GB757900A - Improvements in or relating to pressure ratio sensitive mechanisms - Google Patents

Abstract

757,900. Jet propulsion plant. ROLLSROYCE. Ltd. June 4, 1954 [March 30, 1953], No. 8807/53. Addition to 736,003 [Group XXIX]. Class 110(3) [Also in Group XXIX] In a mechanism sensitive under all conditions of ambient atmospheric pressure to the ratio of the absolute pressures at two compressible fluid-pressure sources as described in the parent Specification (Group XXIX), having a pair of restrictive orifices in series in a flow passage in which at least the downstream orifice is choked and the area of one of the orifices is variable, a further restrictive orifice is provided in the flow passage between the other two and the pressure on the upstream side of this further orifice is used to load the pressureresponsive device to adjust the area of the variable orifice and balance the loads acting on opposite sides of the pressure-responsive device. The invention is described for use in a gas-turbine engine to maintain a preselected value of the ratio of a pressure at a point A in the engine between the compressor delivery and the turbine inlet to a pressure at a point B between the turbine and the propelling nozzle. As shown, a casing 10, Fig. 1, is divided into chambers 11, 12 by a partition 13 having an opening 14 through which passes an arcuate piston element 15 mounted on a radius arm 16 fixed to a shaft 17, and counterbalanced by a weight 18. The chamber 11 is connected to the pressure point A through a choked orifice 20 and a conduit 19 and with exhaust through a restricted outlet 21a controlled by the piston 15 which constitutes the further restrictive orifice and a choked venturi orifice 21. The chamber 12 is connected to the pressure point B through a conduit 22. The shaft 17 carrying the arm 16 also carries a second radius arm 25 operably connected to a piston valve 26 controlling the flow of a servo-pressure fluid from the space 29 of a servomotor cylinder 28 having a piston 31 urged upwardly by a spring 32. The servo-fluid being supplied to a space 30 below the piston and passing to the space 29 through a fixed restrictor 35. The piston 31 operated through its rod 31a and a rack and pinion a throttle valve 23 arranged to control the pressure in the conduit 22 in a manner described in Specification 694,322, by varying the quantity of air supplied to the turbine of an air-turbinedriven fuel pump to control the amount of fuel supplied to the reheater of the gasturbine engine to vary the pressure between the turbine and the propelling nozzle. Opening of the valve 23 increases this pressure and closing thereof decreases the pressure. On, e.g. an increase in the ratio of the pressures at points A and B due to a decrease in pressure at the point B, the pressure in the chamber 12 decreases moving the piston element 15 to increase the opening 21a to decrease the pressure in the chamber 11 and at the same time moving the piston valve 26 to reduce the outflow from the space 29 of the cylinder 28. The piston 31 then moves downwardly to increase the opening of the valve 23 and the pressure in the conduit 22 and the chamber 12 to restore the piston element 15 to its intial position. In a modification, the shaft 17, Fig. 2, carries an obturator device 40 controlling a conduit 44 connecting the servo-pressure fluid supply pipe 43 to the space 45a above the servo-motor piston 46.