GB793798A - Improvements in or relating to fluid flow limiting device - Google Patents

Abstract

793,798. Fluid-pressure servomotor control systems; valves. GARRETT CORPORATION. April 15, 1955 [April 28, 1954], No. 10887/55. Class 135. A fluid flow limiting device, more especially for controlling the outlet from an expansion turbine which feeds a pressurized aircraft cabin, comprises a valve in the form of a resilient, helical tube 61 situated at the outlet from the turbine 11 and controlling the escape of fluid through outlets 35, the tube being compressed to close the outlets by a diaphragm 53 under the control of a pilot valve 77 which is actuated by a pressure-responsive diaphragm 73 subject on its upper surface to pressure at the throat of a venturi 42 and on its lower surface to a reference pressure derived from a point upstream of a venturi 30 in a branch passage 25 and passing through a valve 104 which is actuated by an evacuated bellows 108 so as to compensate for variations of density of the controlled fluid. The pilot valve 77 controls the supply to a chamber 52, which has a restricted outlet 101, of fluid tapped from the inlet 12 to the turbine and pressure-controlled by a valve 116. Flow in the passage 25 is also controlled by a butterfly valve 28 which is actuated by a diaphragm 138 under the control of a pilot valve 128 which is operated by a diaphragm 12 0 subject on its upper surface to pressure at the throat of the venturi 30 and on its lower surface to the pressure from the valve 104. An adjustable restriction 126 interconnects the two sides of diaphragm 120. The arrangement is such that an increased flow through the branch 25 causes the butterfly valve 28 to be moved towards closure whilst an increased flow in the passage 18 causes the helical valve 61 to open to spill fluid through the outlets 35. In a modification, the reference pressure which acts below the diaphragm 73 is taken from a point upstream of the throat of the venturi 42.