U.S. patent application number 11/238674 was filed with the patent office on 2007-03-29 for leak detector for process valve.
Invention is credited to Gregory C. Brown.
Application Number | 20070068225 11/238674 |
Document ID | / |
Family ID | 37650007 |
Filed Date | 2007-03-29 |
United States Patent
Application |
20070068225 |
Kind Code |
A1 |
Brown; Gregory C. |
March 29, 2007 |
Leak detector for process valve
Abstract
A leak detection system is described for detecting a leak
through a closed valve disposed between an upstream pipe and a
downstream pipe of an industrial process. An insertable plate is
coupled to the valve in the pipe in-line with the fluid flow. A
sensor couples to the flow and provides a signature output. A leak
detector is coupled to the sensor and adapted to detect a leak
through the valve based upon the signature output.
Inventors: |
Brown; Gregory C.;
(Chanhassen, MN) |
Correspondence
Address: |
WESTMAN CHAMPLIN & KELLY, P.A.
SUITE 1400
900 SECOND AVENUE SOUTH
MINNEAPOLIS
MN
55402-3319
US
|
Family ID: |
37650007 |
Appl. No.: |
11/238674 |
Filed: |
September 29, 2005 |
Current U.S.
Class: |
73/40.5A ;
73/46 |
Current CPC
Class: |
G01M 3/2876 20130101;
F16K 37/0075 20130101; G01M 3/24 20130101 |
Class at
Publication: |
073/040.50A ;
073/046 |
International
Class: |
G01M 3/08 20060101
G01M003/08 |
Claims
1. A leak detection system for detecting a leak through a closed
valve disposed between an upstream pipe and a downstream pipe of an
industrial process, the system comprising: an insertable plate
coupled to the valve in the pipe in-line with the fluid flow; a
sensor tap extending through the insertable plate to a lumen of the
pipe; and a leak detector coupled to the sensor tap and adapted to
detect a leak through the valve based on a measured acoustic
signature.
2. The system of claim 1 wherein the leak detector is adapted to
identify a leak based on differences between the measured acoustic
signature and a stored reference signature.
3. The system of claim 1 wherein the leak detector is adapted to
generate an alarm signal to a control center if the measured
acoustic signature differs from a stored acoustic signature by more
than a predetermined limit.
4. The system of claim 1 wherein the leak detector is adapted to
detect problems in fixed equipment of the industrial process based
on a change in amplitude and/or frequency of background process
noise in excess of a predetermined noise limit.
5. The system of claim 1 wherein the leak detector is adapted to
predict an extent of a leak through the valve based on a magnitude
of differences between the measured acoustic signature relative to
a stored acoustic signature.
6. The system of claim 1 wherein the measured acoustic signal
comprises a frequency and amplitude pattern, and wherein the leak
detector is adapted to estimate an amount of fluid that has leaked
through the valve based on differences between the frequency and
amplitude pattern and a stored reference pattern.
7. The system of claim 6 wherein an amount of leakage is estimated
based on an end point of the frequency and amplitude pattern
relative to a corresponding point on the stored reference
pattern.
8. The system of claim 1 wherein the insertable plate provides a
variable area channel.
9. An acoustic leak detection system for detecting a fluid leak
through a valve of an industrial process, the valve having an
upstream passageway coupled to a downstream passageway and a valve
closure element adapted to selectively close off fluid flow through
the valve, the valve having one or more sensor taps extending into
the valve adjacent to the downstream passageway, the system
comprising: a leak detector coupled to the one or more sensor taps
and adapted to detect a leak through the valve based on a measured
acoustic signal.
10. The system of claim 9 wherein the leak detector further
comprising: a variable area flow region disposed adjacent to the
valve closure element in the downstream passageway to funnel fluid
build up away from the valve closure element, the variable area
flow region adapted to make the leak detector sensitive to
frequencies associated with leaks resulting in low fluid flow.
11. The system of claim 10 wherein one of the one or more sensor
taps extends into the valve adjacent to the variable flow area.
12. The system of claim 9 wherein the leak detector comprises: an
acoustic transmitter adapted to detect an acoustic signal from
fluid flowing through the valve; and circuitry adapted to detect a
leak through the valve based on differences between the acoustic
signal and a stored reference signal.
13. The system of claim 9 wherein the leak detector comprises: a
differential pressure transmitter coupled to the one or more sensor
taps having sufficient bandwidth to capture a differential acoustic
signal associated with fluid flowing through the valve.
14. The system of claim 9 wherein the leak detector further
comprises: a memory adapted to store a reference acoustic pattern
of a properly functioning valve.
15. The system of claim 9 wherein the leak detector comprises:
circuitry adapted to generate a diagnostic signal to a control
center if differences between the measured acoustic signal and a
stored reference signal exceed a predetermined limit.
16. The system of claim 9 wherein the leak detector is adapted to
estimate an amount of leakage through the valve based on
differences between the measured acoustic signal and a stored
reference signal.
17. A leak detection system for detecting a leak through a closed
valve element of a valve assembly disposed between an upstream pipe
and a downstream pipe of an industrial process, the system
comprising: a first sensor disposed in an upper portion of the
valve assembly downstream from the closed valve element and adapted
to measure pressure in the downstream section; a flow restriction
element disposed in a bottom portion of the valve assembly
downstream from the closed valve, the flow restriction element; a
cross-bore exposed to the fluid flow and extending into the flow
restriction element less than a full width of the flow restriction
element from a direction of the closed valve; a second sensor
disposed in a lower portion of the valve assembly and coupled to
the cross-bore, the second sensor adapted to measure a static
pressure in the downstream section; and a leak detector coupled to
the first and second sensors and adapted to detect a leak through
the closed valve based on a differential signature.
18. The leak detection system of claim 17 wherein the flow
restriction element comprises: a variable area flow channel for
channeling low fluid flow from the closed valve element to the
downstream pipe.
19. The leak detection system of claim 17 wherein the flow
restriction element and the first and second sensors are aligned
substantially axially along an axis substantially transverse to a
direction of fluid flow.
20. The leak detection system of claim 17 wherein the first sensor
and the second sensor comprise pressure sensors, and wherein the
differential signature comprises a differential pressure
signature.
21. The leak detection system of claim 17 wherein the first sensor
and the second sensor comprise pressure sensors adapted to measure
pressure signals in a range of frequencies within the downstream
section, and wherein the differential signature comprises a
differential acoustic signature.
22. The leak detection system of claim 17 wherein the valve
assembly comprises: a valve element comprising a housing coupled
between upstream and downstream pipe sections and defining a fluid
passageway between the upstream and downstream pipe sections, the
valve element including a valve closure element adapted to sealably
close the fluid passageway; and a plate coupled to the fluid
passageway in-line with the fluid flow and between the valve
element and the downstream pipe section, the plate having a
variable flow area on a lower portion of the insertable plate, the
variable flow area adapted to channel low fluid flows between the
closed valve and the downstream pipe; wherein the first and second
sensors, the flow restriction area and the cross bore are disposed
in the plate.
23. The leak detector of claim 22 wherein the plate comprises:
upper and lower pressure taps disposed in the plate and adapted to
host the first and the second pressure sensors respectively, the
lower pressure tap extending into the plate to the cross bore.
24. The leak detector of claim 22 wherein the variable flow area of
the plate comprises: a flattened area integral to a lower surface
of an inside wall of the plate.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to valves in industrial
processes, and more particularly, to detection and diagnosis of
fluid leaks through closed valves.
[0002] In the process control industry, automated control valves
are used extensively to control process fluid mass flow and/or
velocity in industrial processes. In some instances, especially in
batch processes, it is necessary that a valve achieve a tight
shut-off condition when it is closed. The phrase "tight shut-off"
refers to a valve position wherein zero or near-zero fluid flows
through the valve. In particular, a tight shut-off condition exists
where no fluid flows through the valve, or where fluid flow is
reduced to such a level that the flowing fluid had negligible
impact the process.
[0003] In industrial process where a tight valve shut-off condition
is required, if the valve does not shut-off tightly, the resulting
material leakage into a batch recipe can ruin the batch. If a tight
shut-off valve is leaking a noxious or toxic chemical, the leak can
present a hazard for plant personnel and may result in an incident
requiring involvement of the Environmental Protection Agency (EPA).
Both of these outcomes can be very expensive.
[0004] Tight shut-off of a control valve is usually achieved using
seals, such as elastomeric seals or Teflon.RTM. seals. For
corrosive process fluids, Teflon.RTM. and other corrosion resistive
materials are preferably used as the seal material. Unfortunately,
seals fail for a variety of reasons, including corrosion, fouling,
cavitation, physical wear and the like. Corrosion typically erodes
the seal creating surface imperfections that make a tight seal
difficult to achieve. Fouling refers to a material build up on the
surface of the valve seat or seal, which prevents the valve from
achieving a tight shut-off. Cavitation refers to a localized
formation within a fluid flow of air or vapor pockets that expand
explosively within the valve due to lowering of pressure within the
flow (such as when the valve is adjusted from a closed to an open
position). Expansion of vapor pockets within the flow can cause
metal erosion and eventual valve failure. "Physical wear" refers to
an instance where a seal is damaged during the valve closing
process by pinching material between the valve plug and the valve
seat or seal, thereby damaging the seat or seal body. Finally,
debris can also interfere with the seal or valve travel in general,
thereby preventing tight valve shut-off.
[0005] There is an on-going need in the process control industry
for a means of detecting when a valve seal or valve positioner has
failed or if a tight shut-off valve is leaking. Embodiments of the
present invention provide solutions to these and other problems,
and offer other advantages over the prior art.
SUMMARY OF THE INVENTION
[0006] A leak detection system is provided for detecting a leak
through a closed valve disposed of an industrial process. An
insertable plate is coupled to the valve in-line with the fluid
flow. A sensor couples to the fluid flow. A leak detector is
coupled to the sensor tap and adapted to detect a leak through the
valve.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a simplified block diagram of a valve positioner
with an actuator mechanically coupled to a valve and an acoustic
leak detector according to an embodiment of the present
invention.
[0008] FIG. 2 is a simplified diagram of a valve with a leak
detector coupled between a valve flange and a downstream pipe
segment according to an embodiment of the present invention.
[0009] FIG. 3 is a cross-sectional view of the leak detector of
FIG. 2 configured for acoustic leak detection according to an
embodiment of the present invention.
[0010] FIG. 4A is a cross-sectional view the leak detector of FIG.
2 configured for leak detection using differential pressure
measurements according to an embodiment of the present
invention.
[0011] FIG. 4B is a cross-sectional side-view of an embodiment of
the leak detector of FIG. 4A.
[0012] FIG. 5 is a simplified block diagram of a differential
pressure-based leak detector associated with a valve having
differential pressure ports according to an embodiment of the
present invention.
[0013] FIGS. 6A and 6B are simplified block diagrams of leak
detection systems according to embodiments of the present
invention.
[0014] FIG. 7 is a simplified flow diagram of a method of
diagnosing whether the leak detector is functioning properly
according to one embodiment of the present invention.
[0015] FIG. 8 is a simplified flow diagram of a method of
identifying a type of valve failure based on acoustic signature and
valve position information.
[0016] FIG. 9 is a simplified flow diagram of a method for
estimating valve leakage or degree of failure based on a measured
acoustic signal and valve control information.
[0017] While the above-identified illustrations set forth preferred
embodiments, other embodiments of the present invention are also
contemplated, some of which are noted in the discussion. In all
cases, this disclosure presents the illustrated embodiments of the
present invention by way of representation and not limitation.
Numerous other minor modifications and embodiments can be devised
by those skilled in the art which fall within the scope and spirit
of the principles of this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The present invention describes techniques for monitoring
tight shut-off valves for leakage when the valves are in a fully
closed position. Such tight shut-off valves are typically used in
steam or other high-energy gas or liquid delivery systems within
industrial processes.
[0019] FIG. 1 is a simplified block diagram of tight shut-off valve
assembly 100 with a positioner/transmitter 102 adapted to open and
close the valve. Generally the control room 104 transmits a desired
valve position signal to valve positioner/transmitter 102 over a
two-wire current loop 106. Other communications loops may also be
used, including three-wire and four-wire current loops, as well as
wireless communication links.
[0020] Positioner 102 receives a supply of pneumatic air 108 and
provides a control pressure 110 as a function of the desired valve
position set point from the control center 104 and two variables:
the derivative of the control pressure signal 112 and a sensed
position signal 114. Control pressure 110 provides pressurized air
to actuator 116, which is mechanically connected to a linear stem
control valve 118, though rotary or other types of shut-off valves
are also acceptable for use with the present invention.
[0021] Actuator 116 includes a diaphragm 120, which deflects when
the control pressure 110 from the pressurized air pushes against
it, thereby urging the stem 122 downward. The stem 122 is coupled
to valve closure element or plug 124, which is sized to mate with
valve seat 126 to close the valve 118, thereby stopping fluid flow
between first passageway 128 and second passageway 130 when plug
124 is fully seated. Valve 118 is coupled via flanges 132 to pipe
sections 134 carrying the fluid flow, and fixed by fasteners
133.
[0022] Within positioner 102, a transceiver 140 receives a 4-20 mA
signal from control center 104, but may also receive a signal from,
for example, a handheld communicator, a wireless communications
link, or any other communications path. The magnitude of the
current on the loop is representative of the desired valve
position, but digital information including sensor selection
commands and data may be superimposed on the current according to a
protocol such as HART.RTM., Foundation Field Bus, CAN, or other
digital protocols such as DE, BRAIN.RTM., Infinity or Modbus.RTM..
For critical control, position signal 114 may be temperature
compensated within a microprocessor.
[0023] Control circuit 142 provides a command output 144 as a
function of a desired set point from transceiver 140, position
signal 114, and pressure signal 112. A time derivative circuit 146
within circuit and pneumatics 148 provides a rate feedback signal
(a derivative of the pressure signal 112) with respect to time for
the control algorithm within circuit 146. Preferably, the pressure
signal is used as a rate feedback signal, as a torque signal, or a
force signal, depending on the specific implementation.
[0024] The transducer circuit and pneumatics 148 preferably uses an
adaptive control algorithm, which makes use of available sensed
signals such as pressure, position, force, packing and seat wear to
fine tune proportional-integral-derivative control features.
Generally, the transducer circuit and pneumatics 148 receives a
0-200 pounds per square inch (PSI) supply of air 108 and provides
control pressure 110 as a function of the control signal 144 from
control circuitry 142. Sensing means 150 senses signals from a
pressure sensor 152 of control pressure 110 and a mechanical
position sensor 154, and provides conditioned pressure 112 and
position 114 measurements to the control circuitry 142.
[0025] A sensor 160 is coupled to valve 118 adjacent to second
passageway 130 and is adapted to sense acoustic signals within the
second passageway 130 caused by the fluid flowing through the valve
118. The sensed acoustic signals 162 are then processed by leak
detector 156, which compares the sensed acoustic signal 162 to a
stored acoustic signature 159 or template retrieved from memory 158
to determine if the valve 118 is leaking. In one embodiment, the
leak detector 156 monitors the acoustic signature of the valve 118
independent of the valve position (the position of the stem 122 and
plug 124). In an alternative embodiment, leak detector 156
generates a leak output 164 based on both a comparison of the
sensed acoustic signal 162 with the stored signature 159 retrieved
from memory 158 and a position control signal 166. In another
embodiment, leak detector 156 generates a leak output signal 165
based on both a comparison of the sensed acoustic signal 162 with
the stored signature 159 retrieved from memory 158 and a measured
mechanical position 154. In yet another embodiment, the leak
detector 156 only compares the acoustic signal 162 with the stored
acoustic signature 159 from memory 158 upon receipt of a trigger
168 either from the control center 104 or from the control
circuitry 142. The resulting output 164 would then be a "blind"
measurement, meaning that the output is generated without
consideration of the desired or actual valve position. The output
164 can then be processed either by the control circuitry 142 or by
control center 104, depending on the specific implementation.
[0026] Finally, though the various functional blocks are called out
as separate elements, some of the function blocks may be combined.
For example, the leak detector 156 may include the sensor 160.
Specifically, the leak detector may include the sensor, a
microprocessor, and a memory, as well as transmitter circuitry
adapted to send and receive signals to a from a control center.
[0027] FIG. 2 is a simplified block diagram of a process control
valve assembly 200 according to an embodiment of the present
invention. Valve 202 is communicatively coupled with control center
204 through valve monitoring and control electronics 206 via
communications link 208. Much of the detail provided with respect
to the valve is omitted for simplicity.
[0028] As previously discussed, supply 210 provides pressurized
fluid to the valve monitoring and control electronics 206, which
controls the position of stem 212 and plug 214. The valve body 216
includes a first passageway 218 coupled to a second passageway 220
through valve seat 222. As the stem 212 advances downward, the plug
214 mates with valve seat 222 to halt fluid flow between the first
and second passageways 218,220.
[0029] Flanges 224 couple valve 216 to flanges 226 of the adjacent
pipe sections 228. A leak detection plate 230 is positioned between
the valve 216 and pipe section 228 downstream from the valve 216
and in-line with the fluid flow. Fasteners 227 fix the pipe
sections 228 to valve 216, and on the downstream side fasteners 227
fix the pipe section 228 to plate 230 and valve 216. Preferably,
the flanges 224 are in close proximity to the valve seat 222, and
optimally, one of the flanges 224 is integral to the valve body
216.
[0030] Plate 230 is provided with one or more sensor taps (shown in
FIGS. 3-5) for receiving sensors, which are coupled to leak
detector 232. The sensors may be acoustic sensors or pressure
sensors having sufficient bandwidth to capture the target audio
signal. Leak detector 232 is provided with a sensor 233, a memory
234 and a microprocessor 236 for comparing the measured downstream
signal against a reference signal stored in memory 234 and for
generating an output diagnostic signal 238 to the control center
204. The sensor 233 is preferably an acoustic sensor, but may be a
pressure sensor or a differential pressure sensor adapted to
measure process-generated signals within the desired acoustic
frequency range, which may or may not fall within an audible
frequency range.
[0031] For high-energy process fluids, as the valve closes (meaning
plug 214 advances toward and into valve seat 222), the flow path
through the valve 216 narrows, and acoustic noise is generated.
This effect is sometimes noticeable with respect to a standard
household faucet, which generates an audibly changing noise.
Typically, acoustic noise is generated by the fluid flowing through
the valve 216, and the frequency of the acoustic noise increases
until it abruptly stops (or changes) when the valve 216 is fully
closed (meaning that the plug 214 is fully seated in valve seat
222. It should be understood that in some instances, the acoustic
noise falls within an audible frequency range. In other
embodiments, the acoustic noise is at a frequency outside of an
audible frequency range, but is nevertheless detectable by acoustic
sensors or by pressure sensors capable of measuring the frequency
range of the acoustic noise.
[0032] By evaluating the noise signal of the process flowing
through the valve as detected by the acoustic sensor, it is
possible to detect when a valve has not achieved a tight shut-off.
If the valve 216 does not achieve a tight shut-off condition, the
acoustic noise remains at an intermediate value of frequency and
amplitude.
[0033] By monitoring an acoustic frequency progression (from an
open valve position to closed valve position) on a process control
valve 202, it is possible to determine if the valve 202 is fully
shut-off or if the valve 202 is allowing process fluid to leak into
the downstream pipe segment 228. Microprocessor 236 provided in
leak detector 232 is used to process acoustic sensor information
and to provide both a diagnostic output 238, and optionally an
output 240 (shown in phantom) that is responsive to the acoustic
signal picked up by the sensor, which may be indicative of, for
example, a valve position. In this instance, the valve position may
be inferred based on the acoustic frequency relative to a reference
noise signature.
[0034] First, a reference pattern representative of the acoustic
signal generated while the valve is adjusted from an open position
to a fully closed (tight shut-off) condition is stored. This stored
reference pattern contains frequency and amplitude sequential
information that can be used as a reference template to track valve
closing progress. If a frequency and amplitude pattern over time
matches the template, but does not end up in a tight shut-off
condition, the electronics can output an alarm or warning
indicative of a leaky valve. By observing the progress of the
measured signal relative to the template and noting where the end
point occurred that indicated tight shut-off was not achieved, an
amount of leakage (or degree of failure) can be estimated.
[0035] Detecting a leaking valve is accomplished as follows. When
the valve 216 is between 80% closed and fully open, the flow noise
through the valve 216 is substantially constant. However, when the
valve begins to shut off (i.e. when the valve plug 214 is seated
within valve seat 222 so as to close off fluid flow through the
valve 216 by approximately 81% and 99%), the noise generated by the
process flowing through the valve 216 begins to increase in both
amplitude and frequency. Finally, as the valve 216 achieves a tight
shut-off condition (i.e. the plug 214 is fully seated in the valve
seat 222 such that the passageway is 100% closed), the noise signal
decreases rapidly from its maximum frequency and amplitude to
essentially zero.
[0036] It should be understood by workers skilled in the art that
process noise is almost always present. Nevertheless, as the valve
closes, the process noise as measured by the sensor changes. The
microprocessor 236 is adapted to compare the measured acoustic
frequency against a stored template or acoustic signature from
memory 234, and can detect an acoustic change when the valve is
fully shut. Leak detector 232 is adapted to separate process
(background) noise from the sensed signal in order to isolate
leak-related noise.
[0037] It is also possible to detect developing problems in a
process based on changes in the acoustic noise signature as
compared to the baseline signature stored in memory 234. In
particular, changes in background noise may be indicative of
problems developing in fixed equipment in the industrial process,
such as bearing failure, pump failure and the like. For example, as
bearings in rotatable equipment begin to fail, they often produce a
squealing noise, which is an early sign of potential bearing
failure. If such equipment starts generating additional process
noise, that noise aggregates with the existing process noise. A
significant change in process noise amplitude or the convolution of
signals of frequencies outside of the normal range (and which are
not represented in the stored acoustic signature) may be indicative
of a developing problem with fixed process equipment.
[0038] In one embodiment, in addition to generating a diagnostic
signal relating to the valve 216, microprocessor 236 is adapted to
provide a predictive diagnostic signal representative of the
overall health of the process equipment. This optional process
equipment diagnostic signal is based on a difference between the
measured background noise and the background noise of the stored
reference signature. Specifically, if the measured background noise
changes from a stored reference signature by more than a
predetermined limit, the leak detector 232 is adapted to generate
an alarm signal to the control center 204.
[0039] In general, the electronics can be co-located in a single
package (such as shown in FIG. 1). Alternatively, as shown in FIG.
2, the leak detector 232 may be separate from the valve monitoring
and control electronics 206.
[0040] In a preferred embodiment, the leak detector 232 provides
the capability of having initial values set via an external device
or via a local operator interface (LOI) 242, which can be integral
to the transmitter 244 containing leak detector 232. In a preferred
embodiment, the electronics support bi-directional communication
via a digital bus like HART, Foundation Field Bus, CAN, or any
other bi-directional communications standards. This communication
capability is used for setting initial values and outputting
various levels of alarm criticality. For this type of meter, the
electronics are typically 4-20 mA loop powered.
[0041] FIG. 3 is a simplified cross-sectional view of an acoustic
leak detector 300 including plate 302, which is adapted to host
transmitter 304. The transmitter 304 is adapted to detect acoustic
signals caused by fluid flowing through the valve (such as that
shown in FIG. 2) and to send measurement and diagnostic signals to
a control center 306.
[0042] Generally, plate 302 has a ring-shaped body 308 defining a
lumen 310 sized to mate with a downstream pipe segment (such as
element 228 in FIG. 2). Plate 302 is provided with extension 312
adapted to provide a visual reference to an operator in the field
as well as a positioning element for positioning the plate 302
between the valve flange and the downstream pipe segment during
installation. Finally, tap 314 is provided in the body 308 for
receiving a sensing element 316. In general, the tap 314 extends
almost an entire thickness of the wall of plate 302. In an
alternative embodiment, the tap 314 extends entirely through the
wall of the body 308 and into the lumen 310, and the sensing
element 316 is adapted to seal the tap opening and to be in direct
contact with the fluid flow during operation.
[0043] Transmitter 304 includes an acoustic sensor 318 adapted to
detect an acoustic signal measured by the sensing element 316.
Transmitter 304 includes a microprocessor 320 for conditioning the
measured acoustic signal. Transceiver 322 is adapted to send
measurement and diagnostic signals to the control center 306 and to
receive control signals from the control center 306. Finally, a
leak detector 324 is provided for detecting a leak through a valve
based on changes in a measured acoustic signal as compared to a
baseline signal stored in memory 326.
[0044] In general, all of the elements of transmitter 304 are shown
in phantom, in part, because the various functions and
functionality may be combined into a single circuit element or
multiple circuit and/or software elements, depending on the
specific implementation. In particular, each element (318 through
326) is shown only to illustrate the functional capabilities of the
acoustic transmitter 304.
[0045] FIG. 4A illustrates an alternative embodiment of the leak
detector 400. Leak detector 400 includes plate 402 for coupling
between the valve and the downstream pipe segment and in-line with
the fluid flow. The plate 402 is coupled to a differential pressure
transmitter 404, which is in turn coupled to a control center 406.
Plate 402 includes an extension element 408, which can be used
during installation to position and orient the plate 402. As in
FIG. 3, plate 402 defines a lumen 410, which is generally sized to
coupled to a chamber of a valve between the valve and a downstream
pipe segment. Additionally, the lumen 410 of the plate 402 is
fabricated with a flow restriction element 412 including a variable
area flow region 414 that narrows to a point 415. Preferably, the
plate 402 can be inserted between the tight shut-off valve and a
downstream pipe segment.
[0046] The variable area flow region 414 is sized such that the
head of the fluid between the valve outlet and the insertable plate
402 increases with increased leak (flow) rate. In FIG. 4A, this
variable area feature 414 is exaggerated in size for clarity. In
general, the v-shaped variable area 414 makes the differential
pressure transmitter more sensitive to low flows. Two pressure
ports 416 and 418 are provided in the wall of plate 402, and a
cross-bore extends from the valve side of the plate 402 to the
pressure port 418.
[0047] A differential pressure transmitter 404 couples to sensors
417 and 419 disposed within pressure ports 416 and 418 to measure a
differential pressure within the lumen 410 of the plate 402 and by
extension through the associated valve and downstream pipe segment.
The differential pressure transmitter 404 is provided with a leak
detector 422 for identifying a leak through the valve based on
variations in the differential pressure as compared with a baseline
differential pressure stored in a memory. Leak detector 422 is
shown in phantom and overlapping differential transmitter 404 to
indicate that the leak detector 422 may be contained within the
differential transmitter 404 or may be separate. Additionally, the
specific function of the leak detector 422 may be performed by the
control center 406 based on measurement data received from the
differential pressure transmitter 406.
[0048] In general, pressure port 416 is positioned near the top of
the lumen 410 to monitor the head of the process fluid as it flows
through the flow restriction plate 402. Pressure port 418 is
positioned near the bottom of the lumen 410 to measure the pipe
static pressure, such that the pressure measurement is a true
differential pressure. Pressure port 416 and pressure port 418
extend into the plate 402 in a direction that is substantially
transverse to the direction fluid flow through the plate 402 (when
the plate 402 is coupled to a valve). To measure the differential
pressure, the ports 416 and 418 are preferably substantially
aligned along an axis transverse to the direction of flow (as shown
in FIG. 4B) The cross bore 420 extends through the plate 402 and
into the port 418. As fluid builds up in the variable area 414,
static pressure builds in the cross-bore 420 and is measured by the
pressure sensor in pressure port 418. Though the present embodiment
has been described with respect to differential pressure sensors,
two gage pressure or absolute pressure sensors could also be used
to make this measurement.
[0049] Detecting a leaking valve is accomplished as follows. When
the valve is open, the downstream pipe is substantially full of
process fluid. When the valve is shut off, the fluid in the pipe
begins to drain. For the pipe full condition, both pressure ports
416 and 418 are covered by fluid. As long as this is true, the
measured differential pressure remains substantially unchanged.
Once the fluid level in the pipe drops below the top port 416, the
transmitter 404 measures the fluid head in the pipe. If the valve
tightly shuts off, the fluid head continues to decrease until the
height of the fluid is the same as the height of the bottom of the
variable area (channel) 414 of flow restriction 412. At this point,
no additional flow occurs, and the differential pressure
measurement reaches a plateau and remains substantially unchanging.
The transmitter 404 measures the fluid head during tight shut-off
conditions, and stores the head measurement in a memory 424 as a
reference value.
[0050] If the valve is leaking after being shut off, some process
fluid leaks into the area between the plate 402 and the valve. This
fluid flows out over the flow restriction 412 and variable area 414
in the plate 402. The variable area 414 is shaped to readily detect
changes in head for small increments of flow when the flow is near
a zero-flow (or no-flow) condition. As fluid leaks past the valve
seal, the differential pressure measurement changes appreciably. If
the differential pressure measurement changes by more than a
predetermined amount, an alarm or warning is generated by the leak
detector 422 and provided on the output of transmitter 404. In this
embodiment, the installation design is configured such that the
downstream piping from the valve drains when the valve is shut
off.
[0051] In FIG. 4B, the plate 402 is shown in situ and with partial
cross-sectioning. Plate 402 preferably includes upper bore
(pressure tap) 416 and lower bore (pressure tap) 418 substantially
aligned along axis 432, which extends transverse to the direction
of flow. The plate 402 is disposed between valve 426 and downstream
pipe segment 428 and is held in place by clamping means 430.
[0052] As shown, the cross bore 420 (shown in phantom) extends from
an upstream surface 421 of the plate 420 to the lower bore 418. The
cross bore 420 is disposed within the flow restriction 412 and
exposed to the fluid flow. Fluid leakage through a closed valve
received from the valve portion 426 builds up behind the flow
restriction 412 and flows through the variable area v-shaped
portion of the flow restriction 412 (element 414 in FIG. 4A) along
the bottom of the v-shaped area (indicated by phantom line 415). As
fluid builds up behind the flow restriction 412, some of the
leakage fluid flows into the cross bore 420, and a sensor disposed
within the lower bore (pressure tap) 418 can be adapted to measure
the static pressure within the cross-bore. A differential pressure
between the static pressure measurement from the sensor in the
lower bore 418 as compared with a pressure measurement by a sensor
in upper bore 416 may be used to detect very small leaks through
the valve.
[0053] The bottom portion 415 of the variable area flow restriction
is sloped away from the valve 426 toward the downstream pipe
segment 428 to encourage drainage. If the valve is tightly shut
off, fluid drains away from the plate 402, and after a brief
period, all fluid drains away from the flow restriction across the
bottom portion 415 and into the downstream pipe segment 428. If a
leak persists, fluid continues to flow into the valve portion 426,
builds up behind the flow restriction 412 and flows into the cross
bore 420, thereby creating a differential pressure. The leak
detector 422 of FIG. 4A can be used to identify differential
pressures indicative of a leak condition. If a leak is detected, a
control signal may be generated to, for example, a pneumatic
actuator to tighten the valve into a valve seat. Alternatively, an
alarm signal may be generated to the control center (such as
control center 406). In either case, the differential pressure taps
416 and 418 provide a means for detection of a leaking valve.
[0054] FIG. 5 illustrates a simplified block diagram of a tight
shut-off valve with a leak detection system 500 according to an
alternative embodiment of the present invention. In this
embodiment, the tapered flow restriction and pressure ports (or
taps) of FIGS. 4A and 4B are incorporated into the valve body,
eliminating the need for the separate plate.
[0055] The leak detection system 500 includes a transmitter 502
coupled to a pneumatic valve 504 and adapted to open and close the
valve. Additionally, the transmitter 502 is in communication with
control center 506 via communications link 508. In one embodiment,
the communications link 508 is a two-wire loop; however, other
communication links may be used as well, including wireless links,
or three or four-wire links. Generally, the control center 506
transmits a desired valve position signal to valve
positioner/transmitter 502 over a two-wire current loop 508. Other
communications loops may also be used, including three-wire and
four-wire current loops, as well as wireless communication
links.
[0056] Positioner/transmitter 502 receives a supply of pneumatic
air 512 and provides a control pressure 514 as a function of the
desired valve position set point from the control center 506 and
two variables: the derivative of the control pressure signal 516
and a sensed position signal 518. Control pressure 514 provides
pressurized air to actuator 504, which is mechanically connected to
a linear stem control valve 520, though rotary or other types of
shut-off valves are also acceptable for use with the present
invention.
[0057] Actuator 522 includes a diaphragm 524, which deflects when
the control pressure 514 from the pressurized air pushes against
it, thereby urging the stem 526 downward. The stem 526 is coupled
to valve plug 528, which is sized to mate with valve seat 530 to
close the valve 520, thereby stopping fluid flow between first
passageway 532 and second passageway 534 when plug 528 is fully
seated. Valve 520 is coupled to process pipe sections 540, which
carries a fluid flow. The valve 520 is coupled to pipe sections 540
via valve flanges 536 and pipe flanges 538, which are fixed by
fasteners 542.
[0058] Within positioner/transmitter 502, transceiver 510 receives
a 4-20 mA signal from control center 506, but may also receive a
signal from, for example, a handheld communicator, a wireless
communications link, or any other communications path. The
magnitude of the current on the loop is representative of the
desired valve position, but digital information including sensor
selection commands and data may be superimposed on the current
according to a protocol such as HART.RTM., Foundation Field Bus,
CAN, or other digital protocols such as DE, BRAIN.RTM., Infinity or
Modbus.RTM.. For critical control, position signal 518 may be
temperature compensated within a microprocessor.
[0059] Control circuitry 544 provides a command output 546 as a
function of a desired set point from transceiver 510, position
signal 518, and pressure signal 516. Transducer circuit and
pneumatics 548 controls pressure 514 based on control signal 546.
In one embodiment, a time derivative function (not shown) provides
a rate feedback signal (a derivative of the pressure signal 516)
with respect to time for the control algorithm within control
circuitry 544. Preferably, the pressure signal 516 is used as a
rate feedback signal, as a torque signal, or a force signal,
depending on the specific implementation.
[0060] The transducer circuit and pneumatics 548 preferably uses an
adaptive control algorithm, which makes use of available sensed
signals such as pressure, position, force, packing and seat wear to
fine tune proportional-integral-derivative control features.
Generally, the transducer circuit and pneumatics 548 receives a
0-200 pounds per square inch (PSI) supply of air 512 and provides
control pressure 514 as a function of the control signal 546 from
control circuitry 544. Sensing means 550 senses signals from a
pressure sensor 552 of control pressure 514 and a mechanical
position sensor 554, and provides conditioned pressure 516 and
position 518 measurements to the control circuitry 544.
[0061] A differential pressure sensor 556 is coupled to valve 520
adjacent to second passageway 534 and is adapted to sense acoustic
signals within the second passageway 534 caused by the fluid
flowing through the valve 520. In particular, upper pressure tap
558 (or pressure port) and lower pressure tap 560 are provided in
the housing of the valve 520. A cross-bore 561 may be provided in a
variable area flow restriction element 562 extending from a surface
of the flow restriction element 562 facing in a direction of the
valve seat 530. Fluid leaking through the valve builds up behind
the flow restriction element 562, filling the cross bore 561,
thereby providing a static pressure within the cross bore 561 which
can be measured by a sensor within tap 560, which intersects the
cross-bore 561.
[0062] In general, sensing means (not shown) may be positioned
within taps 558,560 and coupled to the differential pressure sensor
556 for measuring a differential pressure within the second
passageway 534. A flow restriction element 562 with a variable area
564 is fabricated within the second passageway 534 for measuring a
low fluid flow through the valve 520.
[0063] As previously discussed, the upper tap 558 measures a head
of the process fluid flowing within the second passageway 534. The
lower tap 560 measures the static pressure of the valve 562, based
on fluid within the cross-bore 561. When the valve 520 is shut off
(meaning that the plug 528 is seated in valve seat 530), the fluid
flow within the passageway 534 begins to drain. When both pressure
taps 558,560 are covered by fluid, the measured differential
pressure does not change (and the measured pressure at each port
558 and 560 is substantially the same). However, as the fluid
drains below the level of the upper tap 558, the transmitter 502
measures the fluid head within the valve 520. If the valve 520 is
tightly closed, the fluid head continues to decrease until the
height of the fluid is zero and no additional flow occurs. At this
point, the pattern associated with the differential pressure
measurement plateaus. The head measurement can be stored in memory
566, and can be used by leak detector 568 to identify valve leaks
if a change in the head measurement at its low point as compared to
the stored head measurement exceeds a predetermined limit.
[0064] The leak detector 568 may be additionally enhanced by making
use of the valve control signal 546 (indicated by arrow 570). In
particular, the leak detector 568 can monitor the valve control
signal 570 to verify tight shut off when a closed valve is
requested by the control center 506. If the flow noise amplitude
and frequency do not indicate that a tight shut-off condition has
been achieved, the leak detector 568 through the transceiver 510
can transmit a diagnostic warning or alarm that the valve 520 may
be leaking. Moreover, by tracking the valve control signal 546,570,
the leak detector 568 can provide secondary indicia of valve
position based on the sensed acoustic frequency of fluid flowing
through the valve 520 as compared to an acoustic frequency profile
stored in memory 566.
[0065] FIGS. 6A and 6B are simplified block diagrams illustrating
two possible implementations of the leak detector of the present
invention. In FIG. 6A, the leak detection system 600 includes a
leak detector 602 coupled to a sensor 604 and a memory 606. The
leak detector 602 receives a measurement signal from the sensor 604
and a valve position signal from a valve position sensor 608. The
leak detector 602 compares the measurement signal from sensor 604
to a stored measurement signal from memory 606, and determines
whether the valve is leaking, taking into account the valve
position measurement of the valve position sensor 608. If the
measurement from sensor 604 indicates fluid flow, but the valve
position sensor 608 indicates the valve is open, there is no leak.
On the other hand, if the valve position sensor 608 indicates a
fully closed valve but sensor 604 indicates fluid flow, leak
detector 602 generates an alarm 610 indicative of a leak on its
output.
[0066] In general, the sensor 604 may be an acoustic sensor, a
differential pressure sensor, or any other type of sensor adapted
to detect low fluid flow in a downstream pipe section or in the
secondary passageway of a valve.
[0067] FIG. 6B illustrates an alternative embodiment of a leak
detection system 620 according to an embodiment of the present
invention. The leak detection system 620 includes leak detector
622, which is coupled to sensor 624 and memory 626. The sensor 624
is coupled to an industrial process adjacent to or integral with a
secondary passageway of a valve. The sensor 624 detects fluid flow
within the lumen of the pipe section or valve, and the leak
detector compares the measured fluid flow against a stored
signature from memory 626. In a preferred embodiment, fluid flow is
measured according to an acoustic signature generated by the fluid
passing through the valve. The acoustic signature may or may not
fall within an audible frequency range, but is nevertheless
detectable by an acoustic sensor or by pressure sensors having
sufficient bandwidth to capture the target acoustic signal.
[0068] The leak detector 622 utilizes a valve position control
signal or detector trigger signal 628. The valve position control
signal (indicating a desired valve position) is used by the leak
detector 628 to provide secondary indicia of whether the desired
valve position is achieved. Specifically, the valve is only
partially closed, the positioning of the valve plug should cause
the acoustic signature to change, and the change should correspond
to an acoustic frequency of the stored reference. If the valve plug
causes an acoustic frequency different from the stored reference
frequency for the desired plug position, the leak detector 622
generates an output indicating that the valve may be more or less
closed than desired. The extent of deviation from the stored
reference frequency may provide an indication of the extent to
which the valve positioner over-shot or undershot the desired valve
position.
[0069] Alternatively, if the signal 628 is a detector trigger
signal, the controller can initiate a test by the leak detector
622. The leak detector 622, upon receipt of the trigger signal 628,
polls the sensor 624 and compares the retrieved measurement signal
against a stored measurement signal from memory 626. If the
difference between the two signals exceeds a predetermined limit,
an alarm signal can be placed on the leak detector output 630.
[0070] While the present invention has largely been described with
respect to a valve having a pneumatic actuator for physically
positioning the valve, other actuators such as electric, hydraulic,
and the like may be used with the present invention as well. In
general, the present invention is intended for tight shut-off
applications, such as in the food processing industry where heat
deliver (via steam) or ingredient delivery to the batch must be
tightly controlled.
[0071] As used herein, the term tight shut-off refers to a
condition where fluid flow through the valve is reduced to zero
fluid flow or to fluid flow at such a slow rate that it has no
impact on the batch process.
[0072] In an alternative embodiment, particularly for use with
steam applications, the pressure or acoustic detectors can be
replaced with a differential temperature transmitter. In
particular, when the valve is closed, steam within the pipe will
condense and flow out into the downstream pipe segment. An upper
tap and lower tap would have a wide temperature differential if
steam were slowly leaking through the valve. In one embodiment, the
steam would quickly condenses, and the upper temperature sensor
measures a much lower temperature than the lower temperature
sensor. Alternatively, the steam escapes through the "closed valve"
rapidly, causing the upper temperature sensor to continue to
measure a high temperature, while the lower temperature sensor
(positioned at the bottom of the valve) cools (after all liquid
should have drained from the valve).
[0073] In general, the present invention provides an on-line method
of detecting if a valve is leaking when it should be shut-off.
Moreover, the variation from the frequency/amplitude template can
provide an indication of the severity or extent of the leak. The
present invention is also simple to implement by a user, in part,
because no welding or hot tapping is required for installation. The
sensor can be readily clamped to the valve body. Alternatively, an
orifice plate with an associated sensor can be readily inserted
between the valve and the downstream pipe section.
[0074] Additionally, the present invention provides a simple means
for testing the leak detector (acoustic sensor), simply by
detecting if normal flow noise is present during operation when the
valve is open. A differential pressure transmitter can be used as
the acoustic sensor if its frequency response is high enough. The
present invention provides a low cost leak detection scheme, as
compared to costs associated with installation of additional
valving, piping, venting, and hardware to deal with critical valves
that require tight shut-off.
[0075] In general, the electronics include circuitry and/or
software adapted to receive the pressure signal and to condition
the pressure signal. Additionally, the electronics includes a leak
detector (or leak detection function) adapted to identify
unacceptable values of leakage flow. Additionally, the electronics
include a memory for storing set-up values, and, at a minimum, a
digital processing capability. In a preferred embodiment, the
memory is a non-volatile memory.
[0076] As a diagnostic, any plugging of the flow restriction
geometry may appear as a leak condition at shut off. As part of
evaluating any alarm or warning, the plate can be easily removed
and checked for plugging before proceeding to determine if the
valve seals need servicing. In an alternative embodiment, the
tapered flow restriction and the pressure ports can be incorporated
directly into the valve body, thereby eliminating the need for a
separate plate.
[0077] FIG. 7 illustrates a method of diagnosing whether the leak
detector is working according to an embodiment of the present
invention. First, the valve is opened (step 700). The sensor
detects the open valve signature of the fluid flowing through the
open valve (step 702). The leak detector retrieves the stored
reference signature of the open valve (step 704) and compares the
measured open valve signature against the stored open valve
signature (step 706). If a difference between the measured open
valve signature and the stored open valve (reference) signature
exceeds a predetermined limit, an alarm indicative of a problem
with the leak detector is generated (step 708).
[0078] FIG. 8 is a simplified flow diagram of a method of
diagnosing valve failure according to an embodiment of the present
invention. The leak detector measures an acoustic signature of a
valve (step 800). The leak detector retrieves valve position
information (step 802) from, for example, a valve stem position
sensor, control circuitry, or other elements adapted to monitor
valve position. The leak detector tests the valve position
information to see if the valve is closed (step 804). If the valve
is closed, the leak detector compares the measured valve signature
to a stored reference signature at the "closed" position (step
806). If the measured valve signature indicates the valve is closed
(step 808), the valve is closed and the leak detector continues to
monitor the valve (block 810). If the measured signature does not
match the reference signature at the closed position (step 808),
the valve is not shut off, and an alarm is generated indicating a
leaking valve (step 812).
[0079] If the valve is not closed (step 804), the measured acoustic
signature of the valve is compared to a stored reference signature
at the retrieved valve position (step 814). If the measured
signature matches the stored reference signature at the valve
position (step 816), the leak detector continues to monitor the
valve (step 810). If the measured signature does not match the
stored reference signature at the valve position (step 816), the
leak detector generates an alarm indicating that there is a problem
with the valve positioner (step 818).
[0080] In this instance, valve position is being monitored by the
positioner or controller circuitry, so the acoustic leak detector
is adapted to provide leaky valve diagnostics as well as secondary
confirmation of valve position. If the positioner is not
functioning properly, the leak detector is unable to match the
measured signal against the reference signal at the desired valve
position, and a valve failure (positioner failure) alarm can be
generated.
[0081] FIG. 9 is a simplified flow diagram of a leaky valve
diagnostic method for estimating leakage based on a measured
acoustic signal. In general, a properly functioning valve is
monitored as it is adjusted from a fully open to a fully closed
position, and the acoustic pattern associated with the adjustment
of the valve is stored in memory as a reference pattern. As used
herein, the phrase "properly functioning" refers to a valve that
achieves a tight shut-off when fully closed. During operation, the
leak detector monitors the valve control signals (step 900). Upon
receipt of a valve adjustment control signal, the leak detector
monitors the changing acoustic pattern of the valve as the valve is
adjusted from a first position to a second position (step 902). The
leak detector compares the measured acoustic pattern to the stored
reference pattern (step 904). If the patterns match (step 906), the
valve is functioning properly and the leak detector continues
monitoring the valve (step 908).
[0082] If the patterns do not match (step 906), the leak detector
identifies an endpoint in the measured acoustic pattern
corresponding to the second valve position (step 910). The leak
detector calculates the distance between the identified endpoint
and the point in the stored reference pattern corresponding to the
second valve position (step 912). The distance calculation is a
measure of the disparity between the identified endpoint in the
measured acoustic pattern as compared to the point in the stored
acoustic pattern. In one embodiment, the distance is the squared
Euclidian distance which is the sum of squared differences across a
set of variables. The leak detector then estimates the amount of
leakage or degree of failure of the valve based on the endpoint
(step 914). More specifically, the leak detector is adapted to
estimate the amount of leakage or degree of failure of the valve
based on the calculated distance. Finally, the leak detector 914
generates an alarm indicative of valve failure and indicative of
the amount of leakage or degree of failure of the valve (step
916).
[0083] In general, the calculated distance between the endpoint and
the desired point in the reference pattern may provide an
indication of the degree of failure or extent of leakage. In one
embodiment, the distance (D) provides an indication of the extent
of leakage according to the following linear equation E=kD where E
is the extent of leakage or failure, D is the calculated distance,
and k is a scalar. In this embodiment, scalar (k) may include a
factor related to the fluid flow rate through the system.
[0084] In a batch process, the amount of leakage or degree of
failure may provide an indication of whether a batch may be
salvaged or if it must be discarded. Moreover, the degree of
leakage or failure is indicative of a deviation from a reference
pattern, which may be used to predict extent of fouling, corrosion,
or damage to the valve seat in order to alert an operator to
inspect the valve before beginning a new batch in order to avert an
unexpected valve failure.
[0085] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *