GB977286A - Improved liquid supply system - Google Patents

Abstract

977,286. Supplying liquid fuel to burners. DOWTY FUEL SYSTEMS Ltd. March 4, 1963 [March 15, 1962], No. 10025/62. Heading F4T. [Also in Divisions F1 and G3] A liquid supply system for feeding liquid at pressure to an hydraulic load comprises a centrifugal pump, fixed or variable liquid flow control means to control flow rate of liquid into the pump, and an adjustable by-pass valve connected to by-pass some liquid delivered by the pump to a low-pressure zone, the pump being so adapted by virtue of its size and running speed as compared with the load and flow rate of liquid into the pump that the liquid within the pump assumes an annular form having a central hollow eore. The invention is described as applied to the fuel supply system of a gas-turbine engine, but is also applicable to the supply of fuel to spray or vaporizing burner nozzles in furnaces or other heating installations. Liquid fuel is supplied to the reheat burners of a gas-turbine engine by an engine-driven centrifugal pump 1, Fig. 1, under the control of a flow metering device 36 comprising a manually-adjustable control valve 38 in the pump-discharge line 2. The pressures upstream and downstream of the valve 38 are applied through pipes 42 and 43 respectively to opposite sides of a diaphragm 44 which controls a half-ball vent valve 48 controlling a servo piston 52 which actuates a throttle valve 66 in the discharge line 2. At high rates of flow, a throttle, valve 12 at the inlet to the pump 1 is in the fully open position shown, and the pump runs full of liquid. For small or medium rates of flow, a valve 29 is moved manually from the position shown to reverse the connections of pipes 23, 24 to a fuel boost pump 9, whereby a piston 14 is moved to the left until it comes against an abutment 18. Valve 12 is then close to its seat to throttle the inflow to the pump 1, causing the liquid within the pump to assume an annular form with a central hollow core of fuel vapour. In addition, a valve 58 in a by-pass pipe 57 is then open, so that the flow metering is done by a by-pass valve 55 controlled by the piston 52 rather than by the throttle valve 66. To cut-off the fuel flow, a manually-operated valve 26 is moved from the position shown to connect pipe 25 to the inlet of boost pump 9 instead of the outlet, whereby the abutment 18 is moved to the left, allowing the valve 12 to close fully. A spring 20 may be provided to hold the valve 12 closed when the engine is inoperative. In the alternative arrangement shown in Fig. 2, the metering device 92 in the discharge line 72 of the reheat fuel pump 71 comprises a manuallyadjustable restrictor 93, the pressures upstream and downstream of which are applied to diaphragms 97 and 98, respectively, acting in opposition on a lever 102 carrying half-ball vent valves 91, 105. Vent valve 105, located downstream of a restrictor 118, controls the pressure at the right-hand end of a piston 107 to operate a by-pass valve 111 to provide a quick but approximate initial adjustment of the flow rate. The piston 107 also operates a movable abutment 109 for a spring 100. A spring 120 counteracts the effect of spring 100 on the piston 107, exactly balancing it at the equilibrium position of the piston to ensure that the position is not affected by variations in the servo pressure fed from the line 72. Vent valve 89, located downstream of a restrictor 87, controls the pressure at the righthand end of a piston 83 through a restricted passage 88 which ensures stability but gives a slow response. The piston 83 actuates a throttle valve 81 at the inlet to the pump 71 to give an accurate but retarded final adjustment of the flow rate. As in the previous embodiment, the throttle valve causes the liquid to assume a hollow form with a central hollow core of fuel vapour. In both embodiments, the hollow core may be connected to a low-pressure gas source such as the atmosphere. The Provisional Specification states that the operating mechanism of valve 29 is operable from the main control for the control valve 38, and further states that it is automatically adjusted by a signal pressure-sensing device.