Patent GB-827282-A (GB)
Title: Improvements in or relating to pressure-sensitive control mechanisms
Inventor: DAVIES DAVID OMRI
IPC: F01D17/08
Filed: 1954-11-15
Abstract: 827,282. Jet propulsion plant; gas turbines. ROLLS-ROYCE Ltd. Feb. 14, 1956 [Nov. 15, 1954; Oct. 10, 1955], Nos. 33074/54 and 28858/55. Class 110 (3). [Also in Group XXIX] A fuel system having a pressure controlled by a control element adapted to be loaded by a pair of loads each of which varies in accordance with the pressure to be controlled but whereof the fluctuations in one load due to cyclical variations in the controlled pressure lag in phase with respect to the fluctuations in the other load, the arrangement being such that the fluctuations of the resultant load on the control element and in effect in advance of the controlled pressure. A fuel system as described in Specification 748,353, [Group XXIX], for controlling the supply of fuel to reheat burners in a gas turbine installation comprises a valve closure member 10, Fig. 1, accompanying the first Provisional Specification, controlling the outlet from a bleed pipe 11 of a servo system controlling a throttle valve of a turbine driving a fuel pump or the delivery varying means of a variable delivery pump and is carried by a lever 12 which is acted upon by springs 22, 23 and diaphragms 17, 19 of differing areas. The space between the diaphragms is connected by a pipe 27 to a conduit 28 containing a pair of restrictions 29, 30 and connected at one end to a point between the compressor delivery and the turbine and at the other end to atmosphere. The restriction on the atmospheric side is arranged to be choked so that the pressure in the pipe 27 is independent of atmospheric pressure. The lower side of the larger diaphragm 19 is subjected to the pressure between the turbine and the propulsion nozzle through a conduit 26 and this pressure is transmitted through a conduit 24 containing a restriction 25 to a chamber 16 above the smaller diaphragm 17. Thus an increase, say, in the pressure below the diaphragm 19 acting to close the valve member 10 to reduce the amount of fuel to the reheat burners is effective firstly on the whole of the area of the diaphragm 19 and subsequently, due to the restriction 25, on the difference between the areas of the diaphragms 17, 19 giving in effect a phase advance of the change of pressure. If the two controlled pressures tend to oscillate in phase with each other a restriction may be placed in the pipe 27. In a modification, the space between the two diaphragms may be evacuated so that the device responds to a single, absolute pressure. The invention may be applied to an arrangement including a capsule connected to the two diaphragms as in Specification 694,322 and in this case the interior of the capsule is connected through a restriction to the chamber bounded by the larger diaphragm to give the phase difference. The invention may also be applied to a fuel flow trimming control as in Specification 782,653. In a further embodiment, the valve member 10 controls a servomotor 42, the second Provisional Specification, which actuates a valve 41 controlling the flow of air in a conduit 40, e.g. compressed air led from the compressor of a gas turbine to auxiliary equipment. The pressure at a point downstream of the valve 41 is fed to the chamber 21 below the larger diaphragm 19 and also passes through the restriction 25 to the chamber above the smaller diaphragm 17. The space between the two diaphragms is vented to atmosphere.