GB1250041A - Improvements in and relating to axial fluid flow machines - Google Patents

Abstract

1,250,041. Axial-flow turbines and compressors. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. April 6, 1970 [Jan. 14, 1969], No. 2096/69. Headings F1C and F1T. An axial-flow turbine or compressor having a carrier 4 supporting several stator diaphragms 5 and enclosed in an inner housing 9 mounted within an outer casing 3 is arranged such that the axial forces transmitted to the carrier 4 by the diaphragms during operation of the machine are substantially balanced by fluid-pressure forces acting on the carrier. In the steam turbine shown, working steam is admitted through a pipe 6 to an annular chamber 6a in the carrier 4 and thence expands through the turbine stages to an exhaust passage 7. Some steam from the latter is ducted into a chamber 7a at the opposite end of carrier 4 and acts on the right-hand end faces of a carrier extension 4c and of an annular seal member 15 surrounding the extension and secured to the carrier by bolts 16. The extension 4c and the seal 15 effectively act as a piston, the seal 15 being slidable within piston rings 17 fitted in a cylindrical bore 9a of the housing 9. The steam in chamber 7a is at relatively low-pressure and the areas on which the various steam forces act are chosen so that the carrier 4 is urged to the right with a force substantially balancing the axial force to the left caused by the steam pressure acting on the diaphragms 5, the net force being such as to lightly urge flange 4a on the carrier into engagement with the adjacent end of housing 9. The loading on bolts 13 is thus reduced. Carrier 4 is located against rotational movement by keys 14, 14a and is also supported by horizontal bearing surfaces. Axial location of carrier 4 and housing 9 is provided by a projection on seal 15 which locates in a groove in the inner surface of casing 3. The carrier 4 can thus expand to the left from this point whilst the housing 9 can expand to the right from the end connected to flange 4a. The carrier is split axially into two or more segments but the surrounding housing 9 is unsplit, the annular gap 10 between the carrier and housing 9 being supplied with steam at inlet pressure to ensure that the carrier is maintained under radial compression. Steam from gap 10 also flows to the space 15b between face 17a of seal 15 and the adjacent piston ring 17, the differential pressures on the seal 15 resulting in substantially zero loading on the seal face 15a. In a modified steam turbine, Fig. 2 (not shown), the inlet chamber 6a is replaced by a nozzle box (20) which directs steam to a first impulse stage and subsequent reaction stages, the steam for gap 10 being tapped through radial passages (23) in carrier 4 from an interstage space (22). In a further modification, rather than using working fluid-pressure to balance axial thrust on carrier 4, the latter is subjected to thrust produced by lubricating oil supplied through a differential pressure amplifier controlled by the pressures at the inlet and exhaust of the machine. The thrust balancing arrangement operates in similar manner when applied to an axial-flow compressor.