Patent GB-1336639-A (GB)
Title: Fluid flow control apparatus
IPC: F02C7/236
Filed: 1971-04-19
Abstract: 1336639 Centrifugal and gear pumps; jet propulsion engine fuel systems CHANDLER EVANS Inc 19 April 1971 [9 March 1970] 23552/71 Headings F1C F1F F1G and F1J Fluid is supplied to two loads by two circuits, one containing a high flow centrifugal pump and the other a low flow centrifugal pump, an input flow being directed to either circuit by a selector, the selector being controlled by a signal generated by a signal generator which is controlled by means responsive to the total flow delivered to the loads. The gas turbine engine fuel system shown comprises a gear pump 42 which supplies fuel during acceleration up to ground idling speed, the fuel passing from an inlet conduit 20 via a conduit 22, a jet pump 24, a conduit 36, an enclosing valve 40, and a conduit 38 to the gear pump, which delivers it via check valve 66 to the fuel delivery line 68. The jet pump, which is unenergized at this stage, is traversed in reverse direction. The delivery line 68 is connected, via respective metering valves (not shown), to the main combustion chamber and reheat burner, the pressure drop across each metering valve being maintained constant by a throttle valve subjected to the pressure drop. The pressures downstream of the two metering valves are directed to a valve (not shown) which selects the higher of the two pressures, this pressure, designated P 2 , together with the pressure P 1  in the line 68, being applied to the unloading valve 40 and also to a regulator valve 192. At this stage, the reheat burner is out of use, and the pressure P 2  is consequently equal to the pressure downstream of the main metering valve. The pressure P 1 -P 2  is maintained constant by by-passing fuel back to the inlet of the pump 42 via the valve 192. When a speed slightly below ground idling is reached, a speed signal applied via a conduit 90 opens a shut-off valve 78 to permit fuel to flow to a selector valve 104. If the valve 104 is in the position shown, it directs the fuel to a two-stage centrifugal pump 134, 138 which then begins to deliver the fuel via a check valve 72 to the delivery line 68. The consequential increase in the pressure differential P 1 -P 2  opens the valve 192 fully and operates the unloading valve 40 to block the inlet flow to the pump 42 and establish a flow via a conduit 242 to the nozzle 28 of the jet pump 24. The pressure P x  in the conduit 242, communicated via a conduit 244 to a piston 54, causes a sealing block 48 to move away from the gears 44, 46 of the pump 42, thereby assisting the unloading of this pump. The jet pump 24 now vents the pump 42 and a vapour-core centrifugal pump 158 via a conduit 170, a vent valve 174, a conduit 191, a cavity 50, a conduit 220, the valve 192 and the conduit 36. If the sum total of fuel delivered through the main and reheat metering valves corresponds to a predetermined low flow rate, a flow sensing means directs a pressure signal to a port 120 of the selector valve 104 to move a valve spool 122 to close a port 114 leading to the pumps 134, 138 and open a port 116 leading to the vapour-core pump 158. When the spool 122 is in this position, a projection 126 displaces the spool 182 of the vent valve 174 to transfer the venting circuit from the pump 158 to the pump 138. The fuel is now pumped by the pump 158, which delivers via a check valve 76 to the delivery line 68. The pump 158 is controlled by an inlet throttle valve 164 actuated by a controller 168 in accordance with the pressure differential P 1 -P 2 .