Patent GB-570236-A (GB)
Title: Cabin pressure control
IPC: B64D13/04
Filed: 1942-12-08
Abstract: 570,236. Cabin pressure control. BENDIX AVIATION CORPORATION. Dec. 8, 1942, No. 17469. Convention date, Jan. 9. [Class] 135] A pressure cabin control system for aircraft maintains the cabin pressure substantially the same as the external pressure up to a predetermined altitude while below the rated altitude during a rapid climb or descent a second control comes into operation to limit the rate of pressure change within the cabin. Once the rated altitude is reached the cabin pressure is either maintained substantially constant or above the rated altitude is proportionately decreased to avoid .undesirable stresses and the rate of change control rendered effective above as well as below the rated altitude. In the arrangement shown in Fig. 1, a valve 11 adapted to be opened by air pressure acting on a spring-loaded diaphragm 48 to connect the cabin with the external air is controlled by a relay valve 28, itself under the control of a valve 16, 22 actuated by an evacuated bellows 13 subject to cabin pressure and a valve 59, 61, 62 actuated by a capsule 52 subject on the outside to cabin pressure and on the inside to the pressure in an expansion vessel 54 connected with the cabin through a trimmer valve 56 and calibrated restriction 55. The bellows 13 is coupled by a link 281 with an arm 15 carrying a vane 16 adapted to obturate a nozzle 22 supplied with compressed air from a source 29 through pipes 39, 37, 41, 43, 44 and passage 40. The nozzle 22 is carried by a pivoted sector 21 adapted to be adjusted by a knob 27 and its position indicated by a pointer 24 co-operating with a scale 26. A pointer 18 carried by a pinion engaging a sector on the arm 15 indicates the position of the bellows and vane. Below the rated altitude the vane closes the nozzle 22 so that pressure builds up to the left of the piston 31 moving the relay valve 28 against the action of a spring 34 to admit pressure above the diaphragm and open the valve 11. Above the rated altitude the relay valve moves to close the connection between the ports 36, 46 and the chamber above the diaphragm is exhausted through a bleed passage 51 to permit the spring to close the valve 11. The movable part of the capsule 52 is connected by a link 83 with an arm 58 carrying vane 59 co-operating with a pair of nozzles 61, 62 in parallel with the nozzle 22 and a vane 60 co-operating with a nozzle 63 to control a second relay valve 67. The valve, 67 is similar to the valve 28 and controls a diaphragm-actuated switch in the control circuit of a motor driving a blower 12. During a rapid descent the nozzle 61 is uncovered to initiate the closing of the valve 11, while during a rapid climb nozzles 62, 63 are uncovered to initiate the closing of the valve 11 and also stop the blower 12. In the arrangement shown in Fig. 2, an additional control is provided responsive to the differential pressure between the inside and outside of the cabin adapted above the rated altitude to reduce the cabin pressure in proportion to the altitude and also to control the rate of pressure change. When the pressure differential exceeds a predetermined value, a bellows 85 collapses and acts through a lever and linkage mechanism to increase the load on the aneroid 13 and also rotates a vane 88 to close a nozzle 95, thus causing pressure to build up in a capsule 97 to move a valve 100 to the right. This puts the nozzle 62 out of action and puts the nozzle 63 and vane 60 in control of a valve 112 in the conduit supplying air to the nozzle 22 in place of control of the switch relay. With a rapid climb, the nozzle 61 is uncovered to initiate the closing of the valve 11, while with a rapid descent nozzle 63 is covered, causing the valve 112 to close and put the nozzle 22 out of action and close or maintain closed the valve 11. In another arrangement (Fig. 3, not shown), the valve 11 is replaced by a number of valves arranged in parallel and each hydraulically actuated by a pair of opposed bellows under the control of a piston'relay valve actuated by a bellows itself controlled by a relay valve similar to the valve 28. To keep the valves in step, each valve spindle is secured to a pair of bellows interconnected with the bellows on the adjacent spindles, the whole system being filled with liquid. In this arrangement, the relay valve is controlled by a single vane and nozzle actuated by an evacuated capsule stack and a differential bellows arranged in tandem. The inside of this bellows is connected through an adjustable throttle and filter with the outside of the cabin and through a restriction with an expansion chamber. In a modification of this arrangement (Fig. 4, not shown), a device responsive to rate of change of cabin pressure controls the communication between the differential-pressure responsive device and the atmosphere to limit the rate at which pressure changes at altitudes above the critical altitude. In this arrangement, the aneroid capsule stack and the differential bellows are connected to the controlling vane by a floating lever, toothed sector and pinion, and the aneroid is mounted on an adjustable plate. Specification 521,623 is referred to.