GB1024843A - A liquid flow control system suitable for a liquid fuel flow control system for a gas turbine engine - Google Patents

Abstract

1,024,843. Centrifugal pumps; jet propulsion plant. DOWTY FUEL SYSTEMS Ltd. July 26, 1962 [Oct. 10, 1961], No. 36358/61. Headings F1C and F1J. [Also in Division G3] A liquid control system including a centrifugal pump has means for controlling the flow by throttling the flow into the pump and by throttling the flow out of the pump. Fig. 1 shows a fuel control system for additional burners 42 of a gas turbine engine of a vertical take-off aircraft. The system is shown in an operating condition when the thrust nozzles 94 are arranged to provide vertical lift. When the pilot's throttle lever 35 has reached a position at which the additional burners 42 are required a switch 107, in series with a closed switch 106, closes to energize a solenoid which opens a valve 49 as shown. This allows the pressure of high pressure fuel from the main system, fed through conduit 46 and restrictor 47, to be relieved below a piston 44 through a conduit 51 leading to a boost pump (not shown). Thus the piston 44 drops to the position shown carrying with it a shut-off valve 15, thereby allowing fuel in a conduit 14, fed by the boost pump, to flow to the rotor 12 of a vapour core pump 11 and thence through a non-return valve 21 and conduit 22 to a throttle control unit 23 provided with throttles 25, 26. The latter are respectively associated with sleeves 27 and 28 which are caused to take up an operative or an inoperative position by movement of a rod 32 in accordance with the position of thrust nozzles 94. For vertical thrust the sleeve 27 assumes the operative position and the associated throttle 25 is moved, for example, by the swash plate mechanism of a variable stroke engine supply pump or by a spill valve 33, which controls the flow in the main fuel system through a lever 34 to control the fuel supplied through a conduit 41 to the additional burners 42. The fuel flow is automatically compensated for ambient conditions since this data is fed into the main fuel system. The burners 42 may be spray nozzles of the kind described in Specification 845549 or may be of any other type which causes fuel flow to be a substantially linear function of fuel pressure. A throttle valve 18 in the inlet of the pump 11 and a by-pass valve 103 at the pump outlet 19, each spring-urged to their open positions are respectively held open and closed as shown during vertical and transitional thrust. When the nozzles 94 take up their position for forward thrust, switch 106 opens. Thus the valve 49 closes and the pressure below the piston 44 builds up to lift the piston 44 and valve 15 and thereby stop the flow of fuel to the pump 11. Additionally, a sleeve 84 of a control unit 53 rotates to a different position so that a conduit 76, supplied with high pressure fuel from conduits 46 and 79 through a restrictor 81, is vented to a conduit 90 leading to the boost pump. This causes the pressure to the right of a piston 77 of a servomotor 54 and above the piston of the valve 103 to be relieved to thereby close the valve 18 and open the valve 103, the latter relieving any pressure in the outlet 19 to atmosphere. Adjustment of throttle lever 35 does not alter the position of a spool 85 of the control unit 53 for the purpose of bringing the additional burners 42 into operation until it is pushed through the throttle gate beyond a maximum forward speed position, which is 95% of the maximum speed during vertical and transitional thrust. This causes the switch 106 to close and thereby open the valve 15. Moreover, the spool 85 is moved to connect the conduit 76 to a conduit 75 associated with a valve 65 controlled in accordance with the engine compressor delivery pressure (or other engine pressure signal) felt through conduit 73 and operating on an evacuated spring bellows 71, and also in accordance with the delivery pressure of the pump 11 felt through conduit 67 and operating on a diaphragm 68, the forces resulting from both pressures and from a spring 62 being applied to a lever 59 pivoted at 61 and carrying the valve 65. The forces applied by the bellows 71 and spring 62 may be adjusted by adjusters 74 and 70 respectively. The pressure in conduits 76 and 104 therefore depends on the degree of opening of the valve 65. This causes by-pass valve 103 to close, and controls the opening of throttle valve 18 and thereby the delivery pressure of the pump 11, in accordance with the engine compressor delivery pressure. Throttle lever 35 controls the position of throttle 26. Wedges 95, controlling the exit area of the nozzles during forward thrust, are caused to open fully when the additional burners are operative, since, by virtue of adjustment of the spool 85, the high pressure fluid in a conduit 80 is caused to flow through conduit 98 instead of 99. Instead of two-position control of the wedges 95, full variable control may be applied. Figure 4 shows a modification in which it is not necessary to have additional burners which provide linear pressure/flow characteristics. The throttle 26 is replaced by a sleeve 118 provided with ports 121, 122 and a spool 119 biased by a spring 125 to close ports 121 and controlled in accordance with the pressure existing in the space above a piston 123. High pressure fuel, supplied through a conduit 126, passes through a restrictor 128, control unit 53 and conduit 131 to a valve 132 carried by a lever 133 pivoted at 134 and controlled by bellows 138 and 141. Bellows 138 is supplied with air at a certain fraction of compressor delivery pressure and bellows 141 is supplied with air through a restrictor 144 at a variable fraction, the variation being effected by means of a variable restrictor 145 which leads to atmosphere and is adjusted by the throttle lever 35. When the lever 35 is moved to increase the main fuel supply, the restrictor 145 is adjusted to further restrict flow to atmosphere and thereby move the lever 133 to increase the opening of valve 132 and ports 121. The position of the valve 18 in the pump 11 is controlled in accordance with the pressure drop across the ports 121 and 122, the pressures being felt at a diaphragm 147 controlling the position of a valve 157 and thereby the pressure in the conduit 76. Thus, the pressure drop across ports 121 and 122 is maintained substantially constant and the fuel flow rate is maintained substantially a linear function of compressor delivery pressure.