Patent GB-969748-A (GB)
Title: Improvements relating to the drainage of fuel-return ducts of gas-turbine power units
IPC: F02C7/232
Filed: 1963-07-18
Abstract: 969,748. Gas turbine plant. DAIMLER-BENZ A.G. July 18, 1963 [July 19, 1962], No. 28545/63. Heading F1G. A gas turbine engine comprises a fuel supply pump driven from the engine shaft, the fuel supply to the engine being controlled by a metering valve, the metering valve being arranged to close the fuel supply line when the engine is set out of operation. A fuel return duct is provided which leads from the fuel nozzles back to the suction side of the pump. Arrangements are provided for draining the fuel return duct and comprise a cut-off valve disposed in the pump suction line, the cut-off valve being open when the engine is in operation and the metering valve is open, and being closed when the engine is shut down and the metering valve is closed. A drainage duct leads from the fuel supply duct back to the fuel reservoir and is also provided with a cut-off valve which is closed when the engine is operating but is opened when the engine is being shut down so that the pump while it is still being driven by the inertia of the engine as it decelerates, draws off the fuel in the return ducts and returns it to the reservoir. The gas turbine engine is indicated at G and the main fuel pump which is mechanically driven thereby is indicated at 42. The pump takes its suction from the fuel reservoir 81 through line 80 and discharges by way of line a 1 , fuel metering valve 40 and line a 2  to the fuel nozzles 60, the fuel spill from the nozzles returning through lines b, b 3 , b 1  to the suction side of the pump. When the engine is operating the metering valve 40 is urged to the right against the loading of a spring 39 by fluid pressure in chamber 37 acting on piston 38, the pressure fluid being supplied by a regulating device F. The position of the metering valve 40 controls the effective opening of the port 46. The pressure drop across the metering orifice 46 is maintained constant by means of the device 45 which comprises a spool valve 67, a diaphragm 65 and a spring 66 controlling a by-pass duct a 3 , 97 back to the fuel return line b 1 . The quantity of fuel returning through the line bi is maintained constant by means of a regulating device 47. A further by-pass c is provided which is controlled by a valve 74 in dependence on engine speed as determined by governor D so that in the event of excess speed, fuel in the line a 2  is by-passed back to the suction side of the pump 42. In the pump suction line 80 is provided a shut-off valve 82 which is normally held in the open position against the loading of spring 91 by means of a solenoid 88. The valve 82 is mounted on the same shaft as a second shut-off valve 84 which is disposed in the drainage line 83 which connects from the discharge side of the pump 42 back to the fuel reservoir 81, a non-return valve 85 being disposed in the line 83 so that fuel can only pass through the line 83 back to the reservoir. When the shut-off valve 82 is open as it is when the engine is operating, the shut-off valve 84 is closed so that no fuel can pass through the drainage line 83. When the engine is being shut down, the lever 11 is moved in the direction indicated by arrow Y to the position shown in full lines. The shut-off valve 53 is linked to the lever 11 and this therefore also moves to the open position shown in full lines and the conract arm 53<SP>1</SP> likewise moves to the position shown in full lines. Opening of the valve 53 releases the servo-fluid in line 54 to the reservoir 90 and the metering valve 40 is moved to the left by the action of spring 39 thus closing the fuel metering orifice 46. The movement of the contact arm 53 breaks the circuit 89 and the solenoid 88 is de-energized so that the valve member 82, 84, 86 moves downwardly by the spring 91, thus closing the valve 82 and opening the valve 84. As the engine decelerates the fuel pump 42 continues to be driven by the inertia of the rotating parts and fuel in the lines b, bi, c is drawn in by the pump and discharged through the drainage line 83 back to the fuel reservoir.