Circumferential hydrodynamic seals for sealing a bidirectionally rotatable member

A seal for sealing between a bidirectionally rotating shaft rotatable in the forward and reverse directions and having a sealing surface thereon located in a pressurized housing containing the shaft. A seal ring mounted in the housing for movement toward and away from the shaft sealing surface and having a high pressure side, a low pressure side, a seal face opposed to the shaft seal surface and an outer face remote from the seal face and exposed to the pressure in the housing. Resilient elements urge the seal ring toward the sealing surface of the shaft. Hydrodynamic elements in the form of a plurality of spaced recesses in the seal face of the seal ring and formed so as to produce negative hydrodynamic lift in the recess and urge the seal ring toward the sealing surface of the rotating shaft during forward rotation thereof. Openings extend through the seal ring from a predetermined section of the grooved seal surface thereof to the remote face of the seal ring to accommodate flow through such openings to reduce pressure build-up in the grooves of the sealing face to prevent seal leakage during reverse rotation of the shaft. A second seal is provided between the housing and the low pressure side of the seal ring.

BACKGROUND OF THE INVENTION 
In his U.S. Pat. No. 4,082,296, issued on Apr. 4, 1978, P. Charles Stein 
provided a plurality of embodiments of sealing members for sealing between 
a rotating member and a housing. The sealing members were provided in 
certain embodiments in the form of a segmented seal ring resiliently 
mounted about a shaft to move toward and away from the shaft to provide a 
seal therebetween. In the circumferential sealing face of each segment 
which faces adjacent the shaft, predetermined precise grooves are provided 
which produce a negative hydrodynamic lift force and urge the seal ring 
segments toward the rotating shaft in order to reduce leakage thereacross. 
In other embodiments of the Stein Patent, particularly the embodiment of 
FIGS. 8 and 9 thereof, the rotating member or shaft is provided with a 
circumferential flange therein and a unitary seal ring effects a seal 
between a radially disposed face on the flange and a radially disposed 
face on the seal ring which coacts with the adjacent radial face on the 
flange. In that arrangement, the seal ring, which may be formed of 
circumferential segments, but normally from a single unitary ring, has on 
the sealing face thereof the grooves which produce the aforedescribed 
negative hydrodynamic lifting force between the seal ring and the 
rotatable flange to provide the reduced seal leakage. 
In certain applications of the Stein Patent seal rings, a seal is provided 
for use with a bidirectionally rotatable shaft. In those examples, during 
forward rotation of the shaft, the medium in which the seal is operating 
(e.g., oil, water or gas), when the shaft is operating in its forward or 
normal direction, is swept out of the sealed grooves by a pumping action 
to provide the negative hydrodynamic lift force and to move the seal ring 
toward the rotatable member to effectuate greater sealing. In these 
applications, however, where a bidirectionally rotatable shaft is required 
to be sealed, when the seal operates in the reverse direction, the medium, 
especially a more viscous medium such as oil, pressure builds up in the 
grooves particularly adjacent the low pressure side of the seal ring which 
in certain instances is sufficient in magnitude to lift the seal ring away 
from the rotatable member causing it to leak. The purpose of this 
invention is to provide a modification of the Stein Patent seal 
arrangements for use with bidirectionally rotatable members to overcome a 
potential leakage problem with the seal ring when the rotatable member is 
operated in reverse. Any potential problem which occurs during reverse 
rotation of the shaft is solved by this invention. 
SUMMARY OF THE INVENTION 
This invention provides in a seal ring having a configuration which 
provides negative lift forces to urge the seal ring toward a rotatable 
member, which ring includes a plurality of grooves in the circumferential 
face of the ring adjacent the rotatable member which provide negative 
hydrodynamic lift. Pressure relief means are provided which releases 
certain pressure build-up in the grooves during reverse rotation of the 
rotating member which includes a plurality of pressure relief openings 
extending through the seal ring from predetermined portions of the grooves 
in the sealing face to the remote face of the ring.

DETAILED DESCRIPTION 
As shown in FIG. 1, a housing 2 forms a chamber 4 adapted to contain a 
fluid. A shaft 6 passes through housing 2 into chamber 4. A seal ring 8 
has four segments 10 (FIG. 2). Each segment 10 has an offset tongue 
portion 12 (FIG. 3) with a diagonal face 14 which mates with a diagonally 
cut groove portion 16 on the adjacent segment 10 to provide for continuous 
sealing structure irrespective of any expansion or contraction of seal 
ring 8. The segments 10 are urged into contact with shaft 6 by a garter 
spring 20. The downstream faces 22 of segments 10 are urged against flange 
24 of housing 2 by compression coil springs 26 contained in pockets 28 of 
closing ring 30 which is retained between casing shoulder 32 and retaining 
ring 34. 
The downstream or low pressure face 22 of each segment also serves as a 
sealing face and is provided on a portion thereof with radial grooves 40 
connected to a peripheral groove 42 to permit the passage of fluid from 
chamber 4 into groove 42 to counterbalance in part the fluid pressure on 
the high pressure side 29 to reduce the pressure loading of the segments 
against flange 24. Locking pins 44 (FIG. 1) mounted in flange 24 fit 
loosely in openings 46 in seal ring 8 to prevent the segments 10 from 
rotating and yet permit the segments to move towards and away from shaft 
6. 
Grooves 40 and 42 would be unnecessary where the fluid in chamber 4 is at 
nominal pressure. 
As shown in Stein Patent 4,082,296, the sealing face 50 has a pair of 
shallow recesses 52. Typically the depth of each recess 52 will be in the 
range of from about 0.002 to about 0.030 cm. depending on fluid viscosity 
and shaft speed. The end of each recess 52 in the direction of the forward 
rotation of shaft 6 opens into an axial cutout portion 54 in face 50 which 
also forms an opening in face 29 so that each recess 52 is thereby placed 
in direct communication with the fluid in chamber 4. Axial cutout portion 
54 has an angled portion 56 which acts as a fluid scraper facilitating the 
flow of fluid into chamber 4. 
In operation with a liquid in chamber 4, the forward rotation of shaft 6 
causes a shear-drag on the liquid in recess 52 which would move the liquid 
in the recess toward the axial cutout portions 54 except that the reduced 
film thickness at the entry surface 52A impedes inflow into the recess. 
This, as explained in the aforementioned Stein patent, results in a 
lowering of the pressure in the recess and effectively creates negative 
hydrodynamic lift. This negative lift force, which urges the seal toward 
the shaft surface can be made of such magnitude that it precludes 
"surf-boarding" and excessive leakage past the seal. 
In accordance with the invention, a circumferential groove 58 of greater 
depth than grooves 52 is provided in the inner circumferential face 50 of 
each segment 10 of seal ring 8 between the grooves 52 and the low pressure 
face 22. Circumferential groove 58 serves as a pressure relief groove for 
the seal ring segments 10 with groove 58 being deeper than grooves 52 and 
being located downstream from each recess 52 on the seal surface. Groove 
58 terminates in this embodiment adjacent to but spaced from the radially 
extending end surfaces of each segment 10. Each of the recesses 52 is 
connected to the pressure relief groove 58 by an axial passage 60. Thus, 
pressure relief groove 58 communicates with each of the recesses 52 in 
each seal ring 10. When shaft 6 is operated in the forward or normal 
direction, a negative hydrodynamic lift force is created on segments 10 of 
ring 8 to move each of the segments 10 toward shaft 6 and reduce any 
leakage therebetween. However, when shaft 6 is operated in the reverse 
direction, fluid is pumped into recesses 52 and into groove 58 and the 
pressure build-up in groove 58 increases to a point where spill-over or 
seal leakage can occur, causing segments 10 to move away from shaft 6. In 
order to avoid such pressure build-up and leakage during reverse rotation, 
especially during low-pressure differential operation of the seal ring in 
a high viscosity (e.g. oil) medium, a plurality of spaced radial openings 
64 are provided in each seal ring segment 10 which originate in the base 
of groove 58 and terminate in the outer, or remote, circumferential 
surface 62 of seal ring segments 10. Radial openings 64 reduce the 
pressure build-up in groove 58 by passing the high viscosity or other 
fluid into the chamber 4 through radial openings 64. In the illustrated 
embodiment of this invention, each of the seal ring segments 10 includes 
four substantially evenly-spaced radial pressure relief openings 64 with 
the size of the pressure relief openings 64 being such as to have 
relatively small, if any, pressure drop thereacross, for example, 3/32 
inch diameter radial openings in a shaft seal for a 35 inch diameter 
shaft. 
An alternative embodiment involving sealing against a rotating ring is 
shown in FIGS. 5, 6 and 7. Here a casing 102 forms a chamber 104 which is 
adapted to contain a fluid. A rotating shaft 106 passes through an opening 
108 in casing 102 and carries a seal mating ring or seal runner 110 which 
is held against a shoulder 112 on shaft 106 by a securing sleeve 114 
secured to shaft 106 by a nut (not shown) on shaft 106. A ceramic or 
graphite rubbing seal ring 120 is carried by a seal holder 122 which has 
an annular ring portion 124 received within the inner diameter of seal 
ring 120. A seal therebetween is effected by O ring 126 which is 
positioned in an annular groove 128 formed in the outer surface of ring 
portion 124 and engages the inner diameter of seal ring 120. A pin 140 
secured in holder 122 is loosely engaged in an opening 142 (FIG. 6) in 
seal ring 120 to prevent the rotation of the seal ring 120. 
Seal ring 120 is urged into contact with ring 110 by compression coil 
springs 130 (only one of which is shown in FIG. 5) carried in pockets 132 
in flange 110, which is bolted to casing 102 by bolts indicated at 134. 
Referring to FIG. 7, it will be seen that the sealing face 150 of seal ring 
120 includes groove means for providing negative hydrodynamic lift between 
the seal ring 120 and the runner 110 to minimize leakage across seal face 
150 during forward rotation of the shaft 106. The sealing surface 150 has 
in this example six pockets or shallow recesses 152 (only four of which 
are shown) having the end thereof in the direction of forward rotation of 
the shaft 106 and runner 110 opens outwardly into radial cutout portion 
154 in the face 150 which also forms an opening in face 129 (a face 
exposed to high pressure) so that each recess 152 is in direct 
communication with the fluid in chamber 104. Cutout portion 154 also has 
an angled portion 156 which acts as a fluid scraper facilitating the flow 
of fluid into chamber 104. The operation of the fluid in recesses 152 is 
the same as described in connection with fluid in recesses 52 of the 
embodiment of FIGS. 1-4 and results in the production of a negative 
hydrodynamic lifting force on seal ring 120. 
A continuous circumferential groove 158 of greater depth than recesses 15 
is provided in seal ring 120 on the downstream or low pressure side of 
seal ring 120 and serves as a pressure relief groove for the seal ring. 
(It will be noted that if seal ring 120 were not made of a single ring, 
but from segments, groove 158 would terminate short of each end of the 
segments.) Groove 158 is connected to each recess 152 by a radial 
passageway 160. For reasons to be explained, seal ring 120 includes a 
plurality (in this example, nine) axial passageways 162 extending 
symmetrically around groove 158 and extending through the ring 120 from 
the base of groove 158 to the remote or high pressure side 164 of the seal 
ring 120. 
When shaft 106 is operated in the forward or normal direction, a negative 
hydrodynamic lift force is created on seal ring 120 to move it toward 
runner 110 and reduce any leakage therebetween. However, when shaft 106 is 
operated in the reverse direction, fluid is pumped into recesses 152 and 
into groove 158 and the pressure build-up in groove 158 increases to a 
point where spill-over or seal leakage can occur, causing seal ring 120 to 
move away from shaft 106. In order to avoid such pressure build-up and 
leakage during reverse rotation, especially during low-pressure 
differential operation of the seal ring in a high viscosity (e.g. oil) 
medium, the axial openings 162 reduce the pressure build-up in groove 158 
by passing the high viscosity or other fluid into the chamber 104 through 
radial openings 162. While the pressure relief openings 64 (FIGS. 1-4) and 
162 (FIGS. 5-7) do function, during normal operation, to reduce the 
negative hydrodynamic lift force on seal ring 8 or 120 during forward 
rotation of the shaft, such reduction in the closure force of seal ring 
segments 10 or seal ring 120 is accommodated in the seal design. Thus, the 
pressure relief openings 64 or 162 are appropriately sized for each seal 
ring size and application, so that appropriate negative hydrodynamic lift 
forces on seal ring segments 10 or seal ring 120 are sufficient to meet 
the operating criteria. Furthermore, in the embodiment of FIGS. 1-4, 
should increased closure force of the seal ring against the shaft 6 be 
required, radial springs (not shown) may be substituted for the garter 
spring 20, which radial springs extend from housing 2 to the remote side 
62 of each of the seal ring segments 10. A plurality, for example, up to 
four radial springs, may be employed with each seal ring segment 10 for 
certain applications to increase the sealing force of the seal ring 8 
against the shaft 6. Such radial springs, not shown, may, of course, have 
their ends received in recesses in housing 2 and in seal ring segments 10, 
respectively, in a manner well known in the art. 
As is known, the seal ring segments 10 may be made of materials usually 
employed for rubbing seal such as carbongraphite or bronze. 
It will be understood that the above-discussed embodiments of this 
invention are illustrative and not intended to be limiting thereof. Other 
modifications may also be employed and fall within the spirit and scope of 
this invention.