U.S. patent application number 13/862683 was filed with the patent office on 2014-05-15 for method and apparatus for continuously monitoring interstitual regions in gasoline storage facilities and pipelines.
This patent application is currently assigned to Franklin Fueling Systems, Inc.. The applicant listed for this patent is Franklin Fueling Systems, Inc.. Invention is credited to Donald P. Kenney, Walt Simmons.
Application Number | 20140130578 13/862683 |
Document ID | / |
Family ID | 37686077 |
Filed Date | 2014-05-15 |
United States Patent
Application |
20140130578 |
Kind Code |
A1 |
Kenney; Donald P. ; et
al. |
May 15, 2014 |
METHOD AND APPARATUS FOR CONTINUOUSLY MONITORING INTERSTITUAL
REGIONS IN GASOLINE STORAGE FACILITIES AND PIPELINES
Abstract
An underground storage system includes a primary containment
unit and a secondary containment unit. The underground storage
system further includes a leak detection system which is fluidly
connected to the secondary containment system, and which is adapted
to detect fluid leaks in the primary containment system and the
secondary containment system.
Inventors: |
Kenney; Donald P.;
(McFarland, WI) ; Simmons; Walt; (Madison,
WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Franklin Fueling Systems, Inc.; |
|
|
US |
|
|
Assignee: |
Franklin Fueling Systems,
Inc.
Madison
WI
|
Family ID: |
37686077 |
Appl. No.: |
13/862683 |
Filed: |
April 15, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13309319 |
Dec 1, 2011 |
8418531 |
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13862683 |
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12505716 |
Jul 20, 2009 |
8069705 |
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13309319 |
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11967760 |
Dec 31, 2007 |
7578169 |
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12505716 |
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11253341 |
Oct 19, 2005 |
7334456 |
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11967760 |
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10842894 |
May 11, 2004 |
7051579 |
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11253341 |
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Current U.S.
Class: |
73/49.2 |
Current CPC
Class: |
G01M 3/32 20130101; G01M
3/3263 20130101; G01M 3/2892 20130101; G01M 3/3272 20130101; G01M
3/3236 20130101 |
Class at
Publication: |
73/49.2 |
International
Class: |
G01M 3/32 20060101
G01M003/32 |
Claims
1. An underground storage system comprising: a primary containment
unit; a secondary containment unit arranged to provide a sealed
interstitial space relative to the primary containment unit; a
vacuum system for periodically applying a vacuum to the secondary
containment unit; and a leak detection system which determines a
rate of change of vacuum pressure in the secondary containment unit
as the vacuum system applies the vacuum, wherein the leak detection
system is fluidly connected to the secondary containment unit and
adapted to learn a vacuum rate of change of the secondary
containment unit when the secondary containment unit is void of
liquid, as the vacuum system applies the vacuum; wherein the leak
detection system is adapted to detect a presence of liquid in the
secondary containment unit if the determined rate of change of
vacuum pressure in the secondary containment unit departs from the
learned vacuum rate of change of the secondary containment system
by a threshold amount.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/309,319, filed Dec. 1, 2011, issuing as
U.S. Pat. No. 8,418,531; which is a continuation of U.S. patent
application Ser. No. 12/505,716, filed Jul. 20, 2009, now U.S. Pat.
No. 8,069,705; which is a continuation of U.S. patent application
Ser. No. 11/967,760, filed Dec. 31, 2007, now U.S. Pat. No.
7,578,169; which is a divisional of U.S. Ser. No. 11/253,341, filed
October 19, 2005, now U.S. Pat. No. 7,334,456; which is a
continuation-in-part of U.S. patent application Ser. No.
10/842,891, filed May 11, 2001, now U.S. Pat. No. 7,051,579, the
disclosures of which are hereby expressly incorporated herein by
reference.
TECHNICAL FIELD
[0002] This patent is generally directed to an apparatus and method
for interstitial monitoring, and more particularly to a system for
continuously monitoring the pressure and vacuum levels within the
interstitial space of an underground storage tank system.
BACKGROUND
[0003] Current and proposed state and federal regulations require
that underground storage tanks used for the storage of hazardous
substances meet certain environmental safety requirements. In
particular, these environmental regulations require that the
underground storage systems include a primary containment unit and
a secondary containment unit. Moreover, the primary and secondary
containment units are required to comply with the environmental
standards that require undeground storage tank systems to be
product tight. The term "product tight," for purposes of these
environmental regulations, is generally defined as impervious to
the substance that is contained to prevent seepage of the substance
from the primary containment unit. Moreover, for tank to be product
tight, the tank cannot be subject to physical or chemical
deterioration by the contained substance over the useful life of
the tank. Further, these regulations require that owners or
operators of an underground storage tank system with a
single-walled component located within 1,000 feet of a public
drinking water well implement a program of enhanced leak detection
or monitoring.
[0004] One known method of monitoring leaks disclosed in U.S. Pat.
No. 6,489,894, entitled "Leak Detection Device for Double Wall
Pipeline Systems and Container Systems," uses a leak detector with
vacuum pump including a pressure-dependent switch and an alarm
device to detect leaks in a double-walled pipeline or container
system. The disclosed leak detector is adapted to simultaneously
monitor several containers connected to a collecting main and a
vacuum pump by vacuum lines. Each monitored container incorporates
a vacuum connector or valve to fluidly connect a control space to
the leak detector. Each vacuum line has a first liquid lock
arranged at the vacuum connector to block liquid that has leaked
into the vacuum lines from a leaky container from penetrating into
the control spaces of the leak-free containers. A second liquid
lock is arranged in the collecting main to prevent liquid from
entering the vacuum pump. While this method can detect leaks within
the control space of a container, it is a mechanically complex
system requiring a great deal of materials and set-up time.
[0005] Other methods of monitoring secondary or interstitial spaces
are well known in the art and include continuous leak detection
using both pressure and brine solution monitoring techniques to
determine the presence or absence of leaks between the storage
system and the surrounding environment. However, to effectively
calibrate all of these known methods and systems for operation, a
great deal of set-up time and system knowledge is required.
Specifically, to configure these monitoring systems for operation,
the user must enter the volume of the secondary or interstitial
space to be monitored, which requires a detailed knowledge of the
layout and the configuration of the double walled piping and
containers used in the underground storage system.
SUMMARY
[0006] An underground storage system includes a primary containment
unit and a secondary containment unit arranged to sealingly
encompass the primary containment unit. The underground storage
system further includes a leak detection system that is fluidly
connected to the secondary containment system, and which is adapted
to detect fluid leaks in the primary containment system and the
secondary containment system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] For a more complete understanding of the disclosed device,
reference should be made to the following detailed description and
accompanying drawings wherein:
[0008] FIG. 1 illustrates the basic components of an exemplary
interstitial vacuum monitoring system;
[0009] FIG. 2 illustrates a flowchart detailing the operation of an
exemplary auto-learn routine;
[0010] FIG. 3 illustrates an exemplary interstitial vacuum curve;
and
[0011] FIG. 4 illustrates a flowchart detailing the operation of an
exemplary monitoring routine.
DETAILED DESCRIPTION
[0012] FIG. 1 illustrates an exemplary underground storage system
10 that includes an underground storage tank (UST) 12 constructed
to securely contain a liquid 20, such as gasoline, diesel fuel or
other hydrocarbon. The UST 12 is a double walled storage tank
constructed with an outer wall 14, and an inner wall 16 separated
to define an interstitial space 18. In this manner, the UST 12 is
divided into a primary containment unit and a secondary containment
unit to provide the underground storage system 10 with redundant
leak protection.
[0013] A submersible turbine pump (STP) 22, such as, for example,
the STP model number STP-75-VL2-7 manufactured by FE PETRO, INC.
(now Franklin Fueling Systems, Inc.), provides a means of pumping
the liquid 20 to a dispenser 24. The STP 22 may fixedly or
removably mount to the UST 12 to position an input nozzle 22a below
the surface of the liquid 20. The input nozzle 22a, in turn,
provides a fluid path for pumping the liquid 20 within the primary
containment unit to the dispenser 24.
[0014] A pump manifold 26, which can be an integral component of
the STP 22 or a separate component fixedly attached thereto,
controls the distribution of the pumped liquid 20 to the dispenser
24. The pump manifold 26 includes a siphon port 28 adapted to
fluidly connect the interstitial space 18 (e.g., secondary
containment unit) to the vacuum generated by the STP 22. Thus, when
the STP 22 is active (e.g., producing a vacuum) the siphon port 28
provides a vacuum path to the interstitial space 18 to evacuate the
fluid contained therein. A control valve 30 can isolate the
interstitial space 18 from the siphon port 28 to prevent a vacuum
drop when the STP 22 is inactive and exposed to atmospheric
pressure via the primary containment unit.
[0015] A vacuum sensor 32 fluidly communicates with the
interstitial space 18 and the siphon port 28 to sample and measure
the vacuum levels therein. The vacuum sensor 32 may be a continuous
analog sensor, a discrete digital sensor, a switch based sensor, or
any other device configured to sample the vacuum level within the
interstitial space 18. The vacuum sensor 32 may be isolated by the
control valve 30 to prevent atmospheric pressure measurements
(i.e., zero vacuum measurements) when the STP 22 is inactive.
However, when the STP 22 is active and generating a vacuum, the
control valve 30 opens to provide a fluid connection between the
vacuum sensor 32, the interstitial space 18 and the siphon port 28.
In this manner, the vacuum sensor 32 samples and measures the
change in the vacuum level within the interstitial space 18
generated by the STP 22.
[0016] Further, the vacuum sensor 32 can communicatively connect to
a control unit 34 having a processor 36 and a memory 38. The
control unit 34 and the memory 38 receive and. store vacuum data,
system information, alarm data, etc., from the vacuum sensor 32 or
any other controlled component. Communications between the control
unit 34 and, for example, the vacuum sensor 32 and the control
valve 30, may be implemented using any desired communications link,
such as a hardwired local area network, a wireless communications
link, a direct communications link or a point-to-point wired
communication link.
[0017] The processor 36 may execute a control routine to direct the
set-up and operation of the underground storage system 10. In
particular, the control routine may be written in any process
control programming language or computer language such as C.sup.++,
Visual C.sup.++, Visual Basic. machine language and may be compiled
(if necessary) and stored in the memory 38. Generally, the control
routine insures the integrity of the underground storage system 10
by detecting unwanted leaks, In particular, the control routine may
execute on the processor 36 to automatically learn the vacuum
characteristics of the interstitial space 18. Further, the control
routine may include additional subroutines adapted to execute on
the processor 36 to continuously monitor the vacuum level within
the interstitial space 18 as a function of time.
[0018] A leak orifice valve 40 fluidly connects to the control
valve 30, the vacuum sensor 32, and a leak orifice 42, to provide a
vacuum path between the interstitial space 18. The leak orifice
valve 40 and the leak orifice 42 can define a removable assembly
adapted to disconnect from the interstitial space 18 when no longer
required for the set-up and operation of the underground storage
system 10. The leak orifice valve 40 allows for the automatic or
manual creation of a calibrated or controlled leak between the
interstitial space 18 and atmospheric pressure beyond the leak
orifice 42. Such a controlled leak results in a decrease in the
vacuum level within the interstitial space.
[0019] The vacuum sensor 32 can, in turn, measure the decreasing
vacuum level and communicate the vacuum level data to the control
routine executing within the control unit 34 via the communications
link, The control routine can, in turn, manipulate the vacuum level
data to establish one or more vacuum characteristics of the
interstitial space 18. In particular, the control routine may
determine a negative vacuum level rate of change based on the
decreasing vacuum level data caused by the introduction of the
controlled leak into the secondary containment unit. It will be
understood that other vacuum characteristics, such as, for example,
a positive vacuum level rate of change, or the time to total
interstitial space evacuation can be additionally or alternatively
established based on the vacuum level data,
[0020] The UST 12 can connect to other components of the
underground storage system 10, In particular, the interstitial
space 18 can fluidly connect to a secondary interstitial space 48
of a dispenser pipe 46 via a plurality of vacuum ports 44-44b. In
operation, the double-walled dispenser pipe 46 can provide the
fluid connection between the liquid 20 stored within UST 12 and the
dispenser 24. Thus, the entire underground storage system 10,
including the UST 12 and the dispenser pipe 46, is double-walled
and product tight against penetrations and corrosion that may be
experienced during normal operations.
[0021] FIG. 2 illustrates a generalized operations flowchart of an
auto-calibrating or auto-learn subroutine 50 adapted to learn the
vacuum characteristics of the interstitial space 18. The auto-learn
subroutine 50 determines and stores the vacuum characteristics
based, in part, on measured changes in the vacuum level as a
function of time. The auto-learn subroutine 50 learns the vacuum
characteristics without the need. to determine or calculate the
overall volume of the interstitial space 18, the vacuum capacity of
the STP 22, the sensitivity of the vacuum sensor 32, etc. In this
manner, the auto-learn routine 50 provides a fast and efficient
means of calibrating and monitoring the interstitial space 18 of
any known or unknown volume or complexity. It will be understood
that the auto-learn routine 50 can act as a stand alone routine
independent of the control routine or other subroutines. However,
the auto-learn routine 50 can integrate with the control routine to
satisfy the calibration requirements of the underground storage
system 10.
[0022] The auto-learn routine 50 can execute whenever a
predetermined criteria has been satisfied. In particular, the
auto-learn routine 50 can execute manually as part of a regularly
scheduled maintenance procedure, or automatically in response to a
change in the configuration of the underground storage system 10,
as part of the initial set-up and configuration of the underground
storage system 10, or to compensate for a change in vacuum level
over time.
[0023] A block 52 loads the stored initial settings and default
conditions required to execute the auto-learn routine 50 front the
memory 38 (see FIG. 1). These initial settings and default
conditions can include, among other things, a maximum desired
vacuum level P.sub.max, a minimum allowable vacuum level P.sub.min,
closing the control valve 30, and calibrating the vacuum sensor
32.
[0024] While the maximum desired vacuum level can be set to
virtually any value, empirical testing indicates that a vacuum
level of approximately 10 in, Hg (254 mm Hg), which represents an
achievable vacuum level that is easily distinguishable from
atmospheric pressure, may be desirable. Similarly, the minimum
acceptable vacuum level may be set to, for example, 2 in. Hg (50.8
mm Hg). Typically, the minimum vacuum level P.sub.min provides a
lower boundary or threshold to identify when the current vacuum
level P.sub.meas within the interstitial space 18 is decreasing
towards atmospheric pressure (i.e., approx 0 in, Hg or zero
vacuum).
[0025] A block 54 causes the vacuum sensor 32 to sample and measure
the current vacuum level P.sub.meas within the interstitial space
18. Typically, the vacuum sensor 32 samples the current vacuum
level P.sub.meas at regular time intervals At throughout the
operation of the auto-learn routine 50. The memory 38 can store the
vacuum level data representing the current vacuum level in a
historical database as a stored vacuum level P.sub.stored. The
stored vacuum level P.sub.stored can be permanently archived in the
historical database (i.e., saved in the database) or can be
temporarily stored for use in calculations, analysis, etc. and
subsequently erased or overwritten as new data is sampled and
stored.
[0026] A block 56 compares the current vacuum level P.sub.meas to
atmospheric pressure (i.e., zero vacuum) to establish a vacuum
baseline prior to the execution of the remaining steps within the
auto-learn routine 50. Upon detection of a vacuum in the
interstitial space 18, a block 58 causes the control valve 30 and
the leak orifice valve 40 to open and vent the detected vacuum to
the atmosphere. A block 60 causes the vacuum sensor 32 to sample
the current vacuum level P.sub.meas until atmospheric pressure is
detected. When the vacuum sensor 32 detects atmospheric pressure, a
block 62 closes the control valve 30 and the leak orifice valve 40
to seal and isolate the interstitial space 18 in preparation for
the execution of an evacuation procedure portion of the auto-learn
routine 50.
[0027] A block 64 initiates the evacuation procedure and the
auto-learn routine 50 begins to learn the vacuum level data
required for generation of an "up curve" (an example of which is
shown in FIG. 3 as the line 102). In particular, the block 64
activates the STP 22, which, in turn, begins to evacuate the
interstitial space 18 via the siphon port 28. A block 66 opens the
control valve 30 to establish fluid communications between the STP
22, the interstitial space 18, and the vacuum sensor 32. Typically,
the control valve 30 opens after a delay period. equal to the
amount of time required for the vacuum sensor 32 to detect the
vacuum generated by the STP 22. It will be understood that the
delay period associated with the vacuum sensor 32 may further
depend on factors, such as the sensitivity of the vacuum sensor 32,
the vacuum capacity of the STP 22, and the overall volume of the
interstitial space 18.
[0028] A block 68 causes the vacuum sensor 32 to sample and measure
the current vacuum level P.sub.meas within the interstitial space
18 at the time interval .DELTA.t. A block 70 causes the processor
36 to set the stored vacuum level P.sub.stored equal to the current
vacuum level P.sub.meas, and store the resulting stored vacuum
level P.sub.stored in the historical database established within
the memory 38. At this point, the evacuation or up curve vacuum
level rate of change within interstitial space 18 can be calculated
based on the difference between the current vacuum level and the
stored vacuum level over a fixed or known time interval. An
evacuation rate of change .DELTA.P.sub.evac can be mathematically
described by the formula:
.DELTA. P evac = P meas - P stored .DELTA. t ##EQU00001##
[0029] The evacuation rate of change .DELTA.P.sub.evac describes
the positive or increasing slope of the evacuation curve
representative of an increase in the vacuum level within the
interstitial space 18. Alternatively, by plotting the current
vacuum level P.sub.meas values, and the stored vacuum level
P.sub.stored sampled during the operation of the auto-learn
subroutine 50 as functions of time the evacuation curve can be
constructed.
[0030] A block 72 compares the current vacuum level P.sub.meas to a
maximum desired vacuum level P.sub.max. If the current vacuum level
is less than the maximum desired vacuum level, the auto-learn
routine 50 enters a loop 74 and continues to sample and store the
current vacuum level P.sub.meas until the maximum desired vacuum
level is achieved. However, when the block 72 detects that the
current vacuum level exceeds the maximum desired vacuum level, a
block 76 closes the control valve 30.
[0031] Subsequently, a block 78 deactivates the STP 22 and the
evacuation procedure concludes. At this point, the interstitial
space 18 is sealed and isolated by the control valve 30, and the
current vacuum level P.sub.meas remains substantially constant at
the maximum desired vacuum level P.sub.max.
[0032] A block 80 causes the vacuum sensor 32 to sample and measure
the current vacuum level P.sub.meas within the sealed interstitial
space 18 at each time interval .DELTA.t. The current vacuum level
P.sub.meas is expected to remain at the maximum desired vacuum
P.sub.max level for a fixed number of time intervals. Further, the
memory 38 may store the current vacuum level P.sub.meas, which
equals the maximum desired vacuum P.sub.max, in the memory 38 as
the stored vacuum level P.sub.stored. At this point, the vacuum
level rate of change within interstitial space 18 is substantially
zero. In other words, the vacuum level within the sealed
interstitial space is constant. A positive or negative change in
the vacuum level during this time interval represents an anomaly,
such as a leak, that will trigger an alarm. A maximum vacuum rate
of change .DELTA.P.sub.max can be mathematically described by the
formula:
.DELTA. P max = P meas - P stored .DELTA. t = 0 ##EQU00002##
The maximum vacuum rate of vacuum ate of change .DELTA.P.sub.max
represents the zero-slope line corresponding to the maximum desired
vacuum level P.sub.max. It will be understood that determination of
the maximum vacuum rate of change .DELTA.P.sub.max is an optional
calculation that may be carried out by the control unit 34.
[0033] A block 82 initiates the decay procedure and the auto-learn
routine 50 begins to learn the vacuum level data required to
generate the "down" or "decay curve" (an example of which is shown
in FIG. 3 as the line 106). In particular, the leak orifice valve
40 opens in response to a command issued by the control routine
executing within the control unit 34. In operation, the leak
orifice valve 40, which may be a manual valve that requires
operator intervention to open, provides a fluid path between the
current vacuum level of P.sub.meas within the interstitial space 18
and the zero vacuum level of the atmosphere. In other words, the
leak orifice valve 40 provides an equalization path between the
high vacuum level within the interstitial space 18 and the zero
vacuum level of atmospheric pressure. The decrease in the current
vacuum level P.sub.meas within the interstitial space 18 caused by
the controlled leak provides a method for characterizing the
performance of the secondary containment unit in the presence of an
actual, uncontrolled leak.
[0034] A block 84 causes the vacuum sensor 32 to sample and measure
the decreasing current vacuum level P.sub.meas within the
interstitial space 18 at each of the time intervals .DELTA.t. A
block 86 instructs the processor 36 to store the deceasing current
vacuum level P.sub.meas in the memory 38 as the stored vacuum level
P.sub.stored. At this point, the decay or down curve vacuum level
rate of change within interstitial space 18 can be calculated based
on the difference between the stored vacuum level P.sub.stored and
the current vacuum level P.sub.meas over a fixed time interval
.DELTA.t. A decay rate of change .DELTA.P.sub.decay can be
mathematically described by the formula:
.DELTA. P decay = P stored - P meas .DELTA. t ##EQU00003##
The decay rate of change .DELTA.P.sub.decay represents the negative
slope of the decay curve, which is the line defined, by the
decreasing current vacuum level P.sub.meas values measured by the
vacuum sensor 32 during the decay procedure of the auto-learn
routine 50.
[0035] A block 88 compares the current vacuum level P.sub.meas to a
minimum desired vacuum level P.sub.min. It will be understood that
the minimum desired vacuum level P.sub.meas could be set to zero
vacuum (i.e. atmospheric pressure) but will typically be set higher
to reduce the overall setup time for the system. In other words,
the closer to atmospheric pressure that the minimum desired vacuum
level P.sub.min is set, the longer the interstitial space 18 takes
to equalize. If the current vacuum level P.sub.meas is greater than
the minimum desired vacuum level P.sub.min, the auto-learn routine
50 enters a loop 90 and continues to sample and store the current
vacuum level P.sub.meas until the vacuum sensor 32 detects the
minimum desired vacuum level P.sub.min within the interstitial
space 18. However, if, at the block 88, the current vacuum level
P.sub.meas is less than the minimum desired vacuum level P.sub.min,
a block 92 cause the control valve 30 to close. At this point, the
decay procedure of the auto-learn routine 50 concludes and the
learned rates of change .DELTA.P.sub.evac and .DELTA.P.sub.decay
can be combined to produce the overall vacuum characteristics curve
shown in FIG. 3.
[0036] FIG. 3 illustrates an exemplary overall vacuum
characteristic curve 100 embodying the learned rates of change
.DELTA.P.sub.evac, and .DELTA.P.sub.decay, and the optionally
derived .DELTA.P.sub.max, measured and derived by the operation of
the auto-calibration routine 50. As previously indicated, the line
102 represents the learned evacuation rate of change
.DELTA.P.sub.evac derived during the auto-learn routine 50 and, in
particular, illustrates a positive increase in the vacuum level of
the interstitial space 18 as a function of time. In physical terms,
the line 102 represents the sealed interstitial space 18 fluidly
connected, via the control valve 30, to the active STP 22. A
maximum time T.sub.max represents the amount of time required for
the STP 22 to increase the current vacuum level within the
interstitial space 18 to the maximum desired vacuum level
P.sub.max.
[0037] An upper range defined by the line 102a and a lower range
defined by the line 102b establish the allowable amount of vacuum
level variation from the learned line 102 during the evacuation
procedure. An alarm subroutine can activate when the current vacuum
level P.sub.meas deviates beyond the acceptable limits established
by the upper and lower ranges defined by the lines 102a and 102b.
For example, the alarm subroutine may determine a leak exists
within the interstitial space 18 when the current vacuum level is
determined to be outside of the upper and lower ranges defined by
the lines 102a and 102b, or the maximum desired vacuum P.sub.max is
not achieved by the time T.sub.max.
[0038] A line 104 represents the maximum desired vacuum level
P.sub.max and the learned maximum vacuum rate of change
.DELTA.P.sub.max equal to zero (i.e., the vacuum is constant). In
physical terms, the line 104 represents the constant current vacuum
level measured when within the interstitial space 18 is sealed and
isolated from the STP 22, and the leak orifice valve 40, The
isolated interstitial space 18 insures that the current vacuum
level P.sub.meas remains virtually constant at P.sub.max over the
fixed number of time intervals.
[0039] As described previously, the line 106 represents the learned
decay rate of change .DELTA.P.sub.decay derived during the
auto-learn routine 50. The line 106 illustrates a decrease in the
measured vacuum level within the interstitial space 18 as a
function of time. In particular, the line 106 corresponds to a
system configuration wherein a controlled leak has been introduced
into the underground storage system 10, and the current vacuum
level P.sub.meas decreases as the vacuum within the interstitial
space 18 equalizes with atmospheric pressure (i.e., a vacuum level
of zero.)
[0040] As illustrated in FIG. 3, a permeation range 108 is defined
by an upper line 108a and a lower line 108b sloping away from the
line 106. The permeation range 108 represents the exemplary vacuum
profile for the sealed interstitial space 18 as a function of time.
In other words, during normal operations (e.g., steady state
operations with no leaks or other variations) the current vacuum
level P.sub.meas is expected to be measured within the permeation
range 108 defined by lines 108a and 108b. The steady vacuum decay
represented by the permeation range 108 is attributable to the
natural permeation properties of the underground. storage system
10, rather than to a leak or other anomaly. However, if the current
vacuum level P.sub.meas or current vacuum level rate of change
.DELTA.P.sub.current deviates from the range defined by the lines
108a and 108b, (i.e., falls outside of the permeation range 108),
then a leak or other anomaly is assumed to exist within the
interstitial space 18 and the alarm subroutine may activate.
[0041] FIG. 4 illustrates a flowchart detailing the operation of an
exemplary monitoring routine 120 employing the overall vacuum
characteristic curve 100. A block 122 causes the vacuum sensor 32
to sample and measure the current vacuum level P.sub.meas within
the interstitial space 18. A block 124 compares the current vacuum
level P.sub.meas to the minimum allowable vacuum level P.sub.min
(e.g., 2 in. Hg or zero vacuum). If the current vacuum level
P.sub.meas is below minimum allowable vacuum level P.sub.min, a
block 126 activates the STP 22 which, in turn, begins to evacuate
the interstitial space 18 as generally indicated by the evacuation
curve 102 illustrated in FIG. 3.
[0042] A block 128 causes the control valve 30 to open, thereby
establishing fluid communication between the STP 22, the
interstitial space 18, and the vacuum sensor 32. Typically, the
control valve 30 opens after a delay period equal to the amount of
time required for vacuum sensor 32 to detect the vacuum generated
by the STP 22. A block 130 instructs the vacuum sensor 32 to sample
and measure the increasing current vacuum level P.sub.meas within
the interstitial space 18 at each of the time intervals
.DELTA.t.
[0043] A block 132 compares a current vacuum level rate of change
P.sub.current to the learned evacuation rate of change
.DELTA.P.sub.evac determined during the auto-learn routine 50. It
will be understood that the current vacuum level rate of change
.DELTA.P.sub.current can be determined based on the difference
between the current vacuum level P.sub.meas and the stored vacuum
levels P.sub.stored as a function of time. A current vacuum level
rate of change .DELTA.P.sub.current can be described by the
formula:
.DELTA. P current = P meas - P stored .DELTA. t ##EQU00004##
If the current vacuum level rate of change .DELTA.P.sub.current is
determined to be less than the learned evacuation rate of change
.DELTA.P.sub.evac, a block 134 may activate the alarm routine.
However, if the current vacuum level rate of change
.DELTA.P.sub.current exceeds the learned evacuation rate of change
.DELTA.P.sub.evac, a block 136 instructs the processor 36 to store
the increasing current vacuum level P.sub.meas the memory 38 as the
stored vacuum level P.sub.stored.
[0044] A block 138 compares the current vacuum level P.sub.meas to
a maximum desired vacuum level P.sub.max. If the current vacuum
level P.sub.meas is less than the maximum desired vacuum level
P.sub.max, the monitoring routine 120 enters a loop 140 and
continues to sample and store the current vacuum level P.sub.meas
until the maximum desired vacuum level P.sub.max is detected.
However, if the current vacuum level P.sub.meas exceeds the maximum
desired vacuum level P.sub.max, a block 142 causes the control
valve 30 to close.
[0045] A block 144 deactivates the STP 22 upon completion of the
evacuation of the now-sealed interstitial space 18. Thus, the
monitoring routine 120 has recharged the vacuum level within the
interstitial space 18. In operation, the evacuation or increase in
the vacuum level of the interstitial space 18 proceeds along the
learned evacuation vacuum curve 102, and the monitoring routine 120
continually verifies that the current vacuum level P.sub.meas
remains within the predefined range defined by the lines 102a and
102b. Simultaneously, the time required to recharge the
interstitial space 18 to the maximum desired vacuum level P.sub.max
can be compared to the maximum time T.sub.max. If the current
recharge time exceeds the maximum time T.sub.max, a leak or other
anomaly is assumed to exist and the alarm routine 134
activates.
[0046] A block 146 restarts the monitoring routine 120 so that the
vacuum sensor 32 samples and measures the current vacuum level
P.sub.meas at the block 122. At the block 124, the recently
recharged current vacuum level P.sub.meas is compared to the
minimum allowable vacuum level P.sub.min (e.g., 2 in. Hg or zero
vacuum). Because the recently recharged current vacuum level
P.sub.meas is greater than the minimum allowable vacuum level
P.sub.min, a block 148 compares the current vacuum level rate of
change P.sub.current to the learned decay rate of change
.DELTA.P.sub.decay determined during the auto-learn routine 50.
[0047] As previously discussed, the interstitial space 18 is sealed
and the monitoring routine 120 measures the current vacuum level
P.sub.meas to determine if the decrease in the current vacuum level
P.sub.meas is attributable to the natural permeation properties of
the underground. storage system 10 or to a leak. Furthermore, the
comparison between the learned vacuum curve and the current vacuum
level P.sub.meas can be based on the difference between the decay
rate of change .DELTA.P.sub.decay and the current rate of change
.DELTA.P.sub.current or simply based on the difference between the
current vacuum level P.sub.meas and the learned vacuum curve
itself
[0048] A block 150 instructs the processor 36 to store the current
vacuum level P.sub.meas in the memory 38 as the stored vacuum level
P.sub.stored. At this point, the monitoring routine 120 enters a
loop 152 and continues to sample and store the current vacuum level
P.sub.meas until the minimum allowable vacuum level P.sub.min is
detected, at which time the STP 22 activates to evacuate the
interstitial space 18.
[0049] Similarly, monitoring of the vacuum level during evacuation
can also be used to monitor for problems. The system uses the
learned evacuation rate of change .DELTA.P.sub.evac, or upcurve, as
illustrated as line 102 (FIG. 3) to determine if any liquid ingress
has occurred inside the secondary containment. This is accomplished
by comparing the learned up-curve in memory to the currently
measured up-curve. If the slope of the current measured up-curve is
greater than the slope of the learned up-curve by a threshold
factor exceeding that defined by line 102a (FIG. 3), (i.e., it took
sufficiently less time to evacuate the containment space than what
was originally learned), then liquid is suspected to have entered
the secondary containment. This is due to the fact that the liquid
ingress has effectively reduced the containment area available to
the vacuum. Additionally, if the slope of the current measured
up-curve is less than the slope of the learned up-curve by a
threshold factor exceeding that defined by line 102b (FIG. 3),
(i.e., it took sufficiently longer to evacuate the containment
space than what was originally learned), then it is possible that
there is a leak in the vacuum suction line, permitting fluid to
enter. In either case (a currently measured slope sufficiently
greater than or sufficiently less than the learned slope) will
trigger an alarm. In this way, a physical liquid collection chamber
and liquid sensor is not required, reducing the cost and complexity
of the system.
[0050] While the embodiments described herein have been directed to
vacuum level measurements and analysis, it will be understood that
an overpressure within the interstitial space 18 may be employed to
provide a pressure gradient suitable for measurement by the
auto-learn routine 50 and monitoring by the monitoring routine 120.
Further, it will be understood that the current vacuum level
P.sub.meas and the calculated rates of change can be determined in
a manual fashion. For instance, manual instructions may direct the
control unit 34 to sample and store the current vacuum level
P.sub.meas within the interstitial space 18. Moreover, an operator
may employ the rate of change formulas and concepts discussed above
in conjunction with the stored vacuum levels P.sub.stored to
manually calculate the desired rates of change.
[0051] Although certain embodiments have been described in
accordance with the teachings of the present disclosure, the scope
and coverage of this patent is not limited thereto. To the
contrary, this patent is intended to cover all embodiments of the
teachings of the disclosure that fairly fall within the scope of
the permissible equivalents.
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