GB577349A - Improvements in and relating to aircraft cabin pressure controllers - Google Patents

Abstract

577,349. Fluid-pressure servomotorcontrol systems; valves. CLEVELAND, F. J. (Boeing Aircraft Co.). April 29, 1942, No. 5779. [Class 135] The pressure in an aircraft cabin continuously supplied with air under pressure is maintained at a preselectable constant value or caused to vary at a predetermined, adjustable rate by servo-mechanism acting principally or wholly upon the outflow from the cabin and influenced by the rate of change of cabin pressure, an over-riding control in all cases preventing the pressure difference between the cabin and external air from exceeding a given amount. Reference is made to Specification 521,623 as proposing mechanism for controlling cabin pressure by regulation of intake to and outflow from the cabin, the. present invention providing a simplified form of apparatus for similar purposes. A valve 1 in the outlet conduit 11 from the cabin is controlled by a piston 13 subject to cabin pressure on its underside and open to atmosphere on its upperside through a conduit 16 and the control device shown in Fig. 2. The piston 13 is a loose fit in the cylinder so that there is a continuous flow of air from its under to its upperside. A passage 14 through the valve stem is normally almost closed by a valve 17, but as the cabin pressure rises above the external atmospheric pressure, a piston 18 rises until, at a predetermined pressure differential chosen in relation to the strength of the cabin structure, it encounters a collar on the stem of the .valve 17 and vents the space above the piston 13 to atmosphere through the passage 14 in the valve stem. The valve shown in Fig. 2 comprises a sleeve 31 rotatable within a casing 3 and having a sleeve 33 slidable therein, but keyed thereto to prevent relative rotation. Three pairs of ports 35, 36, as shown in crosssection, Fig. 4, are formed in the sleeves 31, 33, the ports 35 being elongated axially and the inner parts of the ports 36 contracted as shown. The casing 3 has three corresponding ports so that by turning the sleeve 31 by a handle 23 either or both of the two lateral ports may be put into communication with a port 30 leading to atmosphere ; the side ports are connected to the conduits 16, 16<1>. The sleeve 33 is movable axially against a spring 37 by a control knob 24. Co-operating with the ports 36 is a sleeve valve 4 connected to the flexible diaphragm 43 of a chamber 44 having a bleed port 45 so that the diaphragm, which is subject on one side to cabin pressure through a passage 38, is responsive to rate of change of cabin pressure ; by adjusting the axial position of the sleeve 33 the rate of change of pressure may be preselected and maintained at that rate by the action of the diaphragm 43 and valve 4, or the change of pressure may be rendered independent of the action of valve 4. The sleeve may be set to cause a rise or fall of pressure at a selected rate or the pressure may be made constant by selecting a zero rate ; the rate of change is indicated on a dial 22 and the actual pressure on a dial 20, which may be calibrated to indicate apparent altitude. To prevent reverse of flow through the valve 1 should the atmospheric pressure exceed the prevailing cabin pressure during a descent, a valve 19 provides for equalization of pressure on opposite sides of the piston 13 and the valve 1 closes to raise the cabin pressure.