Note: Descriptions are shown in the official language in which they were submitted.
WO 01/63166 CA 02404629 2002-09-25 pCT/US01/05412
SEAL ASSEMBLY, ITS USE AND INSTALLATION
BRIEF DESCRIPTION OF THE INVENTION
The present invention relates to a seal assembly having an elastomeric seal
bonded to a static
end and a movable end. More particularly, the invention relates to an
apparatus and process whereby
an elastomeric seal is initially stretched in a direction parallel to its axis
and parallel to its comating
surface to reduce its cross-section parallel to the comating sealing surface.
The stretched seal is
installed adjacent the comating surface and then relaxed, permitting the seal
to return to an
unstretched position and to assume a preloaded position against the comating
sealing surface.
BACKGROUND OF THE INVENTION
Elastomeric seals are in very common use in a wide variety of applications as
a means for
closing off a passageway (gap) between two parts. The parts are usually
metallic and will allow fluids
to pass through the gap where the two pieces are joined. To prevent the escape
or loss of fluid at
these gaps, flexible elastomeric seals are used to close the gap between the
two parts. To achieve
this function, one side of the elastomeric seal is placed in a cavity or
groove in a first part and the
exposed side of the seal is comated with the surface of a second part. The
prevention of fluid
passage through a gap between such parts generally relies upon the maintenance
of an initial
interference fit with attendant interface biasing forces between the sealing
element and the two parts.
This interference fit is termed 'presqueeze'. Additional interface biasing
forces are produced
as a consequence of seal distortion and loading by retained pressure. This
behavior is well known
and is described in the design guides provided by 0-ring manufacturers in
their technical literature and
is generally pertinent to all cross-sectional types of seal, not just circular
cross-sections.
Attendant with this interference fit is the risk of physically damaging the
seal during its
installation by abrasion or cutting from contact with the comating surface
during installation. This
damage can result from either cutting on edges or from twisting or tearing
from excessive frictional
drag when presqueeze is excessive. For this reason, the amount of interference
fit often must be
limited in order to ease or even enable assembly. Seals using plastics with
spring expanders instead
of elastomers are particularly sensitive to this type of assembly damage.
As fluid pressure is applied to the elastomeric seal, the seal will deform and
shift in the
direction of the fluid. With time under high pressure loads and/or as the
pressure increases, the seal
will continue to distort or "creep." This behavior is further enhanced if the
elastomeric seal shrinks in
volume or is weakened by its interaction with the retained fluids. Thus,
elastomeric seals may lose a
substantial portion of their interference fit over time due to creep
('compression set') or shrinkage
volume changes. These problems are significantly amplified as the size of the
gap to be sealed is
increased.
A frequent solution often used for large gap situations has been to
selectively compress the
seal by mechanical means after installation in order to achieve adequate
presqueeze. This active,
rather than passive, approach is commonly used for the basically rectangular
cross-section seals used
with both tubular and split pipeline repair clamps, as for example in Reneau,
U.S. Patent 4,728,125.
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The seals for these clamps may be either circumferential or linear face seals,
and the circumferential
seals may also be integral circles or split into semicircles.
Compression applied to the seal by tightening the comating surface against one
lateral side of
the seal causes the seal to extend the seal radially thereby mating and
sealing with the comating
member. For example, for typical tubular pipeline repair clamps, jack bolts
acting parallel to the
tubular axis to provide axial compression on the circumferential seals cause
the seals to fully engage
with the comating member. This approach often requires later recompression of
the seal to offset the
unloading effects of creep or volume reduction. In practice, such
recompression is an operational
nuisance, very expensive, and often impractical.
Stewart & Stevenson of Houston, Texas have used a different approach to seal
installation.
Its seal is initially recessed into a groove and then,forced into contact with
the comating member of the
seal by directly applying hydraulic pressure to the back side of the seal
groove. Sealing relies upon
permanently trapping the actuating pressure behind the seal in its groove.
This system is not
configured for large gaps, but it does avoid interference fit-induced damages
during assembly.
However, reliability of such a seal is questionable because the actuating
fluid may leak off, relieve the
pressure and cause the seal to fail.
The significant areas of performance difficulty for large gaps and high
pressures with the cited
types of existing seals frequently lead to leaks or complete seal failures.
For critical service
conditions, such as deep water subsea pipeline repair clamps or hot-tap
pipeline fittings, revisiting the
clamp for adjusting the compressional preload on installed seals is
prohibitively expensive. Further,
providing more compressional preload in such cases is not practical for
reasons of installation damage
to the seat due to excessive interference and increased tendency of the seal
to creep and extrude
through the gap with high preloads.
Thus, a need exists for a means to install a preloaded seal that does not rely
on applying
external mechanical force to compress the seal against its comating surface.
SUMMARY OF THE INVENTION
The invention contemplates a simple, inexpensive device for eliminating the
problems and
disadvantages of the prior approaches discussed above. The present invention
relates to a seal
assembly having an elastomeric seal bonded to both a static end and a movable
end. An apparatus
and process whereby an elastomeric seal is initially stretched to reduce its
cross-sectional thickness
perpendicular to the comating sealing surface is described. The stretched seal
is installed into the
groove or recess and then relaxed, permitting the seal to return to an
unstretched position and to
assume a preloaded position against the comating sealing surface.
A first aspect of the invention provides a sealing apparatus for sealing a
flow gap
comprising a housing, an elastomeric seal having an internal diameter and a
comatable surface
for sealing against a pipe inserted within the internal diameter of the seal,
wherein the pipe has a
pipe outer diameter; a static seal end, bonded to a one end of the elastomeric
seal on an inner
side of the static seal end and anchored to the housing and a movable seal
end, bonded to a
second end of the elastomeric seal, wherein when the movable seal end is
displaced in a
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direction going away from the static seal end the elastomeric seal is
tensioned and the comatable
surface is not biased against the pipe outer diameter and when the movable end
is moved back
towards the static seal end the tension on the seal is eased and the comatable
surface is
sealingly biased against the outside diameter of the pipe; reciprocable means
for tensioning and
untensioning the seal, the tensioning means operated by selectably moving the
movable end and
actuation means for displacing the movable seal end.
A second aspect of the invention provides a method of sealing a flow gap
between two
parts comprising providing a seal assembly comprising an elastomeric seal,a
static seal end,
bonded to the seal on a one end, and a movable seal end, bonded to the seal on
a second end,
wherein when the movable seal end is displaced to a first position in a
direction going away from
the static seal end the elastomeric seal is tensioned and when the movable end
moves back
towards the static seal end to a second position the tension on the seal is
eased, means for
reciprocably tensioning and untensioning the seal, the tensioning means
operated by moving the
movable end between the first and second positions; and means for selectably
actuating the
displacement of the movable seal end to the first or second position, mounting
the seal assembly
in an annular housing, wherein the static seal end is anchored to the housing,
an internal surface
of the housing being a first seal surface of an annular flow gap, actuating
the tensioning means to
move the movable end to the first position to tension the elastomeric seal and
reduce a radial
cross-sectional thickness of the seal perpendicular to a comating surface of
the elastomeric seal,
inserting an object into a bore of the seal assembly while the seal is
tensioned, wherein an
external surface of the object is a second seal surface of the flow gap; and
deactuating the
tensioning means to move the movable end to the second position thereby
releasing the tension
on the seal to cause an internal elastic force within the seal to bias the
seal against the second
seal surface to seal the flow gap.
The foregoing has outlined rather broadly several aspects of the present
invention in order
that the detailed description of the invention that follows may be better
understood. Additional features
and advantages of the invention will be described hereinafter which form the
subject of the claims of
the invention. It should be appreciated by those skilled in the art that the
conception and the specific
embodiment disclosed might be readily utilized as a basis for modifying or
redesigning the structures
for carrying out the same purposes as the invention. It should be realized by
those skilled in the art
that such equivalent constructions do not depart from the spirit and scope of
the invention as set forth
in the appended claims.
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BRIEF DESCRIPTION OF THE DRAWINGS
The novel features which are believed to be characteristic of the invention,
both as to its
structure and methods of operation, together with the objects and advantages
thereof, will be better
understood from the following description taken in conjunction with the
accompanying drawings,
wherein:
FIG. I shows an end view of a mechanically-operated tubular pipeline end
clamp;
FIG. 2 shows a longitudinal sectional view of the clamp shown in FIG. 1 with a
stretched
symmetrical elastomeric seal;
FIG. 3 illustrates a partial longitudinal quarter section of the clamp shown
in FIG. 1 with a
gripping (or engaged) symmetrical elastomeric seal;
FIG. 4 illustrates a longitudinal sectional view of a mechanically-operated
tubular pipeline with
a stretched unsymmetrical elastomeric seal;
FIG. 5 shows a partial longitudinal section of the clamp shown in FIG. 4 with
an engaged
unsymmetrical elastomeric seal;
FIG. 6A is a side view of a cam;
FIG. 6B is a perspective view of a cam;
FIG. 6C is a perspective view of a hollow retainer screw;
FIG. 7 shows a longitudinal half sectional view of a mechanically-operated
tubular pipeline
end clamp with a stretched elastomeric seal suitable for bidirectional
sealing;
FIG. 8 shows a longitudinal half sectional view of the clamp shown in FIG. 7
with a engaged
elastomeric seal suitable for bidirectional sealing;
FIG. 9 illustrates a partial view of the clamp shown in FIG. 8 retaining
internal pressure;
FIG. 10 illustrates a partial view of the clamp shown in FIG. 8 retaining
external pressure;
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FIG. 11 shows a quarter sectional view of a molded seal assembly having a
relaxed
symmetrical elastomeric seal;
FIG. 12A shows a quarter sectional view of a molded seal assembly having a
relaxed
unsymmetrical elastomeric seal;
FIG. 12B shows a quarter sectional view of a molded seal assembly having a
relaxed
unsymmetrical elastomeric seal with an embedded antiextrusion device;
FIG. 13 shows a quarter sectional view of a molded seal assembly having a
relaxed
elastomeric seal suitable for bidirectional sealing; and
FIG. 14 is a cross-sectional view taken along line 14-14 of FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a method and an apparatus for installing an
elastomeric seal in
a mounting groove in a manner that will be non-interfering or have minimal
interference with the seal's
comating surface during installation thereby avoiding damaging the seal. The
method of installation
does not require active external mechanical compression to be applied to the
seal in order to prevent
fluid passage through a gap between the seal and the comating surface.
Furthermore, the method
provides a novel method of preloading the seal prior to retention of pressure
by the seal. In addition,
the installed seal can readily conform to locally varying gaps, as well as
compensate for shrinkage and
/or creep due to variations in rubber volume, without having to apply
additional external pressure. The
disclosed method for installing the seal allows the seal to be set multiple
times without damage to the
seal.
Referring now to the drawings, and initially to Figures 1 and 2, it is pointed
out that like
reference characters designate like or similar parts throughout the drawings.
The Figures, or
drawings, are not intended to be to scale. For example, purely for the sake of
greater clarity in the
drawings, wall thickness and spacing are not dimensioned as they actually
exist in the assembled
embodiment.
Figure 1 and 2 illustrate a mechanically-operated tubular pipeline flanged end
connector
clamp 10. Figure 1 shows an end view of clamp 10 and Figure 2 shows a
longitudinal half-sectional
view of clamp 10 shown in Figure 1.
The type of clamp shown is suitable for connecting to the end of a section of
pipe in a
pressure-retaining, non-separating state. The internal elements of clamp 10
which are used to grip and
seal to the exterior of a piece of pipe are housed within circular tubular
body 11. Housing 11 has a
female thread 12 at its outer end and smooth first counterbore 13 inwardly
positioned from and
adjacent to thread 12. First transverse shoulder 14 is located at the inner
end of first counterbore 13
and provides a transition between first counterbore 13 and smooth second
counterbore 15.
Second transverse shoulder 16 is located at the inner end of second
counterbore 15 and
provides a transition from the second counterbore 15 to third counterbore 17,
which is sized to admit
the end of a specific diameter of pipe. Transverse shoulder 18 provides an
abutment against which a
pipe end may be positioned. Shoulder 18 is positioned between counterbore 17
and the through bore
5 of housing 11.
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Flange 19 is provided with a circle of bolt holes 3 and is located in a
transverse position at the
outer end of housing 11 opposite the end with female thread 12. Flange 19
provides a simple
mechanical connection means for attachment to other flanges; a groove 23 for a
metal seal gasket is
located on the end face of the flange.
Short annular cylindrical reaction abutment 20 is externally threaded and is
threadedly
engaged with female thread 12 of the body 11. The inner diameter of reaction
abutment 20 is
approximately that of the counterbore 17 of housing 11. Reaction abutment 20
is provided with a
circie of threaded bolt holes 21. The axes of the holes 21 are parallel to the
axis of reaction abutment
20. Hex-headed half-dog machine screws 24 are threadedly engaged in holes 21
so that their heads
are extemally accessible for wrenching when a pipe segment is positioned in
the bore of clamp 10.
Half-dog screws are used so that minor mushro6ming of the screw tips under
compressive loads will
not prevent their retraction.
An array of multiple, coacting gripping elements, illustrated in Figure 4, are
positioned in first
counterbore 13 inwardly from the reaction abutment 20. The array of coacting
gripping elements
consists of outer end rings 29, outer central rings 30, and inner split rings
31.
Outer end rings 29 and outer central rings 30 may or may not be split. The
outer end rings 29
and 30 are sized to slidingly fit against the cylindrical surface of the first
couterbore 13 with a slip fit or
low resistance to movement in the direction of the axis of clamp 10. As shown
in Figure 3, a flat face
transverse to the ring axis is provided on the outer end rings 29 for reducing
contact stresses for axial
loads. Additionally, a cylindrical outer surface is provided on outer end
rings 29 and outer central rings
to reduce contact stresses between said rings and the first counterbore 13.
Inner split rings 31 have a smaller ring centerline diameter than the outer
end rings 29 or outer
25 central rings 30. The inner diameter of split inner rings 31 is
approximately that of counterbore 17 of
housing 11. The arrangement of the array of rings is such that the stack of
rings sequentially
alternates between individual outer and inner rings. All the rings are
constructed of high yield stress
metallic material so that high contact stresses and significant bending of the
inner split rings 3lwill not
produce plastic deformation of the ring surfaces,
30 The materials of construction for all of the clamp and seal embodiments are
steel or other
suitable metallic materials unless otherwise noted. The elastomeric components
of these
embodiments such as seal elements and 0-rings are normally nitrile or VitonTM
or other suitable
rubbers.
At the inner end of first counterbore 13 and positioned between the array of
gripping elements
and the first transverse shoulder 14 is an annular cylindrical seaf anchor 34
(as shown in Figure 3 and
5), which has a male 0-ring groove on its outer cylindrical diameter in which
0-ring 33 is mounted to
seal against first counterbore 13. Seal anchor 34 abuts first transverse
shoulder 14. A circle of
multiple counterbored through bolt holes 35 parallel to the axis of seal
anchor 34 is provided.
A seal assembly is positioned in the second counterbore 15 between seal anchor
34 and
second transverse shoulder 16. Figure 1 1A shows a first embodiment of the
seal assembly 37. The
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seal of the first embodiment of this invention has a symmetric cross-section
and is configured to retain
pressure from the flanged side (internal pressure) better than external
pressure.
Seal assembly 37 consists of static seal end 39, movable seal end 40, and
elastomeric seal
41 molded integrally to the static and movable seal ends in a central
position. Figures 2 and 3 shows
the seal assembly 37 mounted in a mechanically-operated tubular pipeline
flanged end connector
clamp 10. Seal assembly 37 fits closely within second counterbore 15. The
inner diameter of static
seal end 39 is a short annular cylinder with a male 0-ring groove 42 on its
outer cylindrical surface,
wherein 0-ring 43 is mounted to seal against second counterbore 15. The
outwardly facing transverse
surface of static seal end 39 is provided with drilled and tapped holes 44
matching the countersunk
through holes 35 of seal anchor 34. Machine screws 45 are mounted in through
holes 35 to engage
tapped holes 44 and thereby connect static seal end 39 to a fixed seal anchor
34.
To assist in maintaining a good connection between the elastomer of seal 41
and static seal
end 39 or anchored seal part 32 a strong bonding area is provided. This strong
bonding area can be
enhanced by having an undercut face groove 57 with rounded edges on the inside
transverse face of
static seal end 39 as shown in Figure 11. Movable seal end 40 is a short
annular cylinder with a face
groove 58, similar to that of static seal end 39, on its outwardly facing
transverse face. On its outer
cylindrical face, movable seal end 40 has a deep circumferential groove 26
with end faces normal to
the axis of the cylinder.
Referring to the as-molded seal configuration, shown in Figure 11, elastomeric
seal 41 is
bonded to both the static seal end 39 and the movable seal end 40 during
molding. The exposed
outer surface of seal 41 is cylindrical when the seal is relaxed. The exposed
inner surface of seal 41
is not cylindrical, but rather extends inwardly in a symmetrical arcuate or
parabolic or polygonal cross-
sectional projection, although its diameters adjacent to the seal ends 39 and
40 match the inner
diameters of those pieces.
While the inner diameters of the static seal end 39 and the movable seal end
40 are
approximately the same as counter bore 17 so that operating clearance is
provided for installing the
clamp 10 over a pipe end 50, the minimum diameter of the as-molded elastomeric
seal 41 when it is
relaxed is significantly less than the minimum outer diameter of the pipe. The
result will be an
interference fit between the elastomeric seal 41 in its untensioned position
and the pipe when the two
are mated, as shown in Figure 3. When the elastomeric seal 41 is stretched for
installation, as shown
in Figure 2, the tension maintained on the elastomer cross-section is
sufficient to reduce the cross-
sectional thickness of the elastomeric seal 41 so that tendencies to interfere
with insertion of a pipe 50
into the clamp 10 are minimized. Consequently, elastomeric seal 41 will be
less susceptible to
damage during pipe insertion.
Multiple equispaced radial cam holes 46, as shown in Figure 3 and 14, with
their axes in a
common plane transverse to the housing axis penetrate the wall of housing 11
in the region of second
counterbore 15. The cam axes are located slightly outward of the inner
transverse shoulder of the
deep circumferential groove 26 on the outer cylindrical face of the movable
seal end 40 when the
elastomeric seal 41 is in its untensioned position. The outer portion of each
radial hole 46 is tapped
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and the inner end has a smooth inner bore with a tapered lead-in to permit
engagement of an 0-ring
seal.
Identical cams 47 are mounted respectively in each radial hole 46. A side and
a perspective
view of cam 47 is shown in Figures 6A and 6B respectively. Cam 47 has a
cylindrical outer end body
25 of a first diameter, cylindrical inner end body 27 of a larger second
diameter, with a transverse
planar shoulder 53 at the transition in diameters, and wrench socket 55 in its
outer end. 0-ring groove
48 is positioned in the midsection of the cylindrical inner end body 27 to
hold 0-ring 49. 0-ring 49
seals against the smooth inner bores of radial holes 46. Hollow retainer
screws 52 are engaged into
the threads of radial holes 46 to react against the transverse planar
shoulders 53 of cams 47 so that
the cams are retained in housing 11.
The innermost machined ends 28 of the cams 47 are machined away so that the
body of each
cam is removed on one side of a diametric plane to a depth slightly more than
the deep circumferential
groove 26 on the external cylindrical surface of movable seal end 40. The
positioning of the machined
ends 28 of cams 47 into groves 26 of movable seal end 40, as illustrated in
Figures 2 and 3, create
cylindrical operating surfaces for camming action on the inner transverse end
of groove 26.
As shown in Figure 2, the cams 47 are rotated so that their cylindrical
camming surfaces are
on the inward side of their respective axes and reacting against the inward
transverse shoulder of the
deep circumferential groove 26 of movable seal end 40, thereby tensioning the
seal assembly 37.
Figure 3 shows the same seal assembly as in Figure 2, but with the seal
assembly 37 released from
its tensioned installation position so that the seal assembly has assumed an
engaged, preloaded
position against a pipe end segment 50.
The second seal assembly 137, shown in Figure 12A, is similar to that of the
first, but has an
unsymmetric seal cross-section which permits development of less pressure-
biasing force on the
seal/pipe interface. This seal is better suited for holding pressure from one
direction than from the
other direction. Since the tubular pipeline end connector clamp of Figure 4
shown housing this second
seal assembly 137 is identical to the tubular pipeline end connector clamp
shown in Figure 2 housing
the first seal assembly 37, only the differences in the seal assembly are
discussed herein.
As shown in Figure 12A, the seal of the second seal assembly 137 consists of
the same static
seal end 39, the same movable seal end 40, and elastomeric seal 141 is molded
integrally to the static
and movable seal ends in a central position. The difference in the seal
assemblies 37 and 137 is in the
inner profile of the elastomeric seals 41 and 141. Seal assembly 137 also fits
closely within second
counterbore 15 as seen in Figures 4 and 5.
To assist in maintaining a good connection between the elastomer of seal 141
and static seal
end 39 by providing additional bonding area and shear engagement, an undercut
face groove 57 with
rounded edges is provided on the inside transverse face of static seal end 39,
and a similar face
groove 58 is provided on the inside traverse face of movable end 40. Referring
to the as-molded seal
configuration, shown in Figure 12A, elastomeric seal 141 is bonded to both the
static seal end 39 and
the movable seal end 40 during molding. The exposed outer diameter surface of
seal 141 is
cylindrical when the seal is relaxed. The exposed inner surface of seal 141 is
not cylindrical, but
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rather extends inwardly in an unsymmetrical arcuate or polygonal cross-
sectional projection, with its
diameters adjacent to the seal ends 39 and 40 and matching the inner diameters
of those pieces.
The inner diameters of the static seal end 39 and the movable seal end 40 are
slightly more
than the pipe outer diameter so that operating clearance is provided for
installing the clamp 10 over a
pipe end 50. The cross-section of elastomeric seal 141 has its cross-section
sufficiently reduced by
tension, as shown in Figure 4, to ease insertion of pipe 50 and minimize
potential seal damage. The
unsymmetric profile of elastomeric seal 141 of this embodiment aids in
maintaining a lower pressure
bias force on the primary contact region between elastomeric seal 141 and pipe
50.
In Figure 4, the elastomeric seal 141 is shown stretched for positioning
during installation,
while in Figure 5 the elastomeric seal 141 is shown relaxed and sealing to
pipe 50 inserted into the
clamp 11. The minimum diameter of the as-molded elastomeric seal 141 is
significantly less than the
minimum outer diameter of the pipe. Therefore, when elastomeric seal 141 is
relaxed there is an
interference fit between the elastomeric seal 141 in its untensioned and
unpressurized position and
the pipe 50 when the two are mated.
A similar, but alternative style of seal assembly is shown in Figure 12B. In
seal assembly 337,
seal anchor and static seal end are combined into a single anchored static
seal part 32. Static seal
part 32 has an 0-ring 33 in a male groove on the lower end of static seal part
32 which corresponds to
0-ring 33 in seal anchor 34. In addition, seal 341 is bonded to static seal
part 32 and movable seal
end 40 without the undercut face grooves.
In addition, seal 341 is shown with an antiextrusion device 36 embedded in and
bonded to the
elastomeric matrix of seal 341. Antiextrusion device 36 is described in more
detail in a concurrently
pending patent application filed February 19, 2001 and entitled "Antiextrusion
Device".
A preferred antiextrusion device is a corrugated rigid material, positioned
with the midplane
of its corrugations normal to the mating seal surface and parallel to the
midplane of the seal groove. The antiextrusion device 36 is preferably
integrally molded into or onto
the low pressure side of the seal 341. Seal 341 may also have a substance
having a high friction
coefficient, such as silica flour, embedded in its inner surface that will
comate with the object being
gripped.
A third embodiment of a seal assembly 237 is a bidirectional seal which can
retain pressure
equally well from either direction. Seal assembly 237 is shown as molded in
Figure 13. Seal
assembly 237 is mounted in a hydraulically-operated tubular pipeline end
connector clamp shown in
Figures 7, 8, 9, and 10. The tubular clamp 210 shown for this embodiment is
similar in most respects
to clamp 10 shown in Figures 2 and 4 and appears identical in its end view to
tubular clamp 10 shown
in Figure 1. However, tubular clamp 210 differs in the means of tension
application used for stretching
the seal 241. It should be noted that any of the seals shown in Figures 11,
12A, 12B, or 13 can be
adapted as either the cam-operated or the hydraulically-operated actuator.
The internal elements of clamp 210 which are used to grip and seal to the
exterior of a piece
of pipe 50 are housed within the circular tubular extension to clamp housing
211. Housing 211 has a
female thread 212 at its outer end. A smooth first counterbore 213 is inwardly
positioned from and
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adjacent to thread 212. Internal thread 214 is located at the inner end of
first counterbore 213 and has
a smaller minor diameter than that of first counterbore 213, as well as a
thread relief at its inner end.
Smooth second counterbore 215 is located immediately adjacent to and inside of
internal
thread 214. Transverse shoulder 216 is located at the inner end of second
counterbore 215 and
provides a transition from the second counterbore 215 to short third
counterbore 217. Transverse pipe
stop shoulder 218 provides a transition from third counterbore 217 to housing
throughbore 219. Short
annular cylindrical reaction abutment 20 is externally threaded and is
threadedly engaged with female
thread 212 of the body 211. This component and hex-headed half-dog machine
screws 24 are
identical to the items used in pipe clamp 10.
0 Figure 7 shows an array of multiple, coacting gripping elements consisting
of outer end rings
29, outer central rings 30, and inner split rings 31, as described above and
illustrated in Figures 2 and
4, positioned in first counterbore 213 inwardly from the reaction abutment 20.
At the inner end of first counterbore 213 and positioned at the inner end of
the array of
gripping elements is annular seal anchor 233. Seal anchor 233 is generally
cylindrical with a deep
5 counterbore 231 on its inner end as shown in Figures 7,8,9 and 10. External
thread 234 is positioned
on the outer end of seal anchor 233 and is threadedly engaged with internal
thread 214.
A circle of multiple counterbored through bolt holes 235, parallel to the axis
of seal anchor
233, is provided through the outer transverse wall of seal anchor 233 between
the outer end and
counterbore 231 of seal anchor 233. A male 0-ring groove 236 is provided on
the exterior cylindrical
0 surface of seal anchor 233, wherein 0-ring 238 is mounted. 0-ring 238 seals
between second
counterbore 215 and the outside of seal anchor 233.
Seal assembly 237, shown in its as-molded condition in Figure 13, consists of
static seal end
39, movable seal end 240, and elastomeric seal 241 molded integrally to the
static and movable seal
ends in a central position. Static seal end 39 is basically the same as in the
first and second seal
5 assemblies.
The positioning of seal assembly 237 in the housing 211 is shown in Figures
7,8,9 and 10.
Seal assembly 237 fits closely within the deep counterbore 231 on the inner
end of seal anchor 233.
Static seal end 39 is a short annular cylinder with a male 0-ring groove 42 on
its outer cylindrical
surface, wherein 0-ring 43 is mounted to seal against the counterbore on the
inner end of seal anchor
0 233. The outwardly facing transverse surface of static seal end 39 is
provided with drilled and tapped
holes 44 matching the countersunk through holes 235 of seal anchor 233.
Machine screws 45 are
mounted in through holes 235 to engage tapped holes 44 and thereby connect
static seal end 39 to
the fixed seal anchor 233.
To assist in maintaining a good connection between the elastomer of seal 241
and static seal
5 end 39 by providing additional bonding area and shear engagement, an
undercut face groove 57 with
rounded edges is provided on the inside transverse face of static seal end 39.
Movable seal end 240
has a face groove 258 similar to that of static seal end 39 on its outwardly
facing transverse face.
As seen in Figures 9 and 10, the outer cylindrical surfaces of movable seal
end 240 are
stepped in diameter. The first cylindrical section 243, located on the outer
end, has the largest
0 diameter. First cylindrical section 243 has a male 0-ring groove centrally
positioned on its cylindrical
9
WO 01/63166 CA 02404629 2002-09-25 pCT/US01/05412
face and containing 0-ring 242 which seals to counterbore 231. Located
inwardly from the first
cylindrical section 243 of movable seal end 240 is a reduced diameter second
cylindrical section 245
with a male thread and a thread relief adjacent to a transverse shoulder
between the first and second
cylindrical sections. A short third cylindrical section 247 having an outer
diameter smaller than that of
the second section is located at the inner extremity of movable seal end 240.
A transverse shoulder is provided between the second and third cylindrical
sections. The
through bore of movable seal end 240 has a constant diameter equal to the
clearance bore to
accommodate the pipe to be gripped by pipe clamp 210. The elastomeric seal 241
of seal assembly
237 is bonded to both the static seal end 39 and the movable seal end 240
during molding. The
0 elastomeric seal 241 has a symmetric configuration. When the seal is relaxed
as seen in Figure 8, the
exposed outer diameter surface of seal 241 is generally cylindrical, but with
a central annular groove
259. The exposed inner surface of seal 241 is not cylindrical, but rather
extends inwardly in a smooth
curve to two symmetric cusps separated by central annular groove 259. The
inner diameters of the
cusps next to annular groove 259 are smaller than those of the seal ends 39
and 240, while the
5 elastomeric seal diameters adjacent to the seal ends 39, 240 match the inner
diameters of those
pieces.
The inner diameters of the static seal end 39 and the movable seal end 240 are
slightly larger
than the outer diameter of pipe 50 so that an operating clearance is provided
for installing the clamp
210 over a pipe end 50. The minimum diameter of the as-molded elastomeric seal
241 is significantly
0 less than the minimum outer diameter of the pipe 50. The result will be an
interference fit between the
elastomeric seal 241 in its untensioned position and the pipe 50 when the two
are mated, as shown in
Figure 8. On the other hand, when the elastomeric seal 241 is stretched for
installation, as shown in
Figure 7, the tension maintained on the elastomer cross-section is sufficient
to reduce the inward
protrusion of the elastomeric seal 241 so that tendencies to interfere with
insertion of a pipe 50 into the
5 clamp 210 are minimized. At the same time, elastomeric seal 241 will be less
susceptible to damage
during pipe insertion.
Multiple radial connecting ports 249 hydraulically communicate between the
inner 239 and
outer 259 annular grooves of elastomeric seal 241. The chamber formed with
external groove 239 on
the exterior cylindrical face of elastomeric seal 241 between the seal and the
cylindrical counterbore
0 face 231 of seal anchor 233 and isolated between 0-rings 43 and 242 only
communicates with the
inner groove of the seal through ports 249.
Piston 252 has an annular construction and is positioned inwardly from movable
seal end 240.
The extreme outer diameter of piston 252 is a cylindrical surface carrying a
male 0-ring groove in
which 0-ring 256 is positioned so that it can seal between piston 252 and
second counterbore 215.
5 A first reduced outer diameter cylindrical section 244 on the outer end of
the largest diameter
section of piston 252 is sized to slide freely within the counterbore 231 of
seal anchor 233. A second
reduced outer diameter cylindrical segment 248 is positioned on the inner side
of the piston 252 and is
sized to closely fit within third counterbore 217 of housing 210.
A male 0-ring groove is positioned near the inner end of the second reduced
outer diameter
0 cylindrical segment, with 0-ring 257 positioned therein and sealing against
third counterbore 217. The
WO 01/63166 CA 02404629 2002-09-25 PCT/USO1/05412
first counterbore on the outer end of piston 252 has a female thread with a
thread relief, by which
piston 252 is connected to the thread on the inner end of movable seal end
240. A smaller second
counterbore with a female 0-ring groove is positioned inwardly of the thread
and outwardly of the
through bore of piston 252. 0-ring 255 is positioned in the female 0-ring
groove to seal against the
inward projection of the third cylindrical surface of movable seal end 240.
Piston 252 is thus configured to serve as a double-acting piston with an
active area of the
annulus between its extreme outer diameter and its first and second reduced
outer diameters.
Hydraulic ports 260 and 261 are threaded and provide flow passages through the
wall of housing 211
to permit connection with the piston chambers on the outer and inner ends of
piston 252, respectively.
0 Hydraulic ports 260 and 261 are controlled by selectably operable valving.
Figure 7 shows the pipe clamp 210 with the elastomeric seal 241 in a stretched
position for
installation, while Figure 8 shows the clamp 210 with a pipe segment 50 in its
bore and seal 241
untensioned so that it is presqueezed against the pipe 50, but unpressurized.
While seal 241 is
stretched, the pipe 50 is inserted into the through bore of clamp 210 until
its end abuts pipe stop
5 shoulder 218. Figure 9 shows the same situation as for Figure 8, but with
the seal retaining internal
pressure. Figure 10 corresponds to Figure 9, but with the seal retaining
external pressure.
Operation of the Embodiments of the Invention:
The clamp 10 holding the first embodiment of the seal assembly 37 having a
symmetric
0 unidirectional seal is shown in its configuration for receiving the
installation of a pipe into its bore in
Figure 2. In this arrangement, the elastomeric seal element 41 is held in a
stretched position by the
cams 47 which are rotated to cause the movable inward end 40 of the seal
assembly 38 to be forced
inwardly (to the right) in the bore of housing 11. The attendant decrease in
cross-sectional inward
protrusion of elastomeric seal 41 is due to the stretching of the seal. This
decrease in inward
.5 protrusion causes elastomeric seal 41 to readily clear the outer diameter
of a pipe inserted into the
clamp for sealing.
During installation of the pipe, the half-dog machine screws 24 are loosely
adjusted against
the set of clamping rings 29, 30, and 31 so that the rings will freely clear
the outer diameter of a pipe
or pipes inserted into the clamp bore. After a pipe 50 is positioned within
the bore of the clamp as
;0 shown in Figure 3, the half-dog machine screws 24 on each end of clamp 10
are tightened so that the
inner rings 31 are forced inwardly as the ring stack is compressed. A
prescribed torque is then applied
evenly to the screws 24 in order to maintain rings 31 strongly forced against
pipe 50 and thereby to
obtain a strong frictional grip on the pipe. After the pipe is gripped
securely by the gripping rings,
cams 47 are rotated 180 degrees from their installation position, thereby
freeing elastomeric seal 41 to
6 attempt to return to its unstretched position. Because the radial thickness
of elastomeric seal 41 is
monotonically reduced from its smallest diameter to its inner end where it is
bonded to movable seal
end 40, the released seal will smoothly fill the annular seal gap from where
it first rebounds against the
pipe up to the point at which interference ceases. This ensures high
presqueeze without voids.
The diameter and ovality of pipe 50 are made to lie within a known range, such
range tightly
.0 controlled by factory tolerances. Thus, the inner diameter of the seal can
be molded sufficiently
11
WO 01/63166 CA 02404629 2002-09-25 PCT/USO1/05412
smaller than the minimum pipe size to ensure an interference fit with the
pipe. In the process of
attempting to return to its molded shape from its stretched position, the
elastomeric seal assumes a
position such that it conforms to the local contours of the pipe 50 and
presses strongly against it to
effect a highly preloaded interfacial contact ('presqueeze').
If pressure is retained by seal 41, it is permitted to reach the outer
cylindrical surface of
elastomeric seal by passing between clamp body 11 and movable seal end 40.
This retained pressure
on the outside cylindrical surface of the seal permits seal 41 to have a
strong pressure bias tending to
amplify interfacial contact forces between seal 41 and pipe 50. The gripping
of the pipe 50 by the
rings prevents the pipe from being forced out of the bore of clamp 10 by
entrapped internal pressure
0 forces acting on the pipe.
The seal assembly, as shown in Figure 12A, includes an unsymmetrical
elastomeric seal 141,
wherein the primary contact zone (segment with minimal inner diameter as
molded) is displaced to
one side or the other of the middle of the seal section. As shown in Figures 4
and 5, this seal
assembly 137 has its primary contact zone located closer to the low-pressure
side of the seal. The
5 primary contact zone generally has the highest interfacial contact forces to
promote effective sealing.
Varying the axial position of the primary contact zone of seal 141 relative to
its midpoint does not
appreciably influence the presqueeze on the seal, but does permit obtaining
more or less pressure
bias on the sealing interface with the pipe 50. This feature can prove
advantageous for weaker seals,
stiffer seals, or higher pressures. Provision of a smaller pressure bias area
reduces pressure bias
D forces and thereby somewhat reduces extrusion tendencies for a seal of
lesser elastomer stiffness or
exposed to higher pressures. A larger pressure bias area provides more
pressure force on the
seal/pipe interface and thus assists in sealing with stiffer seals and lower
pressures. Otherwise, seal
assembly 137 operates substantially the same as seal assembly 37.
The symmetric seal of Figures 2, 3 and 11 and the unsymmetric seal of Figures
4, 5, 12A and
5 12B have seals that are primarily designed to seal against internal
pressure. However, it should be
noted that for the cam actuated stretching means of Figures 2, 3, 4, 5, and
14, the side of the cam 47
which is not cut away will shoulder against the outer end of groove 26 when
the cam is in its
unactuated position and the normal pressure condition is reversed (i.e., the
pressure is external) .
When the cam 47 is shouldered against the outer end of groove 26, moving seal
end 40 is not
D permitted to shift inwardly (to the right) sufficiently to cause elastomeric
seal 41 to lose its presqueeze
against the comating seal surface of pipe 50. In such an event, substantial
reverse pressures are also
sustainable by these unidirectional seal units 37 and 137, although the
clearances between the uncut
side of cam 47 in its unactuated position and the outer end of groove 26
necessitated by the variation
in the diameter of pipe 50 will typically result in some play which lessens
the presqueeze on
5 elastomeric seal 41 or 141 due to some inward shifting of the moving seal
end 40. Likewise, for
hydraulically actuated seal using the mechanism of Figures 7, 8, 9, and 10,
trapping hydraulic fluid and
pressure by closing the valving controlling hydraulic port 261 makes the
moving seal end 240
immobile so that the seal unit 237 is also able to resist reverse pressures.
The symmetric seal of Figures 2, 3, and 11 and the unsymmetric seal of Figures
4, 5, and 12A
) or 12B are configured to be radially inwardly pressure biased by pressure
differentials in their normal
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WO 01/63166 CA 02404629 2002-09-25 PCT/US01/05412
pressure conditions with internal pressure from the flange side. This pressure
biasing is effected by
providing an isolated pressure path from the region of retained high pressure
(to the right) to the outer
diameter side of elastomeric seal 41. For the symmetric and unsymmetric seal
units 37, the pressure
path is between moveable seal end 40 and the housing 11. The region of the
sealing interface
between pipe 50 and elastomeric seal 41 is considered to start at the line of
initial contact of the
elastomer with the pipe on the high pressure side of the seal. A monotonic
gradation in pressure
between the high pressure and the low pressure across the seal exists across
this region of the
sealing interface. Accordingly, there will be a pressure differential between
the outer diameter face
which is exposed to the full high pressure and the inner diameter face of
elastomeric seal 41 on the
0 low pressure side of the initial high pressure line of contact. This
pressure differential acts in a radially
inward direction on the elastomeric seal 41 to compel higher interfacial
pressures between the
elastomer and the pipe 50, thereby enhancing the resistance of the sealing
interface to escape of
pressure through the interface. This condition is termed pressure bias for the
seal.
In the case of reverse (i.e., external) pressures for the symmetric or
unsymmetric
5 unidirectional seals, the pressure bias is reversed, since the outer
diameter face of elastomeric seal 41
is exposed to low pressure in such a case. The pressure bias then acts
radially outwardly and tends
to reduce the interfacial pressure between elastomeric seal 41 and pipe 50.
However, the elastomer
on the outer diameter face of elastomeric seal 41 is limited in its range of
outward distortion by
abutting against second counterbore 15 and moving seal end 40, which is held
by the restraint of cam
D 47 against the outward end of groove 26. For the case of a unidirectional
seal operated by the
hydraulic piston means of Figures 7, 8, 9, 10, isolation of hydraulic pressure
from closing port 261
similarly restrains the moving seal end. The result is that the reversal of
the pressure bias has only a
limited effect in reducing the interfacial contact pressures between the seals
and pipe 50 from the
interfacial contact pressures which would occur for seals which were not
pressure biased.
5 The bidirectional elastomeric seal 241 of seal assembly 237 is shown mounted
in a
hydraulically-operated clamp 210 in Figures 7, 8, 9, and 10. This clamp 210
holds the elastomeric
seal 241 in a stretched position for installation by maintaining hydraulic
pressure from hydraulic port
260 on the outer side of piston 252 during installation, as is shown in Figure
7, rather than relying upon
cam action for tensioning.
) Piston 252 is attached to movable seal end 240 by threads 245. Thus, the
application of
pressure to hydraulic port 260 causes seal 241 to be stretched. Gripping rings
29, 30, and 31 are
uncompressed for installation in the same manner as for clamp 10 having any of
the other seal
assembly embodiments.
After a pipe segment 50 is positioned in the through bore of clamp 210, the
gripping rings 29,
5 30 and 31 are tightened against the pipe and the hydraulic pressure applied
to the outer side of piston
252 through port 260 is released, as indicated in Figure 8. This permits
elastomeric seal 241 to
assume its preloaded position against the pipe in the same manner as described
for seal assemblies
37 and 137. Additionally, hydraulic pressure may be applied temporarily as a
final installation step to
port 261 to urge the piston 252 outwardly, thereby assisting seal 241 in
reaching a fully presqueezed
condition in spite of high levels of contact friction between the pipe 50 and
elastomeric seal 241.
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WO 01/63166 CA 02404629 2002-09-25 PCT/US01/05412
When the internal pressure across the gap between pipe 50 and clamp 210 is
higher than the
external pressure, as is shown in Figure 9, the pressure acting on seal 241
causes the inside cusp
adjacent to the central annular groove 259 to lift from the pipe sufficiently
to admit that pressure to
reach the central annular groove 259, the multiple radial connecting ports
249, and the outer annular
groove 239. At the same time, the outside cusp does not lift, so that the
pressure is transmitted only
to the outer cylindrical surface of the seal, where it is entrapped by 0-ring
seals. In this manner the
entrapped pressure serves as a pressure bias to maintain a high interfacial
contact force between the
outside cusp and pipe 50. The same sequence of pressure entrapment occurs when
the pressure is
higher on the outside of the seal 241, as is shown in Figure 10. The seal 241
will entrap and retain the
) highest pressure to which it has been exposed as a pressure bias on its
outer diameter cylindrical
face, ensuring good sealing even with pressure reversals or pressure cycling.
Advantages of This Invention:
Conventional seals for large gaps rely upon either: a) passive seals which are
provided with
5 an interference fit and are installed with the interference present during
installation, or b) active seals
which are not molded or formed to have an interference fit and are installed
with no interference fit but
are then actively compressed to cause interference with their comating
surface. The present invention
overcomes many of the problems encountered with conventional seals.
The advantages of this invention accrue primarily from: a) the molded shape of
the
) elastomeric seal being larger than required to span the gap to be sealed so
that an interference fit will
occur between the seal and the comating surface to which it is to seal, b)
stretching of the elastomer in
the direction parallel to the surfaces forming the seal gap to sufficiently
reduce its cross-section
protrusion into the seal gap to avoid significant fit interference when the
seal is being installed adjacent
its comating seal surface, and c) releasing the installation tension on the
elastomer in order to permit it
5 to attempt to return to its as-molded shape and thereby assume a presqueezed
condition against its
comating seal surface. An optional subsequent step is to provide a temporary
axial force to aid in
urging the seal to return towards its unstretched position by overcoming
friction against the elastomer.
Prestretching an elastomeric seal for its installation adjacent a comating
seal surface so that
its cross-section protrusion into the seal gap is reduced permits very high
but controllable presqueezes
for ensuring reliable sealing. While conventional passive seals for large gaps
can also have a
controllable presqueeze, their level of presqueeze is typically limited to
keep the likelihood of
installation damage at acceptable levels.
Having an elastomeric seal which is sized to always assume an interference fit
against its
comating seal surface in attempting to return to its molded shape following
stretching ensures that the
5 seal will always be sufficiently biased against its comating surface due to
the locked-in stresses in the
elastomer. This interfacial bias is maintained passively by the tendency of
the elastomer to return to
its molded shape. Thus, the interfacial biasing force of this invention is
obtained by a means opposite
that used by the active conventional methods for sealing large gaps described
above, which must rely
upon externally applied and maintained compression forces to distort into
sealing engagement an
14
WO 01/63166 CA 02404629 2002-09-25 PCT/US01/05412
initially unstressed elastomeric seal which is molded to a shape which will
not significantly interfere
with the comating surface during installation.
The installation of the seal assemblies described herein under tension ensures
that the seals
are always passively self-urged (i.e., without outside intervention) to have
adequate presqueeze on
the seal interface in spite of elastomer shrinkage or creep. This maintenance
of proper presqueeze
with shrinkage or creep is not feasible with either active or passive
conventional large gap seals
without actively recompressing the seal. Such recompression is often extremely
costly to effect and/or
impractical. Further, in contrast to the conventional large gap active seals,
the level of presqueeze for
the seals of this invention can be predetermined. The level of presqueeze for
the described seal
D assemblies can be controlled by the selection of the general seal geometry,
the type of elastomer
compound, and the amount of interference fit. In contrast, conventional large
gap active seals
frequently are overcompressed by installation personnel when presqueeze is
applied, with the result
that the pipe may be locally necked down in an excessive manner. This
situation is difficult to avoid
with conventional seals, even when jack screw torsions are carefully
controlled, since screw friction is
5 highly variable and unknown.
In addition, the seal assemblies of the present invention have readily
definable and, by design,
controllable pressure biasing behavior for enhancing the reliability of
sealing. In contrast, conventional
seals for large gaps normally have simple rectangular cross-sections and are
force-fitted or clamped
into simple rectangular or near-rectangular grooves. The pressure bias for
such conventional seals is
0 difficult to control and is generally not an important factor in maintaining
sealing.
For situations when the pressure applied to a seal alternates in direction, as
in the case of a
deepwater gas pipeline, the bi-directional seal of the seal assembly 237
offers a vastly improved
pressure capability over conventional passive seals for large gaps.
Conventional passive seals for
large gaps require relief spaces on the high-pressure sides of the seal so
that their substantially
5 constant volume elastomers will have room to displace whenever the seal gap
is smaller than their
expected design maximum gap. Provision of a relief space substantially limits
the capability of such a
passive seal to withstand reverse pressures. While conventional active seals
for large gaps do not
have this same limitation, their other limitations mentioned above still are
major drawbacks.
The hydraulic piston arrangement for stretching seal assembly 237 may cost
slightly more
0 than the cam-operated versions of the first two embodiments, but the
hydraulic operator is easier to
use in the field and offers fewer potential leak paths as well as higher
tensioning forces suitable for
larger seals or stiffer elastomers than is the case for the rotary camming
devices. The ability to
overcome friction, which resists the seal assuming its preloaded condition
after release of the
installation tension, by means of temporarily hydraulically biasing the piston
outwardly to overcome the
friction is another strong advantage of the hydraulic piston tensioning
system. For the hydraulically-
operated clamp, hydraulic pressure only needs to be maintained during
insertion of the pipe into the
clamp bore and then briefly for possible bias of the seal against friction
during release of tension. This
system still permits the passive compensation of the seals of this invention
for seal volume reduction
and creep.
WO 01/63166 CA 02404629 2002-09-25 PCT/US01/05412
It may readily be understood that the seal cross-sections of this invention
may be varied or
changed from the embodiments shown without departing from this invention. For
instance, multiple
ridges can be provided on the seal face which contacts the comating seal
surface for enhancing trash
tolerance and providing redundant seal surfaces. The bonding surfaces of the
static seal end and the
~ movable seal end can be varied from the types shown in the drawings for this
invention without
exceeding the limits of this invention. Likewise, similar seal assemblies can
be adapted to both
semicircular and circular annular seals, linear or near linear or irregularly
shaped seals, and both male
and female seals.
The stretching of the seals can also be performed by a number of mechanisms
such as
) wedging, other types of camming action, or other suitable means without
departing from this invention.
The movable seal end pieces can be segmented for use with irregularly shaped
seal patterns.
Multiple hydraulic cylinders or cylinders with arcuate or lunate or unusually
shaped pistons can also be
used for hydraulic tensioning of the seals for installation. These tensioning
variations are desirable for
semicircular or other irregularly shaped seals. Furthermore, the seals and
seal assemblies of this
invention are broadly applicable and are not limited solely to usage in
pipeline repair clamps. These
seals and their operating systems can also be rendered effective as male seals
simply by inverting the
seals and their operating systems.
Thus, having described several embodiments of seal assemblies and their
installation and use
in pipeline repair clamps, it is believed that other modifications,
variations, and changes will be
) suggested to those skilled in the art in view of the description set forth
above. It is therefore to be
understood that all such variations, modifications, and changes are believed
to fall within the scope of
the invention as defined in the appended claims.
16
