Patent GB-1195239-A (GB)
Title: Improvements in Fuel Delivery System for the Afterburner of a Gas Turbine Engine.
IPC: F02K3/10
Filed: 1967-12-04
Abstract: 1,195,239. Jet propulsion engines; centrifugal pumps. GENERAL ELECTRIC CO. Dec.4, 1967 [March 9, 19671, No.54962/67. Headings F1C and F1J. A fuel system for the re-heat burner of a gas turbine engine comprises a first centrifugal pump having a relatively small capacity and a second centrifugal pump having a relative large capacity, both pumps being continuously driven from the engine rotor and the outputs of both pumps being connected to the re-heat burner, means responsive to a relatively low fuel mass flow-rate to the re-heat burner being provided for selectively connecting only the inlet of the first pump to the fuel supply, and means responsive to a relatively large fuel mass flow-rate to the re-heat burner being provided for selectively connecting only the inlet of the second pump to the fuel supply. The small capacity centrifugal pump 11 and the large capacity centrifugal pump 12 are connected through a common discharge duct 127 and a re-heat fuel control 135 to re-heat burner 27, 28. The pump inlets are connected via respective valves 31, 34 to a fuel supply duct 36. The valves are operated by respective actuators 32, 35 which are spring- biased to close the valves. When the pilot has set control lever 136 for re-heat operation and a valve 91 is opened, either manually or automatically by the main fuel control 92 when the engine is in a suitable operating condition, valve 31 is opened by means of pressure fluid communicated from line 90 to the actuator 32 via the valve 91, line 95, chamber 71 of a selector valve 60 and line 96, and the pump 11 delivers fuel to the re-heat burner. When the re-heat fuel flow reaches the maximum that can be supplied by the pump 11, the pressure drop across an orifice 131, communicated via lines 129, 130 to a piston 75, moves the piston 75 downwardly against the action of a spring 68 to bring a load 69 to a position below line 96 and to bring a load 70 below a line 98. Pressure fluid is then communicated from chamber 71 to the actuator 35 via the line 98, causing valve 34 to be opened so that the large-capacity pump 12 delivers fuel to the re-heat burner. At the same time, line 96 is vented to a drain line 102 via a chamber 83, and valve 31 is consequently closed to shut-off the supply of fuel to the pump 11. The transposition of the pressures in the lines 96 and 98 and the consequent transposition in the pressures communicated via lines 97 and 99 to chambers 80 and 79 causes a reversal of the pressure differential acting on a piston 76. The piston 76 then assists the piston 75 instead of opposing it, and the remainder of the stroke occurs with a snap action. A similar effect occurs when a reduction of re-heat fuel flow causes a change back from use of pump 12 to use of pump 11. Because of the snap action, the change back occurs at a lower flow-rate than the original change over. This eliminates hunting. Non-return valves 106, 126 prevent reverse flow through the pump not in use. When operation of a pump ceases on closure of its valve 31 or 34, the associated non-return valve 106 or 126 closes and fuel bleeds from the pump back to the supply line 36 via a restrictor 109a or 122a and a non-return valve 109b or 122b. The resultant reduction in the pressure exerted by the pump on a drain valve 107 or 121 to keep it closed allows the drain valve to be opened by a spring. This empties the pump to avoid churning losses. In a modification, the piston 76 is omitted, and the hydraulic snap action is replaced by a mechanical snap action provided by spring-pressed ball detents.