Patent GB-796320-A (GB)
Title: Mechanism for controlling the pressure in an enclosure
IPC: B64D13/02
Filed: 1955-01-18
Abstract: 796,320. Fluid-pressure servomotor-control systems. GARRETT CORPORATION. Jan. 18, 1955 [Feb. 5, 1954], No. 1479/55. Class 135. Pressure-control mechanism for an enclosure 10 such as an aircraft cabin comprises two pressure chambers 37, 38 in restricted communication, valve means 43 for controlling the pressure in the chamber 38, a pressure-responsive element, such as the diaphragm 39, responsive to the difference of pressure between the chambers 37, 38 for controlling the valve means, and pressure ratio control means co-operable with the pressure responsive element to control the valve means. The chamber 38 is connected with the enclosure 10 through a calibrated orifice 42 and with the atmosphere through the valve means 43 and a pipe 60. The chamber 38 is also connected with the control chamber 27 of a cabin outflow valve 15 through a pipe 67. The valve 15 is of the kind described in Specification 664,143, but may alternatively be of the kind described in Specification 655,601. The valve means 43 comprises a casing 44 containing a valve seat member 46 adjustable by means of an integral screw 49 carrying a lock-nut 51. A needle valve member 57 connected to the diaphragm 39 by a stem 56 controls a passage 47 in the seat member. The restricted communication between the chambers comprises a rate selector valve 130 having a passage 131, 134 controlled by a throttling pin 139 with an enlarged threaded part adjustable from outside the chamber 37 by a knob 140. The pressure ratio control means acts on the valve stem 56 through a spring link 78 and comprises an absolute pressure responsive device in the form of an evacuated bellows 90 anchored at its upper end to a wall of the chamber 37 and a differential pressure responsive device in the form of a bellows 70, the outside of which is exposed to the pressure in the chamber 37 and the inside of which is connected with the ambient atmosphere through a pipe 73. The bellows 70 acts directly on the spring link 78 through a stem 76 having a knife edge 75 and bearing an adjustable spring abutment 85. The bellows 70 is loaded by a spring 86 acting on the abutment 85 and the compression of the spring 86 is adjusted by the bellows 90 acting through a pair of substantially parallel levers 96, 81. The lever 96 has a fixed pivot 98 at one end and the bellows 90 is connected to the lever 96 by a pivot 97. A spring 100 adjustable by a knob 111 from outside the chamber 37 is connected to a sleeve 103 adjustable on the end of the lever. The other lever 81 has a central pivot 82 and acts on the loading spring 86. The levers are connected by a fulcrum device 115 adjustable from outside the chamber 37 by a knob 121 on a rod 120. The device 115 comprises two rings 116, 117 of triangular section secured to a diaphragm 119 mounted eccentrically with respect to the rod 120 so that as the latter is turned, the points of application of the rings 116, 117 on the levers 96, 81 respectively are moved horizontally. Counterclockwise movement of the lever 96 is limited by a stop 112. Clockwise movement may be limited by a stop within the bellows 90. The pressure at which the control is to commence, usually that at the take-off airfield, is determined by the setting of the knob 111. The pressure ratio to be maintained is determined by the setting of the knob 121. The maximum permitted rate of change of cabin pressure is determined by the setting of the knob 140. The rate of change control overrides the pressure ratio control in the event of the change in altitude of the aircraft being too rapid for the set rate of change of cabin pressure. Below the altitude at which the control becomes operative, the bellows 90 has no effect on the spring 86 which merely presses the lever 81 against the knife-edge 75 adjacent an aperture 80 in the lever. When the end of the lever 96 engages the stop 112, the bellows 90 becomes inoperative and further control is by the differential bellows 70 alone. Specification 796,321 also is referred to.