Improvements in or relating to devices for maintaining a predetermined flow relationship between two or more fluid streams of variable mass flow

摘要

731,591. Fluid-pressure servomotor-control systems; valves. ROTOL, Ltd. Oct. 31, 1951 [Dec. 22, 1950], No. 31296/50. Class 135. A device for maintaining a predetermined flow relationship between at least two fluid streams of variable mass flow comprises a conduit for each stream containing a variable constriction controlled by a mechanism which controls all the variable constrictions together to maintain a substantially constant relationship between the areas of the constrictions and a substantially constant pressure drop through one of the constrictions, in combination with a pressure regulating means which includes a pressure regulating valve disposed upstream of the variable constriction in at least one of the conduits and pressure responsive means responsive to difference of pressures immediately upstream of said variable constrictions for controlling said pressure regulating valve or valves to maintain the pressure immediately upstream of said variable constrictions always substantially equal to one another. When one stream is always at a pressure lower than the other or others it may have no pressure regulating valve therein, the pressure of this stream being used as a datum to which the other or others is or are adjusted. As shown, two conduits 10, 12, Fig. 1, are supplied with fuel from two tanks in an aircraft, and contain respectively, non-return valves 17, 127, pressureregulating valves 18, 28 and variable constrictions 19, 29. The two flows meet beyond the constrictions and pass through a common outlet 15. Each valve 18, 28 comprises a stationary disc 21 with ports 22 and a rotary disc 23 with ports 24, the two discs 23 being operated to control the ports differentially by a common shaft 30. The shaft carries a pinion 31 engaged by a rack 32 extending from a piston 47' controlled by a piston valve 34 slidable in the piston and actuated by diaphragms 36a, 36b. The upper surface of diaphragm 36a and the lower surface of diaphragm 36b are subjected respectively to the pressures immediately upstream of the constrictions via conduits 38, 37, the space between the diaphragms being vented to atmosphere. Thus, variation of one pressure with respect to the other causes movement of valve 34 which is followed by the piston 47 to differentially vary the valves 18, 28 and cause equalization of the pressures. The motive fluid for operation of piston 47 is obtained from a chamber 51 connected through a valve 50 and conduits 48, 49 to the inlets of conduits 10 and 12, the valve 50 causing the supply at the higher pressure to pass to the chamber. Should one supply fail, the piston operates to close the valve 18 or 28 of the remaining supply, and in order to permit flow to pass from the remaining supply to the engine, the valve is by-passed. By-passes 64, 65 are controlled by valves 66, 67 respectively, held closed by pressure liquid from the chamber 51 and springs 72, and when the piston moves on failure of one supply, it relieves by lands 70, 71 the pressure from the appropriate by-pass valve which then opens to pass fuel to the outlet. The variable constrictions 19, 29 are constituted by openings 26 in a fixed disc 25 controlled simultaneously by a shutter 27 movable by a pinion 56 engaged by a rack 55 actuated by a piston servomotor 57 similar to that which controls valves 18, 28. The piston valve is controlled by a diaphragm 58 subjected on one face to the pressure at a point 60 in conduit 12 and on its other face to the pressure at a point 62 plus a spring 63. Thus the piston-will control shutter 27 to maintain a constant pressure drop across the constrictions 19, 29 in accordance with the strength of spring 63. The openings 26 are of such shape and dimensions that the mass flows through them are in the desired relationship at all positions of the shutter 27. In another arrangement, rotary sector members 80, 81, Fig. 4, are used in valves 18, 28 and are controlled by a rack 33 fixed to piston 47. Similar sector members 82, 83 are used in the variable constrictions 19, 29 and are controlled by a rack fixed to the piston of motor 57. In this arrangement the by-passes and valves are omitted, and should one supply fail, a diaphragm-actuated valve 88 moves under spring 86 to apply the pressure of the remaining stream to the space 89 between diaphragms 36a, 36b to move them apart against the walls of chamber 39 to thereby centralise valve 34 and thus operate piston 47 to open the valve of the remaining supply. During normal operation, the diaphragm 85 is subjected to the pressure in outlet 15, through conduit 84, to position valve 88 so that said outlet pressure is applied to the space between the diaphragms. In a further arrangement, the diaphragm 85 is held against spring 86 by the lower of the two inlet pressures. In yet another arrangement, two pistons, urged apart by the lower of the inlet pressures against springs, have a lostmotion connection with the diaphragms so that when one supply fails the pistons move towards one another and carry with them the diaphragms to centralise the piston valve 34.