Patent GB-646780-A (GB)
Abstract: 646,780. Gas turbine plant. BENDIX AVIATION CORPORATION. April 21, 1947, No. 10558. Convention date, May 16, 1946. [Class 110(iii)] [Also in Group XXIX] A fuel feeding system for gas turbines having a conduit for conducting fuel under pressure to the burner and having a variable metering restriction therein, power control mechanism including an element for varying the area of said restriction, a regulating valve for controlling the pressure differential across said restriction, and a pressure responsive member operatively connected to said valve for determining the effective flow regulating position of the valve, is characterized in that the pressure responsive member is subjected to a regulating pressure proportional to the flow of air to the burner. Fuel is delivered by a pump 28 to a conduit 29 whence it flows through valve-controlled openings 66, 66<SP>1</SP> constituting the variable metering restriotion and through a conduit 69 to the burner nozzles. The valve 65 moves, under the control of a turbine driven governor 78 connected with the valve by a rod 75, between adjustable stops 91, 92, the governor being variably loaded by a spring 84 abutting at one end against a member 83 fixed to the rod 75 and at its other end against a member 85 movable on the rod 75 by an arm 86 connected with a manual power control lever 88. The conduit 29 also connects with a chamber D bounded on one side by a diaphragm 30 and having openings 33, 33' by which the chamber communicates, through a conduit 35, with the low pressure or inlet side of the pump 28 under the control of a valve 32 actuated by the diaphragm. A chamber C is connected with the chamber 68 which contains metered fuel whereby the diaphragm 30 and the metering restriction 66, 66<SP>1</SP> are subject to the same pressure difference. The diaphragm 30 is also loaded by a spring 36 having an abutment 39 movable by a servo piston 37 which is controlled by a piston valve 48 connected by a floating lever 41 to the servo piston and having a connection 42 with a lever 43 pivoted at 47 and connected to a bellows 45 subjected internally to the delivery pressure of a centrifugal blower which supplies the air for combustion, and externally to the intake pressure of the blower. The bellows 45, therefore, responds to the pressure rise across the blower which is a measure of the air flow to the burners and adjusts the servo piston 37 such that the spring 36 exerts on the diaphragm 30 a force proportional to the air flow and thus the valve 32 is set to establish a pressure difference across the metering restriction which balances the spring load on the diaphragm, this pressure difference being dependent upon the flow of air to the burners. To compensate for changes in air density, a valve-controlled leak-off orifice 61 is governed by a further bellows 63 sensitive to changes both in pressure and temperature. In operation, movement of the control lever 88, e.g., to increase power, compresses the spring 84 and causes the valve 65 to open fully and increase the flow of fuel to the burners, this increase, however, being insufficient to cause overheating. The fuel flow is then further increased as the turbine speeds up and the pressure rise across the blower causes an increased spring loading on the diaphragm 30 and therefore a greater pressure difference across the metering orifice, until a speed is reached at which the governor balances the spring 84. Similarly, when the lever 88 is moved to reduce power and the valve 65 is urged to its stop 91, the fuel flow is maintained sufficient to prevent extinguishing of the burner by the pressure difference across the metering restriction which is proportional to the flow of air to the burners. A relief valve 93 enables fuel in the chamber D to escape to the pump inlet should the pressure in this chamber rise above a predetermined amount, e.g. by the closing of a shut-off valve 90 in the conduit 69. Specifications 603,884 and 608,031, [Group XI], are referred to.