Brush seal device having a floating backplate

A brush seal device for sealing a high pressure area from a low pressure area. The brush seal device comprises an annular sideplate having a first side facing the high pressure area and a second side opposite the first side, an annular backplate having a first side facing the low pressure area and a second side opposite the first side, and a plurality of bristles between the second side of the sideplate and the second side of the backplate. The backplate is moveable in a radial direction relative to the annular sideplate and the plurality of bristles extend inwardly from an outer peripheral edge of the sideplate. The brush seal device further comprises a retaining washer between the first side of the backplate and the low pressure area, wherein the retaining washer includes a cavity proximate the first side of the backplate, the cavity having an adjustable pressure therein.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to gas or liquid seals and, more 
particularly, to brush seals for sealing high pressure areas from low 
pressure areas. 
2. Description of the Related Art 
Over the last decade, brush seals have emerged to be a very promising 
technology for sealing high pressure areas from low pressure areas such as 
those found in gas turbine engines. Indeed, there is a substantial 
reduction, e.g., an order of magnitude, in brush seal leakage flow over 
the present day technology of labyrinth seals, the main disadvantage 
associated with labyrinth seals being that the clearance of the seal 
around the shaft tends to increase appreciably over time due to shaft 
excursions and thermal growth. The resulting increase in parasitic leakage 
can cause as much as 17 percent loss in power and 7.5 percent increase in 
specific fuel consumption in the case of engines. 
One drawback of current brush seal designs is that the minimum clearance 
between the backplate and the shaft must be at least great enough to 
accommodate various transients that the seal is expected to experience. 
Some of the transients include thermal growth of the shaft, centrifugal 
growth of the shaft, runout of the shaft, thermal bowing of the shaft on 
heat-up, shaft movement due to acceleration (turning acceleration), shaft 
vibration, and eccentricity of the seal housing with respect to the shaft 
center line. 
Seal leakage increases and maximum pressure capability of the seal 
decreases, however, as the clearance between the shaft and backplate is 
increased. Thus, seal performance is improved if the seal can be made with 
a smaller backplate clearance. 
SUMMARY OF THE INVENTION 
Features and advantages of the invention will be set forth in the 
description which follows, and in part will be apparent from the 
description, or may be learned by practice of the invention. The objects 
and other advantages of the invention will be realized and attained by the 
apparatus particularly pointed out in the written description, claims and 
appended drawings. 
To achieve these and other advantages and in accordance with the purposes 
of the invention as embodied and broadly described herein, a brush seal 
device for sealing a high pressure area from a low pressure area is 
provided. The brush seal device comprises an annular sideplate having a 
first side facing the high pressure area and a second side opposite the 
first side, an annular backplate having a first side facing the low 
pressure area and a second side opposite the first side, and a plurality 
of bristles between the second side of the sideplate and the second side 
of the backplate. The backplate is moveable in a radial direction relative 
to the annular sideplate and the plurality of bristles extend inwardly 
from an outer peripheral edge of the sideplate. 
In one aspect of the invention, the brush seal device further comprises a 
retaining washer between the first side of the backplate and the low 
pressure area. The retaining washer defines a cavity proximate the first 
side of the backplate, the cavity having a pressure therein. 
It is to be understood that both the foregoing general description and the 
following detailed description are exemplary and explanatory and are 
intended to provide further explanation of the invention as claimed.

DETAILED DESCRIPTION OF THE INVENTION 
Reference will now be made in detail to the presently preferred embodiments 
of the invention. 
As embodied herein, a brush seal device 10 is provided for inhibiting the 
flow of a gas (or liquid) in a stream along a shaft 20. The gas (or 
liquid) is sealed, for example, within a machine housing (not shown) and 
has a system pressure of P.sub.system. The area outside of the sealed 
machine housing toward which the sealed gas will tend to leak has a 
discharge pressure P.sub.discharge, the system pressure P.sub.system being 
greater than the discharge pressure P.sub.discharge. 
The brush seal device 10 comprises an annular sideplate 30 having a first 
side facing the system pressure P.sub.system and a second side opposite 
the first side, and an annular backplate 40 having a first side facing the 
discharge pressure P.sub.discharge and a second side opposite the first 
side. While the sideplate 30 is preferably fixed to the machine housing 
(not shown), as will be explained below, the backplate 40 is moveable in a 
radial direction relative to the sideplate 30. 
Preferably, both the sideplate 30 and the backplate 40 comprise materials 
that have a high yield strength at high temperatures. For example, the 
sideplate 30 and the backplate 40 can comprise a nickel based alloy such 
as Inconel.RTM. manufactured by Inco Alloys International. It is 
contemplated that the composition of the sideplate 30 and the backplate 40 
can be varied depending on the particular application with which the brush 
seal device 10 is to be used. 
The brush seal device 10 further comprises a plurality of bristles 50 
between the second side of the sideplate 30 and the second side of the 
backplate 40. In particular, the bristles 50 are preferably sandwiched 
between a squeeze plate 90, the squeeze plate 90 being between the second 
side of the backplate 40 and the plurality of bristles 50 and preferably 
fixed to the machine housing (not shown), and the sideplate 30. The 
squeeze plate 90 can comprise the same material as the sideplate 30 and 
the backplate 40. The bristles 50 can be secured between the second side 
of the sideplate 30 and the squeeze plate 90 by, for example, a weld 60 or 
other means known in the art, depending on the materials used for the 
sideplate 30, the squeeze plate 90, the bristles 50, and the housing (not 
shown). 
The bristles 50 extend inwardly from an outer peripheral edge of the 
sideplate 30 such that their free ends run against the shaft 20 to thereby 
seal the system pressure P.sub.system from the discharge pressure 
P.sub.discharge along the shaft 20. Further, the bristles 50 are 
preferably angled relative to respective radii of the sideplate 30 and the 
squeeze plate 90 so as to have a circumferential component of direction 
relative to a direction of rotation of the shaft 20. 
To retain their shape, especially at higher temperatures, the bristles 50 
preferably comprise a high temperature nickel based alloy such as Haynes 
25.RTM. manufactured by Haynes International. It is contemplated, however, 
that the bristles 50 can comprise other materials to a suit a particular 
application. 
Typical dimensions of the bristles 50 include bristle diameters of about 
0.0028-0.0008 inch, and bristle free lengths of about 0.200-0.700 inch. 
Further, the plurality of bristles 50 can be arranged into about 10-26 
rows between the second side of the sideplate 30 and the second side of 
the backplate 40 with a pack width of about 0.020-0.040 inch. Again, it is 
contemplated that the dimensions and configuration of the bristles 50 can 
be varied to a suit a particular application. 
Referring to FIG. 1, there is preferably a clearance c between the inner 
peripheral edge of the backplate 40 and the shaft 20 to accommodate 
centrifugal and thermal growth of the shaft. To reduce friction between 
the backplate 40 and the shaft 20 should they come in contact, a 
nonabrasive coating 120 having a low friction coefficient, such as, for 
example, a TFE, graphite, carbon, or chrome carbide coating, can be 
deposited on the inner peripheral edge of the backplate 40. Alternatively, 
the backplate 40 and/or shaft 20 can be formed of a nonabrasive material 
having a low friction coefficient. 
To respond to radial transients of the shaft 20, the backplate 40 is 
moveable in a radial direction relative to the sideplate 30. To facilitate 
such radial movement, the backplate 40 is preferably provided with a 
recess 42 as shown in FIGS. 1 and 2, wherein the squeeze plate 90 is in 
sliding engagement with the recess 42. Preferably, the dimensions of the 
recess 42 are such that the backplate 40 can respond to radial transients 
of the shaft 20 caused by such factors as runout and thermal bowing of the 
shaft 20, movement of the shaft 20 due to turning acceleration, shaft 
vibration, and eccentricity of the seal housing with respect to the center 
line of the shaft 20. It is contemplated that radial transients of at 
least 0.030 inches can be accommodated by the present invention. 
To inhibit rotational movement of the backplate 40, the brush seal device 
10 is provided with an anti-rotational member. As shown in FIGS. 1 and 2 
by way of example and not limitation, this anti-rotational member is 
represented by an anti-rotation pin 100. A recess 110 is formed in the 
second side of the backplate 40 and the anti-rotation pin 100 is in 
sliding engagement with the recess 110. 
Preferably, the anti-rotation pin 100 comprises the same material as the 
squeeze plate 90 and is secured to the squeeze plate 90 by means known in 
the art. Alternatively, the anti-rotation pin 100 and squeeze plate 90 can 
be formed from a single piece of material. It is contemplated that the 
shape and configuration of both the anti-rotation pin 100 and the recess 
110 can be varied while still inhibiting rotation and allowing radial 
movement of the backplate 40. 
As shown in FIGS. 1 and 3, the brush seal device 10 further comprises a 
retaining washer 70 between the first side of the backplate 40 and the 
discharge pressure P.sub.discharge. The retaining washer 70 is also 
preferably fixed to the machine housing (not shown). To reduce friction 
between the backplate 40 and the retaining washer 70, the retaining washer 
70 is provided with a recess 80 formed therein to define a cavity 
proximate the first side of the backplate 40. The cavity has a pressure 
P.sub.cavity therein. 
Preferably, the cavity pressure P.sub.cavity is equal to about the system 
pressure P.sub.system such that there is a small net force in the 
direction of the retaining washer 70. The cavity pressure P.sub.cavity can 
be fine tuned, i.e., either raised or lowered, as required by the use of 
one or more through ports. For example, as shown in FIG. 1, the brush seal 
device 10 is provided with a plurality of through ports 130 in 
communication with the cavity recess 80 and the system pressure 
P.sub.system. 
With reference to FIG. 1, the brush seal device 10 is preferably assembled 
by squeezing the bristles 50 between the sideplate 30 and the squeeze 
plate 90. The bristles 50, sideplate 30 and squeeze plate 90 are then 
welded at weld 60 and the outside diameter of the subassembly is finished 
ground to a desired diameter. Assembly of the complete brush seal device 
10 can be accomplished by placing the backplate 40 on the anti-rotation 
pin 100 and pressing the subassembly into the inside diameter of the 
retaining washer 70. The retaining washer 70 can be held in place either 
by the press fit, or a weld at the seam formed by the interface of the 
retaining washer 70 and the backplate 40, between the through ports 130. 
FIG. 4 shows this interface. It is contemplated that the foregoing process 
for assembling the brush seal device 10 is not meant to be limiting and is 
shown only as an example. 
While the present invention has been described with reference to a 
preferred embodiment thereof, additional advantages and modifications of 
the present invention will readily occur to those skilled in the art. 
Therefore, the invention in its broader aspects is not limited to the 
specific details, representative devices, and illustrative examples shown 
and described. Accordingly, departures may be made from such details 
without departing from the spirit or scope of the general inventive 
concept as defined by the appended claims and their equivalents.