Patent GB-622283-A (GB)
Title: Improvements in and relating to pressure cabin controls for aircraft
IPC: B64D13/04
Filed: 1942-07-21
Abstract: 622,283. Fluid-pressure servomotor-control systems. BOEING AIRCRAFT CO. July 21, 1942, No. 15704/46. Convention date, Oct. 18, 1941. Divided out of 621,669. [Class 135] A valve controlling the outflow from an aircraft pressure cabin is controlled in such manner that above a datum height at which the cabin pressure and the surrounding air pressure are equal, any further drop in cabin pressure is proportional to the corresponding drop in atmospheric pressure. This is effected by a pressure responsive member such as the diaphragm 52 which is subject over a relatively large area at one side to the cabin pressure and over a relatively small area.at its other side to a pressure intermediate between the cabin pressure and the pressure of the surrounding atmosphere. The construction of the valve 1, its diffuser outlet 2, its actuating diaphragm 13, the differential pressure control piston 4, the control valve seat 34 and its re-setting lever 35 are fully described in Specification 621,669. The absolute pressure - responsive device is modified, however, by dividing the casing 39 containing the evacuated bellows 3 into two chambers 58, 59 by a diaphragm 52. The chamber 58 is exposed to cabin pressure through a port 53 whilst the chamber 59 which contains the bellows 3 is connected to cabin pressure by a small fixed orifice 51 and to atmospheric pressure by a pipe 55 containing an adjustable valve 56. With the latter closed, the apparatus functions as an absolute pressureresponsive control as described in Specification 621,669. With the valve 56 fully open, the pressure in the chamber 59 is substantially the same as the surrounding atmosphere, but as this acts on a much smaller area of the diaphragm 52 than the cabin pressure, the latter continues to maintain the control valve pin 33 and hence the main valve 1 open until the pressure in the chamber 58 can no longer balance that in the chamber 59 plus the force of the spring 30 and that due to the resilience of the bellows itself. When this occurs, the control valve 33 closes and pressure builds up in the chamber 24 so that the main valve closes and so allows the cabin pressure to build up again to a value which will balance the pressure in the chamber 59. As the valve 56 is closed, the pressure in the chamber 59 will approach cabin pressure and the ratio of the drop in cabin pressure to the drop in the pressure of the surrounding atmosphere will decrease. This ratio is a maximum when the valve 56 is fully open. The pressure at which proportional regulation of the cabin pressure commences may be altered by adjusting the base 38 of the bellows by a nut 5. Under all circumstances, the differential pressure control piston 4, also described in Specification 621,669, takes over control of the valve 1 when the difference between cabin pressure and the surrounding atmospheric pressure exceeds a critical value. Specifications 521,623 and 621,670 also are referred to. The Specification as open to inspection under Sect. 91 refers to the adjustment of the valve 56 in accordance with an altitude factor and also to the connection of the chamber 59 through valves to one or more separate air chambers to control the rate of change of cabin pressure. This subject-matter does not appear in the Specification as accepted.