Patent GB-820667-A (GB)
Title: Aircraft cabin air conditioning system
IPC: G05D23/185
Filed: 1957-04-02
Abstract: 820,667. Fluid-pressure servomotor control systems. GARRETT CORPORATION. April 2, 1957 [May 2, 1956], No. 10702/57. Class 135. A fluid-flow system comprises a control passage communicating with a pressure-responsive actuator for operating a control valve, and a pair of bleed valves in communication with the control passage for varying the pressure applied to the actuator, one of these valves being thermostatically operated and the other responsive to fluid pressure, means being provided for selectively placing either valve in primary control of the pressure in the control passage. The invention is described as applied to a temperature control system for the air supply to an aircraft pressure cabin, in which the air is delivered through a duct 10 containing a heat-exchange cooler 11 and cooling turbine 12, respectively provided with by-passes 14, 15 and butterfly control valves 16, 17 operated by actuators 21, 24. Upstream of valve 16 a pressure supply pipe 26 communicates with a control pressure regulator 22 formed with upper and lower chambers communicating through an orifice 23, and connected by pipe-lines 25, 27 to a pneumatic pressure controller 44 and switching valve 29. Extensions 59, 82 of pipelines 25, 27 respectively communicate with a thermostatic valve 60 in the duct 10, and with the underside of a diaphragm 77 operating valve 60 through lever 74. The switching valve 29 determines whether the system operates under automatic or manual control, while valve 44 determines the regulated pressure in pipe-line 25, being provided with a passage 35 communicating with atmosphere through a bleed passage 46 controlled by a valve 45 attached to a diaphragm 48, the upper surface of which is subjected to ambient air pressure through a passage 46a and to the force of a loading spring 51 controlled by a manually adjustable regulator 52. The thermostatic valve comprises a spring-loaded ball element 68 carried in a cage which may be raised or lowered by the end 73 of lever 74 in response to movement of the diaphragm 77, and a seating 69 movable by the differential expansion of thermal elements 61, 62 in the air duct 10. For automatic control the manual lever 40 of valve 29 is set in the left-hand (full line) position, in which condition a ball valve 36 cuts off communication between passage 35 and pipeline 25, and establishes communication with pipe-line 27, whereby the underside of diaphragm 77 is subjected to the regulated pressure in the passage 35 as determined by the setting of regulator 52, and the thermostatic valve 60 bleeds off pressure from pipe-lines 25, 59 through a leak-off passage 70. Control is thus exercised solely by valve 60 in accordance with movements of seating 69. For manual control the lever 40 is moved to the right-hand (dotted) position whereby valve 36 cuts off pipe-line 27 from passage 35, and the full pressure in line 27 is applied to the underside of diaphragm 77 which is thus forced to its uppermost position so that lever arm 73 causes ball element 68 to engage seating 69 and thus prevent flow from pipe-line 59, the pressure in pipe-lines 25 and air temperature accordingly being governed solely by the setting of hand regulator 52. Under these conditions valve 60 remains closed until the temperature of the air supply reaches a predetermined value when the expansion of element 61 causes the valve seating 69 to move away from ball element 68 to allow bleeding from pipe 59 and the closing of valves 16, 17. The arrangement is such that valve 16 closes before valve 17, so that air cooling is effected primarily by the heat exchanger 11, the turbine 12 being brought into operation only when additional cooling is required.