U.S. patent number RE36,069 [Application Number 07/828,528] was granted by the patent office on 1999-02-02 for portable wastewater flow meter.
Invention is credited to Robert M. Hunter.
United States Patent |
RE36,069 |
Hunter |
February 2, 1999 |
Portable wastewater flow meter
Abstract
A portable wastewater flow meter particularly adapted for
temporary use at a single location in measuring the rate of liquid
flow in a circular entrance conduit of a sewer manhole both under
free flow and submerged, open channel conditions and under fill
pipe, surcharged conditions, comprising an apparatus having a
cylindrical external surface and an inner surface that constricts
the flow through the apparatus in such a manner that a relationship
exists between (1) the difference between the static pressure head
of liquid flowing through the entrance of the apparatus and the
static pressure head of liquid flowing through the constriction,
and (2) the rate of liquid flow through the apparatus.
Inventors: |
Hunter; Robert M. (Bozeman,
MT) |
Family
ID: |
27489400 |
Appl.
No.: |
07/828,528 |
Filed: |
January 29, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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51325 |
May 19, 1987 |
4799388 |
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846516 |
Mar 31, 1986 |
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364192 |
Mar 31, 1982 |
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Reissue of: |
286695 |
Dec 20, 1988 |
04896542 |
Jan 30, 1990 |
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Current U.S.
Class: |
73/215;
73/861.63 |
Current CPC
Class: |
E03F
7/00 (20130101); G01F 1/34 (20130101); G01F
23/165 (20130101); G01F 1/002 (20130101) |
Current International
Class: |
E03F
7/00 (20060101); G01F 1/00 (20060101); G01F
1/34 (20060101); G01F 23/14 (20060101); G01F
23/16 (20060101); G01N 001/20 () |
Field of
Search: |
;73/215,216,861.63,861.64 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
BIF Industries Technical Bulletin 110-P1, Aug. 1958, p. 17. .
Harry G. Wenzel, Jr.--"Meter for Sewer Flow Measurement" From
Journal of the Hydraulics Division, Jan. 1975, pp. 115-133. .
Floyd A. Nagler--"New Flow Meter Uses Side Contractions Only".
.
George F. Smoot--"A Rainfall--Runoff Quantity-Quality Data
Collection System" From Proceedings of a Research Conference, Aug.
1974..
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Primary Examiner: Chilcot; Richard
Assistant Examiner: Dougherty; Elizabeth L.
Government Interests
This application discloses improvements that were discovered during
research funded by the U.S. Department of Energy under the
Energy-Related Inventions Program. The invention is described in
detail in a report entitled "The Flumeter.TM.: A New Tool for
Wastewater Management" prepared for the U.S. Department of Energy
by Yellowstone Environmental Science, Bozeman, Mont., May 1988.
Parent Case Text
This application is a continuation-in-part of U.S. Pat. Application
No. 051,325 filed May 19, 1987 now U.S. Pat No. 4,799,388.Iadd.,
which, in turn, was a continuation-in-part of U.S. patent
application Ser. No. 846,516, filed Mar. 31, 1986 abn., which was a
file wrapper Continuation of U.S. patent application Ser. No.
364,192, filed Mar. 31, 1982. The disclosure of U.S. Pat. No.
4,799,388, is incorporated by reference herein as if fully set
forth. .Iaddend.
Claims
I claim:
1. In the process of metering the flow of liquid which is flowing
by gravity in an elongated pipe that is open to atmosphere,
wherein:
tubular venturi metering device is installed in the pipe, which has
an open-ended bore therethrough having an axis extending end-to-end
thereof,
arranging the device in the pipe so that the axis of the bore is
disposed substantially parallel to the longitudinal axis of the
pipe and the bore thus has an end which is normally oriented
upstream of the liquid flow in the pipe and an end which is
normally oriented downstream of the liquid flow in the pipe,
the bore having an axially inwardly tapered entrance section
adjacent the upstream end thereof which converges toward the axis
of the bore in vertical planes paralleling the axis of the bore
relatively toward the downstream end of the bore but terminates
short of the axis of the bore so that a throat is formed in the
bore which opens to the downstream end thereof,
forming a liquid seal between the device and the pipe at the outer
periphery of the device so that the liquid in that section of the
pipe disposed upstream from the upstream end of the bore of the
device, is constrained to flow through the bore of the device,
relatively toward the downstream end thereof,
determining the static pressure head in the liquid in the aforesaid
upstream section of the pipe when the liquid is flowing in the pipe
at a depth less than that adapted to fill the upstream pipe, to
meter the flow in the pipe for the less than full condition
thereof,
configuring the cross-sectional area of the throat, relative to
that of the pipe, transverse the respective axes thereof, so that
the throat will fill with liquid substantially simultaneously with
the upstream section of the pipe, when the liquid depth rises
therein, and
providing means whereby the static pressure head of the liquid in
the throat of the device and the upstream section of the pipe can
be determined when both the upstream section of the pipe and the
throat are filled, so that the difference between the latter two
pressure heads can be determined to meter the flow in the pipe for
the full condition thereof, and thereby enable the flow in the pipe
to be metered for the full condition thereof as well as the less
than full condition thereof and the transition therebetween,
the improvement wherein:
arranging the device in the pipe with its axis and the top of its
throat horizontal thus leveling the device,
the bore having an axially outwardly tapered exit section adjacent
the downstream end thereof which diverges from the axis of the bore
in vertical planes paralleling the axis of the bore relatively
toward the end of the bore that is normally downstream,
providing means whereby the static pressure head of the liquid in
the throat of the device and in both the entrance section and the
exit section can be determined, so that the difference between the
static pressure heads in the entrance section and in the exit
section can be used to determine the direction of flow and, hence,
the actual upstream end of the device, and, during the less than
full condition, an appropriate correction factor for metering the
flow rate, and so that the difference between the throat pressure
head and the actual upstream pressure head can be determined to
meter the flow in the pipe for the full condition thereof.
2. The process in claim 1 wherein the cross-sectional area of the
throat is configured relative to the entrance section of the bore
and the exit section of the bore to cause simultaneous filling of
the throat and the section of the bore that is actually upstream
before the modular limit of the device is reached when the device
is installed in a pipe of minimum slope.
3. In the combination wherein there are:
an elongated pipe which is open to atmosphere and adapted for the
flow of liquid by gravity therein,
a tubular venturi metering device installed in the pipe and having
an open-ended bore therethrough which has an axis extending
end-to-end thereof,
the device being arranged in the pipe so that the axis of the bore
is disposed substantially parallel to the longitudinal axis of the
pipe and the bore thus has an end which is normally oriented
upstream of the liquid flow of the pipe and an end which is
normally oriented downstream of the liquid flow in the pipe,
the bore having an axially inwardly tapered entrance section
adjacent the upstream end thereof, which converges toward the axis
of the bore in vertical planes paralleling the axis of the bore and
in that axial direction of the bore relatively toward the
downstream end of the bore, but terminates short of the axis of the
bore so that a throat is formed in the bore which opens to the
downstream end thereof,
means for forming a liquid seal between the device and the pipe at
the outer periphery of the device so that the liquid in that
section of the pipe disposed upstream from the upstream end of the
bore of the device, is constrained to flow through the bore of the
device, relatively toward the downstream end thereof, and
first means for determining the static pressure head of the liquid
in the aforesaid upstream section of the pipe when the liquid is
flowing in the pipe at a depth less than that adapted to fill the
upstream section of the pipe, to meter the flow in the pipe for the
less than full condition thereof,
the cross-sectional area of the throat being configured relative to
that of the upstream section of the pipe, transverse the respective
axes thereof, so that the throat will fill with liquid
substantially simultaneously with the upstream section of the pipe,
when the liquid rises therein, and
there being second means for determining static pressure head of
the liquid in the throat of the device and in the upstream section
of the pipe when both the upstream section of the pipe and the
throat are filled, so that the difference between the latter two
pressure heads can be determined to meter the flow in the pipe for
the full condition thereof, and thereby enable the flow in the pipe
to be metered for the full condition thereof, as well as the less
than full condition thereof and the transition therebetween,
the improvement comprising
means for leveling the device,
an axially outwardly tapered exit section adjacent the downstream
end of the bore which diverges from the axis of the bore in
vertical planes paralleling the axis of the bore relatively toward
the end of the bore that is normally downstream,
means for determining the static pressure head of the liquid in the
throat of the device and both in the entrance section and in the
exit section whereby the difference between the static pressure
heads in the entrance section and the exit section can be used to
determine the direction of flow and, hence, the actual upstream end
of the device, and during the less than full condition an
appropriate correction factor for metering flow rate and whereby
the difference between the throat pressure head and the actual
upstream pressure head can be determined to meter the flow in the
pipe for the full condition thereof.
4. The combination in claim 3 wherein the cross-sectional area of
the throat is configured relative to the entrance section of the
bore and the exit section of the bore to cause simultaneous filing
of the throat and the section of the bore that is actually upstream
before the modular limit of the device is reached when the device
is installed in a pipe .[.of minimum slope.]. which at least flows
full at an average velocity of about 2 feet/second.
5. The combination in claim 4 wherein means for determining the
static pressure head of the liquid in the entrance section and in
the exit section comprise tubes that discharge bubbles into the
liquid in the annular space between the outside surface of the
device and the inside surface of the pipe.
6. The combination in claim 4 wherein means for determining the
static pressure head of the liquid in the entrance section and in
the exit section comprise tubes that discharge bubbles into the
liquid as it flows through the interior of the device. .Iadd.
7. A process of metering the flow of liquid which is flowing in an
elongated pipe that is open to the atmosphere, wherein a closed
conduit venturi metering device is installed in the pipe, which
device has an open-ended bore therethrough extending end-to-end
thereof, the bore having an entrance section adjacent a first end
thereof, an exit section adjacent the second end thereof, and
intermediate the entrance and exit sections, a throat having a top
and bottom and a smaller cross-sectional area than the entrance and
exit sections, comprising the steps of:
arranging the device in the pipe to accept flow into the entrance
from the pipe and otherwise to substantially block the pipe,
and
configuring the cross-sectional area of the throat, relative to
that of the entrance section, including constricting the throat
across the bore at the throat top or bottom, or both so that the
throat will fill with liquid substantially simultaneously with the
entrance section, when liquid depth rises in the entrance section,
and
providing means for determining the head of the liquid in said
entrance section, in said throat and, in said exit section, for use
at least to determine direction of flow in the device and flow both
in less than full and in full flow through the device.
.Iaddend..Iadd.
8. The process of claim 7 in which the throat is also configured to
impart critical flow depth to liquid flowing through the throat in
less than full flow. .Iaddend..Iadd.9. The process of claim 8
further comprising,
comparing the heads of liquid in said entrance and exit sections of
the device flowing in less than full flow or in full flow, and
determining therefrom the direction of flow in said device.
.Iaddend..Iadd.10. The process of claim 9 further comprising,
determining from said head comparisons the percent submergence of
the device when the liquid is flowing less than full, and
applying a correction factor to flow rate in less than full flow
condition when the percent submergence exceeds the maximum
submergence of the device. .Iaddend..Iadd.11. The process of claim
8 further comprising,
comparing the heads of liquid in said entrance and exit sections of
the device flowing in less than full flow,
determining therefrom the percent submergence of the device,
and
applying a correction factor to flow rate in less than full
condition when the percent submergence exceeds the maximum
submergence of the device.
.Iaddend..Iadd.12. The process of claim 8 in which the
cross-sectional area of the throat is configured, relative to that
of the entrance section, to cause the throat and entrance sections
to fill simultaneously below the modular limits of the device, when
liquid depth rises in the entrance section. .Iaddend..Iadd.13. The
process in claim 12 wherein the device is arranged in a pipe which
at least flows full at an average velocity of about 2 feet/second.
.Iaddend..Iadd.14. A process of metering the flow of liquid which
is flowing by gravity in an elongated pipe that is open to the
atmosphere, wherein a tubular venturi metering device is installed
in the pipe, which device has an open-ended bore therethrough
having an axis extending end-to-end thereof, the bore having an
entrance section adjacent a first end thereof which converges
toward the second end of the bore but terminates short of the axis
of the bore so that a throat is formed in the bore which opens to
said second end, the bore having an exit section adjacent said
second end which diverges from the bore toward said second end,
comprising the steps of:
arranging the device in the pipe to accept flow into said entrance
and otherwise to substantially block the pipe,
configuring the cross-sectional area of the throat, relative to
that of the entrance section, so that the critical flow depth is
imparted to liquid flowing through the throat in less than full
flow and so that the throat will fill with liquid substantially
simultaneously with the entrance section, when the liquid depth
rises in the entrance section,
providing means for determining the head of the liquid in said
entrance section, in said throat and in said exit section,
comparing the heads of liquid in said entrance and exit sections of
the device flowing in less than full flow or in full flow, and
determining the direction of flow. .Iaddend..Iadd.15. The process
of claim 14 further comprising,
determining from said head comparisons the percent submergence of
the device when the liquid is flowing less than full, and
applying a correction factor to flow rate in less than full flow
condition when the percent submergence exceeds the maximum
submergence of the
device. .Iaddend..Iadd.16. The process of claim 14 in which the
cross-sectional area of the throat is configured, relative to that
of the entrance section, to cause the throat and entrance sections
to fill simultaneously below the modular limit of the device, when
liquid depth rises in the entrance section. .Iaddend..Iadd.17. The
process of claim 16 wherein the device is arranged in a pipe which
at least flows full at an average velocity of about 2 feet/second.
.Iaddend..Iadd.18. The process of claim 14 wherein said step of
configuring includes constricting said throat horizontally across
said bore at the throat top or bottom, or both. .Iaddend..Iadd.19.
The process of claim 16 wherein said step of configuring includes
constricting said throat horizontally across said
bore at the throat top or bottom, or both. .Iaddend..Iadd.20.
Apparatus for metering flow of liquid which is flowing in an
elongated pipe which is open to the atmosphere, comprising:
a closed conduit venturi metering device installed in the pipe and
having an open-ended bore therethrough extending end-to-end
thereof, said bore having an entrance section adjacent a first end
thereof, an exit section adjacent the second end thereof, and
intermediate the entrance and exit sections, a throat having a top
and bottom and a smaller cross-sectional area than the entrance and
exit sections,
said device being arranged in said pipe to accept flow into said
entrance from the pipe and otherwise to substantially block the
pipe,
the cross-sectional area of the throat, relative to that of the
entrance section, being configured, including a throat constriction
across the bore at the throat top or bottom, or both, such that the
throat will fill with liquid substantially simultaneously with the
entrance section, when liquid depth rises in the entrance section,
and
means for determining the head of the liquid in said entrance
section, in said throat, and in said exit section, for use at least
to determine direction of flow in the device and flow both in less
than full and in
full flow through the device. .Iaddend..Iadd.21. The apparatus of
claim 20 in which said throat also is configured to impart critical
flow depth to liquid flowing through the throat in less than full
flow. .Iaddend..Iadd.22. The apparatus of claim 21, further
including means for comparing heads of liquid in said entrance and
exit sections in less than full flow or in full flow, and for
determining therefrom the direction of flow in said device.
.Iaddend..Iadd.23. The apparatus of claim 21, further comprising
means for determining the percent submergence of the device in less
than full flow, and for applying a correction factor to flow rate
in less than full flow condition when the percent submergence
exceeds the maximum submergence of the device. .Iaddend..Iadd.24.
The apparatus of claim 21 in which said cross-sectional area of the
throat is configured relative to that of the entrance section to
cause the throat and entrance sections to fill simultaneously below
the modular limit of the device,
when liquid depth arises in the entrance section.
.Iaddend..Iadd.25. The process of claim 24 in which said device is
arranged in a pipe which at least flows full at an average velocity
of about 2 feet/second. .Iaddend..Iadd.26. Apparatus for metering
the flow of liquid which is flowing by gravity in an elongated pipe
that is open to the atmosphere, comprising:
a tubular venturi metering device arranged in the pipe, which
device has an open-ended bore therethrough having an axis
end-to-end thereof, said bore having an entrance section adjacent a
first end thereof which converges toward the second end of the bore
but terminates short of the axis of the bore so that a throat is
formed in the bore which opens to said second end, such bore having
an exit section adjacent said second end which diverges from the
bore toward that second end,
said device being arranged in the pipe to accept flow into said
entrance from the pipe and otherwise to substantially block the
pipe,
the cross-sectional entrance of a throat being configured relative
to that of the entrance section, so that a throat will fill with
liquid substantially simultaneously with the entrance section below
the modular limit of the device, when the liquid depth rises in the
entrance section, and
means for determining the head of liquid in said entrance section
and in said throat. .Iaddend..Iadd.27. The apparatus of claim 26,
further comprising means for comparing the heads of liquids in said
entrance and exit sections of the device flowing in less than full
flow or in full flow, and for determining the direction of flow.
.Iaddend..Iadd.28. The apparatus of claim 27 further comprising
means for determining the percent submergence of the device from
said head comparisons in less than full flow, and for applying a
correction factor to flow rate in less than full flow conditions
when the percent submergence exceeds the maximum
submergence of the device. .Iaddend..Iadd.29. The apparatus of
claim 28 wherein said device is arranged in a pipe which at least
flows full at an average velocity of about 2 feet/second.
.Iaddend..Iadd.30. The apparatus of claim 26 wherein said
configuration of said throat includes a constriction of said throat
horizontally across said throat at the throat top or bottom, or
both. .Iaddend..Iadd.31. The apparatus of claim 28 wherein said
configuration of said throat includes a constriction of said throat
horizontally across said throat at the throat top or bottom, or
both. .Iaddend.
Description
TECHNICAL FIELD
This invention relates to a metering device for use in fluid flow
metering applications and more particularly to such a metering
device for placement in the entrance conduit of a sewer
manhole.
BACKGROUND ART
Millions of dollars are expended annually by communities attempting
to isolate and eliminate storm water inflows to their sanitary
sewer systems. For many years, the engineering profession has
recognized that accurate, temporary measurement of wastewater flows
emanating from subareas within a total sewer system is the most
cost-effective means of determining the portions of the system with
the most serious inflow problems.
Sewers that carry wastewater from areas that experience severe
storm water inflow problems typically operate under surcharged
conditions during and immediately after rainfall events.
Unfortunately, it is under these conditions that accurate flow rate
data are almost impossible to obtain. For a variety of reasons, it
is normally impractical to use a primary flow metering device, such
as a weir or flume, that would allow depths of flow to be converted
into flow rates. Weirs are subject to upstream sedimentation and
fouling by debris; they must be fabricated to suit the physical
configuration of each particular manhole, and are difficult to
calibrate under surcharged conditions. Flumes, such as the Palmer
Bowlus flume and other venturi flumes, are typically inaccurate at
upstream depths of flow that exceed 75 percent of the sewer
diameter and are useless under surcharged conditions. An
alternative is to measure the head loss (usually fractions of an
inch) between two manholes and to use culvert formulas and the
Manning formula to grossly estimate flow rates. Of course, this
method requires that depth of flow measurements be made in two
manholes instead of one, thus doubling the cost of flow
measurement.
Great advances have been made in the last decade in the design of
equipment for measuring, recording, and storing depth of liquid
flow (or pressure) information. No one, however, has developed a
portable primary wastewater flow metering device that would allow
depths of flow or pressure head to be accurately converted into
flow rates under both free flow and submerged flow, open channel
conditions and under full pipe, surcharged conditions.
DISCLOSURE OF THE INVENTION
The invention is concerned with the novel construction of the
device which enables it to meter both forward and reverse flow in
sewers of circular cross section under both free flow and
submerged, open channel conditions and under full pipe, surcharged
conditions wherein the surface elevation of the liquid in the
manhole may be far above the crest of the sewer in which the device
is installed. In general, the invention disclosed herein is for
temporary installation in a sewer as it enters a sewer manhole. The
outer surface of the invention is generally cylindrical to allow
its placement in the entrance pipe. An inflatable collar encircles
the cylindrical outer surface of the apparatus so that when the
apparatus is placed in the inlet pipe and the inflatable collar is
inflated, a seal is provided there between so that the entire flow
in the sewer passes through the apparatus.
The interior surface of the apparatus is so shaped as to cause
there to be a relationship between the depth of flow (static
pressure head) at the upstream entrance section of the apparatus
and the flow rate through the apparatus under free flow, open
channel conditions when the sewer pipe is flowing partially full.
When the apparatus is operating in a submerged mode (above its
modular limit), this condition is sensed by comparing the upstream
and downstream pressure heads and a correction factor is applied to
the flow rate calculated using a free flow calibration curve.
Furthermore, the interior surface of the apparatus is so shaped as
to cause there to be a relationship between the difference between
the static pressure head at the invert of the upstream entrance
section of the apparatus and the static pressure head at the crest
of the constricted throat section of the apparatus under surcharged
conditions when the pipe in which the apparatus is installed is
flowing fall. Flow data are obtained by conventional means
utilizing the relationships between static pressure heads and flow
rate.
The device is an improvement over prior art in that floatable
solids can be conveyed through the device under free flow
conditions, and in that much greater accuracy in liquid flow
measurement is possible. The device is also an improvement over
prior art in that accurate flow metering is possible at one
location in situations in which the manhole in which the device is
installed is surcharged above the crest of the sewer in which the
device is installed. The device is an improvement over prior art in
that the flow constricting surfaces of the device are not
permanently affixed to the walls of the pipe, in that a compact
configuration is proposed, and in that either piezoelectric
pressure transducers or a bubbler-type pressure sensing mechanism
can be used to sense static pressure heads.
In general, it is an object of the present invention to provide an
apparatus for metering forward and reverse flow in a sewer that can
operate under both free flow and submerged flow, open channel
conditions when the sewer is flowing at less than full depth and
under surcharged conditions when the sewer is flowing full and the
metering manhole is surcharged. It is another object of the present
invention to provide a portable flow metering apparatus for quick
installation in a sewer adjacent to a manhole. It is another object
of the present invention to allow floatable sewage solids to be
conveyed through the device when it operates under free flow and
submerged, open channel conditions. It is another object of the
present invention to provide a flow metering apparatus requiring a
relatively small head loss in creating the static pressure head
differences used to calculate flow rates.
For the purposes of this patent, the term tubular venturi metering
device means an apparatus that fulfills the function of a modified
venturi flume when the sewer in which the invention is installed is
flowing less than full and the function of a venturi tube when the
sewer in which the invention is installed is flowing full. The term
tubular venturi metering device also means an apparatus wherein the
constriction is configured so as (1) to cause the device to
maintain its metering function even at low liquid flow rates and
(2) to cause the constriction to fill with liquid at approximately
the same flow rate that the upstream pipe fills with liquid and
thereby maintain its metering function during the transition from
open channel to full pipe flow.
It is well known in the art that a modified venturi flume is a
constriction in an open channel, so proportioned as to produce flow
at critical depth in the open is channel in the vicinity of the
constriction and that a relationship exists between the depth of
flow in the open channel upstream from the constriction and the
rate of liquid flow. Examples of modified venturi flumes include
the Palmer Bowlus flume and the cutthroat flume. It is also well
known in the art that a venturi tube is a constriction in a closed
pipe, so proportioned as to accelerate the fluid flowing in the
pipe and lower its static pressure head in such a manner that a
relationship exists between (1) the difference between the static
pressure head of liquid flowing in the pipe upstream of the venturi
tube and the static pressure head of liquid flowing through the
constriction, and (2) the rate of liquid flow.
Additional objects and features of the invention will appear from
the following description in which the preferred embodiment has
been set forth in detail in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
These features will be better understood by reference to the
accompanying drawings which illustrate presently preferred
embodiments of the invention that includes a portable tubular
venturi metering device adapted to be installed in a cylindrical
sewer pipe to meter the flow in the pipe at a manhole therein.
In the drawings:
FIG. 1 is a perspective view of an embodiment of the device.
FIG. 2 is a longitudinal view of an embodiment of the device
installed in a pipe, said pipe shown in partial cross-section, said
embodiment having entrance section and exit section bubbler tubes
that discharge into liquid in the annular space between the outer
surface of the device and the inner surface of the pipe.
FIG. 3 is a cross-sectional view of the device taken at section 3
shown on FIG. 2.
FIG. 4 is a cross sectional view of the device taken at section 4
shown on FIG. 2.
FIG. 5 is a part cut-away, part perspective view of a manhole, and
sewer pipe with the device being installed in the upstream or
entrance section of the pipe.
FIG. 6 is a highly schematic representation of the bubbler systems
used to sense pressure heads in the device.
FIG. 7 is a longitudinal view of an embodiment of the device with
upstream and downstream bubbler tubes that discharge into liquid
flowing through the entrance and exit sections of the device.
FIG. 8 is a cross-sectional view of the device taken at section 8
shown on FIG. 7.
FIG. 9 is a cross-sectional view of the device taken at section 9
shown on FIG. 7.
FIG. 10 is a typical calibration curve that is used to relate
static pressure head differences to flow rate.
FIG. 11 is a typical correction curve that is used to correct the
flow rate value indicated by reference to the open channel
calibration curve when the device is operating above its modular
limit.
.Iadd.FIG. 12 is another cross-sectional view of the device taken
at section 8 shown on FIG. 7.
FIG. 13 is another cross-sectional view of the device taken at
section 9 shown on FIG. 7. .Iaddend.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to the drawings, it will be seen that the portable
metering device 2 has a elongated, cylindrical body 4, and is
adapted to be lowered into a manhole 6 , and then inserted while
horizontal into the bottom of the upstream section 8 of a sewer
pipe 10 traversing the bottom of the manhole. The manhole 6
upstands from the pipe 10 in sealed engagement with the same about
a part-cylindrical opening 12 in the top of the pipe which extends
for substantially the width of the manhole. Meanwhile, the
remainder 14 of the pipe 10 transverses a portion of the bottom of
the manhole. At a point on the opposite side of the manhole the
pipe resumes full circumference and exits from the manhole.
The body 4 of the device 2 is tubular and has a venturi
cross-section longitudinally thereof. That is, the device 2 has an
open-ended bore 16 through the same, the longitudinal axis 18 of
which coincides with that of the device itself, so that when the
device is installed in the pipe, the axis 18 of the bore 16 is
substantially parallel to the axis 29 of the pipe, however, the
device is leveled in the pipe. The bore itself has a cylindrical
vestibule 22 at that end 24 of the device which is oriented
upstream of the liquid flow in the pipe, and downstream therefrom,
the vestibule opens into a conically axially inwardly tapered
entrance section 26 which converges toward the axis 18 of the bore
in the downstream axial direction thereof. The entrance section 26
terminates short of the axis of the bore, however, and opens into a
throat 28 which interconnects it in turn with an exit section 30
that diverges from the axis 18 of the bore so as to have a
conically axially outwardly tapered configuration. The exit section
30 is followed in turn by a cylindrical outlet 32 which is disposed
at that end 34 of the device that is oriented downstream of the
liquid flow in the pipe. Both the outlet 32 and the vestibule 22
have rounded rims at the respective ends 24, 34 thereof, to
facilitate liquid flow through the bore; and the cross-sectional
area of the throat 28 is configured, relative to the of the pipe
10, transverse the respective axes 18, 29 thereof, so that the
throat will fill with liquid substantially simultaneously with the
upstream section 8 of the pipe when the liquid depth rises therein,
as was explained earlier in the aforementioned co-pending
Application.
The body 4 of the device 2 is generally cylindrical, as indicated,
but the center section 4' of the same, axially of the cylinder, is
reduced in diameter so that the device has a neck 36 midway
thereof, and axially opposing shoulders 38 and 40 on the relatively
upstream and downstream end portions 4" and 4''' thereof, adjacent
the neck. The shoulders and neck, in turn, define an annulus 42 for
accommodating certain additional components of the device, as shall
be explained; and in addition, the relatively upstream end portion
4" has an additional reduced diameter neck 44 thereon for
accommodating a toroidal collar 46 used in forming a liquid seal
between the device and the pipe, at the outer periphery of the
device when it is installed in the upstream section 8 of the pipe,
as shall be explained. The latter neck 44 is larger in diameter
than that, 36, at the center section 4', and is separated from the
center neck 36 by a circumferential flange 48 having substantially
the full diameter of the body 4 of the device. The collar 46 is
nevertheless accomodatable within the annulus 50 about the larger
neck 44, and there is a hole 52 in the annular surface of the neck
44 to accomodate the valve stem 54 of the collar 46 when it is
circumsposed about the neck 44. The hole 52 opens in turn into the
annulus 42 of the center neck 36 to that a compressed gas source 56
can be connected with the stem 54, as seen in FIG. 1. This source
commonly includes a tube 100 which is mated with the valve 54 and
suspended with the device 2 in the manhole 6 when the device is
lowered into the same for use.
The center neck 36 is in fact truncated at the top, so that it has
a bench 60 on the same at the forward end thereof, and a ramp 62 on
the rearward end thereof. The ramp 62 is inclined to the bench 60,
and there is an aperture 64 at the center of the bench 60 which
opens into the top of the throat 28 therebelow. There are also part
circumferential grooves 66 and 88 in the upper anterior quadrant of
the end portions 4" and 4''', on that side of the device seen in
FIG. 2, and the grooves 66 and 68 extend about the outer periphery
of the end portions adjacent the neck 36, and open into the
shoulders 38 and 40 of the portions through holes 70 and 72
overlying the bench 60 and ramp 62, respectively. The hole 72 over
the ramp 62 is disposed in the vertical axial plane of the device,
thereas the hole 70 over the bench 60 is angularly offset from the
same to allow for the hole 52 for the valve stem 54, as seen in
FIG. 1. Meanwhile, a pair of L-shaped shoes 74 and 76, having
raised wing walls 74', 76', and apertures 78 and 80 in the upright
end walls 74" and 76" thereof, is mounted on the bench and ramp,
respectively, and abutted against the shoulders 38 and 40
thereadjacent, so that the apertures in the walls 74", 76" register
with the holes 70 and 72 in the shoulders. The shoe 74 on the bench
has a hole 82 in the bottom 74"' thereof, moreover, and the latter
hole 82 registers with the aperture 64 in the bench, so that each
of the respective holes 70, 72, and 64 opens into the annulus 42
through the shoes 74 and 76.
The part circumferential grooves 66 and 68 in the end portions 4",
4"' extend about the same to points approximating the horizontal
plane coinciding with the bottom of the throat 28, and together
with the holes 70, 78 and 72, 80, the grooves 66, 68 provide means
whereby gas flow passages can be formed within the body of the
device, to meter gas to the outer periphery of the same for
purposes of determining the static pressure head in the liquid flow
at the plane, relatively upstream and downstream of the throat 28.
The respective pressure heads are used in turn to determine the
depth of flow upstream and downstream of the throat, as explained
more fully in the aforementioned co-pending Application. Meanwhile,
the pressure head in the throat is also obtained, at 64, and
together the three pressure heads enable the operator to determine
the flow through the device, whether it is in the more normal
direction from the upstream end 24 of the device to the opposing
end 34 thereof, or in the reverse direction, from the end 34 to the
end 24. Toward this end, flexible tubes 84 and 86 are inserted in
the holes 78, 80 at the shoulders 38 and 40 of the device, and the
tubes are roved about the outer periphery of the same in the
grooves 66, 68, to points adjacent the bottoms of the grooves at
which the ends of the tubes coincide with the plane at the bottom
of the throat. In addition, the tubes 84 86 are secured within the
respective grooves by means of a cementitious packing 88 which is
terminated, however, short of the bottom ends 84', 86' of the
tubes, to enable the metering gas to escape therefrom. The ends
84', 86' are mitered, moreover, to facilitate the escape of the gas
from the grooves. In addition, a third more-rigid tube 90 is
inserted in the holes 82, 64 at the center of the bench, and the
bottom end 90' of this latter tube is positioned flush with the top
of the throat 28, again to enable metering gas to escape from it
into the throat. The upper end portions of the tubes 84, 86, 90 are
retained, meanwhile, well outside of their respective sets of holes
70, 78, 72, 80 and 82, 64 and may even extend sufficient length
therefrom to reach the top 6' of the manhole 6 when the device is
lowered into the bottom of the same, as in FIG. 5. Given any lesser
length, they are stubbed out at least sufficient length to mate
with further tubes 92, 94, 96 of sufficiently greater length to
reach the top 6' of the manhole when the latter tubes are connected
with the stubbed-out ends of the same.
The device 2 is also equipped with a two-direction level 98 at the
downstream end thereof, and the level 98 may be of such size as to
be readily readable from the top 6' of the manhole 6 when the
device is positioned in the bottom of the same and installed in the
pipe, as shall be explained.
When the device 2 is put to use, three supply tubes 92, 94, 96 are
mated with the stubbed-out ends of the feed 30 tubes 84, 86, 90 on
the device, as indicated, if the feed tubes do not have sufficient
length to reach the top 6' of the manhole. In addition, a fourth
tube 100 is mated with the valve stem 54 of the collar 46 in the
hole 52, to enable compressed air or the like to be supplied to the
collar for purpose of inflating it, as mentioned earlier. The
device 2 is then shackled to a rigid stirrup 102 by which it can be
suspended pendulum-like in the manhole 6 and positioned over the
opening 12 of the pipe 10, for cradling in the undersection 14 of
the same and then insertion in the upstream section 8 of the pipe,
in the manner of FIG. 5. This may entail the operator resting
chest-down on the ground about the manhole, as seen in FIG. 5 or
standing above the manhole and positioning the device over and on
the pipe from such a position. In any event, to effect the
operation, the clevis 104 of a U-shaped shackle 106, with threaded
elongated legs 108 on the same, is straddled about the neck 36 of
the device at a point on the ramp 62 between the shoes 74 and 76,
and the legs 108 are oriented about the device, generally
perpendicular to the bench 60 at the top of the same, as seen in
FIG. 1. Next, a pair of nuts 110 is screwed onto the legs to points
below the level of the ramp; and an L-shaped cleat 112 with holes
114 spaced apart to mate with the legs 108 of the shackle, is
lowered onto the body of the same until the cleat 112 abuts the
ramp, as in FIG. 1. Following this, a second pair of nuts 116 is
screwed onto the legs, and the two pairs of nuts 110 and 116 are
adjusted to effectively clamp the shackle 106 to the device between
the clevis 104 and the cleat 112. In this condition, the shackle
becomes a rigid stirrup 102 by which the device 2 can be lowered,
positioned and cradled on the pipe, and thereby leveled as will be
explained, and then slidabley inserted in the upstream section 8 of
the same in the manner of FIG. 2, the undersection 14 of the pipe
serving, meanwhile, as a guide for the device as it is manipulated
in the pipe. The operator then visually levels the device at 98,
using the legs 108 of the shackle 106 as a means for rotating
and/or raising or lowering the device until it is suitably
telescoped within the pipe. The device is telescoped, moreover, to
envelop the collar 46 within the upstream section 8 of the pipe,
and this may be observed by the fact that the flange 48 disappears
in the upstream section, or by the fact that it is plumb with the
wall 6' of the manhole. Finally, when the device is suitably
telescoped in the pipe, the collar 46 is inflated with compressed
gas to form a liquid seal between the device and the pipe at the
outer periphery of the device. The liquid in the pipe is
constrained, as a result, to flow through the bore 16 of the
device, either relatively toward the downstream end 34 thereof from
the upstream end 24 thereof, or in the opposing direction should
the pipe experience reverse flow through the manhole.
Ultimately, then the device is fully installed, the three supply
tubes 92, 94 and 96 are collected in a bubbler-type signal
converter (not shown), which is hung in turn on the wall 6' of the
manhole and equipped with the instrumentation schematically
represented in FIG. 6.
The static pressure head readings of tubes 84, 86 may be taken in
the device, rather than outside thereof. In the embodiment of FIGS.
7-.[.9.]..Iadd.12.Iaddend.. The body of the device 2' has ports 113
and 115 in the end portions 4", 4"' thereof, at the points where
the tubes terminate. The ends 84', 86" of the tubes are inserted in
the ports, as seen in FIGS. 8 and 9, and a pair of plugs 117 is
inserted in the bottoms of the grooves 66, 68 to close the ports to
the outer periphery of the end portions.
Referring now to FIG. 6, compressed gas sources .[.18.]. .Iadd.118
.Iaddend.is used to pressurize bubbler tubes 92, 94 and 96. The gas
may be any nonflammable gas such as nitrogen or air. Compressed gas
source 118 may be a cylinder of compressed gas or a compressor. The
gas flows through pressure regulators 120, 122 and 124 which lower
the pressure to the working pressures of bubbler tubes 92, 94 and
96. These pressure regulators also ensure that changes in pressure
in one of the bubbler tubes do not affect the pressures in the
other bubbler tubes. The pressure in each bubbler tube is thus
determined by the depth of submergence of the open end of the tube
(i.e., the static pressure head).
One end of bubbler tube 92 is connected to the pressure port of
differential pressure gauge 126. Similarly, one end of bubbler tube
.[.94.]. .Iadd.96 .Iaddend.is connected to the reference port of
differential pressure gauge 126. When the entrance section 8, and
hence the throat 28, of the device are not filled with liquid,
differential pressure gauge 126 senses the liquid level in the
entrance section of the device. When the entrance section, and
hence the throat, of the device are filled with liquid,
differential pressure gauge 126 senses the difference between the
pressures in bubbler tube 92 and that in bubbler .[.94.].
.Iadd.96.Iaddend.. Differential pressure gauge 128 functions in a
simmilar manner.
During open channel operation, with the flow direction as shown,
the liquid level sensed by differential pressure gauge 126 is
compared to the liquid level sensed by differential pressure gauge
128. Since the device is level, the open end of bubbler tubes 92
and .[.96.]. .Iadd.94 .Iaddend.terminate at the same elevation. In
the preferred embodiment, they both terminate at the same elevation
as the elevation of the invert of the throat, but any elevation at
or below that elevation is acceptable.
In conventional practice, the ratio of the downstream depth of flow
to the upstream depth of flow (when expressed as a percentage) is
termed the submergence. When the ratio exceeds a certain value,
usually in the, range 65-75 percent, a critical flow flume is said
to be operating above its maximum submergence or above its modular
limit. When such a meter operates below its modular limit, the
device is said to be operating in a free flow mode. In a free flow
mode, a unique relationship exists between the upstream depth of
flow and the flow rate, if the meter is installed in a sewer of low
to moderate slope, say up to about 2 percent slope. When such a
meter operates above its modular limit, the device is said to be
operating in a submerged mode. In a submerged mode, the flow rate
predicted by a free flow calibration curve must be corrected by a
factor that is a function of the percent submergence. Examples of a
free flow calibration curve and a correction curve are presented in
FIGS. 10 and 11, respectively. The flow rate obtained from FIG. 10
would be multiplied by the correction factor obtained from FIG. 11
to determine the corrected flow rate.
During open channel operation, with the flow direction opposite
that shown, differential pressure gauge 128 is used to sense the
"upstream" depth of flow and differential pressure gauge 126 is
used to sense the "downstream" depth of flow .Iadd.by means of a
signal converter, such as computer 200. .Iaddend.Similar
calibration and correction curves would be used to relate pressure
reading into flow rates. Thus the improved meter is capable of
metering flow rates under the following conditions for both forward
and reverse flow:
Open channel
Free flow
Submerged flow
Full Pipe
It should be apparent that, at positive sewer slopes appreciably
greater than zero, reverse open channel flow will typically occur
only momentarily, if at all. This is true because reverse flow is
caused by a downstream increase in liquid depth. If the downstream
increase in depth occurs slowly, the depth upstream will slowly
increase until the increase stops or the sewer fills with liquid,
but reverse open channel flow will not occur. If the downstream
increase in depth occurs suddenly, then a surge will move upstream
as a wave. Only during the passage of the wave might reverse open
channel flow occur.
In an alternative embodiment, shown with dashed lines on FIG. 6,
bubbler tube 92 is also connected to the pressure port of
differential pressure gauge 130 and bubbler tube .[.96.]. .Iadd.94
.Iaddend.is also connected to the reference port of differential
pressure gauge 130. When the device is operating in an open channel
mode, differential pressure gauge 130 is used to directly sense the
difference between the pressures in the bubbler tubes, and, hence,
the difference between the upstream and downstream liquid depths.
This difference is compared to the upstream or downstream liquid
depth to determine (1) the percent submergence and (2) the correct
correction factor, if the meter is operating above its modular
limit.
In the embodiment shown in FIGS. 1-5, the bubbler tubes 92 and 96
sense the static pressure head in the annular space between the
inside wall of the sewer and the outside wall of the meter. The
liquid in the annular space acts as a stilling well to attenuate
variations in the sensed pressure. Furthermore, the open ends of
the tubes are relatively isolated from the flowing liquid, and thus
are less likely to be fouled by gross wastewater solids. Because
the end of the annular space is open in the direction of flow, the
static pressure head sensed by the tubes includes a very small
component of velocity head equal to the head produced by stagnation
of that portion of the velocity profile adjacent to the sewer walls
as it impinges on the open end of the annular space. Even if the
meter is installed in a sewer much larger than the meter outside
diameter, the impact of incorporation of a small component of
velocity head in the upstream and downstream head measurements does
not significantly impact metering accuracy.
In the preferred embodiments of FIGS. 1-5 and 6-9, the entrance
section 26, the exit section 30, the entrance transition 22 and the
exit transition 32 have circular sections with their centers along
the longitudinal axis 18 of the meter. The throat section 28 has a
truncated circular section with a center along the same axis. The
top 28' of the throat section is flat. In the preferred
embodiments, the entrance transition 26 and exit transition 30
converge at a slope of 1:6. This transition slope is best because
it causes the least head loss between the throat section and the
downstream section and, hence, maximizes the modular limit (maximum
submergence of the meter). This design maximizes the amount of
submergence (due to tailwater) that can be accomodated by the meter
before the modular limit is reached and before two depth
measurements are required for metering of open channel flow.
Another improvement in meter design is that the throat section is
adapted relative to the entrance section to cause simultaneous
filling before the modular limit is reached when the meter is
installed in sewers of minimum slope. In conventional practice, a
sewer of minimum slope is one which flows full at an average
velocity of 2 feet per second. Simultaneous filling occurs earlier
(at lower normal depths) in sewers of greater slope providing an
additional factor of safety against submerged operation.
In meters of similar design, the modular limit is a function solely
of the size (inside diameter) of the meter. The modular limit of
meters with nominal diameters of 8 to 12 inches typically ranges
from 65 to 75 percent.
Given a particular sewer diameter, the normal depth of flow at a
given flow rate can be determined using the well-known Manning
formula:
where
Q=flow rate
n=coefficient of roughness (Manning's a)
A=area of flow (which is a function of normal depth of flow)
R=hydraulic radius (which is the area of flow divided by the wetted
perimeter, both a function of the normal depth of flow)
S=sewer slope
The above formula is usually solved by trial and error,
substituting values for depth of flow into the formula until the
sought after flow rate results.
To illustrate the application of the Manning formula, assume the
following:
Sewer diameter--8 inches (0.667 ft)
Sewer slope--0.0033 ft/ft
Manning's n--0.013
By trial and error, wastewater flowing at a rate of 0.525 cubic
feet per second (cfs) will flow at a normal depth of 0.433 ft (5.2
inches).
As was noted above, both the upstream ad downstream depths of flow
are measured by this invention relative to the elevation of the
bottom of the throat. The Manning formula, on the other hand,
predicts the downstream normal depth of flow relative to the invert
elevation of the sewer. With a device with an entrance inside
diameter of 6.9 inches and a throat inside diameter of 5.5 inches
installed in an 8-inch sewer, the throat invert elevation would be
about 1.25 inches (0.104 feet) above the sewer invert, with a
relatively low sewer slope. Thus, a downstream normal depth of
0.433 ft would cause a downstream depth reading of
0.433-0.104=0.329 feet=3.95 inches to be registered by the
meter.
The equations presented in U.S. Pat. Application No. 051,325 could
be used to show that a meter with an entrance section with a 6.9
inch inside diameter and a throat with a centered 5.5 inch inside
diameter and a 4.5 inch height would cause simultaneous entrance
section and throat section filling at a flow rate of 0.525 cfs.
That is, at a flow rate of 0.525 cfs, under free flow conditions,
the upstream depth (measured relative to the throat invert
elevation) would be 6.9-0.7=6.2 inches, because the throat invert
elevation in this design is 0.7 inches above the entrance invert
elevation.
With this meter installed in an 8-inch sewer, the ratio of the
downstream depth reading (3.95 inches) to the upstream depth
reading (6.2 inches) would be 0.64 or 64 percent. With an exit
transition of 1:6, the meter would have a modular limit of about 65
percent. Thus, with this design, the throat section and upstream
section of the meter would simultaneously fill before the modular
limit was reached, if the sewer downstream from the meter were
flowing at the normal depth predicted by the Manning formula. This
is important because one can be assured that submerged operation
will not occur during normal operation of the meter. Metering under
open channel conditions in an unsubmerged mode as well as metering
under full pipe conditions requires obtaining and manipulating only
a single differential pressure reading. On the other hand, metering
under open channel conditions in a submerged mode requires
obtaining and manipulating two differential pressure readings and,
for this reason, is inherently less accurate. Adapting the throat
of the meter to cause simultaneous throat and entrance filling at a
flow rate below the modular limit is thus a significant improvement
in meter design.
A portable wastewater flow metering device has been disclosed for
installation in the entrance pipe to a sewer manhole. The device is
capable of measuring liquid flow both under free flow, open channel
conditions and under full pipe conditions by taking measurements in
a sewer adjacent to one sewer manhole.
The invention is not to be construed as limited to the particular
forms disclosed herein, since these are to be regarded as
illustrative rather then restrictive. It is the intention of this
patent to cover all changes and modifications of the example of the
invention herein chosen for the purposes of the disclosure, which
do not constitute departures from the spirit and scope of the
invention.
* * * * *