GB828689A - Improvements in or relating to pressure responsive devices for indicating or controlling apparatus - Google Patents

Abstract

828,689. Gas turbine Jet propulsion plant. SOLAR AIRCRAFT CO. Dec. 16, 1955 [Sept. 16, 1955], No. 36104/55. Addition to 796,093. Class 110 (3). [Also in Groups XIX, XXIX and XXXV] The pressure-responsive device described in the parent Specification in connection with the control of a jet propulsion engine is modified (a) by providing means to control the inlet orifice 82, Fig. 2, of the flow chamber 76 in response to changes in the temperature of the compressible fluid, or (b) by providing an operating linkage, whereby the inlet orifice may be controlled manually, or (c) by providing an additional inlet orifice, Fig. 10 (not shown,) and means for selectively preventing or permitting flow through the additional orifice, or (d) by providing an additional inlet orifice, Fig. 13, (not shown), in parallel with the first inlet orifice and controlling the effective area of the additional orifice by a control needle operable by a second diaphragm or the like sensitive to changes between another selected pressure and the reference pressure in a second flow chamber having inlet and outlet orifices in series through which compressible fluid flows, or (e) by replacing the single diaphragm by a pair of diaphragms of different area, as in Fig. 9 (not shown), or (f) by arranging that the diaphragmoperated member which extends through one of the orifices has a portion of non-uniform crosssection in or adjacent the orifice so as to cause the member to move with a snap-action from one position to another or to increase the effective area of the outlet orifice when the reference pressure decreases relative to the selected pressure. Fig. 2 shows a practical embodiment of the parent invention, the pressure responsive device comprising a diaphragm 70 clamped between casing sections 66, 64 to form pressure chambers 74, 76 and the inlet and outlet orifices 82, 84 being formed in sheet-metal plates 86, 88 shrouded by a deflector 90. The area of the orifice 82 is adjusted by a screw-threaded needle 104 and that of the orifice 84 by the tapered section 112 of a needle 110 secured to the diaphragm 70 and carrying at its lower end an insulating block 130 bearing wiper contacts 132, 134. The contact 132 co-operates with a potentiometer 138 and the contacts 134 with fixed contact posts 148 having oppositelydisposed insulating and conducting sections 156, 158. The potentiometer and contact assembly and a standard connector 166 are mounted in a housing 100 having a cover plate 102. Bosses 114, 116 limit the movement of the diaphragm 70. Secondary chambers 78, 80 are formed below the orifices 82, 84, respectively. Fig. 1 shows the device at 56 used to maintain a constant pressure ratio across the turbine 24 of a jet propulsion engine by adjusting the area of the outlet nozzle 30 by movement of a shroud 32. Continuous vernier adjustments of the nozzle area are effected through a differential lever 40 and a screw-and-nut mechanism 36 by an electric motor 34 whilst rapid major displacements are effected through the lever 40 by a pneumatic servomotor 42 under the control of a valve 46 actuated by solenoids 48, 50. The chamber 78 at the inlet to the orifice 82 is connected by a conduit 58 to the discharge of the usual compressor 20, the chamber 80 at the outlet of the orifice 84 is connected to the ambient atmosphere by a conduit 62 and the chamber 74 is connected to the discharge side of the turbine 24 by a conduit 60. For small movements of the needle 110, the contacts 134 do not move off the dead band formed by the insulating sections 156 and the motor 34 is energized through an amplifier 52. For larger deviations one or other of the solenoids 48, 50 is energized through an amplifier 54. It is shown in the Specification that if the orifice 82 is fixed and both orifices 82, 84 are choked, the displacement of the needle 110 is proportional to the ratio #, where P2 is the turbine outlet pressure and P1 is the compressor delivery pressure. The diaphragm 70 may be loaded by a spring in the chamber 74, such an arrangement being used to compensate for loss of compressor efficiency by increasing the turbine pressure ratio at high altitudes. To compensate for the increase in compressor inlet temperature the turbine pressure ratio is reduced as this temperature rises by progressively throttling the first orifice 82 by a needle 204, Fig. 8, adjusted by a pile of bimetallic discs and shaped to match the desired engine characteristic. The orifice 82 may be a convergent nozzle and the orifice 84 a convergent-divergent nozzle. Such an arrangement tends to maintain a pressure in the chamber 76 which is lower than the tailpipe pressure until sonic velocity is reached. Thus the nozzle 30 is opened somewhat during warming up and acceleration. Also the operating range in which the orifice 84 is choked is increased. A further arrangement of the pressure-responsive device, Fig. 9 (not shown), includes two diaphragms of different area, separating three chambers, and has connections to the compressor inlet, the turbine outlet, and the compressor outlet. The arrangement is used to add or subtract two ratios, and as applied to a jet-propulsion engine operates to open the nozzle 30 and so increase the turbine pressure ratio when the compressor inlet temperature rises. For use at take-off, a heating element may be provided in the flow chamber between the inlet and outlet orifices. Snapacting or two-position controls may be obtained by forming the needle controlling the second orifice with an upper part of small diameter and a lower part of greater diameter or alternatively by giving the needle a reversely tapered portion as compared with the needle 110, Fig. 2. The two positions correspond to two pressure ratio settings. For a needle of uniform diameter, the two pressure ratio settings are the same. Two adjustable inlet orifices to the control chamber 76 may be provided, the second being rendered effective only on the opening of a solenoid-operated valve in a conduit by-passing the first orifice. Such an arrangement can be utilized to attain an automatic shift in turbine pressure ratio when changing over to " afterburning." A further pressure-responsive device, Fig. 13 (not shown), comprises two units 400, 402, Fig. 16, arranged at right-angles, the inlet orifice of the first unit 400 being controlled by a reversely tapered portion on the control needle of the second unit. Such a device may be arranged to control one pressure ratio in accordance with another according to some non-linear relation. Fig. 16 shows such an actuator 583 operating a compressor blow-off valve 582 in a duct 580. The compound unit 400, 402 of Fig. 13 (not shown), is used to control the bleed air flow of a turbinedriven compressor 572 in a predetermined relation to the compressor pressure ratio. The bleed air flow is measured by the static and dynamic pressures in the pipes 435, 443 respectively, these pressures being applied to the unit 400. The compressor pressure ratio is determined by the pressures in the pipes 443, 537, these pressures being applied to the unit 402.