GB745905A - Improvements in or relating to pressure-ratio sensitive mechanisms - Google Patents

Abstract

745,905. Fluid-pressure servomotor-control systems. ROLLS-ROYCE, Ltd. Nov. 30, 1953 [Sept. 16, 1952], No. 23284/52. Class 135. A mechanism responsive to the ratio between the pressure at two sources of gaseous pressure comprises a conduit connected to one of the sources having two restrictive orifices in series of which at least the downstream orifice is choked and one of the orifices is of variable area and a pressure-responsive device having a first area subjected to the pressure at the higher source, a second area subjected to the pressure at the lower source or the pressure between the orifices, whichever is the lower, and a third area subjected to the pressure at the lower source or the pressure between the orifices, whichever is the higher, the pressure load on the first and second areas being in the same sense and opposite to that on the third area, and the pressure-responsive device being connected to the variable area orifice so that on movement of the pressure-responsive device due to out-ofbalance pressure loads thereon the variable area orifice is adjusted to restore the pressureresponsive device to a state of balance. As shown, the invention is applied to adjust the angle of guide vanes 23 of a compressor 2 in accordance with the ratio between its inlet and outlet pressures. The outlet pressure passing through a conduit 1 having a fixed restrictive orifice 3 in series with a variable choked orifice 4 opening to the atmosphere and controlled by a needle valve 5 connected to the piston 16 of a servomotor 17 supplied with operating fluid directly to its left-hand space 18 through a pipe 19 and indirectly to its right-hand space 20 through a restriction 21. Exhaust from the space 20 is controlled by a leak-off valve 15 carried by a lever 14 connected to the rod 12 of a pressure-responsive device 13 comprising a pair of diaphragms 6, 9. Compressor outlet pressure acts on the outer face of the diaphragm 6, the pressure between the orifices 3, 4 on the outer face of the diaphragm 9 and compressor inlet pressure, i.e. atmospheric pressure, on the inner faces of the diaphragms. Should, e.g., compressor outlet pressure increase, the pressure between the orifices will also increase and acting on the larger area diaphragm will open the leakoff valve 15 to relieve pressure in the space 20 to permit rightward movement of the piston 16 to increase the opening of the orifice 4 and at the same time adjust the angle of the guide vanes 23 through a mechanical linkage 24. The increased opening of the orifice 4 reduces the pressure beneath the diaphragm 9 and restores the pressure-responsive device to a state of balance. The diaphragms may be replaced by a pair of interconnected pistons or by a differential piston. Specification 736,003 is referred to.