1391599 Gas turbine engine reheat fuel systems JOSEPH LUCAS (INDUSTRIES) Ltd 4 Aug 1972 [17 Aug 1971] 38470/71 Heading F1J The invention relates to a fuel control system for a gas turbine engine reheat system which includes a plurality of burners, namely primary, gutter and colander burners. The system comprises a reheat fuel pump 10 of the vapour core type the output of which is controlled by a throttle valve 11 responsive to pump delivery pressure and a servo-pressure supplied through passage 12. Fuel passes to inlet 14 of a metering assembly 13 which comprises three variable metering devices 15, 16, 17 arranged in parallel to control flow of reheat fuel to the primary, gutter and colander burners respectively. The primary metering device 15 comprises a valve spool 19 disposed in sleeve 18 for axial and rotational movement, the spool being formed with an annular recess 19a to control flow of fuel from port 20 to port 21, the fuel then passing through passage 22 and through a variable orifice 43 to outlet 42 and thence to the primary burner. The spool 19 carries a piston 24 the opposite sides of which are subject to different pressures derived from fuel pressure in the inlet duct 14, the pressures being derived by means of a pivotally-mounted lever 31 subject at its lefthand end to pressure Pi P derived from compressor discharge P 2 , pressure P 1 P being communicated to bellows 32. The other end of the lever carries half-ball valves 29, 30 controlling openings 25, 27. Springs 33, 34 extend between the lever and the valve spool 19 and an adjustable stop 35. The spool 19 carries at its upper end a three-dimensional cam 57 and is rotated by a motor 23 in response to air intake temperature Ti. A connection is made from passage 22 through orifice 37 and passage 38 by which fuel at control pressure DP 1 is communicated to chamber 39 of servo control device 40, Fig.2. The variable orifice 43 is controlled by a piston member 44 which is loaded at its lower side by spring 45 also by servo pressure S 1 derived from metering assembly 40 Fig.2, and communicated through passage 46. The gutter metering device 16 comprises a piston member 49 slidable in sleeve 47, the piston and sleeve having openings 50 and 48 which co-operate to define a variable metering orifice through which reheat fuel passes from inlet 14 through a second variable orifice 64 controlled by a piston member 65, through outlet 68 to the gutter burners. The piston 49 is formed with a stem 53 having a bore 54 controlled by a ball valve 56, fuel passing from the inlet 14 through opening 52 to the space 51 above the piston and thence to the bore 54. The pressure in the space 51 and so the axial position of the piston is dependent on the position of the ball valve 56 which is controlled by a spring-loaded lever 58 which in turn is controlled by the threedimensional cam 57. The rotational position of the piston 49 is controlled by means of a lever 62 which engages cam 60 the position of which is controlled by the power selection lever through linkage 61. The pressure downstream of the metering orifice 48, 50 is passed through orifice 69 and passage 70 as pressure DP2 and communicated to the servo control device 40. The piston member 65 is acted on at its lower side by spring 66 and by servo pressure S 2 derived from the control device 40. The colander metering devices 17 is similar to the device 16 and controls flow of reheat fuel through outlet 76 to the colander burners. The throttle valve 72 of the device 17 is acted on by servo pressure S 3 derived from the control device 40, and a control pressure DP 3 derived through orifice 74 is communicated to the control device 40. The servo control device 40 comprises a spool member 80 which is acted on at its left-hand end by pump discharge pressure Pp and at its righthand end by servo pressure DP 1 in chamber 39, also by the governor device 80 responsive to engine speed. The spool controls flow of high pressure fuel from inlet 83 to outlet 84 the resulting pressure being communicated through passage 12 to the left-hand side of the control piston 11 of the reheat fuel pump 10. The governor assembly 80 comprises a cage 97 formed with an internal ring gear 93 which is engaged by a pinion 94 carried by an extension of the drive shaft of the pump impeller 10 whereby the cage 97 and governor assembly is driven. The cage is also formed with a gear 95 and with internal splines 96, the gear 95 serving to drive through gears 98, 99 the valve spools of the devices 92, 86, and the splines 96 serving to drive the spool 80. The spool 86a controls flow of fuel at pump pressure Pp supplied through inlet 87 through outlets 89, 90, the pressure at outlet 89 being the servo pressure S 1 communicated to passage 46, and the pressure S 2 communicated to passage 67. Pressure DP 2 is applied at the left-hand end of the spool 86a and pressure DP 1 in the chamber 39 is applied at the right-hand end. If DP 2 should fall, spool 86 moves to the left whereby pressure S 2 is increased, thus causing throttle piston 65 to move upwardly whereby pressure DP 2 is restored to its former value. A rise in DP 1 again causes spool 86 to move to the left whereupon pressure DP 2 is caused to increase to the same value as DP 1 . The spool device 92 operates in a similar manner so as to maintain pressure DP 3 equal to DP 1 and so also to DP 2 .