Note: Descriptions are shown in the official language in which they were submitted.
CA 02568681 2006-11-23
GATE VALVE WITH OFFSET VALVE STEM
FIELD OF THE INVENTION
The present invention relates in general to gate valves, and in particular to
mud
valves for use in the petroleum industry.
BACKGROUND OF THE INVENTION
Flat slab gate valves are well known, and they have been used in the petroleum
drilling industry for many years. In general, flat slab gate valves are quite
simple in
design. They use a minimum of components, thus giving them reliable
functionality and
making them easy to operate and maintain. A typical flat slab gate valve has a
cylindrical
main body with a flow passage extending between an inlet port and an outlet
port, and a
cylindrical rubber seal element disposed transversely to the flow passage. The
main body
also incorporates a gate chamber into which a flat slab gate can be retracted,
plus a
bonnet section that receives a valve stem operable to move the gate
transversely relative
to the flow passage, between a closed position in which the gate extends
across the flow
passage so as to completely block fluid flow between the inlet and outlet
ports, and an
open position in which the gate is at least partially retracted into the gate
chamber so as to
allow fluid flow between the inlet and outlet ports. The cylindrical seal
element has a
slot that allows the gate to pass through it, so that when the valve is in the
closed position,
fluid pressure on one side of the gate is pressed against one side of the seal
element, thus
creating a seal to prevent fluid leakage across the gate. The slotted seal
element, being
incorporated into the valve body, serves to maintain the gate in transverse
orientation to
the flow passage as it moves between the open and closed positions.
"Mud valves" (as they are commonly called in the petroleum industry) are gate
valves purpose-made for various petroleum industry applications, including
piping or
conduit systems for conveying fluids such as drilling fluids (or drilling
"muds"), cement
slurries (for cementing well bores), "frac fluids" (for fracturing subsurface
oil-bearing or
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natural gas-bearing formations), water, crude oil, natural gas (sweet or
sour), well-
treating chemicals, and drilling chemicals. Mud valves are commonly designed
specifically for use with abrasive and/or erosive fluids.
It is common to use mud valves that are variants of the basic flat slab gate
valve.
However, the use of flat slab mud valves can lead to operational problems or
even valve
failure in certain oilfield applications. One common problem is "sanding" of
the gate
chamber, which can occur during "fraccing" operations when the mud valve is
used in
systems for injecting frac fluids (such as frac gel containing large amounts
of sand or
other particulate "proppant" materials) into a subsurface formation. When it
is necessary
or desirable to relieve frac fluid pressure from the well, the mud valve is
opened to allow
frac gel to flow back up the well and into a blowdown tank. As the mud valve
is opened,
the frac gel passes by the flat slab gate at high velocity. The flat slab
gate, which is still
pressed against the downstream side of the seal element, allows frac gel and
sand to pass
between the gate and seal on the upstream side and into the gate chamber, thus
impeding
gate movement and preventing the valve from opening or closing.
U.S. Patent No. 2,911,186 (Knox) discloses a gate valve that uses an
essentially
cylindrical gate rather than a flat slab gate. It is not possible to seal a
gate of this
configuration in the same fashion as described above for flat slab gates, and
the Knox
valve addresses this problem by providing a seal element disposed within a
continuous
groove in the cylindrical gate, the groove being configured such that when the
valve is in
the closed position, the seal element will seal against adjacent wall surfaces
of the flow
chamber and gate chamber. More specifically, the seal groove has a semi-
circular section
adjacent the outer end of the gate (i.e., the end nearest the bonnet),
transitioning into a
pair of longitudinal legs extending along the sides of the gate, with the ends
of the
longitudinal legs joining a straight section extending transversely across the
inner end of
the gate.
Since the seal element moves with the gate, rather than being incorporated
into
the valve body, proper transverse alignment of the gate cannot be achieved in
the same
way as for flat slab gates. The Knox valve maintains gate alignment by
providing a pair
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of pins projecting laterally from the valve stem into longitudinal guide slots
that extend
through the bonnet wall. This arrangement necessitates that the valve stem is
non-
rotating, so longitudinal movement of the valve stem is enabled by threading
the outer
end of the stem and providing an internally threaded nut rotatably retained
within the
bonnet and engaging the stem threads. A handle (such as a handwheel) is
connected to
the nut such that rotation of the handle rotates the nut around the stem,
thereby causing
the stem to move longitudinally within the bonnet, in turn moving the
cylindrical gate
between the open and closed positions according to the direction of handle
rotation.
In the Knox valve, the lower portion of the cylindrical gate is bevelled on
the
upstream and downstream sides of the seal, and the gate also incorporates a
pressure
equalization passage extending longitudinally through the gate on the side
opposite the
semi-circular portion of the seal groove. The bevelled sides allow fluid
pressures to exert
an upward force component that assists in raising the gate. The pressure
equalization
passage assists in lowering the gate when fluid is flowing from the side
opposite the seal,
in which case fluids can flow through the passage into the gate chamber and
thus exert a
downward force on the top of the gate.
An inherent drawback of the Knox valve is the need to provide guide slots
through the bonnet wall to maintain gate alignment. These guide slots allow
airborne
particulates or other contaminants to enter the bonnet cavity, potentially
clogging the
stem threads and impeding valve operation. The fact that the bonnet cavity is
open to the
outside (through the guide slots) also creates a potential risk of corrosion
on interior
surfaces of the bonnet.
A further drawback of the Knox design is that when the valve is in the open or
partially open position, a portion of the threaded stem will necessarily
project beyond the
valve handle, thus creating a safety hazard that could result in serious
injury if a worker
were to bump into or fall against the handle.
Another drawback of the Knox valve arises from its incorporation of a flat bar
(or
"fence") that protrudes from the inner wall opposite the gate chamber,
transverse to the
direction of flow. The primary purpose of the fence is to enhance seal
effectiveness by
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forming a seat against which the seal element will be compressed as the gate
moves into
the closed position. To prevent a reduction in the effective cross-sectional
area of the
flow passage, the fence is disposed within a recess in the inner wall of the
valve body.
While this feature may be advantageous in some applications, it would render
the Knox
valve unsuitable for many mud valve applications, due to the fact that
particulate
materials in pumped fluids such as drilling mud and frac gel could accumulate
within the
recess and thus impede or prevent proper operation of the valve. Moreover,
this fence
would make the Knox valve particularly unsuitable as a mud valve in fraccing
operations,
which typically use seating cups made of a very hard urethane. When these
seating cups
are pulled back out of the hole, the valve cannot have any obstacles or
impediments (like
the fence) in the seating cups' path; otherwise, either the seating cups or
the gate seal will
become damaged or destroyed.
Accordingly, there is a need for a gate valve suitable for use in "mud valve"
applications, effective to mitigate or prevent the "sanding" problem that can
arise in
fraccing operations, while also preventing the entry of contaminants into the
valve
bonnet. There is a further need for such a gate valve that can be operated
throughout its
full range of gate movement without the valve stem projecting beyond the valve
handle.
There is a yet further need for such a gate valve that ensures effective
sealing between the
gate and internal valve surfaces without requiring a protruding seal seat
element or an
associated recess in which particulate matter might accumulate. The present
invention is
directed to these needs.
BRIEF DESCRIPTION OF THE INVENTION
In general terms, the present invention is a gate valve that uses a
substantially
cylindrical gate member with a seal element disposed within a continuous
groove in the
gate surface. The valve has a valve stem formed with (1) a smooth cylindrical
outer
section that is longitudinally movable through gland means associated with the
outer end
of the valve bonnet, (2) a threaded intermediate section that engages a
threaded bore
associated with the inner end of the bonnet, and (3) a gate-engagement section
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comprising a valve stem "button" separated from the intermediate section by a
transition
element, which preferably (but not necessarily) will be of smooth cylindrical
configuration.
The gate valve of the present invention, in its preferred embodiment, is
particularly distinguished by the fact that the longitudinal axis of the valve
stem is offset
from the longitudinal axis of the cylindrical gate, rather than being
coincidental with the
gate axis as in prior art gate valves. The outer end of the gate (i.e., the
end toward the
bonnet) has a recessed slot configured to receive the valve stem button such
that the valve
stem is free to rotate relative to the gate, while also retaining the button
in the
longitudinal direction such that longitudinal movements of the valve stem will
cause
corresponding movements of the gate. A valve handle (of any suitable
configuration) is
connected to the outermost end of the outer section of the valve stem, which
projects
from the bonnet. Rotation of the handle causes the valve stem to move
longitudinally
within the bonnet due to engagement of the threaded section of the valve stem
with the
threaded bore of the bonnet. The valve stem button rotates within its recessed
slot in the
cylindrical gate, while also moving the gate axially within the gate chamber
in
accordance with longitudinal movements of the stem. Due to the lateral offset
between
the stem and gate axes, the cylindrical gate remains at all times in a
substantially fixed
angular orientation relative to the gate chamber regardless of the gate's
longitudinal
position therein, thus ensuring that the seal element remains oriented for
optimal sealing
effectiveness when the valve is in the closed position.
The valve of the present invention is particularly suitable for use in mud
valve
applications subject to a "sanding" risk, by virtue of its use of a
cylindrical gate rather
than a flat slab gate. Due to the use of a seal element recessed into the
cylindrical gate,
the clearance between the gate and the gate chamber wall can be significantly
less than
for a conventional slab-type gate; in fact, the movement of the cylindrical
gate, when
exposed to full fluid pressure, can be restricted to a few thousandths of an
inch. This
minimal clearance reduces the potential for frac gel and sand to migrate past
the gate and
into the gate chamber.
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The valve of the present invention can be adapted for either bi-directional or
unidirectional fluid flow. By designing the seal element in such a way as to
contain well
pressure on the upstream side of the valve, the valve operator can clear any
sand from the
gate chamber with compressed air, even while the valve is under pressure and
in line.
This feature is enabled by providing a compressed air inlet port and an outlet
port in the
walls of the gate chamber, so that sand or other contaminants can be blown out
of the
gate chamber by introducing compressed air into the gate chamber through the
inlet port
and blowing the contaminants out the outlet port.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described with reference to the
accompanying figures, in which numerical references denote like parts, and in
which:
FIGURE 1 is an isometric view of a gate valve in accordance with a
preferred embodiment of the present invention.
FIGURE 2 is a longitudinal cross-section through the gate valve of Fig. 1.
FIGURE 3 is a longitudinal cross-section through the main body of the
gate valve of Fig. 1.
FIGURE 4 is an end view of the gate housing section of the valve body.
FIGURE 5 is a longitudinal cross-section through the bonnet of the gate
valve.
FIGURE 6 is an end view of the bonnet.
FIGURE 7 is a side view of the cylindrical gate of the gate valve,
showing the seal groove.
FIGURE 8 is an end view of the outer end of the cylindrical gate,
illustrating the recessed slot for receiving valve button.
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FIGURE 9 is an isometric view of a flexible seal element adapted to be
positioned in the seal groove of the cylindrical gate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Figures 1 to 9 illustrate various details of the preferred embodiment of a
gate
valve 10 in accordance with the present invention. Referring to Figs. 2 and 3,
gate
valve 10 includes a main body 20 defining a flow passage 22 extending between
a
first port 22A and a second port 22B, with flow passage 22 having inner wall
surfaces 23. Fig. 1 shows valve 10 oriented in accordance with a typical "mud
valve" application, in which second port 22B of valve 10 is directly connected
to a
well casing 90 extending vertically out of the ground. In such applications,
flow
passage 22 will be oriented substantially vertically as in Fig. 1, such that
flow
passage 22 can be considered as having upper and lower ends corresponding to
first
and second ports 22A and 22B respectively. Accordingly, the adjectives "upper"
and "lower" may be used in this relative sense for convenience to describe and
locate
various components of valve 10. However, it will be appreciated that valve 10
could
be installed in different orientations, so proper interpretation of the
adjectives
"upper" and "lower" will be context-dependent, according to the orientation of
valve
10 in a given application.
Adjoining (or integral with) main body 20 in a medial region between first
port 22A and a second port 22B is a gate housing section 24 having an inner
end
24A, an outer end 24B. Gate housing 24 has a gate housing wall 27 defining a
cylindrical gate chamber 25, which is in fluid communication with flow passage
22
and has inner wall surfaces 26.
Referring to Figs. 2 and 5, gate valve 10 also includes a bonnet 30 having an
inner end 30A and an outer end 30B, with a longitudinal bore 32 extending
between
inner end 30A and outer end 30B. Inner end 30A of bonnet 30 is mountable to
outer
end 24B of gate housing section 24 such that the longitudinal axis X-1 of bore
32 is
offset from, but parallel to, the longitudinal axis X-2 of gate chamber 25 by
a
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selected offset dimension W. As best understood from Figs. 2-6, mounting of
bonnet 30 is preferably facilitated by providing bonnet 30 with a mounting
flange 37
at inner end 30A, with bolt holes 38, enabling bonnet 30 to be mounted to
outer end
24B of gate housing section 24 by means of machine screws 29 inserted through
holes 38 into mating threaded bores 29A in gate housing wall 27 at outer end
24B,
preferably with an associated 0-ring or gasket 31 as shown in Fig. 2. However,
this
means of connection is not essential; bonnet 30 could be connected to gate
housing
section 24 in other functionally equivalent ways without departing from the
present
invention.
Referring to Fig. 2, bonnet bore 32 has a threaded section 34 adjacent to
inner
end 30A of bonnet 30. Adjacent to outer end 30B of bonnet 30, bore 32 has a
gland
section 36 adapted to receive gland means 39 through which an elongate valve
stem
40 may be sealingly disposed, as further described below. Valve stem 40 has a
smooth cylindrical outer section 42, a threaded intermediate section 44 that
engages
threaded bore 34 of bonnet 30, and a valve stem "button" 54 separated from
threaded
intermediate section 44 by a transition element 48 which is preferably but not
necessarily cylindrical, and which is smaller in cross-sectional area than
button 54.
Button 54 is preferably of cylindrical form, but this is not essential to the
invention,
as button 54 could take different forms without materially affecting the
operation of
valve 10.
When valve 10 is assembled, as shown in Fig. 2, cylindrical outer section 42
of valve stem 40 is disposed within gland means 39, with the longitudinal axis
of
valve stem 40 being coincident with axis X-1 of bore 32 of bonnet 30. Gland
means
39 allows for longitudinal movement of cylindrical outer section 42 while
providing
an effective seal to prevent entry of contaminants into bore 32. Gland means
39 may
be of any suitable known type, as will be readily appreciated by persons
skilled in
the field of the invention. As shown in Fig. 2, threaded intermediate section
44 of
valve stem 40 engages threaded section 34 of bonnet bore 32, such that
rotation of
valve stem 40 will cause longitudinal movement of valve stem 40 within bonnet
30.
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Cylindrical outer section 42 is of sufficient length to extend beyond outer
end
30B of bonnet 30 when valve 10 is closed as well as when it is open, with the
extending portion having means for attachment of a handle 70 (of any suitable
type)
for rotating valve stem 40. In the embodiment illustrated in Fig. 2, the
handle
attachment means is shown as a handle-mounting hole 42A, but persons skilled
in
the art will appreciate that there are various alternative ways in which a
handle could
be mounted to valve stem 40.
Referring to Figs. 2, 7, and 8, gate valve 10 has a cylindrical gate 50
disposed
and movable within cylindrical gate chamber 25, with the longitudinal axis of
cylindrical gate 50 being coincident with longitudinal axis X-2 of gate
chamber 25.
Cylindrical gate 50 has an inner end 50A (disposed toward flow passage 22) and
an
outer end 50B (disposed toward gate chamber 25). In preferred embodiments, a
compound slot 52 is formed into outer end 50B of cylindrical gate 50,
comprising:
= an entrance leg 52A, generally centered on axis X-2 and sized to
permit insertion of button 54 of valve stem 40;
= an offset leg 52B contiguous with entrance leg 52A, extending
inward from outer end 50B of cylindrical gate 50, generally centered
on axis X-1, and sized to receive transition element 48; and
= a recess 52C contiguous with both entrance leg 52A and offset leg
52B but underlying offset leg 52B, recess 52C being sized so that
button 54 can be inserted into entrance leg 52A and then shifted
laterally by offset distance W into recess 52C, thereby disposing
transition element 48 within offset leg 52B so that button 54 is
rotatably retained within recess 52C.
Having reference to Fig. 2, it may be readily understood that rotation of
valve
stem 40 will result in longitudinal movement of valve stem 40 within bonnet
30. Due to
the rotatable retention of valve stem button 54 within compound slot 52, as
described
above, longitudinal movement of valve stem 40 causes cylindrical gate 50 to be
either
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pushed toward the closed position within flow passage 22 or pulled into a
retracted
position within gate chamber 25, depending on the direction of rotation of
valve stem 40.
Persons skilled in the art of the invention will appreciate that alternative
details may be
devised for engaging valve stem 40 with gate 50 such that valve stem can
rotate while
being effective to move gate 50 longitudinally within gate chamber 25 as valve
stem 40
moves longitudinally within bonnet 30. Accordingly, the present invention is
not to be
considered limited to the particular details expressly described and
illustrated herein for
providing this functionality, and all functionally equivalent structures are
to be
considered as coming within the scope of the invention.
Referring to Figs. 2 and 7, cylindrical gate 50 has a seal groove 56 for
receiving a
continuous seal element 60 for preventing leaking of fluid across gate 50 when
valve 10
is in the closed position. As seen in Fig. 7, seal groove 56 preferably has a
semi-circular
section 56A adjacent to outer end 50B of gate 50. Semi-circular section 56A of
seal
groove 56 preferably extends around the lower side of cylindrical gate 50 as
shown in the
Figures, but this is not essential; optionally, it could extend around the
upper side of gate
50. Semi-circular section 56A of seal groove 56 transitions into a pair of
longitudinal
legs 56B extending along the sides of gate 50, with the ends of longitudinal
legs 56B
joining a straight section 56C extending transversely across inner end 50A of
gate 50.
Fig. 9 illustrates an exemplary embodiment of seal element 60, with sections
60A,
60B, and 60C corresponding to, and adapted to be received within, sections
58A, 58B,
and 58C, respectively, of seal groove 56 as described above. It may be readily
appreciated that curved section 60A of seal element 60, when disposed within
semi-
circular section 56A of seal groove 56, will seal against cylindrical inner
wall surface 26
of gate chamber 25 regardless of the position of gate 50 within gate chamber
25.
In preferred embodiments of the invention, seal element 60 is made of a
flexible
material such as synthetic rubber (e.g., nitrile) or other flexible sealant
material having
good resistance to hydrocarbons and other chemicals. However, other materials
may be
used for seal element 60 to suit particular applications, and the present
invention is in no
way limited by the use of any particular seal materials.
CA 02568681 2006-11-23
As may be appreciated from Fig. 3, the diameter of gate chamber 25 in the
preferred embodiment is slightly larger than that of flow passage 22, such
that cylindrical
inner wall surface 26 of gate chamber 25 intercepts inner wall surface 23 of
flow passage
22 so as to form a "pinched" section 26A of gate chamber wall surface 26
extending
toward a substantially flattened section 23A of flow passage wall surface 23
opposite
gate chamber 25. Accordingly, sections 60B of seal element 60 disposed within
longitudinal legs 56B of seal groove 56 will seal against gate chamber wall
surface 26
(and/or pinched section 26A thereof) regardless of the position of gate 50
within gate
chamber 25. When gate 50 is in its closed position (i.e., blocking fluid flow
within flow
passage 22), straight section 60C of seal element 60 will seal against flat
section 23A of
flow passage wall surface 23.
As shown in Fig. 9, straight section 60C of seal element 60 may optionally
have
enlarged end portions 62 for enhancing seal effectiveness. As gate 50 moves
into the
closed position and presses straight section 60C of seal element 60 against
flat section
23A of flow passage wall surface 23, enlarged end portions 62 will be urged
into the
corner regions where pinched sections 26A of gate chamber wall surface 26 meet
flat
section 23A of flow passage wall surface 23, thus enhancing seal effectiveness
in these
regions.
In a particularly preferred embodiment of the invention, seal element 60 has
one
or more retainer bosses 60D adapted to be received in mating notches 56D in
seal groove
56. Retainer bosses 60D help to maintain seal element 60 in its proper
position with seal
groove 56, and when positioned as shown in Figs. 7 and 9, they counteract any
tendency
of straight section 60B of seal element 60 to be displaced outward from
section 56C of
seal groove 56 due to elasticity of seal element 60, when gate 50 is being
retracted toward
gate chamber 25.
Although inner end 50A of cylindrical gate 50 has been described and
illustrated
herein as having a substantially straight portion where it meets and seals
against the
portion of flow passage wall surface 23 opposite gate chamber 25, it will be
appreciated
that cylindrical gate 50 could be provided in other configurations without
departing from
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the basic concept and principles of the invention. For example, inner end 50A
of
cylindrical gate 50 could be hemispheric or otherwise curved, with flow
passage wall
surface 23 being correspondingly contoured for sealing with gate 50 in the
closed
position.
In preferred embodiments, as shown in Figs. 2 and 7, cylindrical gate 50 is
bevelled or chamfered on one or both of its upper and lower sides adjacent to
inner end
50A, so as to form upper bevelled edge 51A and/or lower bevelled edge 51B.
This
facilitates the opening of valve 10, because fluid pressure acting against a
bevelled edge
51A or 51B will have a component tending to push gate 50 into gate chamber 25.
In one
alternative embodiment, as shown in Figs. 2 and 7, a pressure equalization
channel 58
extends through gate 50 between outer end 50B and bevelled edge 51A. This
feature
facilitates closing of valve 10 when fluid is flowing downward through flow
passage 22
(i.e., from first port 22A toward second port 22B). Fluids may pass through
channel 58
into gate chamber 25, wherein they will exert pressure against outer end 50B
of gate 50,
tending to push gate 50 into flow passage 22. For applications in which fluids
contain
suspended particulate matter, channel 58 will preferably be of relatively
small diameter,
so that gaseous fluid components can readily pass through into gate chamber 25
and exert
pressure against outer end 50B of gate 50, while particulates will tend to be
carried with
the main fluid stream through flow passage 22 rather than diverting into
channel 58.
In the preferred embodiment shown in Figs. 2 and 3, gate housing section 24
has a
compressed air inlet port 28A and an outlet port 28B, spaced apart from each
other and
extending through gate housing wall 27, and provided with suitable fittings
(e.g.,
compressed air nipple for inlet port 28A and removable plug for outlet port
28B) of any
suitable known types. These ports make it conveniently possible to clean out
any
particulates or other contaminants that might pass into gate chamber 25
without having to
disassemble valve 10 or take it out of service. For example, in the situation
illustrated in
Fig. 1 where valve 10 is mounted to a well casing 90, and gate 50 is closed as
in Fig. 2
with well casing 90 fully pressurized (for example, after injection of frac
fluid),
compressed air may be injected into gate chamber 25 through inlet port 28A to
blow out
any accumulated matter in gate chamber 25 through outlet port 28B, while not
in any way
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affecting the ability of gate 50 to resist and contain upward fluid pressure
from wellbore
90.
In Figs. 2 and 3, inlet and outlet ports 28A and 28B are shown diametrically
opposite each other and adjacent to outer end 24B of gate housing section 24,
but this
specific arrangement is not essential. Inlet and outlet ports 28A and 28B
could be in
different relative positions without departing from the principles and concept
of the
invention, although it is preferable for ports 28A and 28B to be positioned
sufficiently
close to outer end 24B of gate housing section 24 so that they will not be
covered up by
gate 50 when in its retracted position.
It will be readily appreciated by those skilled in the art that various
modifications
of the present invention may be devised without departing from the essential
concept of
the invention, and all such modifications are intended to be included in the
scope of the
claims appended hereto. It is to be especially understood that the invention
is not
intended to be limited to illustrated embodiments, and that the substitution
of a variant of
a claimed element or feature, without any substantial resultant change in the
working of
the invention, will not constitute a departure from the scope of the
invention.
In this patent document, the word "comprising" is used in its non-limiting
sense to
mean that items following that word are included, but items not specifically
mentioned
are not excluded. A reference to an element by the indefinite article "a" does
not exclude
the possibility that more than one of the element is present, unless the
context clearly
requires that there be one and only one such element.
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