Patent GB-1152438-A (GB)
Title: Liquid Supply System particularly a Gas Turbine Engine Fuel System
Inventor: TYLER STANLEY RALPH
IPC: F02C7/22
Filed: 1965-10-20
Abstract: 1,152,438. Centrifugal pumps; gas turbine jet engine reheat fuel systems. DOWTY FUEL SYSTEMS Ltd. Oct. 11, 1966 [Oct.20, 1965], No.44444/65. Headings F1C and F1J. [Also in Division G3] A liquid supply system comprises a centrifugal pump of vapour-core type having an inlet valve which is controllable to vary the rate at which liquid flows from a source of supply and is delivered by the pump to a service, and an auxiliary power circuit including a branch pipe leading from the pump delivery, a return pipe connected to the pump inlet downstream of the inlet valve, and a control valve operable to vary the flow of liquid from the branch pipe to an auxiliary power service and therefore the return of liquid from the auxiliary power service through the return pipe to the pump inlet. Fig. 1 shows a fuel system for a gas turbine engine in which a boost pump 11 delivers to a positive displacement pump 12, and via a conduit 13, to a centrifugal pump 14 of vapour-core type. Pump 12 delivers to the main engine burners via a flow control system 16, while pump 14 delivers to the reheat burners via a throttle valve 25 and a non-return valve 26. A reheat selection device 28 has a fixed restrictor 47 supplied from, say, the compressor delivery, and a manually variable restrictor 48, a pressure signal of demand being taken from the junction of the restrictors and applied via a pipe 51 to a capsule 46. The capsule 46 and a flow measuring device 29 located in the conduit 13 are connected in opposition to a lever 43 which is pivoted at 44 and acts to differentially vary the throttling of two nozzles 31, 32 which are connected to opposite sides of a piston 19 and supplied from pump 12 with fuel as servo-liquid through restrictors 35, 36. The piston 19 operates the inlet throttle valve 18 of the pump 14 to vary the flow to the reheat burners. Jacks 57 for varying the discharge nozzle area of the engine are supplied by the pump 14 with fuel as servoliquid via a pipe 41 and a control valve unit 58, Figs. and 2. The control valve unit 58 comprises a capsule 77 subject to turbine exhaust pressure and a capsule 78 subject to a fraction of compressor discharge pressure, the capsules being connected in opposition to a pivoted lever 83 which differentially varies the throttling of two nozzles 84, 85 which are connected to opposite sides of a piston 75 and supplied with fuel as servoliquid through restrictors 86, 87. The piston 75 operates a spool valve 74, which, when moved from a neutral position, connects either one of two pipes 62, 63 to the supply pipe 41 and connects the other to a return pipe 59 which is connected to the inlet of pump 14 downstream of the inlet throttle valve 18. The pipes 62, 63 are connected to opposite sides of the piston of each jack 57. The compressor discharge pressure is applied to the capsule 78 via a fixed restrictor 79 and a passage 81, a variable restrictor 82 carried by the valve spool 74 co-operating with the fixed restrictor 79 to form a variable potentiometer which varies the pressure applied to the capsule 78 in accordance with the position of the valve spool 74. The control exerted by the capsules 77, 78 causes the jacks 57 to vary the engine discharge nozzle area so as to maintain the pressure ratio across the turbine substantially constant. To ensure that the pressure developed in the pipe 41 by the pump 14 is sufficient for satisfactory operation of the jacks 57 even when the flow of reheat fuel is low, throttle valve 25 is provided. When the valve spool 74 is moved upwards from its neutral position to cause the jacks 57 to reduce the engine discharge nozzle area, it increasingly throttles a variable restrictor 97 connected by pipe 93 to chamber 92. In conjunction with a fixed restrictor 89, this causes the pressure in chamber 92 to increase, whereby the tendency of the pressure in pipe 41 to move the valve piston 88 downwards to increase the opening of a discharge orifice 96 is resisted. Consequently, a back pressure is developed across the orifice 96 to increase the pressure in the pipe 41. When the reheat control lever 49 is moved to the REHEAT OFF position, a valve spool 108 is moved to the right, partly by rack 112 and partly by a feedback link:113 which is movable in accordance with changes in the engine discharge nozzle area. This vents the left-hand side of piston 19 to the inlet pressure of boost pump 11 via pipes 101, 104 whereby the inlet throttle valve 18 closes to reduce the flow through pump 14 to a residual cooling flow. In addition, this residual flow is directed via pipes 106, 104 to the inlet of boost pump 11. Sufficient power for low rates of movement of the jacks 57 and for cooling flow through the jacks is now provided by the pump 12 which, for this purpose, is connected to the pipe 41 via a restrictor 115 and a pipe 114, the return pipe 59 being connected to the inlet of boost pump 11 via a pipe 116 containing a restrictor 117. In addition, a non-return valve 39 and a pressure relief valve 61 isolate the pump 14 from the pipes 41 and 59. The flow resistance of the restrictors 115, 117 is high enough to avoid undue interaction between the pumps 12 and 14 during normal operation of pump 14. A pressure intensifier (121, Fig.4, not shown), may be provided between the pipe 41 and the control valve unit 58.