Note: Descriptions are shown in the official language in which they were submitted.
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Title: Rotary Meter Flexible Edge Impeller Assembly
FIELD
[0001] The embodiments described herein relate to fluid flow measuring
devices, and more particularly to a flexible edge impeller assembly used to
improve the performance of a fluid flow meter.
BACKGROUND
[0002] Positive displacement rotary gas meters generally consist of a
counter module and a gas meter pressure body. The gas meter pressure body
converts gas flow into rotational motion via two solid impellers, which sweep
out
a known volume on each rotation. The impellers are precisely linked together
using timing gears such that they can rotate in a desired configuration. The
clearances between the impellers can be tight in order to minimize the amount
of
gas that leaks around the edges of the impellers. As a result of their fixed
orientation and swept volumes, when the impellers are driven by a gas flow,
the
impellers can allow a set volume of gas to pass through the meter on each
rotation. Accordingly, the quantity of gas passing through the meter can be
calculated by counting the number of rotations of at least one of the
impellers.
Counting impeller rotations is commonly done by configuring the gas meter such
that a mechanical or electronic counter module can be driven by at least one
of
the impeller shafts via the use of a magnetic coupling module or direct drive.
[0003] However, gas flowing through a gas meter may contain dirt, rust
particles and other contaminants that can interfere with the proper operation
of
the meter. Some contaminants may pass through the gas meter causing very
little damage to the meter. However, some contaminants can interfere with the
operation of the gas meter. For example, dirt may become trapped within the
gas meter causing scratching and abrasions between impellers, or between the
impellers and the chamber walls. Damage to the impellers or chamber walls can
lead to increased gas leakage and reduced counting accuracy. In addition to
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damaging gas meter components, some contaminants may be of sufficient size
and strength to interfere with the impellers and prevent their rotation.
Contaminants that are larger than the clearance between the impellers can
become wedged between the impellers (or between an impeller and the chamber
wall) preventing rotation. Such a condition can be referred to as "seizing".
SUMMARY
[0004] The embodiments described herein provide in one aspect, an
assembly for use in a rotary positive displacement fluid meter having an inner
body wall surface, the assembly comprising:
a first impeller having an outer surface, located within the rotary positive
displacement fluid meter and adapted to be directly driven by a fluid flow,
and
a flexible edge member situated at a distal end of the impeller such that
there is a clearance between the flexible edge member and the inner body wall
of
the rotary positive displacement fluid meter,
wherein the impeller defines a longitudinal axis and the flexible edge member
has a length along the longitudinal axis and a width in a direction that is
orthogonal to the longitudinal axis.
[0005] Further aspects and advantages of the embodiments described
herein will appear from the following description taken together with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] For a better understanding of the embodiments described herein
and to show more clearly how they may be carried into effect, reference will
now
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be made, by way of example only, to the accompanying drawings which show at
least one exemplary embodiment, and in which:
[0007] FIG. 1 is a perspective view of a positive displacement rotary gas
meter within which the impeller assembly of the present invention may operate;
[0008] FIG. 2 is a top view of the positive displacement rotary gas meter of
FIG. 1;
[0009] FIG. 3A illustrates a first position of the rotating impellers of the
impeller assembly of the positive displacement rotary gas meter;
[0010] FIG. 3B illustrates a second position of the rotating impellers of the
impeller assembly of the positive displacement rotary gas meter;
[0011] FIG. 4A is a perspective view of an impeller with a rigid edge that is
known in the art;
[0012] FIG. 4B is a front view of the impeller with a rigid edge that is
known in the art;
[0013] FIG. 4C is an end view of the impeller with a rigid edge that is
known in the art;
[0014] FIG. 4D is a sectional view of a rigid edge that is known in the art;
[0015] FIG. 5 is a sectional view of the a positive displacement rotary gas
meter and rigid edge impellers contained therein;
[0016] FIG. 6A is a perspective view of an impeller with a flexible edge
member;
[0017] FIG. 6B is a front view of an impeller with a flexible edge member;
[0018] FIG. 6C is a end view of an impeller with a flexible edge member;
[0019] FIG. 6D is a section view of a flexible edge member;
[0020] FIG. 7 is an end view of an impeller with a flexible edge member;
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[0021] FIG. 8A is an end view of an impeller with an integral flexible edge
member;
[0022] FIG. 8B is an end view of an alternate embodiment of an impeller
with an integral flexibie edge member;
[0023] FIG. 9 is a section view a positive displacement rotary gas meter
and flexible edge impellers contained therein; and
[0024] FIG. 10 is a section view of a positive displacement rotary gas
meter as shown in FIG. 9 containing foreign debris.
[0025] It will be appreciated that for simplicity and clarity of illustration,
elements shown in the figures have not necessarily been drawn to scale. For
example, the dimensions of some of the elements may be exaggerated relative
to other elements for clarity. Further, where considered appropriate,
reference
numerals may be repeated among the figures to indicate corresponding or
analogous elements.
DETAILED DESCRIPTION
[0026] It will be appreciated that numerous specific details are set forth in
order to provide a thorough understanding of the exemplary embodiments
described herein. However, it will be understood by those of ordinary skill in
the
art that the embodiments described herein may be practiced without these
specific details. In other instances, well-known methods, procedures and
components have not been described in detail so as not to obscure the
embodiments described herein. Furthermore, this description is not to be
considered as limiting the scope of the embodiments described herein in any
way, but rather as merely describing the implementation of the various
embodiments described herein.
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[0027] FIGS. 1 and 2 illustrate a positive displacement rotary gas meter 20
within which an impeller assembly operates. Natural gas flows from a pipeline
(not shown) in the form of gas inflow 22 and enters the gas meter pressure
body
cylinder 24. The gas enters upper intake member 26 via upper aperture 28. The
gas passes through gas meter pressure body cylinder 24 and exits gas meter 20
as gas outflow 30. Gas outflow 30 exits via a lower aperture (not shown) of
lower
output member 32, where it is then routed to the end consumer.
[0028] Referring to FIGS. 1 and 2, a rotary gas meter 20 includes a
counter module 46, a magnetic housing 42, a thrust end section 38 and a gas
meter pressure body cylinder 24. It should be understood that the exemplary
rotary gas meter 20 also includes a thrust mounting headplate 40 and a counter
headplate 44 which are mounted to the gas meter pressure body cylinder 24
such that they define a volume within the cylinder. The thrust end section 38
is
coupled to the thrust mounting headplate 40 and the magnetic housing 42 is
coupled to the counter headplate 44. The distal end of the magnetic housing 42
supports the counter module 46 via a counter mounting plate 48. It should be
understood that the exemplary embodiment represents only one form of a
positive displacement rotary gas meter 20.
[0029] The rotary gas meter of FIGS. 1 and 2 includes at least one driven
member within the gas meter pressure body cylinder 24. As shown in FIG. 3A,
the exemplary gas meter pressure body cylinder 24 contains two driven
members, a first impeller 50 and a second impeller 52. Impeller members 50 and
52 are preferably each a lobed figure-eight shape. In the embodiment of FIG.
3A
and FIG. 3B, the impellers are solid figure eight-shaped figures. However, it
should be understood that the impellers can take on different shapes and
designs, so long as the shape allows for a quantifiable volume of gas to flow
through the rotary gas meter. It should be understood that while the exemplary
embodiment discloses a positive displacement rotary meter with two lobed
impellers 50 and 52, other embodiments are contemplated. These other
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embodiments include positive displacement rotary meters with driven member(s)
having different physical configurations. It is important to note that the
impeller
assembly can be used with any type of positive displacement rotary gas meter,
recognizing that rotary gas meters can vary with respect to specific
configuration.
[0030] Gas inflow 22 enters the gas meter pressure body cylinder 24 via
upper aperture 28 and creates a force on impellers 50 and 52. This force
causes
impellers 50 and 52 to rotate through 360 degrees, as successively shown in
FIGS. 3A and 3B. Impellers 50 and 52 rotate because a lower relative pressure
can be created at lower aperture 54 than exists at upper aperture 28. Thrust
end
section 38 (see FIGS. 1 and 2) encloses lubricating oil and timing gears that
fix
the position of the impellers orthogonal to each other and provide for their
contra-rotation. As a result, impellers 50 and 52 can rotate synchronously, in
a
fixed relative position.
[0031] As shown in FIGS. 3A and 3B, each impeller 50 and 52 rotates
about an axis defined by its respective impeller shaft, located at its center
of
gravity. Specifically, impeller 50 is able to rotate about an axis defined by
a first
impeller shaft 56, while impeller 52 is able to rotate about an axis defined
by a
second impeller shaft 58. As impellers 50 and 52 rotate, a fixed volume of gas
is
trapped between the surface of each impeller 50 and 52 and the inner body wall
surface 60. Inner body wall 60 can define an internal chamber 61, which is of
a
specific volume. The fixed volume of gas can then be moved toward lower
aperture 54. Therefore, with each full impeller rotation, a known volume of
gas
travels between upper aperture 28 and lower aperture 54. While the present
description is being provided assuming the medium of a gas (most preferably
natural gas), it should be understood that the positive displacement rotary
meter
20 could be used to measure any type of gas or other fluid.
[0032] With each rotation of impellers 50 and 52, a quantifiable volume of
gas passes through rotary meter 20, ultimately being transferred to the end
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consumer for use. Therefore, the faster the rotation of the impellers, the
larger
the volume of gas that is being used by the end consumer. Because impellers
50 and 52 remain in a fixed relative position, it is only necessary to measure
the
rotational movement of one of them. However, the movement of both impellers
50 and 52 can also be measured.
[0033] FIGS. 4A and 4B illustrate a typical embodiment of an impeller,
either impeller 50 or 52, as known in the art. Assuming the illustrated
impeller is
first impeller 50, first impeller shaft 56 represents the axis of rotation for
impeller
50. It should be noted that although first impeller 50 is being used as an
example, all indicated parts of impeller 50 correspond to like parts of second
impeller 52.
[0034] As is known in the art, impeller shaft 56 divides the impeller into two
lobes 72 and 74. Each lobe is approximately circular in shape, so as to define
a
generally figure-eight shaped impeller 50. However, each impeller 50 and 52
can
take on various designs, as long as the overall assembly functions to trap a
quantifiable volume between each impeller member and the inner body wall
surface 60.
[0035] As illustrated in FIG. 4A, the exterior sides of the impeller lobes 72
and 74 and the transition area between them define the figure eight-shaped
shell
of impeller 50 and form the continuous impeller outer surface 80. The impeller
outer surface 80 is exposed to the gas flow passing through the positive
displacement rotary gas meter 20. In order to reduce the weight of the
impellers
50 and 52, the impeller lobes 72 and 74 can be hollow. During operation of the
positive displacement rotary gas meter 20, the impeller lobes 72 and 74 and
the
rigid edge member 87 must pass in close proximity of the inner body wall
surface
60 (as shown in FIGS. 3A and 3B) in order to maintain the necessary pressure
differential. In order to minimize the free space between the impeller 50 and
the
inner body surface wall 60, the exemplary impeller 50 includes a rigid edge
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member 87 to further decrease the space between the impeller 50 and the inner
body wall surface 60.
[0036] FIG. 4C is a section view of the impeller 50 shown in FIGS. 4A and
4B. This figure further illustrates the figure-eight shape of the impeller 50,
formed
by impeller lobes 72 and 74 and clearly shows the rigid edge member 87 in FIG.
4D. FIG. 4C also illustrates that the rigid edge member 87 is integral to the
exemplary impeller 50. The rigid edge members 87 currently known in the art
are continuous with, and protrude from, the distal ends of the impeller lobes
72
and 74. The rigid edge members 87 are constructed from the same rigid,
inflexible material used to construct the impeller 50. For example, the
exemplary
impellers 50 and 52 and rigid edge members 87 are commonly made from steel
or aluminum but it would be understood that the impellers 50 and 52 and rigid
edge members 87 could alternatively be made from a variety of other inflexible
materials including thermoset plastics, thermoplastics, titanium, copper and
other
ferrous or non-ferrous metals.
[0037] FIG. 5 is a section view of an exemplary positive displacement
rotary gas meter 20 containing the impellers 50 and 52, mounted on the first
impeller shaft 56 and the second impeller shaft 58, respectively. When the
positive displacement rotary gas meter 20 is in operation, the rigid edge
member
87 is the portion of the impellers 50 and 52 that is in closest proximity to
the inner
body wall surface 60. As gas inflow 22 flows into the positive displacement
rotary gas meter 20, it is prevented from passing straight through the meter
when
it contacts the impeller outer surfaces 80. It is common for a small amount of
gas
to pass through the gaps that exist between impellers 50 and 52 and the gaps
between the rigid edge members 87 and the impellers 50 and 52 inner body wall
surface 60.
[0038] Despite the slight leakage flow around the rigid edge members 87
of the impellers 50 and 52, the resistance faced by the gas flow increases the
upstream pressure, at the upper aperture 28, relative to the downstream
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pressure at the lower output member 32. As briefly explained above, this
pressure differential exerts a force on the impeller outer surfaces 80 that
causes
the impellers 50 and 52 to rotate in the directions indicated in FIG. 5. As
each
impeller 50 and 52 rotates, it sweeps a known quantity of gas through the
chambers 61.
[0039] It is important to note that the counting means used with the
positive displacement rotary gas meter 20 depends on the rotation of the
impellers 50 and 52. As discussed above, the quantity of gas passing through
the rotary gas meter 20 is calculated based on the known volume of the
internal
chambers 61 swept by the impellers 50 and 52 on each rotation. When leaks
occur between an impeller 50 or 52 and the inner body wall surface 60 or
between the impellers 50 and 52, then the total volume of gas passing through
the meter can be greater than the swept volume of the chambers 61.
[0040] One method of reducing this leakage gas flow is to decrease the
clearance between the impellers 50 and 52 and between the impellers 50 and 52
and the inner body wall surface 60. As discussed above, a known method of
reducing the clearance between the impellers 50 and 52 and the inner body wall
surface 60 is the use of the rigid edge members 87. Using rigid edge members
87, the meter gap clearance (i.e. the distance between impellers 50 and 52 and
between the impellers 50 and 52 and the inner body wall surface 60) can be in
the range of .003 - .005 inches for small gas meters, and .005 - .007 inches
for
large meters. Reducing the clearance distance can reduce the amount of gas
flow leakage.
[0041] However, operational gas flow conditions can interfere with the
operation of the gas meters known in the prior art, as described in relation
to
FIGS. 4A through 5. Specifically, the gas flowing through a positive
displacement rotary gas meter 20 can contain a variety of contaminants.
Contaminants carried within the gas flow can include tar, puddy, rust
particles,
dirt, sand, weld beads and other substances. As described above, when
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contaminants enter a traditional positive displacement rotary gas meter 20
they
can cause damage to the impellers 50 and 52 and the inner body wall surface 60
and can result in the seizing of the meter.
[0042] The following description, relating to FIGS. 6A through 7, relates to
a flexible edge impeller that may be used in place of the rigid edge impellers
described above. The use of a flexible edge impeller may improve positive
displacement rotary gas meter 20 performance and reliability. As the flexible
edge impeller may be used in place of a rigid edge impeller, some of the
reference numerals used in FIGS. 1 through 5 will also be used in FIGS. 6A
through 7 to describe features common to all embodiments for ease of
description.
[0043] For example, positive displacement rotary gas meter 20 was
described above as housing first and second impellers 50 and 52. The flexible
edge impeller may be used within a gas meter, so a positive displacement
rotary
gas meter 20 as described in relation to FIGS. 1 through 5 may be the same
positive displacement rotary gas meter 20 shown in FIGS. 6A through 7 and will
be referred to using the same reference numeral.
[0044] Similarly, impellers 50 and 52 (and their respective features, except
the rigid edge members 87) will be described in relation to FIGS. 6A through
7,
using the same reference numbers as the impellers 50 and 52 can perform
substantially the same task in both embodiments. However, it should be noted
that flexible edge member 88 in the new, flexible edge design replaces the
rigid
edge member 87 known in the prior art. The advantageous features of the new
flexible edge impeller are described below.
[0045] FIGS. 6A through 6D show impeller 50 with flexible edge members
88. FIG. 6A is a perspective view of a first impeller 50 that comprises
flexible
edge members 88. The first impeller 50 also comprises an outer surface 80,
first
and second lobes 72 and 74 and a first impeller shaft 56. For ease of
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description, the flexible edge design will be explained in relation to first
impeller
50 but it is understood that corresponding flexible edge members 88 may be
also
used with second impeller 52.
[0046] FIG. 6B shows a side view of first impeller 50 and illustrates flexible
edge members 88 that protrude from the distal ends of the impeller lobes 72
and
74. As illustrated, the flexible edge members 88 may extend the complete
longitudinal length of the impeller lobes 72 and 74. The flexible edge members
88 may also be configured such that they do not extend the entire longitudinal
length of the impeller lobes 72 and 74. For example, only selected portions of
the impeller edge may be flexible. An impeller edge may contain a combination
of flexible edge 88 portions and rigid edge portions 87.
[0047] Unlike rigid edge members 87 (as shown in FIGS. 4A through 4D),
the flexible edge members 88 may not be integrally formed with impeller lobes
72
and 74. Flexible edge members 88 may be formed from separate pieces of
material that are coupled to the impeller lobes 72 and 74. Forming the
flexible
edge members 88 from separate pieces of material allows the flexible edge
members 88 to be a different material than the impeller 50 and the impeller
lobes
72 and 74.
[0048] For example, impeller 50 may be formed from steel or aluminum as
described above, but unlike rigid edge members 87 (which were integrally
formed
with the impeller lobes 72 and 74), flexible edge members 88 may be formed
from nylon, polypropylene, polyester, polyethylene and any other thermoplastic
with the desired mechanical and chemical properties. The flexible edge
members 88 may also be formed from a thermoplastic elastomer, rubber or
natural hair fibers.
[0049] In addition, flexible edge members 88 may also be formed from
metal, including steel, stainless steel, aluminum, copper, titanium and any
other
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ferrous or non-ferrous metal that can be formed in the desired configuration
to
have the desired mechanical flexibility and chemical properties.
[0050] FIG. 6C shows a section view of impeller 50 with flexible edge
members 88 and a detail view showing an example of a flexible edge member 88
received within the distal end of impeller lobe 72. As illustrated in FIG. 6C,
the
flexible edge members 88 protrude from the distal ends of the impeller lobes
72
and 74.
[0051] FIG. 6D shows an example of a method for coupling a flexible edge
member 88 to the distal end of impeller lobe 72. In the example shown, the
flexible edge member 88 comprises upper portion 94 and a lower portion 96 that
is wider than upper member 94. Impeller lobe 72 comprises a mounting channel
98 that runs the length of impeller 50 beneath the impeller outer surface 80
and
is configured to receive the upper and lower portions 94 and 96 of the
flexible
edge member 88. During assembly of the impeller 50, the flexible edge member
88 may be aligned with the mounting channel 98 and inserted longitudinally
along the length of the impeller 50.
[0052] During operation of the positive displacement rotary gas meter 20,
the rotation of the impeller 50 may exert force on the flexible edge member 88
in
the radial direction, however, the relatively wider bottom portion 96 of the
flexible
edge member 88 may be constrained within the relatively wider portion of the
mounting channel 98 and the flexible edge member 88 may be prevented from
moving in the radial direction. Longitudinal movement of the flexible edge
member 88 may be restrained by friction forces between the flexible edge
member 88 and the mounting channel 98, mounting channel end caps (not
shown), securing clips (not shown), chemical adhesive or any other appropriate
method.
[0053] For example, rather than being received within a mounting channel
98 and secured by frictional, a flexible edge member 88 may be injection
molded
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to the impeller 50. Alternatively, a flexible edge member 88 may be coupled to
the outer surface 80 of an impeller 50 using glue, adhesives, screws, rivets,
crimping and any other appropriate chemical or mechanical fastening means.
[0054] The portion of flexible edge member 88 protruding from the lobe
wall 76 may have a triangular cross-sectional shape, as shown in FIGS. 6C and
6D. However, the shape of the flexible edge member 88 may be any cross-
sectional shape that can provide the necessary flexibility. For example, the
cross-sectional shape of the flexible edge member 88 may be rectangular,
concave, circular, arcuate or a convex shaped flexible protrusion.
Alternatively,
flexible edge member 88 may be flush with the impeller outer surface 80.
[0055] As shown in FIG. 7, the flexible edge members 88 may also be
formed as integral components of a flexible impeller skin 82. In some
applications, the impeller 50 may be covered by a flexible impeller skin 82
that
covers the impeller outer surface 80. The flexible impeller skin 82 may cover
both of the impeller lobes 72 and 74. In this configuration, the flexible edge
members 88 may be formed as protrusions extending from the distal portions of
the flexible impeller skin 82. For example, an impeller 50 may be formed from
aluminum (or any other material described above) and the impeller outer
surface
80 may then be encased by a flexible impeller skin 82 made from a
thermoplastic
elastomer (or any other flexible material described above). Flexible edge
members 88 may then be formed by protrusions of thermoplastic elastomer that
extend from the flexible impeller skin 82 at locations that correspond with
the
distal ends of the impeller lobes 72 and 74.
[0056] In such a configuration, the flexible edge members 88 may not be
attached directly to the impeller outer surface 80, but instead the flexible
edge
members 88 may be held in place by the flexible impeller skin 82. The flexible
impeller skin 82 itself may be held in position by frictional forces between
the
impeller skin 82 and the impeller outer surface 80, or by any other fastening
and
securing means described above. If the flexible edge members 88 or the
flexible
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impeller skin 82 should become worn or damaged during the operation of the
rotary gas meter 20, the flexible impeller skin 82 may be replaced, without
having
to replace the underlying impeller 50.
[0057] The flexible edge members 88 may also be integrally formed with
the impeller lobes 72 and 74, as is shown in FIGS. 8A and 8B. FIG. 8A shows
an end view of an impeller 50, wherein the impeller 50 is formed from the same
material used to form the flexible edge members 88. For example, the impeller
50 may be formed from a flexible thermoplastic. The flexible edge members 88
may also be formed of flexible thermoplastic, and may be integrally attached
protrusions extending from the distal ends of the impeller 50. In this
configuration, the flexible edge members 88 integrally formed with the
impeller 50
may be created by molding, casting, machining, extruding or any other suitable
manufacturing process.
[0058] While the flexible edge members 88 shown in FIG. 8A are intended
to be flexible, the impeller lobes 72 and 74 may be intended to retain their
initial
shape. That is, during the operation of a rotary gas meter 20, it may be
desired
that the impeller 50 retain its original form, and that only the flexible edge
members 88 deflect or deform. If such a result is desired, the properties of
the
material used to form the impeller 50 comprising the integrally formed
flexible
edge members 88 may be selected such that the material is sufficiently
flexible
when used to form relatively thin formations (i.e. the flexible edge members
88),
but is also sufficiently stiff when used to form relatively thick formations
(i.e. the
impeller lobes 72 and 74).
[0059] FIG. 8B shows another embodiment of an impeller 50 that
comprises flexible edge members 88 that are integrally formed with the
impeller
lobes 72 and 74. As in FIG. 8A, the flexible edge members 88 shown in FIG. 8B
are integrally formed with the impeller lobes 72 and 74, and are formed from
the
same material as the impeller 50. The embodiment shown in FIG. 8B is an
example in which the impeller 50 is reinforced using stiffening members 100
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inserted in the impeller lobes 72 and 74. By using additional stiffening
members
100, the impeller 50 can be formed from a flexible material and still achieve
the
desired operational stiffness.
[0060] For example, the impeller 50 may be formed from rubber (or any
other suitable material described above). The rubber chosen may be
sufficiently
flexible to allow the flexible edge members 88 to flex around foreign debris
92 in
the gas flow, however the impeller lobes 72 and 74 formed from the rubber may
be too flexible to function properly with the rotary gas meter 20. To increase
the
stiffness of the impeller lobes 72 and 74, stiffening members 100 may be
inserted
into cavities created in the rubber the impeller lobes 72 and 74. The
stiffening
members 100 may be formed from metal, rigid plastic or any other sufficiently
stiff material (as described above). The use of additional stiffening members
100
enables an impeller 50 to be formed from a material that is flexible enough to
form the flexible edge members 88 while still maintaining the necessary
operational stiffness. In addition, the use of stiffening members 100 may
enable
the impeller 50 shown in FIG. 8B to be formed from a more flexible material
than
the impeller 50 shown in FIG. 8A.
[0061] As shown in FIG. 9, first and second impellers 50 and 52
comprising flexible edge members 88 can be installed within the positive
displacement rotary gas meter 20. The flexible edge members 88 can replace
the rigid edge members 87 and can be configured to provide the same operation
clearances described above. That is, the flexible edge members 88 can be
coupled to the distal ends of the impeller lobes 72 and 74 such that the
distance
between the distal end of the flexible edge members 88 and the inner body wall
surface 60 is between .003 - .005 inches for small gas meters, and .005 - .007
inches for large gas meters. The impellers 50 and 52 may also be configured
such that the distance between a flexible edge member 88 of the first impeller
50
and the outer surface 80 of the second impeller 52, and vice versa, is also
between .003 - .005 inches for small gas meters, and .005 - .007 inches for
large
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gas meters when the impellers 50 and 52 move past each other during operation.
The distance between the impellers 50 and 52 or between an impeller 50 or 52
and the inner body wall surface 60 can be referred to as the clearance between
the components.
[0062] As described above, the tight clearances between impellers 50 and
52 and inner body wall surface 60 can reduce gas leakage through the positive
displacement rotary gas meter 20 which can force gas inflow 22 to cause the
impellers 50 and 52 to rotate thereby sweeping out the known volume of the
internal chamber 61 and triggering a counting mechanism (not shown).
[0063] While it can be important that the flexible edge members 88 of the
impellers 50 and 52 are in close proximity to each other and the inner body
wall
surface 60, it can also be important that the flexible edge members 88 of the
impellers 50 and 52 do not come into contact with each other or the inner body
wall surface 60 during the operation of the positive displacement rotary gas
meter 20. If the flexible edge members 88 contact an impeller 50 and 52 or the
inner body wall surface 60 they can create a frictional force opposing the
rotation
of the impellers 50 and 52 that can cause the rotation of the impellers 50 and
52
to slow or even stop.
[0064] FIG. 10 is a section view of a positive displacement rotary gas
meter 20 that contains some foreign debris 92 within its internal chambers 61.
As described above, during the operation of gas meter 20, debris 92 may be
carried by the gas inflow 22. This debris 92 can include any matter that is
ancillary to the gas being measured by gas meter 20, such as tar, puddy, rust
particles, dirt, sand, weld beads, dust, dirt, pollutants, and other
substances.
Materials of particular concern are solid materials and gases or liquids that
can
form solid deposits within internal chamber 61, over time.
[0065] Also of concern is the accumulation of liquids that may not be
readily drainable from internal chambers 61. For example, liquids may form
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within gas meter pressure body 24 due to their introduction into gas inflow
22, or
due to condensation taking place within internal chamber 61. Although some
examples of foreign materials have been provided, unwanted foreign debris 92
that can be introduced into the internal chamber 61 of gas meter pressure body
24 may include any matter that is ancillary to the gas being measured.
[0066] Debris 92 that has entered internal chamber 61 may be carried by
the gas inflow 22 and may accumulate on inner body wall surface 60. If debris
92
is sufficiently large, solid and abrasive, it can damage impeller primary
surfaces
80 and inner body wall surfaces 60 and possibly cause the meter to seize as
described above, if a solid debris 92 particle exceeds the clearances of the
meter. As a given impeller (50 or 52) continuously contacts the debris 92 with
each successive rotation, abrasions, chips, cracks, or the like may form on
the
impeller surfaces 80 of the given impeller (50 or 52). The incidental friction
may
be sufficient to break off pieces of the impellers 50 and 52. The continuous
frictional forces may also create abrasions, cracks, broken portions, or the
like,
on the inner body wall surface 60.
[0067] The imperfections created within primary impeller surfaces 80, or
inner body wall surface 60 may cause the rotary gas meter to miscalculate the
volume of gas being passed though the internal chamber 61. For example, if a
portion of impeller 50 that has broken off, a greater volume will be defined
between impeller 50 and inner body wall surface 60. The rotary gas meter 20
may continue to associate one full impeller rotation cycle with the pre-
damaged
volume, thus, underestimating the actual volume of gas passing through the
meter. Such an inaccurate measurement can result in revenue losses.
[0068] Use of the flexible edge members 88, shown in FIG. 8, may reduce
the damage caused to the impellers 50 and 52 and the inner body wall surface
60.
CA 02635166 2008-06-16
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[0069] For example, the flexible edge members 88 can sweep away debris
92 that has accumulated on inner body wall surface 60. For debris 92 that is
relatively loosely attached to inner body wall surface 60, the flexible edge
members can serve to contact debris 92 that has a thickness larger than the
specified clearance between the distal end of the flexible members 88 and
inner
body wall surface 60. Through such contact, the flexible edge members may
sweep away debris that has become lodged on inner body wall surface 60, with
each successive rotation. The debris 92 may become completely dislodged with
one or multiple rotations, destroying the bonds between the debris 92 and
inner
body wall surface 60. Alternatively, the debris 92 may be worn down, by
contact
with the flexible edge members 88, to a thickness that will not impeded
impeller
50 and 52 rotation, either through one rotation or over a series of successive
rotations. In the former case, the flexible edge members destroy the bonds
existing between the debris 92 and inner body wall surface 60. In the latter
case,
the flexible edge members destroy bonds existing within the debris 92 itself.
[0070] The flexible edge members 88 may also prevent rotary gas meter
20 damage and seizing by flexing around solid debris 92 particles that exceed
the clearance between impellers 50 and 52 and the clearance between the
impellers 50 and 52 and the inner body wall surface 60.
[0071] As an illustrative example, consider a rotary gas meter 20 with an
operating clearance of 0.005" as described above. That is, the distance
between
the distal edge of an impeller edge member (87 or 88) and the inner body wall
surface 60 is 0.005". For the purposes of this example, it is assumed that a
solid
debris particle 92 with a diameter of 0.007" is carried into the meter by the
gas
inflow 22.
[0072] If the rotary gas meter 20 contained impellers 50 and 52 with rigid
edge members 87 (as shown in FIGS. 1 - 4D), the debris 92 may become
lodged between the inner body wall surface 60 and a rigid edge member 87.
Because the 0.007" diameter of the debris 92 is larger than the 0.005"
operation
CA 02635166 2008-06-16
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clearance of the gas meter 20, the rigid edge member 87 may be prevented from
rotating past the debris 92, thereby seizing the rotary gas meter 20.
Alternatively, if the rotary gas meter 20 is not completely seized, the force
exerted on the debris 92 by the rigid edge member 87 may be still sufficient
to
break a portion of the debris 92 and the rigid edge member 87 itself. The
force
exerted on the debris 92 may also cause the debris 92 to be scraped along, or
pressed into, the inner body wall surface 60 causing additional damage to the
rotary gas meter 20 as described above.
[0073] However, if the rotary gas meter 20 contained impellers 50 and 52
with flexible edge members 88 (as shown in FIGS. 5- 10), the debris 92 may not
become lodged between the inner body wall surface 60 and the impeller (50 or
52) because the flexible edge member 88 may flex and temporarily deform
around the debris 92. That is, while the clearance between the distal end of
the
flexible edge members 88 and the inner body wall surface 60 is 0.005", the
actual
clearance between the rigid impeller surfaces 80 and the inner body wall
surface
60 may be greater than 0.005".
[0074] For example, if the flexible edge members 88 extend 0.010" from
the distal end of the impellers 50 and 52, then impellers 50 and 52 may be
installed within the rotary gas meter 20 such that the clearance between the
inner
body wall surface 60 and the flexible edge members 88 is 0.005", but the
actual
clearance between the inner body wall surface 60 and the hard, rigid impeller
surface 80 is 0.015" (0.010" flexible edge member 88 height + 0.005" clearance
between the flexible edge member 88 and the inner body wall surface 60). The
flexible edge members 88 can be configured such that they are stiff enough to
resist the gas flow pressure forces acting on them, but flexible enough to
flex and
deform around solid debris 92.
[0075] The flexible edge members 88 may also be resiliently flexible, such
that after they flex around debris 92, they return to their original,
undeformed
configuration. Therefore, when the 0.007" debris 92 particle enters a rotary
gas
CA 02635166 2008-06-16
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meter 20 containing flexible edge members 88, the flexible edge members 88
can deform around the debris 92, thereby allowing the impeller (50 or 52) to
pass
over the debris 92 without causing damage to the impeller (50 or 52) or the
inner
body wall surface 60.
[0076] In another embodiment, the flexible edge members 88 may enable
a rotary gas meter 20 to operate with tighter clearances between the flexible
edge members 88 and the inner body wall surface 60. For example, consider a
rotary gas meter 20 may be configured such that the impellers 50 and 52
comprise flexible edge members 88 that extend 0.010" as described above. The
impellers 50 and 52 could then be installed within the rotary gas meter 20
such
that the clearance between the inner body wall surface 60 and the flexible
edge
members 88 is only 0.001". Such a configuration may be desired because it may
reduce the amount of gas leakage around the impellers, thereby improving the
accuracy of the gas meter.
[0077] If the impellers 50 and 52 were configured with rigid edge members
87, the rotary gas meter 20 would be damaged or seized when a 0.007" debris
92 particle entered the meter as described above. However, when the impellers
50 and 52 comprise the 0.010" flexible edge members 88 the actual clearance
between rigid surfaces (60 and 80) is 0.011" (0.001" + 0.010"). When the
0.007"
debris 92 particle enters the rotary gas meter 20 comprising the 0.010"
flexible
edge members 88, the flexible edge members 88 can flex around the debris 92,
reducing the likelihood of damage or seizing, and the meter 20 can continue to
operate. Flexible edge members 88 may allow for rotary gas meters 20 to be
designed with tighter clearances between components. This reduced clearance
may allow for more accurate fluid metering.
[0078] Despite the flexibility of the flexible edge members 88 described
above, it is possible that extended use or particularly large and abrasive
debris
92 may damage an impeller 50 or 52 equipped with a flexible edge member 88 or
the flexible edge member 88 itself. The flexible edge members 88 may also
CA 02635166 2008-06-16
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degrade over time during normal operation of the rotary gas meter 20. If
necessary, the flexible edge members 88 may be replaceable such that a new
flexible edge member 88 could be installed on an impeller 50 or 52 to replace
a
worn or damaged flexible edge member 88. Replacing the flexible edge member
88 may reduce the frequency of repair and replacement of the impeller 50 or 52
and the inner body wall surface 60, thereby reducing the operating costs of
the
rotary gas meter 20. The properties of the material of the flexible edge
member
88 may be chosen such that the flexible edge member 88 is intended to wear out
before the other components of the meter. The flexible edge member 88 can
then simply be replaced. The ability to replace just the flexible edge member
88,
as opposed to the pressure body cylinder 24 or the complete impeller 50 or 52
comprising an integral rigid edge member 87, is an advantage of the flexible
edge design.
[0079] The flexible edge members 88 shown in FIGS. 6A through 10 are
shown having a continuous, uniform profile. That is, the distal portions of
the
flexible edge members 88 are shown as continuous and smooth, without
variations in height, thickness or composition. A uniform profile
configuration
may be appropriate when the flexible edge member 88 is formed from a
relatively
deformable material. If the material is sufficiently flexible, a portion of
the flexible
edge member 88 can easily deform to flex around contaminants in the meter.
However, the flexible edge members 88 can be formed from a variety of
materials and may also be formed in a variety of configurations.
[0080] For example, if the flexible edge member 88 is formed from a
relatively stiffer material, such as steel, the flexible edge member 88 may be
formed in a non-continuous, bristle-type configuration. In a bristle
configuration,
the distal portion of the flexible edge member 88 may be formed from a
plurality
of individual bristles rather than a single, continuous member, such that any
given bristle, or local group of bristles, may freely deflect without
affecting, or
being constrained by, the neighbouring bristles. This isolation of the
individual
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bristles allows a section of a bristle-type flexible edge to deform more
easily than
a similar section of a continuous flexible edge formed from the same material.
The plurality of bristles may overlap each other to form a relatively gas-
impermeable surface. The plurality of bristles may be formed from a plurality
of
discrete bristles individually attached to an impeller 50 or 52, or the
plurality of
bristles may be formed by a series of cuts lines in a single strip of material
attached to an impeller 50 or 52 such that the proximate portion of the
bristle-
type flexible edge member 88 is continuous and the distal portion of the
bristle-
type flexible edge member 88 forms the plurality of bristles.
[0081] A flexible edge member 88 formed of relatively stiffer material may
also be configured in a non-continuous, leaf-type configuration. In a leaf-
type
configuration, at least the distal portion of the flexible edge member 88 may
be
formed from a plurality of individual panels, or leaves, that can move and
flex
independently from each other. The plurality of leaves may be configured to
abut
each other to form a relatively gas impermeable surface, but do not overlap
each
other, such that the deflection of a given leaf would not affect the adjacent
leaves. Alternatively, the plurality of leaves could be configured such that
they
overlap each other. The plurality of leafs may be formed from a plurality of
discrete panels individually attached to an impeller 50 or 52, or the
plurality of
leaves may be formed by a series of cuts lines in a single panel of material
attached to an impeller 50 or 52 such that the proximate portion of the leaf-
type
flexible edge member 88 is continuous and the distal portion of the leaf-type
flexible edge member 88 forms the plurality of leaves.
[0082] While the above description provides examples of the
embodiments, it will be appreciated that some features and/or functions of the
described embodiments are susceptible to modification without departing from
the spirit and principles of operation of the described embodiments.
Accordingly,
what has been described above has been intended to be illustrative of the
invention and non-limiting and it will be understood by persons skilled in the
art
CA 02635166 2008-06-16
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that other variants and modifications may be made without departing from the
scope of the invention as defined in the claims appended hereto.
