Floating seal

A high pressure floating ring assembly includes a floating ring having a sealing surface thereon closely fit with respect to the outer diameter of a cylindrical shaft and wherein relative motion occurs between the inside diameter of the floating ring and the outside diameter of the shaft. Passages are provided to produce a high differential pressure across the sides of the seal and a side thrust reaction pin is located in each of a plurality of circumferentially spaced openings formed in the seal housing and in the body of the seal thereby to define a close tolerance seal to housing gap which permits the floating ring to readily reposition while the shaft is radially shifted with respect to the seal either by misalignment or eccentric shaft motion.

This invention relates to floating ring seals and, more particularly, to 
floating ring seals including means therein to accommodate eccentric 
motion in a rotary shaft sealed by the floating ring seals. 
Floating ring seals that operate with a differential pressure thereacross 
may have a radial lockup tendency caused by side thrust exerted on the 
floating ring by the pressurized fluids that are sealed by the ring seal 
components. In the past, such side thrust was reduced to a minimum 
practical level by including a pressure balance cut on the downstream 
pressure side of the seal. However, remaining side thrust effects can 
produce noticeable resistance to free radial motion of the ring. In such 
cases, if the rotating shaft assumes a radially shifted position relative 
to a seal housing or operates with an eccentric motion while the seal is 
under a high pressure mode of operation, the floating ring seals can be 
worn by radial loads thereon and by rubbing of the shaft with respect to 
the wear surface of the seal. 
Accordingly, an object of the present invention is to include an improved 
floating ring seal assembly having means therein for reducing the radial 
load required to reposition the floating ring under conditions of 
differential pressure load on the seal and wherein the means includes 
reaction pins that react against a floating ring seal side load to 
maintain a minimum gap between the downstream face of the floating ring 
seal and a facing portion of the seal support housing while maintaining 
reduced resistance to radial movement of the seal, thereby to accommodate 
eccentric motions of the shaft or realignment of the shaft with respect to 
the seal housing. 
Yet another object of the present invention is to provide an improved 
floating seal assembly having annular floating seal components with a wear 
surface thereon and including cylindrical bores on the same downstream 
side of a depth to accommodate pins having a length that is controlled to 
maintain a close tolerance leakage path between the downstream side of the 
seal components and a facing surface of the housing for the components and 
wherein an anti-rotation stop is included on the floating seal components 
to insure full effective side thrust accommodation by the side thrust 
reaction pins. 
Yet another object of the present invention is to provide an improved 
floating ring seal assembly having one or more axially spaced seal rings 
thereon, each including an anti-rotation stop component thereon and each 
further including a continuous annular side surface having a plurality of 
axially extending side load reaction pins therein, all joined at a fixed 
end thereon to a support housing for the seal rings and each of the pins 
extending into an annular groove in the seal ring having a depth and 
length to maintain a close tolerance for equal load sharing between each 
of a plurality of circumferentially spaced reaction pins on the continuous 
annular side surface and wherein the joined pins flex under load to 
produce bending of the pins at their fixed ends to maintain a minimum gap 
between the annular side surface of the floating ring and a facing portion 
of its support housing, thereby to reduce radial seal resistance to 
accommodate eccentric motions of the shaft thereby to maintain close 
positioning of a wear face on the seal ring and a rotary shaft at high 
rubbing speeds between the shaft and the wear face of the seal.

Referring now to the drawings, in FIG. 1 a double floating ring seal 
assembly 10 is illustrated having a shaft 12 of a rotary machine directed 
therethrough. A high pressure fluid region 14 is present on one end of 
shaft 12 and a lower pressure region 16 is on the opposite end thereof. 
The direction of pressure force (side thrust) produced by the pressure 
differential between the regions 14, 16 is shown by the arrow 18 in FIG. 
1. 
A typical problem in such floating ring seals which operate with a high 
differential pressure between the region 14 and the region 16 is radial 
lockup caused by side forces exerted on the floating rings of the 
assembly. More particularly, in the illustrated arrangement, the assembly 
includes an upstream floating ring seal unit 20 and a downstream floating 
ring seal unit 22 located within housing openings 24, 26, respectively. 
The housing openings 24, 26, are defined by an intermediate housing member 
28 including an upstream undercut shoulder 30 on one end thereof and a 
flat radial annular surface 32 on the opposite side thereof. An upstream 
end closure plate 34 is held against an upstream surface 36 on the 
intermediate housing member 28 by a suitable fastening means illustrated 
as a threaded screw 38 that extends through a bore 40 in the intermediate 
member 28 into threaded engagement with an internally threaded bore 42 on 
a downstream end closure member 44. The downstream end closure member 44 
thereby has an inboard surface 46 thereon held against the downstream face 
32 of the intermediate member 28 and includes a dependent leg 47 thereon 
with an inner surface 48 spaced from the surface 32 of the intermediate 
housing member 28 to form the housing opening 26 for the downstream 
floating ring seal unit 22. Likewise, the upstream end plate 34 has a 
dependent portion 49 thereof with an inboard surface 50 that cooperates 
with the undercut shoulder 30 of the intermediate member 28 to define the 
housing opening 24 of the upstream floating ring seal unit 20. Axially 
aligned bores 52, 54 are formed through the dependent leg portions 47, 49 
of the downstream and upstream end closure members 34, 44, respectively, 
to receive the shaft 12 for rotation with respect to the seal housing 
members. 
The upstream floating ring seal unit 20 includes a carriage ring 56 having 
an upstream facing, pressure surface 58 thereon and includes an annular 
channel opening 59 therein in which an annular seal element 60 is 
supportingly received. Element 60 has a wear surface 62 thereon slidably 
engaged with an outer surface 64 on the shaft 12. The carriage ring 56 
includes an axial slot 65 formed therethrough at the upper end thereof 
which has an anti-rotation pin 66 directed therethrough with its opposite 
ends received in aligned bores 68, 70 formed in the intermediate housing 
member 28 and the upstream end closure 34. The axial slot 65 has a depth 
greater than that of the pin 66 so that the carriage ring 56 can float 
radially within the opening 24. Likewise, the downstream floating ring 
seal unit 22 has a carriage ring 72 with an upstream pressure surface 74 
thereon and a downstream pressure surface 76. The carriage ring 72 
includes an inboard channel 78 in which is supportingly received an 
annular seal element 80 having a wear surface 82 thereon in sliding, 
sealing relationship with outer surface 64 of shaft 12. 
The carriage ring 72 is held against rotation by an anti-rotation pin 84 
that is located within an axial slot 86 through the radially outer portion 
of the carriage ring 72. The pin 84 has its opposite ends received in 
aligned bores 88, 90 formed respectively in the downstream end closure 
member 44 and the intermediate housing member 28. The depth of the slot 86 
is greater than that of the diameter of pin 84 so that the carriage ring 
72 is free to move in a radial direction within the opening 86. 
In accordance with certain principles of the present invention, the 
downstream surface 76 on the carriage ring 72 and a like downstream 
surface 92 on the upstream carriage ring 56 are maintained at a minimum 
gap relationship with respect to the adjacent housing surface 48 and 
shoulder 30, respectively. To accomplish this result, the upstream 
carriage ring 56 includes a plurality of circumferentially spaced, 
cylindrical bores, one of which is shown at 94 in FIG. 1. The end of the 
cylindrical opening 94 includes a hemi-spherically formed bearing surface 
96 thereon. A plurality of circumferentially spaced cylinder bores 98 are 
formed in shoulder 30. Each bore 98 has a hemi-spherical bearing surface 
100 at the inboard end thereof. The bores 94, 98 are axially aligned and 
each of them receives a thrust pin 104 having rounded end portions 106, 
108 supportingly engaged with the hemi-spherical bearing surfaces 96, 100 
formed within the floating carriage ring 56 and the intermediate housing 
member 28, respectively. Likewise, the downstream ring seal unit 22 
includes a plurality of circumferentially spaced cylindrical bores 110 
therein, each having an inboard hemi-spherical bearing surface 112. The 
downstream closure member 44 also has a plurality of cylindrical bores 114 
formed therein located at circumferentially spaced points on the surface 
48. Each of the bores 114 includes a hemi-spherical bearing surface 116 
therein. The cylindrical bores 110, 114 are axially aligned and each of 
them receives a thrust bearing pin 118 having rounded ends 120, 122 
thereon engaged with the hemi-spherical bearing surfaces 112, 116, 
respectively. 
By virtue of the aforedescribed structure, when fluid pressure is in the 
high pressure region 14, a high pressure condition exists within the 
opening 24 which is balanced between the surfaces 58 and 92 on the 
upstream seal carriage ring 56. 
Side loads can be produced by pressure forces acting on the surface 58 and 
on the surface 74 of the rings 56, 72, respectively. Such side loads are 
accommodated in part in prior arrangements by provision of a pressure 
balance cut formed on the downstream faces of such seals. In heavily 
pressure loaded seals, however, side thrust force remains high and in some 
cases can close a desired minimum gap between the floating carriage rings 
and adjacent housing surfaces. If a rotating shaft assumes a different 
position relative to the seal housing components or operates with a slight 
eccentric motion while the seal is under such side loads, the seal rings 
may bind on the downstream surfaces of the housings and no longer freely 
float. Accordingly, in the present invention, the plurality of thrust pins 
104 serve to accommodate differential pressure loads across the ring 56. 
The floating ring side load is reacted by the rounded ends 108, 106 on 
each of the thrust pin 104 and the parts have a closely controlled 
tolerance so that a minimum dimension gap 130 will be maintained 
continuously between the ring 56 and the facing shoulder 30 on the 
intermediate housing member 28. As a result, when the shaft 12 moves with 
respect to the housing components in a radial direction, the carriage ring 
56 will float within the opening 24 to accommodate for the change in 
operating position of the shaft 12. The same result is produced by the 
component parts of the downstream floating seal unit 22 which has a 
minimum dimensions gap 132. As result, a minimum gap between the 
downstream surfaces of the floating seal units 20, 22 and adjacent housing 
surfaces is maintained to minimize leakage across the seal components from 
the high pressure region 14 to the low pressure region 16. At the same 
time, the load necessary to move the seal units 20, 22 radially is 
reduced. Accordingly, seal wear and seal leakage are improved. 
Referring now to the embodiment in FIG. 2, an upstream floating seal unit 
134 is illustrated located within a housing opening 136 formed by an 
intermediate housing member 138, a portion of which is shown in FIG. 2, 
including an upstream undercut surface 140 thereon. An upstream end 
closure 142 is held against the undercut surface 140 to bound opening 136. 
In this embodiment, the upstream seal unit 134 includes a floating 
carriage ring 144 having an upstream surface 146 thereon and a downstream 
surface 148 thereon. An annular channel 150 is formed on the radially 
inner surface of the carriage ring 144 and receives an annular seal 
element 152 with its wear surface 154 in sliding engagement with an outer 
seal surface 155 on rotating shaft 158. The aforedescribed components are 
fixed against rotation by an antirotation pin 156 directed through a slot 
159 in ring 144 of greater depth than that of the diameter of the pin 156. 
The opposite ends of the pin 156 are supported in housing bores 161, 162 
formed in the intermediate member 138 and the upstream end closure 142 to 
prevent rotation of the floating seal carriage 144 within the opening 136. 
Aligned bores 164, 166 in the closure 142 and intermediate housing member 
138 accommodate eccentric motion of the shaft 158. Low forces are required 
for such radial movement because an annular, multiple pin thrust member 
168 is utilized in place of the plurality of thrust pins 104, 118 
described in the embodiment in FIG. 1. More particularly, the multiple pin 
thrust member 168 includes a generally rectangularly configured base 
portion 170 supportingly received within an annular groove 172 formed in 
the undercut surface 140 of the intermediate housing member 138. The 
thrust ring 168 includes a plurality of axially directed spaced pins 174 
thereon, each of which is directed into a slot 176 formed in the carriage 
144. When a pressure load is applied on the surface 146, the carriage is 
shifted in a downstream direction so that end surfaces 178 on each of the 
pins will engage a slot surface 180. The length of each of the pins 174 is 
selected so that a carefully controlled clearance gap 182 will be held 
between the carriage 144 and the housing components. In this arrangement, 
radial flexure of the member 168 under radial loading produces bending of 
the pins 174 from the fixed end of the base 170 thereof to readily 
accommodate unrestrained radial movement of the floating seal 134. The gap 
182 will prevent side frictional engagement between the carriage element 
144 and adjacent housing portions. The gap 182 is selected, however, to 
prevent excessive leakage across the seal unit. 
While the embodiments of the present invention, as herein disclosed, 
constitute a preferred form, it is to be understood that other forms might 
be adopted.