Abstrict 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.
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. 051325 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.
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