Patent GB-804815-A (GB)
Title: Compressor pressure limiter for gas turbine engines
IPC: F02C9/16
Filed: 1955-07-06
Abstract: 804,815. Gas turbine plant. BENDIX AVIATION CORPORATION. July 6, 1955 [July 28, 1954], No. 19555/55. Class 110 (3). [Also in Group XXIX] Construction.-Fuel is metered to the burner nozzles of a gas turbine engine by a control device comprising a housing 30 in which fuel from a pump 34 passes to a nozzle supply conduit 17 via a metering orifice 38 controlled by an axially and rotatably movable valve 40, the pressure drop across which is kept constant by a regulator valve 46; the valve 40 is fixed to a governor and acceleration control unit 56 as well as a rack 60 attached to a servopiston 62; the unit 56 is connected to a pilot's lever 70 and the engine drive shaft 72, and is responsive to compressor inlet pressure and temperature. The servo-cylinder 84 and rack mechanism 60 are in separate cavities 86, 88, respectively, that are interconnected by a passage 90, cavity 86 opening to the pump inlet via a conduit 92; piston 62 forms chambers 94, 96, the former of which is connected to the pump discharge by passages 98, 102, 104 and a restriction 100 whilst chamber 86 is connected to chamber 94 by passage 104, a calibrated restriction 106 and a half-ball valve 138 controlling the opening of the latter. Chambers 96 and 84 are in communication through the open end 156 of the cylinder 84. An air chamber 110 connected to the compressor discharge passage 112 through passages 118, 120 and restrictions 116, 122 contains an evacuated bellows 124 which, by means of a lever 132, is attached to the piston 62, the lever carrying the half-ball valve 138 and being connected to a piston spring 142 and a balance spring 148. A compressor pressure limiter 158 comprises a valve member 160 held in the seated position in an orifice 161 by an adjustable spring 164 in a chamber 166 which is open to passage 118. A bellows 176 in a chamber 178 is connected to the compressor discharge via passage 112 and a restriction 180 that controls the pressure level in chamber 110 in the event of failure of bellows 176, the interior 182 of the latter being connected to the compressor inlet or to atmosphere by channel 186; the left-hand end 190 of then bellows is closed and joined to the valve member 160 by a rod 192. If desired both ends of the bellows may be sealed and the bellows evacuated to respond to compressor discharge pressure only. The bellows 176 may be responsive to the differential pressure between only two compressor stages or to the pressure in any one stage. OPERATION. (a) Engine idle.-The governor 56 controls the axial position of the metering valve 40 to supply idling fuel whilst the angular position of this valve is determined by the compressor discharge pressure acting on bellows 124 which positions the half-ball valve 138 so that the pressure in chamber 94 holds the piston 62 in such a position that the resultant movement of the springs 142, 148 about the fulcrum 134 of the lever 132 balances the movement of the bellows 124 acting about the same fulcrum. Any change in the compressor discharge pressure causes a movement of the valve 138 to restore the force balance on the lever. (b) Acceleration.-The pilot's lever 70 is rotated and the metering valve 40 is lifted to increase the fuel flow whereupon the compressor discharge pressure increases and the bellows 124 rotates the lever 132 clockwise and decreases the flow past the half-ball valve 138 thereby increasing the pressure in chamber 94 and actuating the piston 62 so increasing the loading of spring 142 and rotating valve 40 to enlarge the area of the metering orifice 38; the piston travel ceases when the forces on the lever 132 again balance. (c) Controlling compressor pressure.-If at any time the compressor differential pressure exceeds the set force of the spring 164, the bellows 176 open the valve 160 thereby exhausting the compressor discharge pressure to atmosphere by way of channel 186 and hence cause an expansion of bellows 124 and a movement of pistons 62 to reduce the fuel supply until the pressure has reduced sufficiently to enable the spring 164 to re-seat the valve 160.