GB672929A - Improvements in or relating to a pneumatic valve - Google Patents

Abstract

672,929. Fluid-pressure servomotor-control systems. GARRETT CORPORATION. June 10, 1949 [June 18, 1948], No. 15505/49. Class 135. A pressure regulating mechanism for controlling the pressure within an enclosure such as a pressurized aircraft cabin 10 comprises a valve seat 52 having an opening 20 between the enclosure and the atmosphere, a casing 23 forming a pressure chamber 25, pressure responsive means including a flexible sealing element 49 and a valve member 40 with a part 42 projecting towards the valve seat and cooperable therewith, one side of the pressure responsive means being exposed to the pressure in the pressure chamber and the other side to enclosure pressure, a fixed member 30 and flexible seating means 48 connecting the fixed member and the pressure responsive means. The flexible sealing element 49 and the flexible sealing means 48 each form part of a single diaphragm 38 which extends across the top of a valve body 15 and is secured at its inner periphery to the fixed member 30, and at an intermediate point to the valve member 40. The fixed member 30 is of disc-like form and is carried by a hub 31 which is secured by a bolt 32 to a spider 21<SP>1</SP> in the opening 20. The annular part of the diaphragm 38 is bolted between a rigid annular clamping plate 44 and a flange 41 on the valve member. The enclosure pressure acts through openings separated by struts 18 on the valve member 40 and the flexible sealing element 49. The projecting part of the valve member is frustro-conical in shape and terminates in a knife edge 43. The pressure in the pressure chamber acts on an annular area of the diaphragm 38 denoted by the dimension A. A light spring 53 also tends to close the valve. When the valve is closed, the valve assembly is balanced as regards atmospheric pressure. Fig. 4 shows a modification in which the'clamping plate 44 is replaced by a shell 96 which forms with the central part of the diaphragm 85 held between discs 83 on a post 82, an auxiliary pressure chamber 103. The latter is connected by a passage 104 passing through the shell 96, the diaphragm 85, and a flange 99 on the valve member with openings 106 leading to the enclosure. Thus the pressure in the control chamber 92 is effective over the whole of the upper surface of the valve assembly comprising the shell 96 and the diaphragm convolution 115 whilst the enclosure pressure is effective over an equal area comprising the convolution 115, the flange 99, the frustro-conical portion 107 of the valve member 98 and the area of the shell 96 within the projection of the valve knife edge 108. This construction enables valves of smaller diameter to be used for a given range of pressure. In either case, a pipe 27 connects the control chamber with a regulator chamber 57 connected with the enclosure through a restriction 64. The chamber 57 contains two needle valves 61, 71 communicating with the atmosphere through passages 62, 72 respectively and a pipe 63. The valve 61 is opened against the force of an adjustable spring 65 by the control or regulating chamber pressure acting on an evacuated bellows 60. A screw 66 which adjusts the pressure in the isobaric range may be adjusted during flight in accordance with a predetermined flight plan. Similarly in the differential pressure range, the control chamber pressure is regulated by the valve 71 connected to a bellows 70 exposed to atmospheric pressure internally through the pipe 63 and to the regulating chamber pressure externally, the pressure differential which is maintained being adjusted by a screw 74 connected to a spring 73.