GB763448A - Improvements in or relating to gas turbine engine fuel systems - Google Patents

Abstract

763,448. Gas-turbine plant ;centrifugal pumps. ROLLS-ROYCE, Ltd. July 29, 1954 [Sept. 9, 1953], No. 24945/53. Classes 110 (1) and 110 (3). A gas-turbine engine fuel system comprises a gear pump or other positive-displacement pump 10, Fig. 2, and a centrifugal pump 11 delivering fuel in parallel to a control means 18 for regulating the flow of fuel to the engine, at least the pump 10 being mechanically driven by the engine, by-pass ducting for returning fuel delivered by at least the pump 11 to the inlet side of at least one of the pumps, and flow control means in the by-pass ducting arranged on closure of a non-return valve 52, Fig. 5, contained in a device 25, Figs. 2 and 5, to allow fuel delivered by the pump 11 to pass through a by-pass duct 31 and to close when the rate of flow of fuel through the valve 52 exceeds a predetermined value. The control means 18 is manually settable by lever 19 and preferably includes means for compensating for changes in aircraft altitude and flight speed. The non-return valve 52 closes the delivery pipe 16 of the pump 11 at low engine speeds and during starting. The flow of fuel through the by-pass duct 31 is restricted by a restrictor 54. When the delivery pressure of pump 11 increases sufficiently to open the valve 52, a valve 56 is moved into the position shown to close the by-pass duct 31, by means of a piston 57 which is subjected on its two sides to the pressures upstream and downstream respectively of the valve 52. A relief valve 24 in the by-pass duct 30 of the pump 10 limits the maximum pressure developed by pump 10. When the delivery pressure of pump 11 exceeds this maximum delivery pressure of pump 10, it closes a non-return valve 26 in the delivery pipe 15 of pump 10, whereupon the whole of the delivery of pump 10 passes through the by-pass duct 30. Some of the fuel delivered to the common pipe 17 is returned to the fuel tank 12 by way of by-pass ducts 32 and 27 and a cooler 20 to cool lubricating oil circulated through the cooler by way of pipes 28. The flow of fuel through the cooler is controlled by a relief valve 33 which is set to open at a pressure below the pressure setting of relief valve 24. To ensure a minimum flow through the cooler under starting and other conditions, a duct 34 containing a fixed restrictor 35 may be provided in parallel with the relief valve 33. The pump 11 is driven mechanically by the gas-turbine engine or, as shown, by an air turbine 29 fed with air tapped from a compressor forming part of the engine. A booster pump 14 may be provided. In modifications, the by-pass duct 32 is eliminated, and flow of fuel through the cooler 20 is provided by returning one of the by-pass ducts 30, 31 to the cooler 20 instead of to the pump inlets, the other by-pass duct being returned to the duct 27; alternatively both by-pass ducts are returned to the cooler 20. Specification 763,449 is referred to.