Patent GB-1525602-A (GB)
Title: Fluid flow control valves
IPC: G05D7/00
Filed: 1975-02-05
Abstract: 1525602 Centrifugal governor: Fluid-pressure servomotor systems LUCAS INDUSTRIES Ltd 14 Jan 1976 [5 Feb 1975] 4830/75 Headings G3B and G3P [Also in Division F1] A fluid-flow control valve 50, in particular a gas turbine engine fuel supply valve, comprises a body 51 having a movable control element 59 cooperating with ports in the body to define a variable flow restrictor 63 between an inlet 52 and an outlet 54, a variable flow restrictor 69 between an inlet 53 and an outlet 55, and two further variable flow restrictors (formed by ports 65, 67 and 64, 66 respectively) in series between the inlet 53, and the outlet 54, and a pilot valve 72 responsive to a difference between the pressure at the inlet 52 and the pressure between the two restrictors in series, for varying a servo pressure to move the control element 59 so that an increase in the pressure at the inlet 52 results in an increase in flow through the restrictors 63, 65/7 and 64/6 (to the outlet 54) and a decrease in flow through the restrictor 69 (to the outlet 55). The pilot valve 72 includes a diaphragm acted on by the said pressures and arranged to control a nozzle outlet of chamber 61 in which the servo pressure acts on the control element 59. The control element 59 is rotationally adjustable by means of a crank 68 to vary the restrictors 64/6 and 65/7, and there is an adjustable restrictor 73 in parallel with the restrictor 63. The inlet 52 receives fuel from a pump 11, Fig. 1, via a variable metering device 13 responsive to engine operating parameters, while the inlet 53 receives unmetered fuel direct from the pump, so that the metering device 13, by controlling the pressure at the inlet 52, controls the total flow of fuel to the outlet 54, whence it flows to the engine 10 via a servo-operated throttle valve 81 which is controlled by a pilot valve 86 responsive to the engine low speed shaft speed NL and the combustion temperature Tg. Fuel from the outlet 55 of the valve 50 and fuel spilled from the throttle valve 81 is returned upsteam of the pump 11. The variable metering device 13. Fuel from the pump enters the device 13 through a metering orifice whose flow area is determined by a relative positions of a stem 15 and a sleeve 21, and through a port 39 in the stem whose flow area is determined by the axial position of the stem; fuel leaves the device 13 through ports 36, 37 whose flow area is determined by the axial position of a sleeve 35, to pass along a line 38 to the inlet 52 of the valve 50. The sleeves 21, 35 are moved axially by governor weights 19, 20 on a carrier 18 rotated by a shaft of the engine. The sleeve is biased against the action of the weights 19 by a spring 23 which acts between cam surfaces 24 and 25, the latter on a lever 26 engaging the sleeve 21. The bias thus applied to the sleeve is dependent on the point of application of the spring force on the lever 26, varied by lever 28, and the position of cam 24, varied by a torque motor 33 controlled by a circuit 34 receiving signals representing compressor inlet pressure P1 and temperature T 1 , high and low shaft speeds NH and NL and combustion temperature Tg. The axial position of the stem 15 is influenced by the intermediate compressor pressure P 2  acting on the end and the pressure between restrictors 16 and 17, connected to P2 and to compressor outlet pressure P 3 , acting on the other end.