Patent GB-717990-A (GB)
Title: Pressure regulating mechanism applicable to pressurized aircraft cabins
IPC: B64D13/02
Filed: 1952-06-25
Abstract: 717,990. Fluid-pressure servomotor-control systems. GARRETT CORPORATION. June 25, 1952 [July 25, 1951], No. 16012/52. Class 135 Means for controlling the pressure in, e.g. a pressurized aircraft cabin, comprises a cabin outlet valve 14 as described in either of Specifications 655,601 or 664,143, and means connected by a conduit 197 with a pressure chamber 27 of the valve and effective to control the rate of change of cabin pressure during ascent or descent until a predetermined pressure is reached, thereafter maintaining the cabin pressure at that value, and to prevent the cabin pressure differential over ambient atmospheric pressure from exceeding a predetermined amount. A control pressure chamber 42 to which the conduit 197 is connected has a restricted opening 51 to the cabin interior and an outlet to atmosphere via a valve 63 actuated by a flexible diaphragm 46, a passage 77, a chamber 80 and a passage 82. The diaphragm 46 separates the chamber 42 from a chamber 45 and the two chambers are interconnected by a passage incorporating a restriction adjustable by a knob 190. Within the chamber 45 is an evacuated bellows 105 which is connected to a lever 109 pivoted at 112 and also, by a spring link 116, to the diaphragm 46. A spring 130 loading the lever 109 is adjustable by a knob 133 which rotates a screwed post 121 to cause axial movement of a spring abutment 126. The knob 133 is also geared to an indicator which shows the cabin altitude for which the mechanism is set. The mechanism is such that, if an aircraft is to fly from, say, an aerodrome at a comparatively low altitude to one at a higher altitude, the knob 133 is set to the higher altitude resulting in contraction of the bellows 105 such that the free end of the lever 109 engages a stop formed by the upper end of the post 121 and a force is applied to the diaphragm 46 through the spring 116 causing the valve 63 to vent the chamber 42 to atmosphere. As altitude is gained the pressure in the chamber 42 falls until the pressure difference across the diaphragm balances the force of the spring 116. The valve 63 is then operated to maintain a substantially constant pressure difference across the diaphragm 46 and, consequently, across the adjustable restriction interconnecting the chambers 42, 45. The pressure in the chamber 42, and, therefore, in the chamber 27 of the outlet valve, is thus caused to diminish at a rate determined by the setting of the restriction between the chambers 42, 45. When the cabin pressure reaches the value corresponding to the altitude set by the knob 133 the bellows 105 will have expanded to operate the valve 63 to maintain constant and substantially equal pressures in the chambers 42, 45. When the final cabin pressure is to be higher than the initial pressure the initial setting of the knob 133 results in extension of the bellows 105 to cause the lever 109 to engage a stop 120. The operation is then the reverse from that described. If, at any time, the aircraft ascends to such height that the cabin pressure differential with respect to ambient atmospheric pressure exceeds a predetermined amount a spring-loaded diaphragm 84 is deflected to cause the pin 95 of a tyre valve carried by it to engage an abutment 97 and vent the chamber 42. Specification 655,616 also is referred to.