Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02509716 2007-11-09
VALVE TRAVEL INDICATOR
TECHNICAL FIELD
This invention relates in general to valves, and more specifically, to a
valve travel indicator.
BACKGROUND
Valves are used in many industries to control the flow of liquids and
gases. Many of the valves are automated such that the valves can be opened
and closed from a remote location, such as by a computer control system.
Thus, many of these valves may only be inspected by a human at periodic
intervals, such as during annual inspections or while resolving valve
operatiorn
problems. Valve travel indicators have been used in many valve systems to
indicate whether a valve is open, closed or partially open. These valve travel
indicators are often located in an open portion of a yoke used to couple the
valve to a control mechanism, such as an actuator.
SLJMMARY
According to one embodiment of the present invention, a valve travel
indicator associated with a control valve is described. The valve travel
indicator includes an indicator portion that shows a location on a valve
indicator scale. The valve indicator scale represents the position of a valve
plug relative to a valve seat to indicate whether the control valve is open,
partially open, or closed. The valve travel indicator also includes a
retaining
portion -that is fixed to a valve plug stem with a predetermined breakaway
force. The breakaway force is selected to prevent movement of the indicator
with respect to the valve stem during normal operation of the control valve
while allowing movement of the valve travel indicator relative to the valve
stem when the breakaway force is exceeded. The present invention provides
various technical advantages. Various embodiments of the present invention
may provide all, some or none of these technical advantages. One such
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technical advantage is the capability to manually manipulate the valve travel
indicator on a valve stem without tools by sliding the indicator along the
valve
plug stem. For example, the breakaway force may be selected such that a
human can align the valve travel indicator with the valve indicator scale or
completely remove the valve travel indicator without the use of tools. Another
such technical advantage is the capability of the valve travel indicator to
move
relative to the valve stem if an obstruction proximate to the valve travel
indicator or the valve indicator scale is encountered. Also, manufacturing
costs by may be decreased by using a valve indicator scale cast as part of a
valve and/or a yoke instead of using a separate, adjustable indicator scale
with
a valve travel indicator fixed to the valve stem.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is best understood from the detailed description
which follows, taken in conjunction with the accompanying drawings, in
which:
FIGIJRE 1 is a cross-sectional view illustrating a valve according to
one embodiment of the present invention;
FIGURE 2 is a cross-sectional view illustrating further details of a
valve travel indicator associated with the valve according to one embodiment
of the present invention;
FIGiJRE 3 is a cross-sectional view of the valve travel indicator
according to one embodiment of the present invention;
FIGURE 4 is a cross-sectional view of the valve travel indicator
according to an alternative embodiment of the present invention;
FIGURE 5 is a top view of the valve travel indicator according to
another alternative embodiment of the present invention; and
FIGURE 6 is a cross-sectional view of the valve travel indicator
according to yet another alternative embodiment of the present invention.
DETAILED DESCRIPTION
FIGURE 1 is a cross-sectional view illustrating a control valve
assembly 10 according to one embodiment of the present invention. Control
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valve assembly 10 may comprise a valve 12 and an actuator 14 (partially
depicted).
Valve 12 may comprise a valve body 20 and a moveable operator 22
including a valve plug 24 attached to a valve stem 26 to control the fl,ow of
materials, such as liquids and gases. Additionally, valve body 20 includes a
valve packing box 28 and valve packing 29 to create a fluid seal and a guiding
surface for valve stem 26. As known to those skilled in the art, the valve
stem
is typically polished to approximately a 4 micron Ra (arithmetic average)
finish to reduce valve packing degradation and increase control valve
assembly cycle life.
Valve stem 26 is mechanically coupled (not shown) to actuator 14 that
applies an axial force to valve stem 26 to control the relative position of
valve
plug 24 with respect to a valve seat 30. The relative position of valve plug
24
creates a variable orifice within control valve assembly 10 to modulate and -
control the fluid flow through control valve assembly 10. As known to those
in the art, the axial force exerted. by actuator 14 may be provided by
pressurized air supplying a conventional spring and diaphragm actuator. In
one embodiment, valve stem 26 comprises a generally cylindrically shaped
rod having a generally smooth surface. In one embodiment, valve plug stem
26 is 0.375 inches in outer diameter and may alternatively range from 0.375
inches to 2 inches in outer diameter.
A yoke opening 31 in an actuator yoke 32 provides access to valve
stem 26 and a valve travel indicator 34 (described in greater detail below).
In
one embodiment, yoke opening 31 is 1 inch to 2 inches in height and is 2
inches to 3 inches in width. Alternatively, yoke opening 31 may range in
height from 1 inch to 26 inches and in width from 2 inches to 7 inches.
Indicator scale 36 comprises a portion of control valve assembly 10
used with valve travel indicator 34 to indicate whether valve 12 is open,
partially open, or closed. In one embodiment, indicator scale 36 may have
gradations or marks upon an inner surface 38 to approximately quantify the
relative position of the valve plug 24 with respect to valve seat 30. Valve
travel indicator 34 comprises a generally circular element movably coupled to
valve stem 26. Various embodiments of valve travel indicator 34 are
described in association with FIGURES 2 through 6.
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As understood by those skilled in the art, valve 12 is opened and closed
by sliding valve stem 26 axially along a longitudinal axis 40 defined by valve
stem 26. As valve stem 26 moves away from the valve body 20, valve plug 24
is pulled upwards and opens valve 12. As valve stem 26 moves towards the
valve body 20, valve plug 24 is pushed downward and closes valve 12. The
movement of valve stem 26 will change the position of valve travel indicator
34 with respect to indicator scale 36. The position of valve travel indicator
34
with respect to indicator scale 36 provides a visual and/or mechanical
indication local to valve 12 of the relative position of valve plug 24.
Furthermore, valve travel indicator 34 may be used to determine the condition
of valve 12. If valve travel indicator 34 does not correspond to a commanded
travel, it may indicate a maintenance or operational problem within control
valve assembly 10. For example, valve 12 may be set in a partially open
position that only allows a portion, such as 30%, of the valve's flow capacity
to be used. As valve 12 is used, wear on valve 12 may change the position of
valve plug 24 needed to get a desired flow rate. A technician may visually,
mechanically, electronically or otherwise inspect valve travel indicator 34.
For example, if the technician notices that valve travel indicator 34 does not
indicate a position corresponding to a 30% flow rate, the technician may
conclude that valve plug 24 has eroded and therefore is to be repaired or
replaced.
Automated systems for valve control may require calibration with
respect to the individual valves the automated system is controlling. For
example, generalized control and monitoring systems may be used to control
various sizes of valves. Valve travel indicator 34 may be used to calibrate
the
automated system. For example, one technician may visually or mechanically
determine the position of valve travel indicator 34 for a particular valve and
communicate that information to another technician responsible for calibrating
the automated system controlling the particular valve.
FIGURE 2 is a cross-sectional view illustrating further details of valve
travel indicator 34 according to one embodiment of the present invention.
Valve travel indicator 34 further comprises an indicator portion 50 and a
retaining portion 52.
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Indicator portion 50 comprises a generally circular, tapered disk with a
central opening disposed therethrough. Indicator portion 50 further comprises
a portion of valve travel indicator 34 indicating the current position of
valve
plug 24 with respect to indicator scale 36.
In one embodiment, indicator portion 50 further comprises a cavity 54.
Retaining portion 52 may be disposed within cavity 54 and retained withiri
cavity 54. Retaining portion 52 may be retained within cavity 54 by friction,
force and/or the design of retaining portion 52 such that retaining portion 52
is
not generally permitted to escape from cavity 54 during movement of
indicator portion 50 with respect to valve stem 26.
Retaining portion 52 comprises a portion of valve travel indicator 34
operable to movably couple indicator portion 50 to valve stem 26. In one
embodiment, retaining portion 52 may comprise an element providing a
friction coupling between indicator portion 50 and valve stem 26, such as an
o-ring. Retaining portion 52 may be selected such that valve travel indicator
34 is relatively fixed to valve plug stem 26 during normal use and operation
of
valve stem 26, while allowing valve travel indicator 34 to be moved in
response to a predetermined level of force upon valve travel indicator 34. The
level of force may. be determined using suitable criteria. For example, the
level of force may be selected to allow valve travel indicator 34 to -be
manually moved by a human without tools while not allowing valve travel
indicator 34 to be moved during normal operation of valve stem 26. In one
embodiment, about 4-25 pounds of force are required to move valve travel
indicator 34 with respect to valve stem 26, but other suitable levels of force
may be used.
In operation, valve travel indicator 34 is initially aligned with indicator
scale 36. For example, valve 12 may be fully closed and valve travel indicator
34 manually aligned with the fully closed marking on indicator scale 36;
however, any suitable technique for aligning valve travel indicator 34 and
indicator scale 36 may be used. As valve travel indicator 34 moves with valve
stem 26, the tapered end of indicator portion 50 may be used with markings on
indicator scale 36 to determine whether valve 12 is open, closed or only
partially open. Allowing manual alignment, such as by a human in the field,
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of valve travel indicator 34 provides improved functionality and decreased
cost for valve 12.
As valve stem 26 moves up and down to open and close valve 12,
valve travel indicator 34 moves up and down relative to indicator scale 36.
The position of valve travel indicator 34 with respect to indicator scale 36
provides a visual and/or mechanical indication local to valve 12 of the status
of valve 12. For example, a technician visually inspecting the status of valve
12 can see whether valve 12 is open, closed or partially open.
One traditional valve travel indicator involved etching a groove into
the valve stem and then aligning the indicator scale with the groove. This
technique increased the cost of the valve because of the need for a separate,
movable indicator scale which typically required a screwdriver or other tools
for alignment. In contrast, one embodiment of valve travel indicator 34 may
allow a human without tools to align travel indicator 34 by sliding valve
travel
indicator 34 to a suitable location on the smooth valve stem 26 relying upon
the friction between valve stem 26 and retaining portion 52 to fix valve
travel
indicator 34 in position. Further, valve travel indicator 34 may allow
indicator
scale 36 to be formed as part of valve 12 and/or actuator 14, which may
decrease the cost of valve 12 by eliminating the use and manufacture of the
separate, movable indicator scale of traditional designs.
As valve travel indicator 34 is movably coupled to valve stem 26, ease
of disassembly of control valve assembly 10 may also be increased. More
specifically, as moveable operator 22 is removed from the control valve
assembly 10, valve travel indicator 34 can easily be slid from valve stem 26
without the use of tools. Valve stem 26 may be reinserted into valve 12
through retaining portion 52 during the reassembly process and valve travel
indicator 34 may then be re-aligned with respect to indicator scale 36.
Also, valve travel indicator 34 may support a decrease in the injuries
suffered by technicians working with control valve assembly 10. As known to
those skilled in the art, traditional valve travel indicators are rigidly
coupled to
the valve stem and could catch a technician's hand or a portion of the hand
while the technician was working on the valve. In contrast, valve travel
indicator 34 may avoid injury to the hands of the technician by slipping on
valve stem 26 instead of damaging the technician's hand. More specifically,
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as valve travel indicator 34 is movably coupled to valve stem 26, if valve
travel indicator 34 encounters an obstruction in the path of valve travel
indicator 34, valve travel indicator 34 may begin to slide along valve stem 26
instead of crushing the obstruction. For example, the obstruction may
comprise cumulative debris such as ice or an improperly mounted valve
accessory, such as a position transmitter or a pressure regulator. Further,
valve travel indicator 34 may increase the operational lifetime of control
valve
assembly 10 by sliding along valve stem 26 in response to the obstruction
instead of impacting the obstruction and possibly damaging control valve
assembly 10 with the impact.
FIGURE 3 is a cross-sectional view of valve travel indicator 34
according to one embodiment of the present invention. In one embodiment,
indicator portion 50 has an outer diameter of 1.5 inches and an inner diameter
of 0.8 inches. Alternatively, indicator portion 50 may have an outer diameter
from 1.5 inches to 7 inches and an inner diameter from 0.375 inches to 2
inches. The taper begins relatively close to the inner diameter and tapers to
the outer diameter. In one embodiment, the tapered portion of indicator
portion 50 extends 0.7 inches from the outer diameter. Indicator portion 50 is
0.21 inches in height and tapers to 0.06 inches in height at the end of the
tapered portion. Alternatively, indicator portion 50 may have a height ranging
from 0.21 inches to 0.5 inches and the edge of the taper may range from 0.05
inches to 0.1 inches in height. In one embodiment, indicator portion 50 has an
outer length slightly less than the inner diameter of yoke opening 31, such
that
indicator portion 50 has an edge disposed proximate to indicator scale 36. For
example, if the inner diameter of yoke opening 31 is 2 inches, indicator
portion 50 may have an outer diameter of slightly less than 2 inches so that
the
position of indicator portion 50 relative to indicator scale 36 may be more
easily determined.
Cavity 54 has an outer diameter of 0.673 inches, an inner diameter of
0.5 inches and a height of 0.135 inches. Alternatively, cavity 54 may have an
outer diameter ranging from 0.673 inches to 2.2 inches, an inner diameter
ranging from 0.5 inches to 2 inches, and a height ranging from 0.135 inches to
0.145 inches.
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Indicator portion 50 may be made from any suitable material, such as
plastic or metal, based on the environment valve travel indicator 34 is to be
used in, cost and other suitable criteria. In one embodiment, indicator
portion
50 is made from ultraviolet stabilized acrylonitrile styrene acrylate (ASA).
Alternatively, indicator portion 50 may be made from brass, aluminum, or
other suitable metals or plastics. In general, the selection of material for
indicator portion 50 may be based on the expected environment of valve 12 to
increase the lifetime of indicator portion 50. For example, indicator portion
50
may be exposed to environmental factors such as corrosive and non-corrosive
fluids, temperature extremes, high or low humidity levels, precipitation,
snow,
and ozone.
In one embodiment, retaining portion 52 comprises an o-ring. The
outer diameter, material and thickness of retaining portion 52 is selected
based
on the diameter of valve stem 26 such that retaining portion 52 grips valve
stem 26 with sufficient force to support indicator portion 50 and maintain the
position of indicator portion 50 with respect to valve stem 26 during normal
operation of valve stem 26. The outer diameter, material and thickness of
retaining portion 52 may also be selected such that retaining portion 52 does
not grip valve plug stem 26 with excessive force that would prevent movement
of indicator portion 50 by a human without tools or prevent removal of valve
plug stem 26 from valve 12 during disassembly: In this embodiment, retaining
portion 52 has an inner diameter of 0.5 inches, an outer diameter of 0.6875
inches, a cross-sectional diameter of 0.09375 inches, and is formed from 70
durometer-shore A nitrile. Alternatively, retaining portion 52 may have an
inner diameter of from 0.480 inches to 2 inches, an outer diameter of 0.6875
inches to 2.1875 inches, a cross-sectional diameter ranging from 0.09375
inches to 0.106 inches and may be formed from fluoro-elastomer, ethylene-
propylene or any suitable rubber-like material with an appropriate hardness
rating capable of handling the expected environmental factors such as ozone
and extreme temperature changes.
In another embodiment, valve travel indicator 34 may comprise a
generally homogerieous piece of material operable to provide a suitable
interference fit between valve stem 26 and valve travel indicator 34. This
embodiment may be used without retaining portion 52 and cavity 54 as the
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material used to form indicator portion 50 provides the intei-Ference fit with
respect to valve stem 26 and indicator portion 50 comprises the whole of valve
travel indicator 34. For example, indicator portion 50 may comprise a single
piece of hard rubber, such as 90 durometer shore-A ethylene-propylene.
Indicator portion 50 may be formed from one or more individual pieces that
are suitably coupled together. In this embodiment, suitable materials may be
selected for indicator portion 50 that provide sufficient friction force to
allow
valve travel indicator 34 to operate as described above.
Further, as valve travel indicator 34 may be used with smooth valve
stems while avoiding damage to the smooth valve stem. For example, valve
stem 26 may, in one embodiment, be polished to a 4 micron Ra finish. More
specifically, by sliding along valve stem 26 valve travel indicator 34 avoids
damaging valve stem 26 when an obstruction is encountered and when valve
stem 26 is removed from valve 12. When smooth valve stems are scraped,
nicked or otherwise damaged, the damage to the smooth valve stem may
damage the valve during normal operation. For example, a nicked smooth
valve stem may damage the packing in the valve as the stem moves in and out
of the valve and the damaged packing may cause the valve to leak.
FIGURE 4 is a cross-sectional view of valve travel indicator 34
according to one embodiment of the present invention. Retaining portion 52
may alternatively comprise a set screw 56 according to one embodiment of the
present invention. Set screw 56 is disposed through indicator portion 50
perpendicular to valve stem 26 and operates to movably couple indicator
portion 50 to valve stem 26. More specifically, by tightening set screw 56
against valve stem 26, indicator portion 56 may be movably coupled to valve
stem 26. The amount of force needed to move valve travel indicator 34 may
be determined by the tightness of set screw 56. Set screw 56 may comprise a
suitable set screw, such as a nylon tipped, plastic set screw, or other
suitable
fastener, suitable for use in the environment surrounding valve travel
indicator
34.
FIGURE 5 is a top view of valve travel indicator 34 according to one
embodiment of the present invention. In this embodiment, indicator portion
50 further comprises a channel 60. Channel 60 may comprise an appropriately
sized cut extending from the outer edge to the inner edge of indicator portion
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50 and extending from the top to the bottom of indicator poi-tion 50. The size
of channel 60 may be determined based on a desired amount of adjustability in
the outer diameter of indicator portion 50. For example, an indicator portion
50 designed to be used with valve stems 26 of various diameters may have a
channel 60 of sufficient width to allow indicator portion 50 to fit the
various
sized valve stems 26.
In one embodiment, retaining portion 52 may comprise a first flange
62, a second flange 64 and a squeeze element 66. First and second flanges 62
and 64 comprise extensions of indicator portion 50 operable to receive
squeeze element 66. Squeeze element 66 comprises a suitable element
operable to tighten first and second flanges 62 and 64 to decrease the inner
diameter of indicator portion 50 such that indicator portion 50 grips valve
stem
26. In one embodiment, squeeze element 66 comprises a screw.
Alternatively, squeeze element 66 may comprise a suitable element for
adjustably closing flanges 62 and 64. In this embodiment, retaining portion 52
movably couples indicator portion 50 to valve stem 26 through tightening of
squeeze element 66.
Often, traditional valve travel indicators have been designed in
association with larger valve assemblies. As valve assemblies have become
smaller, different designs of valve. travel indicators may be more
appropriate.
For example, valve travel indicator 34 may be used with relatively small
control valve assemblies 10.
FIGURE 6 depicts yet . another alternative embodiment of the
invention, in the form of a single-piece valve travel indicator 134. Single-
piece valve travel indicator 134 may be manufactured using an injection
molding process, and may be made from thermoplastic rubber, such as, for
example, Santoprene blend 121-87, available from Advanced Elastomer-
Systems, L.P. of Akron, Ohio, USA.
By forming single-piece valve travel indicator 134 from thermoplastic
rubber, an interference fit between single-piece valve travel indicator 134
and
valve stem 26 may be used to maintain single-piece valve travel indicator 134
in a desired position on valve stem 26.
Single-piece valve travel indicator 134 may include an indicator
portion 150 comprising a generally circular, tapered disk that is formed
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integrally with a circularly cvlindrical retaining portion 152. Circularly
cylindrical retaining portion 152 may sized and shaped to include an inside
diameter sized such that it will have an interference with valve stem 26 when
disposed on valve stem 26. For example, if valve stem 26 has a diameter of
one-half inch, circularly cylindrical retaining portion 152 may have an inside
diameter of about 0.475 inches to about 0.480 inches, an outer diameter of
about 0.67 inches, and an overall height of about 0.39 inches. Indicator
portion 150 may have a thickness of about 0.14 inches in the vicinity where
the indicator portion 150 meets the outer diameter of circularly cylindrical
retaining portion 152, and the indicator portion 150 may begin to taper at a
diameter of about .085 inches to a thickness of 0.6 inches at the periphery of
the indicator portion 150. The indicator portion may have an overall diameter
of about 1.50 inches. The circularly cylindrical retaining portion 152 may
include an upper inner edge portion 154 and a lower inner edge portion 156,
each having a radius of curvature of about 0.3 inches.
In order to move the single piece valve travel indicator 134 along the
valve stem 26, a user may grasp the indicator portion 150 and slightly rotate
or
rock the single-piece valve travel indicator 134 as indicated by the arrows
158
in FIG. 6. This rotational motion of the single-piece valve travel indicator
134
permits a reduction in friction between valve stem 26 and the single-piece
valve travel indicator 134 so that a sufficient reduction in friction is
achieved
to permit the single-piece valve travel indicator 134 to be moved to a desired
position on valve stem 26.
Other changes, substitutions, and alterations are also possible without
departing from the spirit and scope of the present invention, as defined by
the
following claims.
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