Patent GB-713254-A (GB)
Title: Improvements in or relating to means for controlling the pressure in an enclosure such as an aircraft cabin
IPC: B64D13/02
Filed: 1951-03-19
Abstract: 713,254. Fluid-pressure servomotor-control systems. GARRETT CORPORATION. March 19, 1951 [April 7, 1950], No. 6494/51. Class 135 In pressure regulating means for an enclosure such as the aircraft cabin 11 which include a control pressure chamber and pressure ratio control means for maintaining in one range of operation a predetermined ratio between the pressure in the control pressure chamber and the ambient pressure external to the enclosure, means are provided for rendering the pressure ratio control means ineffective. In Fig. 1, air is supplied to the cabin 11 by a supercharger 10 or a ram, and is vented therefrom through an outlet 8 under the control of a pressure regulator similar to that described in Specification 648,002 and comprising a valve 17 actuated by a spring-loaded diaphragm 22 subject to cabin pressure on one side and to the pressure in a control chamber 24 on the other side. The chamber 24 has a restricted connection 34 with the cabin. The control chamber pressure is controlled by an isobaric control unit 28 and a combined differential pressure and pressure ratio control unit 29. The isobaric unit 28 comprises an aneroid controlling a leak-off valve 31, the outlet of which leads to atmosphere through a pipe 33 and the outlet 8. The unit 29 operates a similar leak-off valve 36 controlling an outlet pipe 37. The valve 36 is carried on a spring- loaded lever 39 connected by a link 42 to a diaphragm 43 supported by a coupling member 44. The diaphragm 43 is exposed to the control chamber pressure on one side and its other side is connected to the atmosphere through a pipe 45. The diaphragm 43 carries an adjustable screw 51 engaged under certain conditions by the head 50 of an evacuated bellows 46. Under these conditions, i.e. when the pressure in the chamber 24 is sufficiently low, the pressure ratio control is effective. This control is rendered ineffective by the forked end 81 of a lever 77, Fig. 2, engaging the head 50 of the bellows 46. The lever 77 is connected by a rod 75 to a diaphragm 64 which divides a casing 60 into chambers 65, 66 The chamber 65 is open to the control chamber 24 through a passage 67 and ports 83 whilst the chamber 66 has a restricted connection 84 with the cabin and has a vent 85 to atmosphere controlled by a valve 61. The valve 61 comprises a spring-closed valve member 91 which is opened by the energization of a solenoid 95 on closure of a manual switch 100. To change from the differential pressure control to the pressure ratio control, for instance in the case of an aircraft in combat, the switch 100 is opened so that the valve 91 closes and air bleeds gradually into the chamber 66 through the connection 84. The diaphragm 64 aided by a spring 71 moves to withdraw the forked end of the lever 77 from the head of the bellows 46. When the switch 100 is closed again, the change from ratio control to differential control is rapid due to the rapid venting of the chamber 66. Figs. 3 and 4 show the application of the invention to a regulator similar to that described in Specification 656,256 and comprising a main valve 124 controlling an outlet throat 122 and actuated by a diaphragm 127 under the varying pressures in a control chamber A. The pressure in the control chamber A and therefore in the cabin is controlled at appropriate stages by an isobaric control unit 145, a differential pressure control unit 146, and a pressure ratio control unit 147. Each of these units comprises a pressure responsive device operating a pilot valve comprising a valve pin such as 205 movable in a seat or sleeve such as 203 itself slidable in a valve casing or guide such as 201. The sleeves are movable to follow-up the movement of their respective valve pins and so close the pilot valves under the action of levers such as 175a, 175b pivoted on the pilot valve casings and having forked ends 199 engaging the rim of a disc 180. The disc 180 is carried by a hub member 131 and moves with the diaphragm 127. The pressure responsive device of the isobaric unit 145 comprises an evacuated bellows, that of the differential pressure control unit 146 a spring-loaded diaphragm 185 exposed to cabin pressure on its under side and to atmospheric pressure on its upper side, and that of the pressure ratio control unit 147 a spring-loaded diaphragm 215 subject to atmospheric pressure over substantially the whole of its under side and subject to cabin pressure over an annular area on its upper side surrounding an evacuated bellows 216. The bellows is adjustably anchored at its upper end and at its lower end is clamped in contact with the diaphragm 215. The pressure ratio control becomes operative when the cabin pressure acting over the annular area is sufficiently large as to overcome the atmospheric pressure acting on the underside of the diaphragm 215 and so displace a washer 217 from a shoulder 226 and open the pilot valve pin 205. The pressure ratio control can be rendered inoperative at will by the upward movement of the pilot valve sleeve 203 by the forked end of a lever 261. The lever 261 has a pivot 262 and is operated by a spring- loaded diaphragm 253 dividing a casing 251 into two chambers 254, 255. The chamber 254 is open to the cabin through openings 267. The chamber 255 has a restricted connection 268 with the cabin and may be selectively connected with the atmosphere through a solenoid-operated valve 271 similar to the valve 61, Fig. 2, and controlled by a manual switch 100. The valve 61 may be arranged so as to be normally open and closed by the energizing of the solenoid. In a further modification of the means for rendering the ratio control inoperative, a spring-loaded diaphragm which at one side is exposed to control chamber pressure is selectively connected on its other side with the atmosphere or with the cabin through a rotary valve which may be actuated by a solenoid under the control of a manual switch. The connection to atmosphere has a restricted orifice therein. Specifications 521,623 and 628,455 also are referred to.