GB1107984A - Improvements in or relating to volumetric fuel-control devices suitable for engine fuel systems - Google Patents

Abstract

1,107,984. Fluid-pressure control valves etc. PLESSEY-UK Ltd. 14 Jan., 1965 [31 Oct., 1963], No. 43052/63. Heading F2V. [Also in Division F1] The invention relates to volumetric fuel control devices and the object is to adapt automatically the quantity of fuel metered to the engine to the momentary density of the fuel so as to convert the volumetric flow control at least approximately to mass flow control. The invention is described with reference to a gas turbine engine fuel system in which flow from an engine-driven fixed-displacement fuel pump shown as a gear pump 1, is divided into engine flow and spill flow by a distributer valve 4 in which the aggregate area of two ports, one leading to the engine through line 3 and the other leading back to the pump inlet through line 8, is independent of the position of the valve. The spill return line 8 contains a valve 9, termed a link valve, which automatically controls a throttle aperture in the spill return line so that the pressure between the spill port of the distributer valve and the throttle aperture of the valve 9 is always equal to the pressure between the engine port of the distributer valve and the engine burner, so that there is in effect one single pressure drop in the distributer valve. In accordance with the invention an auxiliary spill path is provided to by-pass the spill port of the distributer valve and leading to the inlet of the throttle aperture of the link valve, the auxiliary spill path containing a valve which maintains a pressure drop which is a suitable compound function of the density of the fuel and of the square of the engine speed. This valve is open when and as long as the force exerted by the pressure drop in the distributer valve acting upon a predetermined area, overcomes the centrifugal force of a centrifugal weight suspended in and rotating with a body of the metered fuel at a speed proportional to engine speed. In the embodiment shown the device 10 comprises a rotary block 11 having journals 12, 13 mounted in bearings 14, 14a, the block being driven at a speed proportional to engine speed. Fuel in the line between the gear pump 1 and the distributer valve 4 is tapped off through line 15a and passes to chamber 15 and a duct 17 formed in the rotary block 11 leads from the chamber 15 to a valve orifice 17a which opens into a chamber 19 in which is disposed a centrifugal weight 20 which constitutes a movable valve element cooperating with the valve orifice 17a, being movable radially towards and away from the orifice. The outlet from the chamber 19 is through a duct 18 formed in the rotary block 11 which communicates with a chamber 16, the chamber 16 in turn communicating through line 16a with the line between the spill outlet of the distributer valve 4 and the throttle aperture of the link valve 9. The centrifugal weight 20 is formed of aluminium and is formed with a through bore 20a which provides communication between the two ends of the chamber 19. The position of the distributer valve 4 is controlled in dependence on compressor intake and compressor discharge pressures by the device 5. The mathematical theory of the invention is set forth in the Specification.