Turbines

Claim 1

A turbine including a rotor having at least one rotor stage, and a stator having at least one stator stage, the rotor and the stator defining between them an annular clearance passage at each stage, there being provided a seal for at least one passage for maintaining a pressure difference between the upstream and downstream sides thereof, the seal including: means within the stator which define a first circumferentially extending duct which communicates with the passage; fluid-feeding means connected to the first duct for feeding a fluid thereto at a pressure greater than the pressure obtaining on either side of the passage, the first duct being arranged to direct an annular jet of fluid into the passage to provide therein a moving curtain of fluid which can be deflected owing to the said pressure difference, the said jet having sufficient initial velocity that changes of fluid momentum during deflection of the jet are sufficient to maintain the said pressure difference; further means within the stator which define a circumferentially extending chamber communicating with the passage at a point axially adjacent to the first duct; and fluid release means comprising a conduit connected to the chamber, such that at least part of the fluid in the said jet can be deflected into the chamber and released therefrom via the said conduit to a second duct for use in a further annular jet, whereby to form a further moving curtain of fluid.