GB713436A - Improvements in or relating to axial-flow compressors - Google Patents

Abstract

713,436. Axial-flow compressors. ROLLSROYCE, Ltd. March 5, 1952 [March 14, 1951] No. 6209/51. Class 110(1) [Also in Group XXIX] In a multi-stage axial-flow compressor, air is bled off from a later stage through a bleed valve, the opening of which is controlled by a pressuresensitive element which is loaded in one sense by a fluid pressure which is a function of the compressor rotational speed, and in the opposite sense by a force which is a function of the opening of the bleed valve. In a compressor forming part of a gas turbine engine, Fig. 3, air is bled from intermediate stages through ports 33 into annular chambers 31 and thence through ports 36 the opening of which is controlled by slide valves 37. The latter are connected by linkage 41 to a hydraulic ram 42. The ram piston 44 has a hollow stem 46 which is in communication with the inside of the ram cylinder 43 to the right of the piston head 47; thus the effective area of the right-hand side of the piston head is greater than that of the left-hand side. The delivery pressure of a swashplate-type fuel pump 13 is applied through a pipe 50 directly to the left-hand side of the head 47 and by way of a restriction 53 to the right hand side. A centrifugal pump formed integrally with the pump 13 develops a pressure which is a function of the rotational speed of the engine (since the pump is driven by the engine), the pressure being, applied through a pipe 60 to one side of a diaphragm 58, the suction pressure of pump 13 being applied to the other side through a pipe 59. The diaphragm 58 is connected by a rod 67 to a half-ball valve 69. Increase of engine speed produces an increase of fluid pressure loading tending to move the diaphragm 58 against the action of a spring 62 and thereby to lift the valve 69 from its seat, so venting the right-hand end of the cylinder 43 to the pump suction through duct 52 and pipe 59. The resultant pressure drop due to the restriction 53 causes the piston 44 to move to the right, thereby increasing the opening of bleed valves 37. until the resultant increase of the force exerted on the diaphragm 58 by the spring 62 due to the increased compression of the latter by the piston 44 returns the valve 69 towards its closed position. A lower limit to the range of engine speeds over which the bleed valves 37 are adjusted is set by a secondary spring 66 which exerts a load on the diaphragm 58 which is independent of the position of the piston 44. Below this lower limit of speed, the bleed valves are maintained fully open. Stator blades 112 of the compressor may be connected to the ram 42 by linkage 110 so that their pitch is adjusted in unison with the bleed valve opening. In the modification shown in Fig. 4, the diaphragm 58 is loaded by the pressure drop across an orifice 100. the area of which is controlled, so as to be proportional to the square root of the engine intake temperature, by a capsule 101 connected to a bulb 108 in the engine intake. The pressure fluid for this purpose is supplied by a positive displacement pump 104 driven by the engine, producing a flow through the orifice 100 which is proportional to the engine speed. Thus the pressure drop across the orifice 100 is proportional to the corrected engine speed, i.e., the actual engine speed divided by the square root of the engine intake temperature, and the bleed valve opening is consequently a function of the corrected speed. In a further embodiment. the bleed valves each comprise a piston valve sliding in a cylinder having ported walls and conveniently forming part of the compressor casing. That part of the cylinder on the side of the piston valve remote from the ports is closed and is connected by way of a restriction to a source of high pressure, for example the delivery duct of the compressor. Downstream of the restriction, a connection is made to a point of low pressure such as the atmosphere through a valve of which the opening is controlled by the hydraulic ram 42. As this valve is progressively opened by the ram, the pressure downstream of the restriction (i.e., the pressure in the closed end of the cylinder tending to keep the piston valve in the closed position) is progressively reduced, so that the bleed valve opening is progressively increased. The piston valve may be lightly spring loaded towards the open position. Specification 704,849 is referred to.