Patent GB-962878-A (GB)
Title: Improvements in gas turbine engine fuel control
IPC: F02C7/22
Filed: 1963-12-20
Abstract: 962,878. Gas turbine jet engines. GENERAL ELECTRIC CO. Dec. 20, 1962 [Dec. 29, 1961], No. 48107/62. Heading F1J. A fuel control system for a gas turbine engine comprises fuel pumping means, a metering valve connected in series flow relation with the fuel pumping means for controlling the output flow thereof, and a pressure regulating valve connected in series flow relation with the metering valve for maintaining a substantially constant pressure drop across the metering valve, a fluid flow by-pass being connected in parallel with the pressure regulating valve for establishing a minimum fuel flow rate for the system. In Fig. 1 fuel from the pump passes through the line 10 to the metering valve 11 and passes through the metering orifice formed by the cooperating ports 20, 21 to the pressure regulating valve 12 and passes through the port 13a, the open area of which is determined by the axial position of the piston 23, to the outlet line 13 which leads to a reheat combustion system. The metering valve comprises a piston member 16 mounted on a rod 15, the axial position of the piston 16 being controlled in dependence on P3, the compressor discharge pressure, by means of a capsule controlled servo leak-off valve 47. The rod is also connected by a link 35 and pin 36 to a device which is responsive to W # /P 3  where W f  is the desired fuel weight flow and P 3  the compressor discharge pressure whereby the rotational position of the piston is dependent on W f /P 3 . The piston wall is formed with a rectangular shaped port 20 which co-operates with a correspondingly shaped port 21 formed in the valve casing to form a metering orifice, see Fig. 2. The pressure regulating valve 12 comprises a piston 23 which is urged to the left by a spring 25, the loading of which may be varied by an adjuster screw 31. The left-hand side of the piston is connected to the chamber 22 upstream of the metering orifice 20, 21 by way of ducts 32, 33, while the right-hand side of the piston is connected to the duct 21 downstream of the metering orifice 20, 21. The pressure regulating valve thus serves to maintain the pressure drop across the metering valve 20, 21 constant. A by-pass 61 is connected across the pressure regulating valve. The P 3  control device 38, 39 comprises a capsule 38 which is subjected internally to pressure P 3 , and a capsule 39 which is evacuated, the capsule being disposed with a chamber 40 which is connected to ambient pressure, the capsules being connected by a rod 42 which controls the position of the flapper member 44, which is pivotally mounted at 45, in dependence on the absolute value of the compressor discharge pressure. The flapper member 44 is connected by a spring 49 to the feedback link 50 which is connected to the piston rod 15 and is pivotally mounted at 51. The flapper 44 is also connected to a reference spring 52. The flapper controls the outlet through the orifice 47, the orifice being connected in series with an orifice 46 provided in the piston 17. The total flow area of the metering orifice 20, 21 is proportional to the product of W f /P 3  and P 3 , that is, it is proportional to the desired fuel flow rate Wf. With an increase in P 3  the flapper member 44 will move away from the orifice 47, thus producing an increase in the pressure drop across the orifice 46 and so a downward movement of the piston 17, the link 50 thereupon pivoting about 51 so increasing the loading of the spring 49 and restoring the flapper member to its former position. A stop 57 is provided to limit upward movement of the piston 17. In a second embodiment, a stop is provided to limit movement of the piston 23 of the pressure regulating valve to the right.