Patent GB-672116-A (GB)
Title: Improvements in and relating to fuel control systems
IPC: F23N5/18
Filed: 1948-02-28
Abstract: 672,116. Fluid-pressure servomotor-control systems. ASKANIA REGULATOR CO. Feb. 28, 1948 [July 31, 1941 ; July 31, 1941 ; July 31, 1941 ; July 31, 1941], Nos. 6343/48, 6344/48, 6345/48, and 6346/48. Class 135. A fuel supply system for a furnace &c. comprises two fuel supply ducts and a common air supply duct, means for setting the rate of air supply, and means for automatically maintaining a rate of fuel supply appropriate to the air supply. As shown in Fig. 1, the sum of the flows through primary and secondary fuel ducts 10, 11 respectively is controlled through a differential gear 33 driven by a gear 52 rotatable through a rack 53 on a slide 54 carrying a cam 55 by which the air flow through a common supply duct 12 is set, said slide being adjustable through rack and pinion mechanism by a handwheel 58. The output of the differential is distributed through linkage between slides 21, 41 carrying cams 19, 40 by which the flows through the ducts 10, 11 are set. The set flows through the fuel and air ducts 11, 12 respectively are maintained through servomotors 45, 62 controlling valves 46, 61 in the ducts and supplied with pressure fluid by pivoted jet pipes 35, 65, the positions of which are determined by springs 39, 67, loaded by the cams 40, 55 and diaphragms 38, 68 subject to the pressure differentials across constrictions 34, 69 in the ducts. Variation in the flow of primary fuel through the duct 10 results in a change in the pressure differential across a constriction 13 and hence on the opposite sides of a diaphragm 16 controlling pivoted jet pipe 17, the pressure fluid from which controls a servomotor 25 which, through rack and pinion mechanism, adjusts the position of the cam 19. The movement of the cam .19 effects through the differential a complementary movement of the cam 40, so that an increase in the flow through the duct 10 is accompanied by a decrease in that through the duct 11. When the flow through the duct 10 exceeds that required by the furnace, the flow may be controlled by the hand-operated valve 10a. The air requirements are indicated on scales 29 by pointers 28. In a modification, in which the set flow through the primary duct is also maintained by a pivoted jet pipe associated with a servomotor controlling the valve in the duct, manually-adjustable means are provided in combination with the differential to maintain a constant ratio between the flows through the fuel ducts. Fig. 3 shows a system similar to that of Fig. 1 but having means to ensure that the primary fuel flow is controlled by the secondary fuel regulator when its flow exceeds that required by the furnace. In this case, the primary fuel valve 74 is controlled by a servomotor 72 connected by pipes 76, 77 to the servomotor 45 of the secondary fuel control valve 46. The pressure-fluid pipes 43, 44 of the regulator 35 are connected to the servomotors 45, 72 respectively. When the primary fuel flow is equal to that required by the furnace, the primary fuel regulator 17 effects, through the servomotor 25, slide 21, differential 33, slide 41 and cam 40, closure of the valve 46 and at the same time opens up communication between the pipes 43 and 77, so that the primary fuel valve servomotor 72 is controlled by the secondary fuel regulator 35. In another system, the valves 74, Fig. 4, in the primary and secondary ducts 10, 11 respectively may be controlled either manually through members 61 or automatically through servomotors 45 operated by pressure fluid supplied to either of the pipes 55, 56 by the pivoted jet pipes 17 which may also supply pipes 23, 24 connected to servomotors 25 via manually-operable three-way valves 57, 58. To permit of manual control of the valves 74, by-pass valves 90 are opened. The cams 19, 55 may be set manually through handwheels 82, 58 respectively, and the flow of the fuels may be controlled by setting the cam 55 to ensure the delivery of a predetermined quantity of air through the duct 12. The fuel valves and the cams may be set so as to permit of uncontrolled flow of one fuel and controlled flow of the other, the air cam being set through the differential. Specification 672,115 is referred to.