Patent GB-714859-A (GB)
Title: Improvements in or relating to systems for automatically controlling the pressure inenclosed spaces, e.g. aircraft cabins
Inventor: WIDGERY WILLIAM MACEY
IPC: B64D13/04
Filed: 1951-10-15
Abstract: 714,859. Fluid-pressure servomotor-control systems. NORMALAIR, Ltd. Oct. 3, 1952 [Oct. 15, 1951], No. 23985/51. Class 135 In a system for automatically controlling the pressure in an enclosed space, such as an aircraft cabin a having a discharge valve o exposed on one side to the pressure of a control chamber which pressure is regulated conjointly by a differential-pressure-sensitive controller (D.P.S.C.) b and by an absolute-pressure sensitive controller (A.P.S.C.) c so that a predetermined differential of enclosure pressure over the external pressure is not exceeded, both the pressure sensitive controllers are freely exposed to the pressure in the enclosed space and air is admitted to the control chamber by way of a single pilot valve k. The outlet from the control chamber is bled to the atmosphere through an opening r of predetermined area. By this arrangement the cabin or enclosure pressure is not appreciably affected by changes in the air flow through the cabin. In Fig. 2, the control chamber n has one side formed by the back of the valve o the cabin pressure acting on a smaller area of the valve o when it is closed than the control chamber pressure. The chamber n is connected by a pipe m with a pilot valve k opening into the cabin and also by a pipe p and the bleed opening r with the external atmosphere. The connection to atmosphere past the opening r may be bye-passed by a further pilot valve 2. The valves k, 2 are small valves such as tyre inflating valves and are operated by a pivoted beam g adapted to engage in turn the stems of the valves k, 2. The beam g is actuated conjointly by the A.P.S.C. c and the D.P.S.C. b these being mounted on rods w, t adjustable with respect to a fixed structure by cams w, v respectively, e.g. as described in Specifications 602,311 and 602,338. Rods f, e on the controllers c, b respectively pass freely through holes in the beam which is operated on contraction of the capsules of the controllers by pins h, z respectively. Adjustable stops j, x limit the movements of the ends of the beam. When the aircraft is on the ground the valve k is closed and the valve h is held open by the beam g so that as the aircraft takes off the decrease in atmospheric pressure acting in the chamber n causes the valve o to open so that the cabin pressure is substantially equal to atmospheric pressure. As the aircraft climbs, extension of the A.P.S.C. c pivots the beam about the stop x so that the valve 2 first closes and subsequently the valve k is opened. This results in the closure of the discharge valve o. Thereafter the cabin pressure is held substantially constant until at a predetermined altitude the clearance between the beam g and the pin z is taken up so that the beam is moved away from the stop x and the valve k closes. This causes the valve o to open slightly and the subsequent drop in cabin pressure causes further extension of the A.P.S.C. c which re-opens the valve k. Equilibrium is established in this way until the beam is arrested by the stop j. Thereafter control is effected wholly by the D.P.S.C. b as the aircraft continues to ascend. In a simplified form, the controllers b, c are not adjustable, the stop x and the valve 2 are dispensed with, and the beam g is pivoted directly to the rod e. The pressure sensitive controllers and the discharge valve with the ancilliary piping may be mounted externally of the cabin. Also two discharge valves may be arranged in cascade as described in Specification 602,311. Specifications 563,553, 602,339, and 602,340 also are referred to.