Pressure balanced brush seal

#The present invention relates to brush seals between static and rotary components, sealing between high and low pressure regions and particularly relates to a balanced pressure brush seal for producing either a desired nonuniform or a substantially uniform pressure distribution on opposite sides of the bristle pack achieving an anti-hysterisis effect.

#Typically, brush seals disposed between static and rotary components, for example between a packing and a rotary shaft or between a shroud and a bucket tip in a turbine include a bristle pack disposed between a fence on the high pressure side and a pressure plate on the low pressure side of the seal. The bristle pack normally includes a plurality of densely packed bristles fixed at one end adjacent the static component and cantilevered to extend substantially freely toward the rotor where the tips of the bristles engage the rotor. Typically, the bristles extend normally in the direction of rotation i.e. in the circumferential direction of rotation of the rotor forming an angle with the radius. The fence as well as the pressure plate have free ends which terminate short of the surface of the rotary component. Because of the pressure drop across the bristles, including the frictional engagements between the bristles and the pressure plate, and between layers of bristles, temporary excursions of the rotor, for example during turbine start up may permanently deflect or bend the bristles such that the tips no longer engage the rotor. Alternately, temporary rotor excursions may displace bristles radially away from the rotor with the seal under pressure whereby the bristle to bristle and bristle to pressure plate friction prohibits the bristles from returning to their position very close to the rotary component. This of course degrades the seal and has other deleterious effects on the wear life of the seal.

#This phenomenon known as an anti-hysterisis effect, previously has been addressed. For example, in U.S. Pat. No. 5,799,952, a brush seal is provided having radially extending circumferentially spaced grooves formed in the pressure plate in an effort to obtain a balancing of the pressure on opposite sides of the bristle pack. In another known form of brush seal, a plurality of circumferentially extending grooves of varying width at discrete radial locations about the brush seal segment have been proposed and constructed in order to substantially balance the pressure on the opposite sides of the brush seals. It is also noted that suppliers of brush seal backing plate material, such as 409 stainless steel, have material availability problems as well as manufacturing difficulties in the formation of the brush seals. Accordingly, it has been found desirable to provide an improved pressure balanced brush seal which is readily and easily manufactured, provides substantially balanced pressure and which may be formed of more readily available materials.

#FIG. 1 is a fragmentary perspective view of a pressure balanced brush seal according to an aspect of the present invention disposed between a static and rotary component of a turbine.

#FIG. 2 is an enlarged cross-sectional view of the brush seal;

#FIG. 3 is a fragmentary enlarged elevational view of the bristle backing plate;

#Referring to FIG. 1, there is illustrated a brush seal generally designated 10 disposed between static and rotary components 12 and 14, respectively, e.g. of a turbine. The rotary component may for example comprise a shaft 14 or the tips of buckets with the static component comprising a packing or a shroud 12 mounting the brush seal 10. As illustrated, the brush seal is mounted on opposite sides of high and low pressure regions. The brush seal 10 includes a fence 16, a plurality of bristles forming a bristle pack 18, a bristle backing plate 20 and a pressure plate 22. The fence 16, bristle pack 18, backing plate 20 and pressure plate 22 are joined one to the other and to the static component 12 in a known manner e.g. by welding. It will be appreciated that the brush seal 10 may be provided in arcuate segments about the axis of the rotary component 14, for example six segments of 60° each may be provided. Thus, the fence, bristle backing plate and the pressure plate are generally circumferentially coextensive with one another. The bristle pack is similarly coextensive except that the bristles angularly project from one end of the segment while the opposite end of the segment may include a pocket for receiving the projecting bristles of an adjacent brush seal segment.

#As illustrated, the fence 16 extends radially inwardly from the static component 12 terminating in an edge 24 spaced radially from the rotary component 14 a distance typically to avoid interference with the rotor in the event of any rotary excursions of the rotor. The bristle pack may be formed of bristles in a conventional manner and extends from the static component or the weld at the proximal end of the brush seal toward the rotary component such that the tips 26 of the bristles engage the rotary component. The bristles, as is conventional, extend from the static component at an angle to a radius and typically in the rotary direction. The bristles may be formed of any known materials typically used in brush seals, for example see U.S. Pat. No. 5,474,306, the disclosure of which is incorporated by reference.

#Located between the bristle pack 18 and the pressure plate 22 is a bristle backing plate 20. Plate 20, as illustrated in FIGS. 3 and 4, preferably includes a plurality of circumferentially extending slots 30 arranged in radially spaced rows. Each slot 30 extends through the bristle backing plate 20. The slots 30 also extend discontinuously in circumferential directions. Further, adjacent slots 30 are staggered relative to one another in a circumferential direction at each radial location relative to the adjacent radial location. For example, the first row of slots 30a at a radially innermost position has end portions in radial alignment with the second row of slots 30b radially outwardly of the first row. Similarly, the third row of slots 30c has end portions which are radially aligned respectively with end portions of adjacent slots of the second row of slots 30b as well as end of portions of circumferentially adjacent slots 30d in the outermost row of slots 30 in the bristle backing plate 20. It will be appreciated that additional or fewer circumferentially extending rows of slots may be formed in the bristle backing plate 20. Further, it will be seen in FIG. 3 that the slots 30a and 30c at opposite ends of the brush seal segment open toward and into the corresponding slots of the backing plates 20 of adjacent brush seal segments. In the preferred embodiment, any radial line passing through the backing plate 20 passes through at least two of the circumferentially extending slots 30 and, for large circumferentially portions of the plate 20 passes through the slots of all four rows of slots.