Note: Descriptions are shown in the official language in which they were submitted.
CA 02305957 2000-04-10
SEALING ASSEMBLY FOR A TUBING ROTATOR
FIELD OF INVENTION
The within invention relates to a sealing assembly in combination with an
apparatus for attachment to a wellhead for suspending and rotating a tubing
string contained
within a wellbore, referred to as a tubing rotator. Further, the within
invention relates to a tubing
rotator comprised of at least one sealing assembly as described herein. More
particularly, the
invention relates to a tubing rotator having particular application for use
with wells experiencing
relatively high temperatures and pressures.
BACKGROUND OF INVENTION
A typical oilfield wellhead includes a casing head, casing bowl or tubing head
which engages or is otherwise mounted to a casing string contained within a
wellbore of a well at
the surface. The casing head, casing bowl or tubing head is typically directly
or indirectly
connected or engaged with an upper end of a tubing string which is contained
within the
wellbore. Thus, the tubing string is suspended within the wellbore. A
reciprocating rod or tube
or a rotating rod or tube is then run through the tubing string for production
of the well.
Often a typical oilfield wellhead will further include a tubing rotator to
suspend
and rotate the tubing string within the wellbore. By rotating the tubing
string, typical wear
occurring within the internal surface of the tubing string by the
reciprocating or rotating rod
string is distributed over the entire internal surface. As a result, the
tubing rotator may prolong
the life of the tubing string.
Typically, a sealing assembly or seals are required within the tubing rotator
to
prevent leakage of production fluids from the rotating tubing hanger back down
the wellbore
annulus, to a drive gear system or drive mechanism of the tubing rotator or to
the outside
environment.
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Typically, oil wells produce at a temperature of less than or equal to about
300°F.
Therefore, the seal materials within the tubing rotator may be comprised of
standard elastomeric
O-rings or polyseals capable of operating at temperatures of up to
400°F. In addition, some more
exotic elastomers such as KalrezTM may be used at temperatures of up to
S50°F.
However, temperatures greater than about 300°F often occur in oil
wells that
employ steam injection to heat the oil in-situ. Such wells usually produce
from zones containing
heavy (viscous) oil that will not flow into the wellbore without the addition
of heat. Increasing
the temperature of heavy (viscous) oil drastically reduces its viscosity so
that it will flow to the
wellbore. Where steam injection or other thermal methods of causing
temperature increase
within the formation are employed, the temperature of the produced fluids from
the wellbore may
reach temperatures as high as about 650°F. Further, steam injection is
typically done at
saturation pressure, being 2208.8 psia for steam at 650°F.
Saturation pressure and temperature is the state at which water and water
vapor
(steam) co-exist. Typically, steam injection is done with a mixture (quality)
of 80%; that is, 80%
by weight of the mixture is water vapor and 20% is liquid. This mixture has
been found to be
optimal in that the 20% water will carry all minerals that are contained
within the softened source
water and prevent the minerals from scaling or plating out on the steam boiler
heating surfaces.
Accordingly, the tubing rotator used in these applications is preferably
capable of withstanding
such relatively high temperatures of up to about 650°F., as well as
withstanding such relatively
high pressures of up to about 2208.8 psia while at this temperature.
Conventional elastomeric seals for sealing between rotating parts or members
tend
to break down under these conditions due to the combined effects of the high
temperature, the
high pressure and the rotation. As a result, other packing or sealing
materials, such as graphite,
may be used that will withstand such temperatures and pressures. However,
these materials are
non-elastomeric, which means that they have no "memory" and thus will not
rebound or return to
their original shape when the compressive sealing forces are removed from
them. As a result,
even if these materials are initially compressed sufficiently to cause a seal,
as soon as they wear
or the compressing force is relaxed, they will begin to leak. In other words,
non-elastomeric
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seals, such as graphite seals, are therefore "all or nothing" seals in that
they are either pressurized
or energized or non-pressurized or non-energized.
Consequently, as seals comprised of non-elastomeric material become worn, the
S compressive sealing forces applied to them must continuously be increased to
compensate for
any loss in thickness of the seal. In other words, the seals are initially
energized to provide the
seal and then re-energized as wear occurs to maintain the seal. As a result,
these packing
materials tend to be employed where the compressing or re-energizing force can
be manually or
mechanically re-applied when wear occurs. For instance, these types of packing
materials are
often employed in oil well stuffing boxes or on valve stem packings of high
temperature valves
where the packing force can be re-introduced manually when required. In some
cases, springs
such as Belleville springs, being dish-shaped washers, are used to maintain
the compressive force
on the packing.
Further, packing materials, such as graphite packing, which are a relatively
solid
non-elastomeric material often require a relatively high compressive force to
cause them to flow
and seal between the two surfaces where the seal is desired. As a result, the
use of non-
elastomeric materials may make it relatively difficult to move or rotate one
surface relative to
another due to the friction drag of the highly compressed packing material.
In high temperature, high pressure applications for tubing rotators, leakage
to the
drive system or drive mechanism compartment of the tubing rotator or
externally to the
environment cannot be tolerated and must be minimized if not prevented
altogether.
Specifically, any leakage at these high temperatures and pressures will
increase rapidly if not
immediately stopped. In addition, the seals typically located within the
tubing rotator are not
readily accessible for tightening or re-energizing manually. Finally, seals
located within the
tubing rotator must be dynamic seals such that adjacent surfaces must be
permitted to rotate
relative to one another.
There is therefore a need in the industry for a tubing rotator including or
combined
with a sealing assembly capable of withstanding relatively high temperatures
and high pressures,
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such as those typically found in steam injection wells experiencing
temperatures of up to about
650°F. and pressures of up to about 2208.8 psia. Further, there is a
need for the sealing assembly
to be energized, pressurized or compressed by a mechanism, device or method
that is self
actuating as needed such that it does not require external intervention.
Finally, there is a need for
a sealing assembly that does not require an excessive energizing or
compressive force that will
result in a heavy drag between the sealing surfaces such that the operation of
the tubing rotator is
impeded or otherwise interfered with.
In addition, the overall configuration or design of the tubing rotator
including the
sealing assembly preferably maintains the overall strength and integrity of
the wellhead, adds a
minimum of height to the wellhead, facilitates or permits existing well
servicing procedures to be
carried out and is relatively safe and reliable as compared to known tubing
rotators.
SUMMARY OF INVENTION
The within invention relates to a sealing assembly in combination with an
apparatus for attachment to a wellhead for suspending and rotating a tubing
string contained
within a wellbore, referred to as a tubing rotator. Further, the within
invention relates to a tubing
rotator comprised of at least one sealing assembly as described herein. As
well, the invention
relates to a dynamic sealing assembly for use in applications where a
relatively high temperature,
a relatively high pressure and rotating parts or members are encountered. For
instance, the tubing
rotator comprised of the sealing assembly of the within invention has been
found to be
particularly useful for suspending and rotating the tubing string within a
wellbore experiencing
temperatures as high as about 650°F. and pressures as high as about
2208.8 Asia.
Further, the within invention relates to a sealing assembly which provides
some
"memory' for non-elastomeric type seals. Specifically, the sealing assembly
combines a non-
elastomeric seal material or sealing element with a self actuating biasing
mechanism so that a
compressive sealing force may be continuously applied when the non-elastomeric
seal material
experiences the effects of wear without the need for external intervention. In
other words, once
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the sealing material or sealing element is energized, the biasing mechanism
preferably
compensates for wear of the sealing material by automatically re-energizing
the seal material.
In addition, the sealing assembly of the within invention is preferably
unaffected
by the elements within its environment. In particular, the biasing mechanism
is preferably
positioned within the tubing rotator such that it is not readily clogged or
contaminated with
debris which may interfere with its proper functioning. As well, the biasing
mechanism
preferably acts upon other elements or components of the sealing assembly
which similarly are
not readily clogged or contaminated with debris.
In a first aspect of the invention, the invention is comprised of a sealing
assembly
in combination with an apparatus for attachment to a wellhead for suspending
and rotating a
tubing string contained within a wellbore. The apparatus is comprised of an
outer member and
an inner mandrel rotatably supported within the outer member for connection
with the tubing
1 S string and defining an annular space between the outer member and the
inner mandrel. The
sealing assembly is comprised of
(a) a sealing element contained within the annular space for sealing between
the outer
member and the inner mandrel;
(b) a biasing mechanism contained within the annular space for applying an
axial
force to the sealing element such that the sealing element is compressed to
seal the
annular space; and
(c) an energizing mechanism associated with one of the outer member and the
inner
mandrel for loading the biasing mechanism.
In a second aspect of the invention, the invention is comprised of an
apparatus for
attachment to a wellhead for suspending and rotating a tubing string contained
within a wellbore,
the apparatus comprising:
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(a) an inner mandrel for connection with the tubing string;
(b) an outer member for rotatably supporting the inner mandrel therein,
wherein an
annular space is defined between the outer member and the inner mandrel;
(c) a drive mechanism operatively engaging the inner mandrel for rotating the
inner
mandrel within the outer member; and
(d) at least one sealing assembly for sealing the annular space between the
outer
member and the inner mandrel, wherein the sealing assembly is comprised of:
(i) a sealing element contained within the annular space for sealing between
the outer member and the inner mandrel;
(ii) a biasing mechanism contained within the annular space for applying an
axial force to the sealing element such that the sealing element is
compressed to seal the annular space; and
(iii) an energizing mechanism associated with one of the outer member and the
inner mandrel for loading the biasing mechanism.
In both the first and second aspects of the invention, the apparatus may be
any type
or configuration of tubing rotator comprised of an outer member, outer housing
or outer mandrel
connectable with or mountable upon the wellhead and further comprised of an
inner mandrel,
inner member or inner tubing connectable with the tubing string and rotatably
supported within
the outer member such that an annular space is defined therebetween. The
sealing assembly of
the within invention is provided for sealing between the outer member and the
inner mandrel.
Preferably, the outer member has an upper end and a lower end. The apparatus
may include a single sealing assembly of the within invention such that the
sealing assembly
seals the annular space between the outer member and the inner mandrel at any
location or
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position therein between the upper end and the lower end of the outer member.
However,
preferably, the annular space is sealed adjacent the upper end of the outer
member and is further
sealed adjacent the lower end of the outer member. As a result, fluids are
inhibited from passing
into or out of the outer member, between the outer member and the inner
mandrel, at both the
upper and lower ends of the outer mandrel. Accordingly, a sealed chamber is
preferably
provided between the upper and lower ends of the outer member. In this case,
the particular
sealing assembly of the within invention would seal the annular space adjacent
either the upper
end or the lower end of the outer member. Sealing adjacent the other end of
the outer member
would be provided or performed by any other type or configuration of seal,
sealing structure or
sealing mechanism.
However, preferably, the apparatus or tubing rotator is comprised of an upper
sealing assembly for sealing the annular space adjacent the upper end of the
outer member and a
lower sealing assembly for sealing the annular space adjacent the lower end of
the outer member.
In other words, both sealing assemblies adjacent the upper and lower ends of
the outer member
are preferably configured in accordance with the sealing assembly of the
within invention. As a
result, fluids are inhibited from passing into or out of the outer member,
between the outer
member and the inner mandrel, at both the upper and lower ends of the outer
mandrel to provide
a sealed chamber in the outer member between the upper and lower sealing
assemblies. Further,
in the preferred embodiment, each of the upper sealing assembly and the lower
sealing assembly
are substantially similar. Thus, any discussion or description herein relating
to the sealing
assembly generally is equally applicable to both the upper sealing assembly
and the lower sealing
assembly.
Further, the outer member preferably defines a drive chamber communicating
with
the annular space between the upper sealing assembly and the lower sealing
assembly. Thus, the
drive chamber preferably comprises the sealed chamber between the upper and
lower sealing
assemblies. The drive chamber is provided for containing all or any part or
portion of the drive
mechanism of the apparatus or the tubing rotator therein. In the event that
any part or portion of
the drive mechanism exits or passes out of the outer member, the outer member
is preferably
further sealed at this location such that the sealing of the drive chamber is
maintained. This
CA 02305957 2000-04-10
further seal may be provided by a sealing assembly of the within invention or
it may be provided
by any other type or configuration of seal, sealing structure or sealing
mechanism.
Any type or configuration of drive mechanism may be used which is capable of
S operatively engaging the inner mandrel in order to rotate the inner mandrel
within the outer
member. The drive mechanism may operatively engage the inner mandrel at any
location or
position along the length of the inner mandrel. However, preferably, the drive
mechanism
operatively engages the inner mandrel within the drive chamber. Thus,
preferably, any type or
configuration of drive mechanism may be used which is capable of operatively
engaging the
inner mandrel within the drive chamber.
Further, the drive mechanism is preferably comprised of a driven gear
associated
with the inner mandrel and a drive gear for engaging the driven gear. Thus,
preferably, the drive
gear operatively engages the driven gear within the drive chamber. Any type or
configuration of
drive gear and driven gear system may be used. However, preferably, the gear
system is
comprised of a worm and worm gear. More particularly, in the preferred
embodiment, the driven
gear is comprised of a worm gear associated with the inner mandrel, while the
drive gear is
comprised of a worm. Thus, rotation of the worm acts upon the worm gear in
order to rotate the
inner mandrel within the outer member.
In addition, in the preferred embodiment, the worm is associated with a worm
shaft such that rotation of the worm shaft rotates the worm. Further, the worm
is contained
within the drive chamber, while the worm shaft extends from the drive chamber
and exits out of
the outer member through the outer member. As a result, in the preferred
embodiment, as
discussed above, the worm shaft is sealed with the outer member as it passes
through the outer
member in order to maintain the sealed drive chamber. This seal may be
provided by a further
sealing assembly of the within invention or by any other type or configuration
of seal, sealing
structure or sealing mechanism.
As well, in the first and second aspects of the invention, the sealing element
of
each sealing assembly may be comprised of any type of material capable of
sealing the annular
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CA 02305957 2003-05-29
space. For instance, the sealing element may be elastomeric or non-
elastomeric. In the preferred
embodiment, the sealing element is comprised of a non-elastomeric seal. More
particularly, the
non-elastomeric seal is preferably comprised of graphite. In the preferred
embodiment, the non-
elastomeric seal is comprised of at least one graphite ring.
Thus, the sealing element of each sealing assembly, being a non-elastomeric
seal, may be comprised of a single graphite ring contained within the annular
space for sealing
between the inner mandrel and the outer member. However, preferably, the
sealing element is
layered in that the sealing element is comprised of at least two, and
preferably at least three,
graphite rings layered or stacked together within the annular space to
comprise the sealing
element. In the preferred embodiment, the sealing element or non-elastomeric
seal is comprised
of at least three graphite rings wherein at least one central graphite ring is
positioned between
two outer graphite rings .
Each of the graphite rings may be comprised of any type or configuration of
graphite or graphite packing suitable for sealing the annular space. Further,
each central graphite
ring and each of the two outer graphite rings may be comprised of the same
type or
configuration of graphite or graphite packing or may be comprised of different
types or
configurations of graphite or graphite packing. However, preferably, each
central graphite ring
is comprised of the same type or configuration of graphite or graphite
packing. Further, each of
the outer graphite rings is preferably comprised of the same type or
configuration of graphite or
graphite packing. In the preferred embodiment, the outer graphite rings are
comprised of
graphite packing rope. In addition, in the preferred embodiment, the central
graphite ring or at
least one central graphite ring is comprised of a graphoif~ seal.
With respect to each sealing assembly, the application of the axial force to
the
sealing element by the biasing mechanism may compress the sealing element to
seal the annular
space in any manner and by any structure or mechanism capable of compressing
the sealing
element. However, preferably, the sealing assembly is further comprised of a
shoulder
associated with one of the inner mandrel and the outer member and extending
within the annular
space. In this instance, the sealing element is contained within the annular
space between the
shoulderand
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the biasing mechanism such that the sealing element is compressed between the
shoulder and the
biasing mechanism upon application of the axial force. In the preferred
embodiment, the
shoulder is associated with the outer member such that the shoulder extends
from the outer
member within the annular space. The shoulder may be integrally formed with
the outer member
or it may be mounted, fastened, connected or otherwise attached with the outer
member.
Further, in order to facilitate or enhance the sealing of the annular space by
the
non-elastomeric seal, while still permitting the rotation of the inner mandrel
within the outer
member, the sealing assembly is further preferably comprised of a chevron
bushing contiguous
with the non-elastomeric seal for deflecting the non-elastomeric seal
laterally within the annular
space upon the application of the axial force by the biasing mechanism. More
preferably, the
chevron bushing is contiguous with one or more of the graphite rings such that
the graphite ring
is deflected laterally. In the preferred embodiment, the chevron bushing is
contiguous with the
central graphite ring for deflecting the central graphite ring laterally
within the annular space
1 S upon the application of the axial force by the biasing mechanism. Where
the non-elastomeric
seal is comprised of greater than one central graphite ring, a chevron bushing
is preferably
contiguous with each central graphite ring.
The biasing mechanism may be comprised of any mechanism, structure or device
able to be contained within the annular space and capable of applying the
axial force to the
sealing element. However, the biasing mechanism is preferably comprised of at
least one spring
for applying the axial force to the sealing element. Thus, in the preferred
embodiment, the
biasing mechanism is comprised of at least one spring for applying the axial
force to one or more
graphite rings which comprise the non-elastomeric seal such that the graphite
ring is compressed
and deflected laterally to seal the annular space. Although any type or
configuration of spring or
springs may be used, the biasing mechanism is preferably comprised of at least
one Belleville
spring.
The energizing mechanism of each sealing assembly may be associated with
either
the outer member or the inner mandrel and may be comprised of any mechanism,
structure or
device capable of loading the biasing mechanism in order to energize the
sealing element.
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Preferably, the energizing mechanism is comprised of an adjustable retainer
associated with one
of the outer member and the inner mandrel and movable within the annular space
such that the
retainer is adjustable towards the biasing mechanism for loading the biasing
mechanism. In the
preferred embodiment, the adjustable retainer is associated with the outer
member.
More particularly, the adjustable retainer is preferably comprised of a
tightening
mechanism associated with the outer member and a retainer plate having an
inner end movable
within the annular space and an outer end associated with the tightening
mechanism such that
tightening of the tightening mechanism adjusts the position of the retainer
plate within the
annular space towards the biasing mechanism. In the preferred embodiment, the
tightening
mechanism is comprised of a bolt or screw which extends through the outer end
of the retainer
plate for engagement with the outer member. More particularly, the bolt or
screw is preferably
threaded for threaded engagement with the outer member such that turning or
screwing of the
bolt into or out of the outer member moves the inner end of the retainer plate
within the annular
space. In the preferred embodiment, tightening of the screw into the outer
member adjusts the
position of the retainer plate towards the biasing mechanism.
Finally, the sealing assembly is further preferably comprised of at least one
bushing contained within the annular space for laterally supporting the inner
mandrel. More
preferably, at least one bushing is preferably positioned or located adjacent
each end of the
sealing element, or adjacent each of the outer graphite rings, such that the
sealing element is
positioned therebetween. Any type of bushing may be used, such as a bronze or
steel bushing.
BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the invention will now be described with reference to the
accompanying drawings, in which:
Figure 1 is a side view of a wellhead wherein a preferred embodiment of an
apparatus for suspending and rotating a tubing string within a wellbore is
attached thereto;
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Figure 2 is a longitudinal sectional view of the apparatus shown in Figure 1
including a preferred embodiment of a sealing assembly;
Figure 3 is a more detailed view of the sealing assembly shown in Figure 2;
and
Figure 4 is a cross-sectional view of the apparatus taken along line 4 - 4 of
Figure
2.
DETAILED DESCRIPTION
Refernng to Figure 1, a typical wellhead (20) is comprised of a plurality of
components mounted at the ground surface above the wellbore. A rod or rod
string (22) is run
through the wellhead (20) and into the wellbore through a continuous fluid
passage or pathway
which extends through each of the components of the wellhead (20). As shown in
Figure 1, the
1 S well may be produced by a reciprocating rod or tube (22) reciprocated by a
pump jack or walking
beam (24) at the surface. Alternately, the well may be produced by a rotating
rod or tube (22)
driven by a rotary pump drive (not shown) at the surface.
Further, a typical wellhead (20) is comprised of a casing head (26), casing
bowl,
tubing head or tubing bowl which engages or is otherwise mounted to a casing
string (28)
contained within the wellbore of the well at the surface. An apparatus (30)
for suspending and
rotating a tubing string (32) contained within the wellbore, referred to
herein as a tubing rotator,
may be mounted upon an upper surface of the casing head (26). As indicated,
the tubing rotator
(30) is connected to or engages an upper end of the tubing string (32) which
is contains within
the wellbore.
Refernng to Figures 2 - 4, the apparatus or tubing rotator (30) is comprised
of an
inner mandrel (34) for connection with the tubing string (32) and an outer
member (35) for
rotatably supporting the inner mandrel (34) therein such that an annular space
(38) is defined or
provided between the inner mandrel (34) and the outer member (36).
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More particularly, refernng to Figures 2 and 4, the outer member (36) has an
upper
end (40), a lower end (42), an internal bore (44) extending between the upper
and lower ends (40,
42) and an outer wall (46). The outer member (36) may be of any shape or
configuration suitable
for its intended function purpose as described herein. However, the outer
member (36) is
preferably tubular on cross section, as shown in Figure 4, such that the
circumference of the outer
member (36) defines the outer wall (46).
The upper end (40) of the outer member (36) is preferably connectable to other
components of the wellhead (20) or other wellhead equipment by any fastening
or connecting
means, mechanism, structure or device suitable for temporarily fastening or
connecting the outer
member (36) to such other wellhead equipment. Although the connection is
preferably a
temporary connection, permitting the removal of the other equipment, where
required or desired
the connecting or fastening means may permit or cause a permanent connection
between the
outer member (36) and the other equipment.
In the preferred embodiment, the upper end (40) of the outer member (36) is
connected with other wellhead equipment by a connecting flange (48), as shown
in Figure 1,
associated with the other wellhead equipment. However, the connecting flange
(48) may
alternatively be integrally formed, connected, mounted, attached or otherwise
associated with the
upper end (40) of the outer member (36). In addition, in the preferred
embodiment, the upper
connecting flange (48) defines at least two apertures, and preferably a
plurality of apertures,
spaced circumferentially about the upper connecting flange (48). The apertures
are provided for
receiving fasteners (50), such as bolts, screws, studs or the like, therein
such that the other
wellhead equipment may be fastened to the outer member (36). Further, the
upper end (40) of
the outer member (36) preferably defines at least two, and preferably a
plurality of, internally
threaded cavities (52) spaced circumferentially about the bore (44) of the
outer member (36) for
receiving the fasteners (50) therein. Finally, an annular groove (54) may be
defined by the upper
end (40) of the outer member (36) about the circumference of the internal bore
(40) for receiving
a flange ring or other seal for sealing between the adjacent surfaces of the
outer member (36) and
the other wellhead equipment.
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Similarly, the lower end (42) of the outer member (36) is preferably
connectable to
the casing head (26) or any other suitable components of the wellhead (20) or
wellhead
equipment by any means, structure, device or mechanism suitable for mounting
the outer
member (36) to the particular wellhead structure may be used as long as it is
compatible with the
function and purpose of the outer member (36) and the tubing rotator (30).
Further, the
connection may provide for either a temporary or a permanent connection
between the outer
member (36) and the wellhead structure to which it is attached. In the
preferred embodiment, the
lower end (42) of the outer member (36) is removably or detachably mounted or
connected with
the casing head (26).
In the preferred embodiment, the lower end (42) of the outer member (36) is
connected with the casing head (26) by a connecting flange (56), as shown in
Figure 1, associated
with the casing head (26). However, the connecting flange (56) may
alternatively be integrally
formed, connected, mounted, attached or otherwise associated with the lower
end (42) of the
outer member (36). In addition, in the preferred embodiment, the lower
connecting flange (56)
also defines at least two apertures, and preferably a plurality of apertures,
spaced
circumferentially about the connecting flange (56). The apertures are provided
for receiving
fasteners (50), such as bolts, screws, studs or the like, therein such that
the casing head (26) may
be fastened to the outer member (36). Further, the lower end (42) of the outer
member (36)
preferably defines at least two, and preferably a plurality of, internally
threaded cavities (58)
spaced circumferentially about the bore (44) of the outer member (36) for
receiving the fasteners
(50) therein. Finally, an annular groove (60) may be defined by the lower end
(42) of the outer
member (36) about the circumference of the internal bore (40) for receiving a
flange ring or other
seal for sealing between the adjacent surfaces of the outer member (36) and
the casing head (26).
Further, the outer member (36) may be comprised of one integral piece or
element
or it may be comprised of two or more pieces, parts or elements connected,
temporarily or
permanently together to form the outer member (36). In the preferred
embodiment, the outer
member (36) is comprised of two pieces, parts or members removably connected
together in
order to facilitate the manufacture and maintenance of the tubing rotator (30)
and the placement
and removal of the inner mandrel (34) within the bore (44) of the outer member
(36).
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Specifically, the outer member (36) is comprised of a tubular outer mandrel
(62) removably
connected with or mounted within a surrounding housing (64).
Specifically, the outer mandrel (62) has an outer surface (66) and an inner
surface
S (68). Further, the housing (64) has an outer surface (70) and an inner
surface (72). The outer
mandrel (62) is preferably removably mounted within the housing (64) adjacent
either the upper
end (40) or the lower end (42) of the outer member (36). Alternatively, an
outer mandrel (62)
may be mounted within the housing adjacent both the upper and lower ends (40,
42) of the outer
member (36). In the preferred embodiment, a single outer mandrel (62) is
removably mounted
within the housing (64) adjacent the upper end (40) of the outer member (36).
In particular, the outer mandrel (62) is mounted within the inner surface (72)
of the
housing (64) adjacent the upper end (40) such that the outer surface (66) of
the outer mandrel
(62) sealingly engages the adjacent inner surface (72) of the housing (64). In
particular, a
threaded engagement is preferably provided therebetween to provide a metal to
metal seal. In
other words, a threaded inner surface (72) of the housing (64) engages a
threaded outer surface
(66) of the outer mandrel (62). Further, the outer mandrel (62) is configured
and mounted within
the housing (64) such that the inner surface (68) of the outer mandrel (62)
defines the bore (44)
of the outer member (36) adjacent its upper end (40), while the inner surface
(72) of the housing
(64) defines the bore (44) of the outer member (36) adjacent its lower end
(42).
With respect to the threads between the outer surface (66) of the outer
mandrel
(62)and the adjacent inner surface (72) of the housing (64), these threads are
preferably tapered
so that the screwing of the outer mandrel (62) into the housing (64) creates
the metal to metal
seal between the threads of the outer mandrel (62) and the housing (64). A
torque of 700 to 1000
foot-pounds applied to the outer mandrel (62) has been found to provide a
positive seal. In
addition, a thermal seal thread compound, such as that provided by Topco
Company, may also be
used to facilitate a positive seal.
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CA 02305957 2000-04-10
Further, the outer member (36), and in particular the housing (64), defines a
drive
chamber (74) therein which communicates with the annular space (38) provided
between the
bore (44) of the outer member (36) and the inner mandrel (34) rotatably
suspended therein.
The inner mandrel (34) may be comprised of any tubular member, element or
structure permitting the passage of the rod string (22) and wellbore fluids
therethrough. Further,
the inner mandrel (34) includes an upper end (76), a lower end (38), a bore
(80) extending
therethrough and an outer surface (82). The upper end (76) of the inner
mandrel (34) is
preferably positioned adjacent the upper end (40) of the outer member (36),
while the lower end
(78) of the inner mandrel (34) preferably extends from the lower end (42) of
the outer member
(36) for connection with the tubing string (32). However, the lower end (78)
of the inner
mandrel (34) need not extend from the lower end (42) of the outer member (36).
The annular
space (38) is defined between the bore (44) of the outer member (36) and the
outer surface (82)
of the inner mandrel (34).
Further, the upper end (76) of the inner mandrel (34) is preferably
connectable
with other tools or tubing within the wellhead (20) such that the rod string
(22) and wellbore
fluids may pass therebetween or in order to remove the inner mandrel (34) or
the tubing rotator
(30) from the wellhead (20). Thus, the bore (80) of the inner mandrel (34)
adjacent the upper
end (76) is preferably threaded. Similarly, the lower end (78) of the inner
mandrel (34) is
connectable with the tubing string (32) within the wellbore such that the rod
string (22) and the
wellbore fluids may pass between the tubing string (32) and the inner mandrel
(34). Thus, the
bore (80) of the inner mandrel (34) adjacent the lower end (78) is also
preferably threaded.
As indicated, the inner mandrel (34) is rotatably supported by the outer
member
such that the longitudinal movement of the of the inner mandrel (34) relative
to the outer member
(36) in a direction towards the lower end (42) of the outer member (36) is
inhibited. Any means,
mechanism, device or structure capable of supporting the inner mandrel (34) in
the required
manner which is compatible with the function of the tubing rotator (30), may
be used. However,
preferably, the inner mandrel (34) is rotatably supported within the outer
member (36) by at least
one bearing (84) located between the inner mandrel (34) and the outer member
(36) such that the
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bearing (84) is seated on the outer member (36) and the inner mandrel (34) is
rotatably supported
upon the bearing (84). Any bearing (84) suitable for, and compatible with,
this intended purpose
or function may be used. For instance, the bearing (84) may be comprised of a
thrust bearing, a
radial bearing, a tapered roller bearing, a roller thrust bearing or a
combination thereof.
S
In addition, the tubing rotator (30) is comprised of a drive mechanism (86)
operatively engaging the inner mandrel (34) for rotating the inner mandrel
(34) within the outer
member (36). More particularly, the drive mechanism (86) preferably
operatively engages the
inner mandrel (34) within the drive chamber (74). Although any type or
configuration of drive
mechanism (86) may be used, the drive mechanism (86) is preferably comprised
of a driven gear
(88) associated with the inner mandrel (34) and a drive gear (90) for engaging
the driven gear
(88). As indicated, the drive gear (90) preferably engages the driven gear
(88) within the drive
chamber (74).
Further, the inner mandrel (34) is associated with the driven gear (88) such
that
rotation of the driven gear (88) causes the inner mandrel (34) to rotate
within the outer member
(36). Any structure, device, mechanism or means for associating the inner
mandrel (34) and the
driven gear (88) in the described manner may be used. However, in the
preferred embodiment,
the driven gear (88) is fixedly mounted or connected about the outer surface
(82) of the inner
mandrel (34) such that the driven gear (88) extends from the inner mandrel
(34) towards the
drive chamber (74) for engagement with the drive gear (90). Thus, the driven
gear (88) is
preferably located along the inner mandrel (34) at a position such that the
driven gear (88) is
adjacent to the drive gear (90) when the inner mandrel (34) is located within
the internal bore
(44) of the outer member (36).
The driven gear (88) may be mounted or otherwise fastened to the inner mandrel
(34) by any suitable means, structure, device or mechanism for mounting or
fastening the driven
gear (88) thereto. However, in the preferred embodiment, as shown in Figures 2
and 4, an inside
surface (92) of the driven gear (88) defines a keyway (94) which is compatible
with a keyway
(96) defined by the adjacent outer surface (82) of the inner mandrel (34).
Alignment of the
keyways (94, 96) and the insertion of a key or dowel (98) therein provides at
least in part for the
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CA 02305957 2000-04-10
mounting of the driven gear (88) with the inner mandrel (34) and inhibits the
rotation of the
driven gear (88) relative to the inner mandrel (34).
In addition, the particular manner in which the inner mandrel (34) is
rotatably
supported by the outer member (36) further provides for the mounting of the
driven gear (88)
with the inner mandrel (34). In the preferred embodiment, the bore (44) of the
outer member
(36), and particularly, the inner surface (72) of the housing (64) includes an
upwardly facing
support shoulder (100). A lower end of the bearing (84) is seated upon the
shoulder (100). The
driven gear (88) is then seated upon an upper end of the bearing (84) such
that the driven gear
(88), and therefore the inner mandrel (34), is rotatably supported upon the
outer member (36).
Finally, the outer surface (82) of the inner mandrel (34) defines a downwaxdly
facing shoulder
which is seated upon the driven gear (88).
In this manner, the downward longitudinal movement of the inner mandrel (34)
relative to the outer member (36) is inhibited. Further, downward longitudinal
movement of the
inner mandrel (34) relative to the outer member (36) is also inhibited by the
engagement of the
shoulder (102) with the outer member (36), and particularly with the outer
mandrel (62).
However, any means, mechanism, structure or device capable of performing this
function may be
used.
As stated, the drive mechanism (86) of the apparatus (30) is comprised of the
drive
gear (90) and the driven gear (88). The drive gear (90) is preferably of a
type and conf guration
which is able to be accommodated or contained within the drive chamber (74)
and which is
compatible with the driven gear (88) such that the drive gear (90) may
releasably engage the
driven gear (88) when the inner mandrel (34) is located within the bore (44)
of the outer member
(36). The driven gear (88) is also of a type and configuration which is able
to be accommodated
or contained within the drive chamber (74) and which is compatible with the
drive gear (90) such
that the driven gear (88) may releasably engage the drive gear (90).
The drive gear (90) and the driven gear (88) may be comprised of any gears
capable of performing the functions or purposes set out above, and which
permit the drive gear
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CA 02305957 2000-04-10
(90) and the driven gear (88) to engage each other within the drive chamber
(74). However,
preferably, the drive gear (90) is comprised of a worm and the driven gear
(88) is comprised of a
worm gear. Any suitable worm (90) and worm gear (88) may be used.
Referring to Figure 4, in the preferred embodiment, the worm (90) is comprised
of
a worm shaft (104) having a first end (106) and a second end (108). The worm
(90), and in
particular the worm shaft (104), is rotatably supported within the drive
chamber (74) such that
the worm shaft ( 104) may rotate about its longitudinal axis and such that the
worm (90) is
positioned to engage the worm gear (88) so that rotation of the worm shaft
(104) causes rotation
of the worm gear (88).
The worm (90), and more particularly the worm shaft (104) may be rotatably
supported within the drive chamber (74) by any means, mechanism, structure or
device suitable
for, and capable of, supporting the worm shaft (104) in the desired manner
such that the worm
(90) may perform its function or purpose as described herein. In the preferred
embodiment, the
first end (106) of the worm shaft (104) is positioned within the drive chamber
(74) and rotatably
supported by a bushing (110), preferably a bronze bushing. The second end
(108) of the worm
shaft (104) extends through and beyond the outer wall (46) of the outer member
(36).
Thus, the outer wall (46) of the outer member (36) defines an opening for
passage
of the second end (108) of the worm shaft (104) therethrough such that the
second end (108) of
the worm shaft (104) is outside of the outer member (36). Preferably, the
outer member (36) is
sealed with the worm shaft (104) as it passes out of the outer member (36), as
discussed further
below. Further, one or more bearings (112) and one or more bushings (114) are
preferably
mounted about the worm shaft (104) to rotatably support the worm shaft (136)
within the outer
member (36). Any bearing (112) suitable for, and compatible with, this
intended purpose or
function may be used. For instance, the bearing (152) may be comprised of a
thrust bearing, a
radial bearing, a tapered roller bearing or a combination thereof.
The apparatus (30) is further comprised of at least one sealing assembly for
sealing
the annular space (38) between the bore (44) of the outer member (36) and the
outer surface (82)
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of the inner mandrel (34). However, preferably, the annular space (38) is
sealed adjacent the
upper end (40) of the outer member (36) and adjacent the lower end (42) of the
outer member
(36). As a result, fluids are inhibited from passing into or out of the drive
chamber (74) defined
by the outer member (36). In other words, the drive chamber (74) is preferably
sealed at the
upper and lower ends (40, 42) of the outer member (36).
Thus, in the preferred embodiment, the apparatus or tubing rotator (30) is
comprised of an upper sealing assembly (116) for sealing the annular space
(38) adjacent the
upper end (40) of the outer member (36) and a lower sealing assembly (118) for
sealing the
annular space (38) adjacent the lower end (42) of the outer member (36). More
particularly, the
upper and lower sealing assemblies (116, 118) provide a seal between the outer
surface (82) of
the inner mandrel (34) and the bore (44) of the outer member (36). Thus, in
the prefer~:ed
embodiment, the upper sealing assembly (116) provides a seal between the outer
surface (82) of
the inner mandrel (34) and the inner surface (68) of the outer mandrel (62),
while the lower
sealing assembly (118) provides a seal between the outer surface (82) of the
inner mandrel (34)
and the inner surface (72) of the housing (64).
Both the upper and lower sealing assemblies (116, 118) are preferably
configured
in accordance with the preferred embodiment of the sealing assembly as
described herein.
Therefore, the description contained herein relating generally to the sealing
assembly is equally
applicable to both the upper and lower sealing assemblies (116, 118).
As indicated, the sealed drive chamber (74) communicating with the annular
space
(38) is preferably provided between the upper sealing assembly (116) and the
lower sealing
assembly (118). As a result, in the preferred embodiment, in order to maintain
a sealed drive
chamber (74), a further seal or sealing structure (120) is provided where the
worm shaft (104)
exits the outer member (36). This further sealing structure (120) may
similarly be comprised of a
sealing assembly of the within invention substantially similar to the upper
and lower sealing
assemblies (116, 118). However, given that the sealing structure (120) of the
worm shaft (104) is
externally accessible, any other type or configuration of seal, sealing
structure or sealing
mechanism may be used.
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CA 02305957 2000-04-10
Refernng to Figures 2 and 3, each sealing assembly (116, 118) of the apparatus
(30) is comprised of a sealing element (122) contained within the annular
space (38) for sealing
between the outer member (36) and the inner mandrel (34) as described above.
In the preferred
embodiment, the sealing element (122) of each sealing assembly (116, 118) is
maintained in a
desired position within the annular space (38), at least in part, by a
shoulder (124) extending
within the annular space (38). Specifically, each sealing assembly (116, 118)
is preferably
comprised of a shoulder (124) associated with one of the inner mandrel (34)
and the outer
member (36) which extends within the annular space (38).
In the preferred embodiment, the shoulder ( 124) is preferably positioned or
located
at an innermost end of each sealing assembly (116, 118) within the outer
member (36) in order to
inhibit the passage or movement of the sealing assembly (116, 118) into the
drive chamber (74).
Further, in the preferred embodiment, the shoulder (124) of each sealing
assembly (116, 118) is
associated with the outer member (36) such that the shoulder (124) extends
from the outer
member (36) within the annular space (38). Preferably, the shoulder (124) is
integrally formed
with the outer member (36). Thus, in the preferred embodiment, the shoulder
(124) of the upper
sealing assembly (116) is integrally formed with the inner surface (68) of the
outer mandrel (62),
while the shoulder (124) of the lower sealing assembly (118) is integrally
formed with the inner
surface (72) of the housing (64).
The sealing element (122) of each sealing assembly (116, 118) may be comprised
of any type of material capable of sealing the annular space (38). However,
preferably, the
sealing element (122) is comprised of a non-elastomeric seal. In addition, the
non-elastomeric
seal is preferably comprised of graphite. In the preferred embodiment, the non-
elastomeric seal
is comprised of at least three graphite rings wherein at least one central
graphite ring (126) is
positioned between two outer graphite rings (128). More preferably, two
central graphite rings
(26) are positioned between the outer graphite rings (128).
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CA 02305957 2003-05-29
In the preferred embodiment, the outer graphite rings (128) are each comprised
of graphite packing rope. In addition, in the preferred embodiment, the
central graphite rings
(126) are each comprised of a graphoilTM seal.
It has been found that graphite is a preferable seal material as it has been
found
to withstand temperatures of up to 1200°F. It also tends to be
relatively chemically resistant to
steam, crude oil, salt water, HZS, COZ and other corrosive fluids. Graphite
alone, however, will
extrude. As a result, a carbon yarn material or metallic mesh may be
interwoven with the
graphite to form a graphite ring or packing which resists extrusion. This form
of graphite ring or
packing is available commercially in the form of a long square rope and is
referred to herein as
graphite packing rope. The graphite packing rope is typically cut to lengths
equal to the
circumference of the annular space (38) and is stacked into the annular space
(38) with the splice
of each succeeding graphite packing rope situated 180° from that of the
next. The cut of each
graphite packing rope is usually made at a 45 degree angle. In the preferred
embodiment,
graphite packing rope has a cross-section '/a inch x '/ inch. As stated, the
outer graphite rings
(128) are each preferably comprised of graphite packing rope. An example of
graphite packing
rope is supplied by A.R. Thompson Group and is referred to as "HS-3000 RGS
Graphite
PackingTM."
The central graphite rings (126) are each preferably comprised of a type of
graphite ring or packing referred to herein as a graphoil seal. A graphoil
seal is a die cast
graphite ring, typically 1/a inch x 1/4 inch in cross-section. An example of a
graphoil seal is a
"GOFR Graphoil SealT""' supplied by A.R. Thompson Group. To manufacture the
graphoil seal,
the graphite is formed into a long ribbon which is wrapped around an inner
mandrel of a die.
The inner mandrel of the die is then placed inside an outer mandrel of the
die. The space
between the two mandrels forms a space identical to that of the rotator
annular space (38). A
cylindrical sleeve is then pressed into the space between the mandrels of the
die mould to form
the graphite ring or seal. The graphoil seals comprising the central graphite
rings (126) are
inhibited or prevented from extruding by the presence of the graphite packing
rope which
comprises the outer graphite rings (128) surrounding, or at either end of, the
central graphite
rings ( 126) .
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CA 02305957 2000-04-10
Each sealing assembly (116, 118) is further comprised of a biasing mechanism
(130) substantially contained within the annular space (38) for applying an
axial force to the
sealing element (122), preferably the graphite rings (126, 128), such that the
sealing element
(122) is compressed to seal the annular space (38). More particularly, in the
preferred
embodiment, the sealing element (122) is contained within the annular space
(38) between the
shoulder (124) and the biasing mechanism (130) such that the sealing element
(122) is
compressed between the shoulder (124) and the biasing mechanism (130) upon
application of the
axial force.
The biasing mechanism (130) is preferably comprised of at least one spring
(132),
and preferably two springs (132) in a stacked or layered arrangement, for
applying the axial force
to the graphite rings (126, 128). In addition, each spring (132) is preferably
separated form the
adjacent spring (132) by one or more washers (133). In the preferred
embodiment, each spring
(132) is preferably a Belleville spring. As well, each Belleville spring (132)
is preferably
manufactured from InconelTM so that it will not be tempered by the high
temperature and lose its
spring force.
In addition, in the preferred embodiment, in order to facilitate or enhance
the
sealing of the annular space (38), each sealing assembly (116, 118) is further
preferably
comprised of at least one chevron bushing (134) contiguous with the non-
elastomeric seal (122)
for deflecting the non-elastomeric seal (122) laterally within the annular
space (38) upon the
application of the axial force by the biasing mechanism (130). More
preferably, the chevron
bushing (134) is contiguous with one or more of the graphite rings (126, 128).
In particular, the
central graphite rings (126) are each comprised of a graphoil seal which is
more likely to extrude
upon the application of the axial force. As a result, in the preferred
embodiment, a chevron
bushing (134) is contiguous with each central graphite ring (126) for
deflecting the central
graphite ring (126) laterally within the annular space (38) upon the
application of the axial force
by the biasing mechanism (130).
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CA 02305957 2000-04-10
Further, the chevron bushings (134) are preferably positioned in the sealing
assemblies (116, 118) as described in order that the pressure required to
create a seal in the
annular space (38) is not so high as to cause an unacceptable drag on the
rotating inner mandrel
(34). The chevron bushings (134) deflect the graphite material of the inner
graphite rings (126)
S laterally against the sealing surfaces so that a seal is obtained without
applying extreme pressure.
Typically, the required pressure applied at the Belleville springs (132) is
about 3000 pounds, and
the springs (132) are designed to exert this pressure when fully compressed.
When this pressure
is applied, typically the torque required to rotate the inner mandrel (34) is
about 40 foot-pounds.
Each sealing assembly ( 116, 118) is further preferably comprised of at least
one
bushing (136) contained within the annular space (38) for laterally supporting
the inner mandrel
(34). It has been found that lateral force on the inner mandrel (34) results
from the driving force
of the worm (90) on the worm gear (88) and can also result on wells that are
slant drill. More
preferably, at least one bushing (136) is preferably positioned or located
adjacent each end of the
sealing element (122), or adjacent each of the outer graphite rings (128),
such that the sealing
element (122) is positioned therebetween. Any type of bushing (136) may be
used, such as a
bronze or steel bushing. However, the bushing (136) located or positioned
between the shoulder
(124) and the outer graphite ring (128) is preferably bronze, while the
bushing (136) located or
positioned between the springs (132) and the other outer graphite ring (128)
is preferably steel.
Each sealing assembly (116, 118) is further comprised of an energizing
mechanism (138) associated with one of the outer member (36) and the inner
mandrel (34) for
loading the biasing mechanism (130). Preferably, each energizing mechanism
(138) is associated
with the outer member (36) such that the energizing mechanism (138) remains
relatively
stationary as the inner mandrel (34) rotates within the outer member (36).
Further, once the
biasing mechanism (130) is loaded or energized by the energizing mechanism
(138), the entire
sealing assembly ( 116, 118) tends to remain relatively stationary as the
inner mandrel (34) rotates
relative to the outer member (36). As well, as each energizing mechanism (138)
is associated
with the outer member (36), in the preferred embodiment, the energizing
mechanism (138) of the
upper sealing assembly (116) is particularly associated with the outer mandrel
(62). The
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CA 02305957 2000-04-10
energizing mechanism (138) of the lower sealing assembly (118) is particularly
associated with
the housing (64).
Preferably, the energizing mechanism (138) of each sealing assembly (116, 118)
is
comprised of an adjustable retainer (140) associated with the outer member
(36) and movable
within the annular space (38) such that the retainer (140) is adjustable
towards the biasing
mechanism (130) for loading or energizing the biasing mechanism (130). More
particularly, the
adjustable retainer (140) is preferably comprised of a tightening mechanism
(142) associated
with the outer member (36) and a retainer plate (144). The retainer plate
(144) is tubular and has
an inner end (146) and an outer end (148). The inner end (146) of the retainer
plate (144)
extends into and is movable within the annular space (38).
The outer end (148) extends from the annular space (38) and is adjustably or
movably mounted, connected or affixed with the adjacent end of the outer
member (36) by the
tightening mechanism (142). Specifically, the outer end (148) of the retainer
plate (144) of the
upper sealing assembly (116) is adjustably or movably mounted, connected or
affixed with the
upper end (40) of the outer member (36) or outer mandrel (62), while the outer
end (148) of the
retainer plate (144) of the lower sealing assembly (118) is adjustably or
movably mounted,
connected or affixed with the lower end (42) of the outer member (36) or
housing (64).
In the preferred embodiment, the outer end (148) of the retainer plate (144)
is
comprised of a flange (150) which is associated with the tightening mechanism
(142) such that
tightening of the tightening mechanism (142) adjusts the position of the
retainer plate (144)
within the annular space (38) towards the biasing mechanism (130). Further, in
the preferred
embodiment, the tightening mechanism (142) is comprised of a bolt or screw,
preferably a hex
head screw. The flange (150) of the retainer plate (144) defines one or more
apertures therein for
the passage of the screw (142) therethrough. Specifically, the screw (142)
extends through the
aperture in the flange (150) for engagement with the outer member (36).
Accordingly, both the
upper end (40) and the lower end (42) of the outer member (36) define one or
more holes (152)
therein, compatible with the apertures in the flange (150), for receiving the
screw (142).
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CA 02305957 2000-04-10
More particularly, the screw (142) is preferably externally threaded and each
hole
(152) is preferably internally threaded such that the screw (142) is
threadably engaged with the
hole (152). As a result, turning or screwing of the screw (142) into or out of
the holes (152) in
the outer member (36) adjusts the position of the retainer plate (144) and
causes the inner end
(146) of the retainer plate (144) to move or be adjusted within the annular
space (38). In the
preferred embodiment, tightening of the screw (142) into the hole (152) in the
outer member (36)
adjusts the position of the retainer plate (144) towards the biasing mechanism
(130). Thus, the
retainer plate (144) may be tightened down onto the Belleville springs (132).
Preferably, the total
height of the sealing assembly (116, 118) including the springs (132) is
selected or configured
such that when the retainer plate (144) is tightened down completely, the
sealing element (122) is
compressed or pressed sufficiently to form a positive seal and the Belleville
springs (132) are
fully compressed or collapsed. Thus, as the sealing element (122) wears, the
Belleville springs
( 132) will extend to maintain sufficient pressure on the sealing element (
122) to maintain the
seal.
As indicated, a similar sealing assembly may be provided between the outer
member (36) and the worm shaft (104). However, the seal (120) about the worm
shaft (104)
need not be similar given that the seal (120) is externally accessible and
thus, the sealing element
may be manually re-energized as it wears. Accordingly, the worm shaft seal
(120) may be
comprised of any seal, sealing mechanism or sealing structure. However,
referring to Figure 4, in
the preferred embodiment, the worm shaft seal (120) is comprised of a bushing
(114), preferably
bronze and preferably having a chevron-shaped end. The chevron shaped end of
the bushing
(114) is preferably contiguous with an inner graphite ring (156) comprised of
a graphoil seal and
substantially similar to that described above for the central graphite rings
(126) of the sealing
assemblies (116, 118). Further, the inner graphite ring (156) is preferably
contiguous with an
outer graphite ring (158) comprised of graphite packing rope and substantially
similar to that
described above for the outer graphite rings (128) of the sealing assemblies
(116, 118).
A junk ring or washer (16) is preferably positioned adjacent the outermost end
of
the outer graphite ring (158). All of these components or elements of the worm
shaft seal (120)
are held in position and compressed or energized between a roller bearing
(112), as described
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CA 02305957 2000-04-10
above, and a packing screw (162), preferably a hex head packing screw,
externally accessible.
Specifically, the packing screw (162) is preferably threadably engaged with
the housing (64) such
that the packing screw ( 162) may be screwed or tightened into the housing
(64) to energize and
re-energize the seal (120) as desired. This seal system (12) is viewed as a
secondary seal system,
since leakage must first occur past the upper and lower sealing assemblies
(116, 118) before it
can reach the worm shaft (104).
Finally, the drive chamber (74) is preferably filled with a suitable lubricant
such as
a high temperature lubricant. In order to access the drive chamber (74) to
introduce the lubricant
as necessary, the outer member (36) preferably defines one or more vents (164)
or conduits
therein extending from the drive chamber (74) to the outer wall (46) of the
outer member (36).
In the preferred embodiment, the outer member (36) defines two vents (164). As
shown in
Figure 4, one vent (164) extends into the drive chamber (74) adjacent or in
proximity to the
worm gear (88) opposite the worm (90), while the other vent (164) extends into
the drive
chamber (74) adjacent or in proximity to the worm shaft (104). Each vent (164)
is comprised of
a vent fitting or cap (166). Any type or configuration of vent fitting or cap
(166) may be used for
maintaining a desired pressure of the lubricant within the drive chamber (74).
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