Patent GB-1402625-A (GB)
Title: Gas turbine engine fuel systems
IPC: F02C7/22
Filed: 1972-07-28
Abstract: 1402625 Gas turbine engine fuel systems GENERAL ELECTRIC CO 28 July 1972 [9 Aug 1971] 35402/72 Heading F1G The invention relates to a fuel system of a gas turbine engine and to means for returning fuel from the system back to the fuel pump inlet upon engine shut-down. The fuel system shown comprises a low-pressure fuel pump 38 and a highpressure fuel pump 40, a fuel control unit 32 having a shut-off valve 54, fuel passing from the control unit through lines 62, 68, 70, 61 to the burners 26 in the combustion equipment 14 of the engine. The system also comprises a drain valve 60 and drain tank 58, also an ejector pump and valve assembly 74, the drain valve 60 being such that when the engine is in normal operation, fuel pressure is communicated thereto through lines 62, 64, 66 so closing the valve, but when the engine is shut-down by closing shut-off valve 54 the pressure in lines 62, 64, 66 is released and the valve 60 opens whereupon fuel in the lines 62, 68, 70, 61 downstream of the shut-off valve passes to the drain tank 58. The fuel is then transferred through line 86 to the ejector pump and valve assembly 74 from which it is passed through line 90 to the inlet of the low-pressure fuel pump 38. The ejector pump and valve assembly 74 comprises a casing 76 containing a sleeve 100 and piston member 96, the piston member carrying a valve member 102 which co-operates with inlet 78 to control flow of drainage fuel from tank 58 through line 86. The piston is acted on at its left hand end in normal engine operation by fuel pressure communicated through lines 64, 66 to inlet 82 whereby the valve 102 is closed. In this position the piston member also closes off communication between the fuel inlet 80 from line 88 to the nozzle 136 of the ejector pump 92. The inlet 80 communicates through line 88 with the discharge line 50 from the fuel pump system 38, 40, while the outlet 84 communicates through line 90 with the suction side of the low pressure pump 38. When the engine is shut-down by closing of theshut-off valve 54, the pressure acting at the left hand end of the piston 96 through line 66 is released and the piston moves to the left by action of the spring 108, the valve member 102 continuing to close off the inlet 78 through loading of the spring 116. With the piston in its lefthand position fuel pressure in line 88 now passes through inlet 80 and passages 124, 120, 126, 144 and discharges from the nozzle 134 of the ejector pump across the suction chamber 128 to the receiver 132 and thence through return line 90. The suction in chamber 128 acts to open the valve 102 against the action of spring 116, so that drainage fuel in tank 58 is drawn through line 86 and inlet 78 through passage 154 to the suction chamber 128 from which it is discharged through return line 90 to the low-pressure pump 38. The pumps 38 and 40 continue to operate even though the shut-off valve 54 is closed since the engine takes some time to come to rest; thus the ejector pump is supplied from the pumps 38, 40 during this run-down period. The object of the invention is to prevent wastage of the drainage fuel.