GB772689A - Dual differential pressure regulating control suitable for pressurized aircraft cabins - Google Patents

Abstract

772,689. Fluid-pressure servomotor control systems. GARRETT CORPORATION. March 7, 1955 [March 26, 1954], No. 6595/55. Class 135. Means for controlling the pressure in an enclosure such as a pressurized aircraft cabin comprises a control unit with means to limit the rate of change of cabin pressure and also two differential - pressure responsive means, whereby the cabin pressure above a certain altitude may be controlled at a high or a lowdifferential pressure. A pressurized aircraft cabin 10 is supplied by a supercharger 11 and an outlet 18 from the cabin is controlled by a valve 14, e.g. of the kind described in Specifications 655,601, 664,143, or 672,929 the control chamber 27 of the valve being connected by a conduit 211 with the control unit. More than one outflow valve may be controlled by a single control unit. The control unit has a chamber 42 with a restricted connection 51 with the cabin and a restricted passage 190 communicating with a second chamber 45, the passage 190 being controlled by a valve 196, e.g. as described in Specification 717,990; having an adjusting member 210, The chambers 42, 45 are separated by a flexible diaphragm 46 to which is connected a control valve 63 and an evacuated. bellows 150. The bellows is connected to the diaphragm through a spring 160 and is also connected to a lever 154 pivoted at 156 and loaded by an adjustable spring 177. Adjustable stops 166, 168 for the lever are provided. At ground level the bellows 150 is compressed by atmospheric pressure in the chamber 45 so that the valve 63 is open whereby the chamber 42 is vented through passages 75, 77, a chamber 80, and a passage 82, 83. At a certain altitude the bellows 150 will expand and move the valve 63 towards closure to maintain a constant cabin pressure up to a second predetermined altitude at which the atmospheric pressure will have fallen to such a value that the value 63 is completely closed and a diaphragm 84 in the chamber 80 moves upwardly against a loading spring 101 to cause a valve 91 to engage an adjustable abutment 97 whereby the valve 91 is opened to vent the chamber 42, the valve 91 thereby maintaining the chamber 42 at a constant differential pressure with respect to atmospheric pressure. Should it be desired to maintain the cabin pressure at. a lower differential a switch S is closed, energizing a solenoidoperated valve 125 so as to open the chamber 120 to atmosphere through the passage 83 whereby a second diaphragm-actuated valve 133 controls the venting of the chamber 42 to maintain the lower differential pressure. The diaphragm 46 and the restricted passage 190 interconnecting the chambers 42, 45 limit the rate of change of cabin pressure under certain circumstances. The closure member 16 of the outlet valve 14 may be held positively open by an electric actuator 240 which is controlled by a relay 222 under the control of a switch 229 actuated by the landing gear of the aircraft and of a manually actuated switch 235. The relay 222 also controls a solenoid-actuated valve 217 in a passage 215 interconnecting the chambers 42, 45. Thus the valves 14, 217 are opened when either of the switches 229, 235 is closed. The valve 217 equalizes the pressures in the chambers 42, 45 so that the rate of change control operates correctly should pressurization be initiated after a period when the outlet valve 14 has been held open.