three chambers 61, 62, 63. The chamber 63 is connected directly to a supply of compressed air by a pipe 56 and the chamber 62 is connected to the same supply through a restricted orifice which may be cleared of dirt or other matter at any time by a spring- retracted plunger 86 carrying a needle. The chamber 63 is connected to the chamber 61 through a tubular arm 67 having a passage 66 the outlet of which is controlled by a valve 80. The valve 80 is rigid with a further valve 82 controlling the outlet of the chamber 61 to atmosphere. A spring 85 seats both valves against the pressures to which they are exposed. The chamber 61 is connected to the output pressure conduit 18 leading to the valve 3, and also through the pipe 54 to the bellows 50. The tubular arm 67 is pivotally supported by a diaphragm 68 and is linked to a lever 75 similarly supported by a diaphragm 76. One end of the lever 75 is connected to the free end of the bellows 71 which is loaded by a spring 72. In the practical embodiment of the relay shown n Fig. 7, 'the spring 72 is arranged between discs 100, 101 and is adjustable by means of an, externally and internally threaded sleeve 105 in which is mounted a screwed spindle 104 with flanges 102, 103 for limiting the movement of the disc 100 and hence of the bellows 71. A filter is arranged in the relay 55 at the connection for the pipe 56. A selector 5 is arranged between the pressure transmitter 1 and the valve 3 to permit of automatic control of the valve 3 in dependence on the output pressure or remote manual control from the selector. The pressure transmitter may respond to other variable conditions such as flow, temperature, relative humidity, or electromotive force.