Patent GB-629889-A (GB)
Title: Improvements relating to speed governors, for example, for gas turbines
IPC: G05D13/00
Filed: 1946-01-07
Abstract: 629,889. Fluid-pressure servomotor-control systems; valves. POWER JETS (RESEARCH & DEVELOPMENT), Ltd., SHARP, J. G., and INGHAM, R. E. Jan. 7, 1946, No. 618. [Class 135] [Also in Group XXVI] A fluid-pressure servomotor-control system for controlling the speed of an engine, comprises two pressure-sensitive valves, each adapted to spill fuel from a delivery line, one of said valves being operable in direct response to pressure variations in an operating fluid consequent upon variations in engine speed whilst the other of said valves is operable by the first valve and indirectly responsive to the said pressure variations. As shown, a pump 1, Fig. 1, delivers fuel to an aircraft gas turbine through a supply line 2 having a restricted orifice 3 on each side of which is a pipe leading to either side of a diaphragm 12 housed in a chamber 9 secured to the casing 6 of a valve 4. The valve 4 houses a spring - urged plunger 8 operativelyconnected to the diaphragm, slidable in a bore 7 in the casing, and formed with recesses 21, 24 and an axial bore 15. The bore 7 communicates through a T-shaped port 17 and a slotted port 19 with the supply line 2 and a spill return line 5 respectively, and through ports 22, 23 with either end of a spring-urged plunger 31 slidable in the bore 30 of an auxiliary valve 28. The bore 30 communicates through a slotted port 70 and a round port 32a with the supply and spill lines respectively whilst the plunger 31 is provided with recesses 34, 35 to form substantially equal lands 36, 37 which are connected with each other by a bleed line 36a. In operation, an increase in engine speed increases the pump delivery and hence the pressure difference on the two sides of the diaphragm 12 to urge it and the plunger 8 to the left to increase the opening of the port 17 to the spill line 5 and hence reduce the engine speed. If this speed reduction is insufficient, the plunger 8 will continue its leftward movement to open communication between the left-hand side of the diaphragm 12 and the lefthand end of the plunger 31 through the bore 15 and the port 22 whence the plunger 31 will move to the left to increase the opening of the port 70 to further increase the amount of fuel being spilt to the line 5 and further decrease the speed of the engine. Conversely on a decrease in engine speed, the plungers 8, 31 are moved to the right to decrease the openings of the ports 17, 70. In this case the left-hand end of the plunger 31 is opened through the port 23 to communication with the left-hand side of the diaphragm and fuel at the right-hand end of the plunger escapes through the clearance between the land 37 and the bore 30. In a modification, a diaphragm 51, Fig. 3, is fitted to the right-hand end of the auxiliary valve 28 and the two sides thereof are connected through a pipe 83 and a pipe 53 having a restriction 52 with ports 49, 50 respectively in the valve 4. In this case supply and spill ports 45, 46 are arranged opposite to each other in the valve, the former being diamond-shaped. As before, on an increase in engine speed, the plunger 8 moves to the left and due to the shape of the port 45 the amount of fuel returned through the spill line 5 is increased whilst the pressure in a recess 48 increases relatively to that in a recess 47 to move the plunger 31 to the left to increase still further the amount of fuel spilt and hence decrease the engine speed. In a further modification, fuel in excess of that required by the burners 72, Fig. 4, is ejected into the spill line 5. In this case, the plunger 8 is formed with recesses 58, 59, 60 and the casing 6 of the valve 4 with spill ports 67, 68, a preferably T-shaped port 69, ports 65, 66 and bleed lines 78, 79. The port 65 being connected by a pipe 85 with the left-hand end of the plunger and through a restriction 52 with the right-hand side of the diaphragm 51 whilst the port 66 is connected by a pipe 86 with the left-hand side of the diaphragm 51. In operation on an increase in engine speed, the pressure drop across the orifice 3 increases and the plunger 8 is moved to the left to increase the amount of fuel being spilt from the burners through the ports 69, 67 to the line 5. At the same time the line 85 is opened to the increased pressure on the left-hand side of the diaphragm 12 through the bore 15, bleed line 78, recess 59 and the port 65 to move the plunger 31 to the left to increase the spill from the burners. Conversely on a decrease in engine speed, the plungers 8, 31 move to the right to decrease the spill from the burners. The pipe 85 now being opened to the spill line 5 through the port 65, recess 59 and the spill port 68, whilst the now decreased pressure to the left of the diaphragm 12 passes through the bleed line 79, port 66, and the pipe 86 to the left-hand side of the diaphragm 51.