Patent GB-817934-A (GB)
Title: Devices for sensing the rate of change of flow of liquids
Inventor: MCKEGGIE WILLIAM ARTHUR
IPC: F02C7/22
Filed: 1956-06-11
Abstract: 817,934. Gas turbine plant. NAPIER & SON Ltd., D. May 23, 1957 [June 11, 1956], No. 18016/56. Class 110 (3). [Also in Group XXIX] A fuel system for a gas turbine running on liquid fuel has a control means for varying the fluid flow and a device for sensing the rate of change of flow of the liquid flowing through a pipe 10, the device comprising a main orifice 11 in the pipe, a spring-loaded piston 13 in a cylinder 12 opposite ends of which communicate with the pipe upstream and downstream of the main orifice respectively, an auxiliary orifice 17 in a passage leading from the pipe to one end space of the cylinder, and a pressure-sensitive element 22 for sensing a pressure drop across the orifice. Passages 18, 19 lead from the passage 16 on opposite sides of the auxiliary orifice 17 and communicate respectively with spaces 20, 21 above and below a flexible diaphragm 22. The diaphragm is urged downwardly by a spring 23 and controls a half ball valve 24. This valve controls the flow of liquid from a pipe 25 into a drain pipe 26. When there is a steady flow of liquid in the pipe 10 there will be no pressure drop across the orifice 17. If the flow of the liquid increases slowly the piston 13 will move to a new equilibrium position, the pressure difference being balanced by the spring 14. Although liquid will flow into the right-hand end of the cylinder 12 through the orifice 17 it will produce only a negligible pressure drop across this orifice owing to the slowness of piston movement. When the liquid flow in the pipe 10 increases quickly the movement of the piston will be more rapid and there will be a greater pressure drop across the orifice 17. This pressure drop acts on the diaphragm 22 and moves it upwardly against the action of the spring 23 and lifts the valve 24 to an extent depending on pressure drop across the orifice 17 and hence upon the rate of change of flow in the pipe 10. When the device is applied to a gas turbine fuel system (Fig. 4) the fuel is drawn from a fuel tank by a variable delivery pump 45 and delivered through a pipe 47 to a fuel metering unit 48 which varies the flow of fuel in response to movements of a pilot's control 49. The metered fuel passes through a pipe 50 to one or more burner nozzles 51 in the combustion chambers of the prime mover. In the pipe 50 there is provided an orifice 52 corresponding to the orifice 11 in Fig. 1. The rate of change of flow through the orifice 52 is sensed by an accelerator control device 53 provided with a half ball valve which controls an hydraulic servomotor 54. The servomotor 54 controls the delivery to the pump 45. Alternatively the half ball valve may permit metered fuel to bleed off from the pipe 50 through a spill pipe 56 or the valve may control a servomotor 57 influencing a control element of the fuel metering unit 48. When the flow of liquid is large it is desirable to provide a larger main orifice area than when the flow is small in order to maintain a more nearly constant pressure drop. In an embodiment shown in Fig. 2 the flow is through a pipe 30 containing a variable orifice controlled by a tapered needle 32 which is mounted on a spring-loaded piston 33. If the flow of liquid in the pipe increases the pressure drop across the orifice 31 will increase and force the piston 33 to the right against the action of the spring 34 and withdraw the tapered needle 32 from the orifice 31. The change iri volume in the space to the right of the piston 33 causes a flow through the auxiliary orifice 37, the pressure drop across the orifice being utilized by the pressure-sensitive element 38 in the same manner as in Fig. 1. In a further embodiment the area of the auxiliary orifice is varied in dependence on the flow through the pipe so that the pressure-sensitive element will differ at different flows.