Patent GB-1469926-A (GB)
Title: Fluid control valves
IPC: F02C9/26
Filed: 1973-07-09
Abstract: 1469926 Gas turbine engine fuel systems LUCAS INDUSTRIES Ltd 19 June 1974 [9 July 1973] 32667/73 Heading F1G [Also in Divisions F2 and G3]  A valve 12 in an air-pressure ratio control apparatus of a gas turbine fuel system comprises a closure plate 32 mounted on a pivoted arm 27 and co-operating with ports 22 in a wall 21 so as to control air-flow between chambers 20, 11 in body 10. The valve can be adjusted by control lever 23 which rotates a hollow shaft 28 carrying a cam 24 engaging a roller follower 25 carried by a pivotally mounted arm 26. The other end of the latter has a flat face 26a, Fig. 3, opposing a corresponding face 27a on closure carrying arm 27. Disposed between faces 26a, 27a is a roller 37 carried by an arm 36 pivotally connected to a crank 34 having a toothed quadrant meshing with worm 35. Rotation of the latter by means of stem 40 thus causes roller 37 to move upwards or downwards to alter the transmission ratio between lever 23 and closure plate 32. Arms 26, 27 are maintained in contact with roller 37 by pins 38 on arm 36. Arm 27 is biased to the valve closed position by a torsion spring 39 disposed about the arm shaft 29, the latter being rotatably carried within the hollow shaft 28 of lever 23. Closure plate 32 is mounted on arm 27 by means of a blade 30 and carrier 31, a spring 33 being disposed between the latter and arm 27 to urge closure 32 into engagement with ported wall 21. The air-pressure ratio control apparatus, shown diagrammatically in Fig. 9, acts to provide a pressure output signal through line 84 to a fuel metering device, which signal is a substantially linear function of the position of control lever 23. The apparatus receives through port 14 air at compressor output pressure P 4 , which air flows past flapper valve 51 at a rate dependent on the compressor inlet pressure P 1  acting via port 54 on an evacuated bellows 55 contained within body 10 and connected to flapper 51 by an arm 56 and shaft 52. This air flows through valve 12 and a parallel restriction 43 in wall 21, see also Figs. 4, 6 (not shown) to return to pressure P 1 , thus generating an intermediate control pressure P 4J  in chamber 20 dependent on the setting of valve 12. Pressure P 4J  is communicated to the interior of a bellows 70 which, together with evacuated bellows 71, acts on a beam 72 to control via shaft 73 a flapper 74 obturating the leak-off through an orifice 75, see also Fig. 8 (not shown) at one end of line 81. The latter communicates at its other end with a fluid potentiometer having an inlet 15 at pressure P4 connected via a filter, restriction 76 and venturi 77 to a port 18 at intermediate compressor pressure P 3 , see also Fig. 7 (not shown). Line 81 also communicates via adjustable restriction 82 with pressure P 1 . The resultant pressure KP 4P  in line 81 is communicated to output signal line 84. The effective size of restriction 43 in wall 21 can be adjusted by a threaded stud (44), Fig. 6 (not shown) rotatable by a worm and wheel (45). Wall 21 includes a further restriction (41) which is normally closed but which can be opened by a solenoid valve 42 to cause a sudden drop in  pressure P 4J  in chamber 20 and bellows 70. Means are provided Figs. 4 and 10 to 12 (not shown) to permit adjustment of flapper 51 relative to its drive shaft 52.