Patent GB-806609-A (GB)
Title: Improvements in or relating to apparatus for controlling the emptying of tanks
IPC: B64D37/20
Filed: 1956-01-18
Abstract: 806,609. Fluid-pressure servomotor-control systems. PARKER APPLIANCE CO. Jan. 18, 1956 [Jan. 24,1955], No. 1692/56. Class 135. The relative rate at which the liquids in the tanks 1, 2, Fig. 1, are discharged is controlled in such a way as to maintain a predetermined relationship of liquid heads within the tanks. The tank 1 discharges directly into the main conduit 6. The liquid from the tank 2 passes via a conduit 4 and a regulating valve 5 to the main conduit 6. Shut-off valves 7, 8 are provided in the conduits 4, 6 respectively. The regulating valve 5 is controlled by a pneumatically-operated differential pressure control device 9 and comprises a casing 65, 66 forming a chamber 68 and having an inlet port 69 from the conduit 4 and an outlet port 70 to the conduit 6. The valve closure member 76 closes against a seat 77 and is carried by a diaphragm 73 attached to a cup-shaped member 71 extending into the chamber 68 and forming a pressure chamber 72 connected by an orifice 81 to the chamber 68. The differential pressure control device 9 comprises a housing within which are fixed'two flexible diaphragms 16, 18 which divide the casing into four pressure chambers 55, 11, 12, 54, Fig. 4. A piston pilot valve member 25 is connected at opposite ends to the diaphragms 16, 18 and moves within a sleeve 19. In operation valves 85, 92, Fig. 1, are opened to admit air under pressure to the lines 84, 87. Air passes from the line 87 through the line 89 into the tank 2 and is maintained at a predetermined pressure, say 5 p.s.i., by a regulator 90. Air also passes from the line 87 through the line 88 to the tank 1 and is maintained at a predetermined lower pressure, say 2 p.s.i., by a regulator 91. The higher pressure in tank 2 prevents back flow from tank 1 to tank 2. Valves 7, 8 are opened and fuel from tanks 1 and 2 pass to main conduit 6. Air under pressure passes from supply line 84 through a filter 40, passages 42, 43, 44, 45 and restricted orifices 46, 47, 48, 49 into pressure chambers 54, 12, 11, 55 respectively. The tank 1 is connected at the top and bottom to pressure chambers 54, 12 respectively by pipes 94, 96. The top and bottom of tank 2 are connected to chambers 55, 11 respectively by pipes 98, 100. The pilot valve 25 determines the rate of flow of air from the supply via lines 84, 86, filter' 31, conduit 33, inlet port 22, outlet port. 34, line 80 into the pressure chamber 72 within the regulating valve. As described, it is desired to have a predetermined constant difference in the heads of liquid in the two tanks and the liquid head in tank 2 is to be maintained at a fixed percentage of the head in tank 1 after allowing for the constant difference. The diaphragm 18 is urged upwardly by a spring 58, the force of which is equivalent to the constant difference liquid head. The relative areas of the diaphragms 16, 18 are selected so that the resultant pressures thereon keep the valve piston 25 in the equilibrium position in which the port 22 is uncovered sufficiently to allow a small flow of air through the port 34 and the line.80 into the pressure chamber 72 from which the air escapes through the orifice 81 into the chamber 68 so that the correct pressure is maintained in the chamber 72 for positioning the valve closure member 76. If too much fuel has emptied from the tank 2 the pressure in the chamber 11 of the control device due to the head of liquid in tank 2 is less than required so that the valve member 25 is moved downwardly to allow more air into the pressure chamber 72 and the increase in pressure in this chamber causes closure movement of the valve member 76 to shut off flow from the tank 2 until the liquid heads in the tanks return to the desired relationship. If the liquid level in tank 1 has fallen too far the pressure in the chamber 12 of the control device 9 falls to allow upward movement of the piston 25 to close the port 22 and the resulting fall in pressure in chamber 72 causes the valve member 76 to move further from its seat 77 and fuel is taken from the tank 2 at a greater rate until the liquid heads in the tanks return to the desired relationship. The only effective fluid pressure acting on each of the diaphragms 16, 18 is that due to actual liquid head in the associated tank. Liquid is prevented from entering the lines 96, 100 by making the velocity of air flow in said lines sufficiently high.