Patent GB-718674-A (GB)
Title: Pressure regulating mechanism for enclosures such as aircraft cabins
IPC: B64D13/02
Filed: 1952-11-03
Abstract: 718,674. Fluid-pressure servomotor-control systems. GARRETT CORPORATION. Nov. 3, 1952 [Nov. 26, 1951], No. 27588/52. Class 135 In mechanism for regulating the pressure in an enclosure such as the aircraft cabin 10, Fig. 1, in which an outflow valve 11 is controlled by the pressure in a control pressure chamber 22, Fig. 2, the pressure in the chamber 22 is controlled by pressure ratio control means 145 responsive to the ratio of the control chamber pressure to the ambient atmospheric pressure so as to maintain in one range of operation a predetermined ratio between these pressures and is also controlled by differential pressure control means 240 responsive to the differential between control chamber pressure and ambient atmospheric pressure so as to maintain in another range of operation this pressure differential at a predetermined value, both these control means controlling a passage connected to the control chamber 22. The differential pressure control means 240 maintains a relative low pressure differential suitable for use under combat conditions at high altitude. The mechanism is also provided with an isobaric control 38 and a high differential pressure control 85. A rate of pressure change control is also provided to prevent the control chamber pressure and therefore the enclosure chamber pressure increasing too rapidly on changing from ratio or low differential pressure control back to high differential pressure control. Means are also provided for rendering the pressure ratio control and the low differential pressure control effective or ineffective. When the said controls are effective, the rate of pressure change control is rendered ineffective. The outflow valve 11 is as described in Specifica- . tion 664,143 and its control chamber 20, Fig. 1, is connected by a pipe 21 to the control chamber 22 of a control unit 23 formed with a base 26 on which the isobaric control 38, the pressure ratio control 145, and the two differential pressure controls 85, 240 are mounted. These four controls are generally similar each having a pressure responsive element connected to a rocking lever which is loaded' by an adjustable tension spring and operates a metering or leak off valve connecting the control chamber 22 directly or indirectly with the atmosphere. The chamber 22 is directly connected to the interior of the cabin through a bleed hole 35 in a plug 36, Fig. 5. The isobaric control 38 has an evacuated or gasfilled bellows 39 loaded internally by a spring 50 and prevented from collapsing by a tubular stop 46 with apertures 48. The lower end of the bellows is adjustably screwed to the base 26 and the upper end is connected by a hook 44 to a channel-section rocking lever 45. The lever 45 carries a knife edge 54 supported in a fulcrum block 58 which is itself carried by a generally L-shaped plate 59 mounted on studs 60 attached to the base 26. The lever 45 is loaded by a tension spring 75 the lower end of which is fixed to a retainer 78 mounted on a screwed adjusting spindle 79. The retainer 78 is prevented from rotating when the spindle 79 is adjusted by an arm having a notch which engages a pin fixed in the base 26. The metering or leak-off valve comprises a ported seat member 67 screwed into the base 26 and having a central outlet passage 68 controlled by a valve member 66 guided in the seat member 67. The valve 66 has a stem 65 the rounded end of which is pressed into a recess in the lever 45 by a light spring 71. The passage 68 communicates with a passage 83 leading directly to the atmosphere. The high differential pressure control 85 has a metering valve 121, a rocking lever 105, and adjustable tension spring 127 all generally similar to the corresponding parts of the isobaric control. The rocker arm 105 is connected by a hooked stem 97 to a diaphragm 86 exposed on its upper side to the pressure in the chamber 22 and having at its lower side a chamber 88 connected directly to the atmosphere through the passages 89, 90. The fulcrum 111 of the lever 105 is carried on an' apertured plate 99 mounted on studs 100. The chamber below the valve 121 communicates with the atmosphere through passages 139, 83a. The corresponding parts of the low differential pressure control comprises a metering valve 278, a rocking lever 261, an adjustable tension spring 293, a fulcrum member 257 on a plate 252, a hooked stem 250, and a differential pressure responsive diaphragm 241 the chamber 245 below which communicates with the atmosphere through the pipe 90. The outlet chamber 280 of the metering valve 278 communicates with the atmospheric passage 83 through a passage 281, the metering valve 200 of the pressure ratio control 145, a solenoid-operated valve 284 and elbows 288, 286, Fig. 4. The pressure ratio control 145 has besides the metering valve 200, a tension spring 225 and a rocking lever 181 supported on a fulcrum 160 carried by a plate 161 supported on studs 162. A knife-edge 185 engaging the fulcrum 160 is carried on a plate 181 secured to the lever 182 and having an extension with a stirrup 180 on its under side. The stirrup is connected by a pin 178 to two vertical arms 177 supported on the upper plate 152 of a diaphragm assembly on which is adjustably mounted a spring-loaded evacuated bellows 159 the head 160 of which is secured to the fixed plate 161. The chamber 147 below the diaphragm 146 is connected to the atmosphere by passages 147a, 89, 90. The stem 195 of the valve 200 is sealed by a flexible boot 218. The rate of pressure change control which controls the rate of repressurization inc!udes a chamber 31 above the chamber 22 and connected thereto by a calibrated orifice 310. The wall 30 between the chambers 22, 31 has an aperture 311 which is closed by a diaphragm 312 loaded by a spring 345. When the pressure in the chamber 22 increases faster than the orifice 310 can equalize the pressure in the chamber 31, the diaphragm 312 is moved upwardly allowing a valve 335 loaded by a light spring 340 to open and connect the chamber 22 through a solenoid operated valve 326 to the passage 83 and hence to the atmosphere so that the increase in pressure in the chamber 22 and hence in the cabin is halted. The valves 284, 326 are similar each being closed by a spring and opened on energizing its solenoid. The solenoids are arranged in parallel across a battery 370. Only one of the solenoids can be energized at once due to the provision of a two-way switch 372. The circuit 379 of the valve 326 also contains a micro-switch 376 mounted on a U-shaped leaf spring 390, Fig. 6, and opened by the rocking lever 261 of the low differential pressure control 240. When the switch 372 is in the "combat"  position engaging the fixed contact 381, the pressure ratio control 145 and the low differential pressure control are fully effective at high altitudes since the valve 284 is open. The rate of pressure change control however is ineffective as no current is being supplied to the fixed contact 374 and therefore to the valve 326. When the switch 372 is changed over to engage the contact 374, the valve 326 is only opened if the micro-switch 376 is engaged and this only occurs when the pressure differential between the chamber 22 and the atmosphere is so low that the rocking lever 261 fails to engage the plunger 404 of the micro-switch 376. The rate of pressure change control is 'thus effective only during the transition from combat operation, i.e. under low differential pressure or pressure ratio control; to normal high differential pressure operation. Spaces 406, 407 between a top plate 410 of the unit 23 and the top 30 of the chamber 22 facilitate mounting of the unit. Specification 521,623 also is referred to.