CA1315130C - Apparatus and technique for metering liquid flow - Google Patents
Apparatus and technique for metering liquid flowInfo
- Publication number
- CA1315130C CA1315130C CA000545117A CA545117A CA1315130C CA 1315130 C CA1315130 C CA 1315130C CA 000545117 A CA000545117 A CA 000545117A CA 545117 A CA545117 A CA 545117A CA 1315130 C CA1315130 C CA 1315130C
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- pipe
- section
- throat
- flow
- bore
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Abstract
APPARATUS AND TECHNIQUE
FOR METERING LIQUID FLOW
ABSTRACT
The gravity flow of a liquid in an open pipe is metered during open channel flow, during surcharged flow, and during the transition between the two. A
tubular venturi metering device is employed, and when during open channel flow, the liquid depth rises in the section of the pipe upstream from the device, the throat of the device fills with liquid substantially simutan-eously with the upstream section of the pipe, so that during the transition, the device continues to provide a flow determination.
FOR METERING LIQUID FLOW
ABSTRACT
The gravity flow of a liquid in an open pipe is metered during open channel flow, during surcharged flow, and during the transition between the two. A
tubular venturi metering device is employed, and when during open channel flow, the liquid depth rises in the section of the pipe upstream from the device, the throat of the device fills with liquid substantially simutan-eously with the upstream section of the pipe, so that during the transition, the device continues to provide a flow determination.
Description
l 131513~ 73818-19 DescriPtlon APPARATUS AND TECHNI~U~
FOR METERING LIOUID FLOW
Technlcal Fleld This lnventlon relates to an apparatus and technique for meterlng the flow of a llquld such as sewage, whlch ls flowlng by gravlty in an elongated plpe that ls open to atmosphere, both for the condltlon whereln the plpe ls less than fllled wlth the llquld, and the condltlon whereln the plpe ls fllled wlth the llquld. In partlcular, lt relates to an apparatus and technlque of thls nature for meterlng the flow of storm dralnage ln a sewer plpe at a manhole thereln.
Backaround Art The rate of flow of sewage ln a sewer plpe ls common-ly determlned by determlnlng the depth of flow ln the same and then convertlng that lnto a flow rate. The depth of flow ls often determlned ln turn by means of a welr or flume. Welrs and flumes do not provlde a fully satlsfactory means for measurlng the rate of flow, however, when the sewer plpe ls operatlng under surcharged condltlons, that ls, when the sewer plpe 18 fllled to its top and perhaps flowlng under a sllght pressure condltlon. Under such condltlons, a welr ls dlfflcult to callbrate and - ~31313~
must be fabricated to suit the physical configuration of each sewer or manhole. It is also subject to upstream sedimentation and to being fouled by debris.
Flumes, on the other hand, such as a Palmer Bowlus venturi flume, are inaccurate at upstream depths of flow that exceed 75% of the sewer diameter, and therefore, are useless under surcharged conditions.
As an alternative, the head loss between two manholes may be measured (usually in fractions of an inch), and certain culvert formuli and the Manning formula may be used to estimate the flow rate. The estimate is in terms of a gross figure only, however, and of course, this method requires that the depth of flow be measured in two manholes, rather than one, thus doubling the cost of the operation.
Disclosure of the Invention The present invention provides an apparatus and technique for measuring the flow in a sewer pipe under both full and less-than-full conditions.
According to the invention, a tubular venturi metering device is installed in the pipe so that the longitudinal axis of the open ended bore through the device is disposed substantially parallel to the longitudinal axis of the pipe. The bore has 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 i5 formed in the bore which opens to the downstream end thereof. A liquid seal is formed between the device and the pipe at the outer periphery of the device so that the liquid in that section of the pipe upstream from the device is constrained to flow through the bore of the device, relatively toward the downstream end thereof. The static pressure of the liquid in the aforesaid upstream section of the pipe is determined 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. Meanwhile, the cross-section of the throat is adapted, relative to that of the upstream section of the pipe, transverse the respective axes thereof, so that the throat fills with liquid substantially simultaneously with the upstream section of the pipe, when the liquid depth rises therein. Accordingly, when both the upstream section of the pipe and the throat are filled, the static pressure of the liquid in the throat of the device and the upstream section of the pipe can be determined, so that the difference between the latter two pressures can be determined in turn to meter the 3 ~
~ 73818-l9 flow Ln the plpe for the full condltlon as well as the less-than-full condltlon of the same.
The bottom of the throat ls commonly leveled before the respectlve determinatlons are made, and ln the presently preferred embodlments of the lnventlon, the throat has a poly-gonal cross-sectlon, transverse the longltudlnal axis of the bore.
The apparatus compr1ses a tubular venturl meterlng devlce whlch ls lnstalled ln the plpe so that the long~tudinal axls of the open ended bore through the device ls dlsposed sub-stantlally parallel to the longltudlnal axis of the plpe. The bore has an axlally lnwardly tapered entrance sectlon ad~acent the upstream end thereof, whlch converges toward the axls of the bore ln vertlcal planes parallellng the axls of the bore and ln that axlal dlrectlon of the bore relatlvely toward the downstream end of the bore, but termlnates short of the axls of the bore so that a throat ls formed ln the bore whlch opens to the downstream end thereof. In addltlon, there are means for formlng a llquld seal between the devlce and the plpe at the outer perlphery of the devlce so that the llquld ln that sec-tion of the plpe upstream from the devlce ls constralned to flow through the bore of the devlce, relatlvely toward the downstream end thereof. There are also flrst means for deter-mlnlng the statlc pressure of the llquld ln the aforesald 13 ~ ~ ~ 3 ~
73818-l9 upstream sectloll of the pipe when the liquld ls flowing ln the plpe at a depth less than that adapted to fill the upstream sectlon of the plpe, to meter the flow ln the plpe for the less-than-full condltion thereof. Meanwhile, the cross-sectlon of the throat ls adapted, relatlve to that of the upstream sectlon of the plpe, transverse the respectlve axes thereof, so that the throat fllls wlth llquld substantlally slmultaneously wlth the upstream sectlon of the plpe, when the llquld depth rlses thereln. Second means are provlded for determlnlng the statlc pressure of the llquld ln the throat and the upstream sectlon of the plpe when both the upstream sectlon of the plpe and the throat are fllled, so that the dlfference between the latter two pressures can be determlned to r,~eter the flow ln the plpe for the full condltlon as well as the less-than-full condltion thereof.
In many of the presently preferred embodlments of the lnventlon, the axlally lnwardly tapered entrance sectlon of the bore of the devlce has a top, bottom and sldes whlch taper axlally lnwardly of the axls of the bore ln the aforesald down-stream axlal dlrectlon thereof. Moreover, ln certaln embodl-ments, the wall of the axlally inwardly tapered entrance sec-tlon of the bore has the trapezoldal sectlon ln a truncated conlcal cross-sectlon ln that vertlcal plane colncldlng wlth the axls of the bore.
~3~ 5~ ~
In some of the presently preferred embodlments of the lnventlon, the bore also has an axlally outwardly tapered exit sectlon ad~acent the downstream end thereof, whlch dlverges from the axls of the bore ln the aforesald downstream axlal dlrection thereof. Moreover, ln certaln of these embodlments, the wall of the axlally outwardly tapered exlt section of the bore has the trapezoidal section ln a truncated conical cross-section 1n that vertlcal plane coincldlng wlth the axis of the bore.
In some of the presently preferred embodiments of the lnvention, the flrst pressure determinatlon means lnclude a pressure sensor whlch ls dlsposed on the devlce ad~acent the upstream end of the bore. Preferably, the pressure sensor ls dlsposed ad~acent the bottom of the upstream end of the bore.
In certain embodlments, moreover, the second pressure determl-nation means lnclude a pressure sensor which is dlsposed on the devlce ad~acent the throat of the bore therein, and preferably ad~acent the top of the throat.
Preferably, the apparatus further comprises means for leveling one side of the device ln the plpe, and preferably the bottom of the throat ln the bore of the device. Also, the throat preferably has a polygonal cross-sectlon, transverse the longltudlnal axls of the bore.
13~5~
Where the pipe and the device have cylindrical cross-sections transverse the respective longitudinal axes thereof, the seal forming means may include an inflatable tube which is circumposed about the device between it and the pipe. Preferably, the inflatable tube is seated in an annular groove formed about the outer periphery of the device.
The device may have a hollow or solid body construction between the outer periphery of the same and the bore therethrough.
In most of the presently preferred embodiments of the invention, there are also means for determining the flow in the pipe under the full and less-than-full conditions thereof, from the pressure of the liquid in the throat and the upstream section of the pipe.
Where there is a manhole to the sewer pipe, the metering device is often inserted in that portion of the pipe through which the flow enters the manhole.
In one group of presently preferred embodiments, the apparatus comprises, in combination, a cylindrical member having end portions disposed at substantialy the same elevation and an inner surface forming a tubular venturi type device which in turn has an entrance section and a throat section. It also comprises means circumposed about the cylindrical member and operable to establish a fluid 1 3 ~
tight connection between the member and the internal wall of the pipe when the member is substantially coaxially inserted therein, whereby the li~uid in that section of the pipe upstream from the member is constrained to flow through the entrance and throat sections of the venturi type device. In addition, there are means for sensing the pressure of the liquid at the crest of the throat section of the tubular venturi type device, and means for sensing the pressure of the liquid at the invert of the entrance section of the tubular venturi type device.
Brief Description of the Drawings These features will be better understood by reference to the accompanying drawings which illustrate a presently preferred embodiment 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:
FIGURE l is a part cut-away, part perspective view of the manhole and the pipe when the device has been installed in the upstream or entrance section of 2S the pipe;
FIGURE 2 is a longitudinal cross-sectional view of the device along the longitudina:L axis of the pipe;
1 3 ~
FIGURE 3 is an end view of the device from the manhole;
FIGURE 4 is a cross-sectional view of the device along the line 4-4 of Figure 2, FIGURE 5 is a schematic illustration of the flow through a prior art device when the liquid in the pipe is flowing in the less-than-full or open channel flow condition thereof;
FIGURE 6 is a similar illustration when the pipe has filled to the top thereof;
FIGURE 7 is a similar illustration when the pipe is surcharged by the flow;
FIGURE 8 is a 8C ,hematic illustration of the operation of the inventive device in the open channel flow condition of Figure 5;
FIGURE 9 i8 a similar illustration of the operation of the device when the flow has reached the top of the pipe, as in Figure 6 and FIGURE 10 is a similar illustration of its operation when the pipe is surcharged by the flow, as in Figure 7.
Best M _ for Carrying Out the Invention Referring to the drawings, it will be seem that the portable device 2 has a cylindrical body 4 and is adapted diametrically to be slideably inserted into the entrance section 6 of a sewer pipe 8 from a 131~ ~ 3 ~
manhole 10 therein. If necessary or desired, the body 4 of the device may be subdivided into two or more longitudinal sections (not shown) to facilitate its insertion in the pipe from the manhole; but in any event, the central portion of the device has an annular groove 12 about the circumference thereof, for receiving an inflatable collar 14 with which to fix and seal the device in the pipe. The collar 14 is mounted in the groove 12 prior to the insertion of the device in the pipe, and is e~uipped with an elongated valve stem 16, and a valve 15 thereon, through which gas can be charged into the collar 14 from the manhole 10, for purposes of inflating the collar.
As a tubular venturi metering device, the device 2 has an open-ended bore 18 through the same, and the longitudinal axis of the bore coincides with that of the device itself, so that when the device is installed in the pipe, the axis of the bore is substantially parallel to the axis 20 of the pipe.
The bore 18 also has an axially inwardly tapered entrance section 22 adjacent the upstream end 25 thereof, which converges toward the axis of the bore in the downstream axial direction thereof. In addition, the bore 18 has an axially outwardly tapered exit section 26 adjacent the downstream end 28 thereof, which diverges from the axis of the bore in the aforesaid downstream axial direction thereof.
11 13 ~
The entrance and exit sections are interconnected at the axis of the bore by a polygonal throat 30. The cross-section of the throat 30 is adapted, relative to that of the pipe upstream from the device, transverse the respective axes thereof, so that the throat fills with liquid substantially simultaneously with the upstream section of the pipe, when the liquid depth rises therein, as shall be explained.
However, for the present, suffice it to say that the throat 30 is orthogonal, and in fact, square in cross-section, whereas the entrance and exit sections 22 and 26 of the bore 18 are truncated cones 32 cut by vertical chords 34 at the sides thereof. See Figure 3. The chords 34 are planar and terminate just short of the respective ends 24 and 28 of the device, so that in the end elevational view of Figure 3, the cylindrical exit end 28 of the device is immediately apparent to the viewer, whereas the planar side walls 34 and the part conical top and bottom walls 34 of the exit section 26 lie therebehind.
As seen in Figures 1 - 3, moreover, the device 2 is equipped with a bench 36 on the top of the same, at the exit end 28 thereof, and a level indicator 38 is mounted on top of the bench. The level indicator 38 may be of the bubble-level type, with a crosshair for indicating the level condition. Both the bench 1 3 ~ 0 12 73818-lg 36 an~ the lndicator 38 are on parallels to the top 40 and/or bottom 42 of the throat, so that the lndlcator 38 can be used to level the throat for the meterlng operatlon.
In addltlon, the devlce 2 has a pressure sensor 44 mounted beneath the entrance sectlon 22 at the lower part conlcal wall or surface 32 thereof; and a second pressure sensor 46 ls mounted at or near the top or crest 40 of the throat, at the surface thereof. The pressure sensors 44 and 46 may be elther plezometers or plezoelectrlc pressure trans-ducers.
The pressure sensor 44 ls employed to determlne thestatlc pressure of the llquld ln the upstream sectlon of the plpe when the liquld ls flowlng ln the plpe at a depth less than that adapted to flll the upstream sectlon of the plpe, so that the devlce can be used to meter the flow ln the plpe for the less-than-full condltion thereof. The pressure sensor 46 ls employed to determlne the statlc pressure of the llquld ln the throat 30 of the devlce, so that the devlce can be employed to meter the flow ln the plpe for the full condltlon thereof.
Thls ls commonly done by determlnlng the dlfference between the pressure ln the upstream sectlon of the plpe and the pressure ln the throat of the devlce.
For thls purpose, a slgnal converter 48 ls mounted on .~'`
~ 3 31 ~3~ ~ ~
13 7381~-19 the wall of the manhole lO to receive the pressure slgnals from the sensors 44 and 46 through a two-lead conductor 50 extending therebetween. The converter 48 converts the slgnals to flow rates, and the flow rates are stored ln turn ln an electronlc memory (not shown~ wlthin the converter. The converter 48 may also convert the dlfference between the pressure signals, to meter and store the flow rate of the plpe for both the full condltion and the less-than-full conditlon thereof, as indlca-ted.
The converter 48 may be a conventional bubbler-type mechanlsm, that ls, one in whlch gas bubbles are discharged from the end of a tube (not shown) submerged ln a llquld. The pressure requlred to malntaln a predetermlned bubble rate ls measured uslng a bellows (not shown) or some other such mechan-lsm. The pressure ls proportlonal to the depth of submergence of the end of the tube, and a dlfferentlal between two pres-sures can be determined by measurlng the deflectlon of the dlaphragm (not shown) of the bellows when one pressure is lm-posed on each slde of the dlaphragm. Of course, the statlc pressure at the top of the throat 30 ls amblent alr pressure until the throat fllls wlth llquld.
The flow data may be recorded ln the converter by an lnk pen and a paper chart (not shown~, or by a 14 ~3~
stylus and a pressure sensitive chart (not shown).
Alternatively, the converter may be a conventional electronic mechanism such as a piezoelectric mechanism (not shown) which emits elec-trical signals that are proportional to the pressureexerted on them. Furthermore, a digital integrated circuit mechanism (not shown) may be programmed to intermittently calculate a flow rate, and to store it in an electronic memory, given the static pressure at the entrance section 22 of the device and/or the differential pressure across the device.
In use, the device 2 is inserted into the open end of the entrance section 6 of the pipe and installed in the same in the manner of Figure 1. At the same time, the body of the device i8 rotated to place the level indicator 38 at the top of the same, and to level the device using the indicator. A
source of pressurized gas (not shown) is attached to the valve 15 to introduce gas into the inflatable collar 14, and the collar is inflated between the body of the device and the inside surface of the entrance section of the pipe. When inflated, the collar 14 fixes the device in position and provides a fluid tight seal between the device and the pipe.
Thereafter, the conductor 50 to and from the pressure sensors 44 and 46, i5 routed to the top of the manhole, the converter 48 is attached to it and mounted on the wall of the manhole, and the pressure ~ 3 ~
slgnals to the converter are employed to meter the flow in the pipe for the full condltion, as well as the less-than-full condltlon of the same.
Referrlng now to Flgures 5 - 10, lt will be seen that when a sewer pipe 8 is open to atmosphere and the llquld 51 thereln flows by gravlty in the same, the liqui~ normally flows under open-channel flow condltlons, that ls, condltlons whereln the pipe ls less than filled with the llquld, as ln Flgure 5.
However, on occaslon, the plpe may be flooded because of a downstream constrlctlon, or by some unusual surge of llquld through lt from upstream. In the past, lt was possible, uslng a venturl meterlng devlce 42, to meter the flow under normal open channel flow condltlons. But as the depth of flow rose to the polnt where the llquld fllled that sectlon of the plpe up-stream from the device, it was no longer possible to get an accurate readlng of the liquld flow rate. Thus, when there was flooding, the devlce no longer gave an accurate readlng of the flow rate. Ultlmately, the plpe would become so surcharged wlth llquld that the upstream llquld level ln the plpe would rlse above the top of the plpe. In thls condltlon, the devlce could be employed to meter the flow as a venturl tube type pressure differentlal produclng devlce. However, ln the transltlon stage between (1) the tlme when the flow ~3 ~ `x~ ~
was such that the venturi device performed as a venturi flume, and (2) the time when the pipe was surcharged to the extent that the device performed as a venturi tube, no flow measurement was possible.
According to the present invention, the flow can be metered at all times, even in the transition stage, if the throat is dimensioned so that there is (1) "necking downn of the liquid during open channel flow and (2) zero "necking down" of the liquid when the upstream section of the pipe fills with liquid.
To explain, when a venturi metering device 42 is installed in a sewer pipe 8 or the like, the device operates as a flume so long as the flow 52 is open channel flow. That is,'when the flow 52 reaches the throat 56 of the device, it dips or "necks down" as seen at 54 in Figure 5, and assumes a depth that can be calculated. This depth is termed the "critical depth." The operation of the device as a flume makes it possible, in turn, to determine the flow rate in the pipe, since a relationship exists between the upstream depth of flow and the rate of flow itself.
As the depth of flow in the upstream section of the pipe increases, however, the "necked down" flow in the throat 56 of the venturi device does not increase correspondingly, and there is a point when the upstream section of the pipe fills with liquid 51 while the throat 56 continues to have "necked down"
flow 54 therethrough - - that is, flow with an airgap 17 1 3~
above the same, as in Figure 6. At this point that is, the point when the upstream section of the pipe fills with liquid - it is no longer possible to monitor the depth of flow in the upstream section of the pipe, and therefore, no longer possible to determine the rate of flow through the pipe.
Meanwhile, since the throat 56 is not filled with liquid at this time, the device cannot be employed as a venturi-tube type pressure differential producing device. In fact, it will not be possible to use the device as such until the throat is force-filled with liquid, such as when the pipe becomes so surcharged with liquid that the upstream liquid level in the pipe rises above the top of the pipe. See Figure 7.
This transition stage - - when the device is no longer operating as a venturi flume and yet the pipe is not so surcharged that the device will perform as a venturi tube - - may exist for a considerable length of time.
~0 Referring now to Figures 8 - 10 and the inventive device 40', 42' therein, the cross-section of the throat 30 is dimensioned, relative to that of the upstxeam section of the pipe, transverse the respective longitudinal axes thereof, so as to dictate that the throat 30 will fill with liquid substantially simultaneously with the upstream section of the pipe. That is, the flow 54 through 13~i3~
the throat 30 ls controlled so that the flow no longer tends to "neck: down~' ln lt when the llquid ln the upstream section reaches the top of the plpe. Put another way, the "necking down~ effect 54 ahates to zero at that tlme when the upstream sectlon of the plpe fllls wlth llquid. In thls way, a statlc pressure readlng of the throat, and a statlc pressure readlng of the upstream sectlon of the plpe, wlll give a true readlng of the flow through the plpe slnce the dlfference between the two pressures can be used to determlne the flow ln thls transi-tlon condltlon.
Of course, as ln the prlor art devlces, one can stlllread the statlc pressure of the upstream sectlon of the plpe durlng open channel flow (Flgure 8), and can contlnue to read the throat and upstream pressures ~urlng surcharged flow (Flgure 10), so as to determlne flow under all condltlons, whether open channel flow, transltlon flow, or surcharged flow.
In order to control the flow through the throat ln thls fashlon, however, it is necessary to provide an axlally lnwardly tapered entrance sectlon 22 to the throat, as shown ln Flgures 1 - 4, and the entrance sectlon must converge toward the axls of the bore in vertlcal planes parallellng the axls and ln that axial dlrectlon relatlvely toward the downstream end 28 of the bore. Only when the entrance sectlon converges in thls fashlon can the cross-sectlon of l9 1 ~ ~3~3~
the throat be dimensioned so that the "necking down"
effect abates to zero when the upstream section of the pipe fills with liquid. One may constrict the sides of the entrance section, or one side, but he must also constrict the entrance section in vertical planes parallel to the axis of the bore.
Given the diameter of the sewer pipe and the range of flow rates in the same, the cross~section of the throat can be determined empirically using the following equations:
Qc = ~ (a3/T) x g or v2 = a/2T
2g D1 + v2 = Z + Dc + v2 + hL
2g 2g In the above equations, "Qc" i8 the flow rate in the throat under open channel flow conditions; "a" is the cross-sectional area of flow in the throat and thus the cross-sectional area of the throat itself when the throat is filled with liquid; "T" is the width of the top of the flow in the throat and thus the width of the throat at the top of the same when the throat is filled with li~uid; and "g" is acceleration due to gravity. "D1" is the depth of flow in the upstream section of the pipe; "V2" is the average velocity of flow in the th:roat; llZ~ is the 13 ~ 3 helght to whlch the bottom of the throat ls raised above the bottom of the plpe (l.e., the "slll helght"); ''Dc'' ls the depth of flow ln the throat; "hL" ls the head loss between the up-stream sectlon of the plpe and the throat.
Typlcally, the head loss can be expected to be 5 - 10 percent of the difference in kinetlc energy (velocity head) be-tween the upstream sectlon of the plpe and the throat. Thls is a very small number for practical purposes, and therefore, for slmpliclty, ls ignored ln the example followlng.
To lllustrate the appllcatlon of the equatlons, assume that the plpe diameter ls 8 lnches, that the devlce lt-self has a 1/4 lnch wall thlckness and that because of lts wall thlckness, the plpe dlameter at the mouth of the devlce ls effectlvely 7-1/2 lnches. Assume, moreover, that a devlce wlth an orthogonal throat ls to be used, and that the throat has a wldth of 4 lnches and a slll helght of 1-3/4 lnches. For such an orthogonal throat, Qc = ~ x T x DC/2' and Dl ~ Dc + Z + a/2T - v2 2g ~5`~ 3~
Uslng conventlonal emplrlcal practlce, Dc 15 4 inches or .333 feet.
Qc \/32.16 x .333 x (.333)2/3 Qc = .363 cfs a = .333 x .333 = .111 sf Dl 5 .333 + .146 + .111/t2 x .333) - V~
2g Followlng the same practlce, Dl ls the effective plpe diameter of .625 foot.
.625 = .333 + .146 + .167 - .022 ~ .624 Thus, when a devlce wlth 1/4 lnch thlck walls ls ln-serted lnto an 8 lnch plpe, a throat that ls 4 lnch square and centered ln the devlce wlll cause the throat to flll wlth llquld substantlally slmultaneously wlth the upstream sectlon of the plpe when the llquld depth rlses thereln.
The equatlons are equally appllcable to other throat conflguratlons. In the case of a rectangular conflguratlon, the cross-sectlon can be vertlcally rectangular, but wlth a rlsk of clogging ln small dlameter sewers. On the other hand, wlth large dlameter sewers, a vertlcally rectangular cross-sectlon may in fact be the most deslrable to accompllsh the slmultaneous flll functlon.
The throat need not be orthogonal, nor even poly-gonal. It may, for example, have convexly bowed sldes, and ln fact, sldes formed by the plpe ltself, as ln Flgures 8 - 10.
~3~
Similarly, the body 4 of the device need not be solid.
It nnay be hollow between the outer cylindrical wall and the hore 18 l;hereof; and if desired, when hollow, the cylindrical wall of the same may be perforated (not shown) to allow alr and liquid to escape from within the device.
; 1.
FOR METERING LIOUID FLOW
Technlcal Fleld This lnventlon relates to an apparatus and technique for meterlng the flow of a llquld such as sewage, whlch ls flowlng by gravlty in an elongated plpe that ls open to atmosphere, both for the condltlon whereln the plpe ls less than fllled wlth the llquld, and the condltlon whereln the plpe ls fllled wlth the llquld. In partlcular, lt relates to an apparatus and technlque of thls nature for meterlng the flow of storm dralnage ln a sewer plpe at a manhole thereln.
Backaround Art The rate of flow of sewage ln a sewer plpe ls common-ly determlned by determlnlng the depth of flow ln the same and then convertlng that lnto a flow rate. The depth of flow ls often determlned ln turn by means of a welr or flume. Welrs and flumes do not provlde a fully satlsfactory means for measurlng the rate of flow, however, when the sewer plpe ls operatlng under surcharged condltlons, that ls, when the sewer plpe 18 fllled to its top and perhaps flowlng under a sllght pressure condltlon. Under such condltlons, a welr ls dlfflcult to callbrate and - ~31313~
must be fabricated to suit the physical configuration of each sewer or manhole. It is also subject to upstream sedimentation and to being fouled by debris.
Flumes, on the other hand, such as a Palmer Bowlus venturi flume, are inaccurate at upstream depths of flow that exceed 75% of the sewer diameter, and therefore, are useless under surcharged conditions.
As an alternative, the head loss between two manholes may be measured (usually in fractions of an inch), and certain culvert formuli and the Manning formula may be used to estimate the flow rate. The estimate is in terms of a gross figure only, however, and of course, this method requires that the depth of flow be measured in two manholes, rather than one, thus doubling the cost of the operation.
Disclosure of the Invention The present invention provides an apparatus and technique for measuring the flow in a sewer pipe under both full and less-than-full conditions.
According to the invention, a tubular venturi metering device is installed in the pipe so that the longitudinal axis of the open ended bore through the device is disposed substantially parallel to the longitudinal axis of the pipe. The bore has 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 i5 formed in the bore which opens to the downstream end thereof. A liquid seal is formed between the device and the pipe at the outer periphery of the device so that the liquid in that section of the pipe upstream from the device is constrained to flow through the bore of the device, relatively toward the downstream end thereof. The static pressure of the liquid in the aforesaid upstream section of the pipe is determined 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. Meanwhile, the cross-section of the throat is adapted, relative to that of the upstream section of the pipe, transverse the respective axes thereof, so that the throat fills with liquid substantially simultaneously with the upstream section of the pipe, when the liquid depth rises therein. Accordingly, when both the upstream section of the pipe and the throat are filled, the static pressure of the liquid in the throat of the device and the upstream section of the pipe can be determined, so that the difference between the latter two pressures can be determined in turn to meter the 3 ~
~ 73818-l9 flow Ln the plpe for the full condltlon as well as the less-than-full condltlon of the same.
The bottom of the throat ls commonly leveled before the respectlve determinatlons are made, and ln the presently preferred embodlments of the lnventlon, the throat has a poly-gonal cross-sectlon, transverse the longltudlnal axis of the bore.
The apparatus compr1ses a tubular venturl meterlng devlce whlch ls lnstalled ln the plpe so that the long~tudinal axls of the open ended bore through the device ls dlsposed sub-stantlally parallel to the longltudlnal axis of the plpe. The bore has an axlally lnwardly tapered entrance sectlon ad~acent the upstream end thereof, whlch converges toward the axls of the bore ln vertlcal planes parallellng the axls of the bore and ln that axlal dlrectlon of the bore relatlvely toward the downstream end of the bore, but termlnates short of the axls of the bore so that a throat ls formed ln the bore whlch opens to the downstream end thereof. In addltlon, there are means for formlng a llquld seal between the devlce and the plpe at the outer perlphery of the devlce so that the llquld ln that sec-tion of the plpe upstream from the devlce ls constralned to flow through the bore of the devlce, relatlvely toward the downstream end thereof. There are also flrst means for deter-mlnlng the statlc pressure of the llquld ln the aforesald 13 ~ ~ ~ 3 ~
73818-l9 upstream sectloll of the pipe when the liquld ls flowing ln the plpe at a depth less than that adapted to fill the upstream sectlon of the plpe, to meter the flow ln the plpe for the less-than-full condltion thereof. Meanwhile, the cross-sectlon of the throat ls adapted, relatlve to that of the upstream sectlon of the plpe, transverse the respectlve axes thereof, so that the throat fllls wlth llquld substantlally slmultaneously wlth the upstream sectlon of the plpe, when the llquld depth rlses thereln. Second means are provlded for determlnlng the statlc pressure of the llquld ln the throat and the upstream sectlon of the plpe when both the upstream sectlon of the plpe and the throat are fllled, so that the dlfference between the latter two pressures can be determlned to r,~eter the flow ln the plpe for the full condltlon as well as the less-than-full condltion thereof.
In many of the presently preferred embodlments of the lnventlon, the axlally lnwardly tapered entrance sectlon of the bore of the devlce has a top, bottom and sldes whlch taper axlally lnwardly of the axls of the bore ln the aforesald down-stream axlal dlrectlon thereof. Moreover, ln certaln embodl-ments, the wall of the axlally inwardly tapered entrance sec-tlon of the bore has the trapezoldal sectlon ln a truncated conlcal cross-sectlon ln that vertlcal plane colncldlng wlth the axls of the bore.
~3~ 5~ ~
In some of the presently preferred embodlments of the lnventlon, the bore also has an axlally outwardly tapered exit sectlon ad~acent the downstream end thereof, whlch dlverges from the axls of the bore ln the aforesald downstream axlal dlrection thereof. Moreover, ln certaln of these embodlments, the wall of the axlally outwardly tapered exlt section of the bore has the trapezoidal section ln a truncated conical cross-section 1n that vertlcal plane coincldlng wlth the axis of the bore.
In some of the presently preferred embodiments of the lnvention, the flrst pressure determinatlon means lnclude a pressure sensor whlch ls dlsposed on the devlce ad~acent the upstream end of the bore. Preferably, the pressure sensor ls dlsposed ad~acent the bottom of the upstream end of the bore.
In certain embodlments, moreover, the second pressure determl-nation means lnclude a pressure sensor which is dlsposed on the devlce ad~acent the throat of the bore therein, and preferably ad~acent the top of the throat.
Preferably, the apparatus further comprises means for leveling one side of the device ln the plpe, and preferably the bottom of the throat ln the bore of the device. Also, the throat preferably has a polygonal cross-sectlon, transverse the longltudlnal axls of the bore.
13~5~
Where the pipe and the device have cylindrical cross-sections transverse the respective longitudinal axes thereof, the seal forming means may include an inflatable tube which is circumposed about the device between it and the pipe. Preferably, the inflatable tube is seated in an annular groove formed about the outer periphery of the device.
The device may have a hollow or solid body construction between the outer periphery of the same and the bore therethrough.
In most of the presently preferred embodiments of the invention, there are also means for determining the flow in the pipe under the full and less-than-full conditions thereof, from the pressure of the liquid in the throat and the upstream section of the pipe.
Where there is a manhole to the sewer pipe, the metering device is often inserted in that portion of the pipe through which the flow enters the manhole.
In one group of presently preferred embodiments, the apparatus comprises, in combination, a cylindrical member having end portions disposed at substantialy the same elevation and an inner surface forming a tubular venturi type device which in turn has an entrance section and a throat section. It also comprises means circumposed about the cylindrical member and operable to establish a fluid 1 3 ~
tight connection between the member and the internal wall of the pipe when the member is substantially coaxially inserted therein, whereby the li~uid in that section of the pipe upstream from the member is constrained to flow through the entrance and throat sections of the venturi type device. In addition, there are means for sensing the pressure of the liquid at the crest of the throat section of the tubular venturi type device, and means for sensing the pressure of the liquid at the invert of the entrance section of the tubular venturi type device.
Brief Description of the Drawings These features will be better understood by reference to the accompanying drawings which illustrate a presently preferred embodiment 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:
FIGURE l is a part cut-away, part perspective view of the manhole and the pipe when the device has been installed in the upstream or entrance section of 2S the pipe;
FIGURE 2 is a longitudinal cross-sectional view of the device along the longitudina:L axis of the pipe;
1 3 ~
FIGURE 3 is an end view of the device from the manhole;
FIGURE 4 is a cross-sectional view of the device along the line 4-4 of Figure 2, FIGURE 5 is a schematic illustration of the flow through a prior art device when the liquid in the pipe is flowing in the less-than-full or open channel flow condition thereof;
FIGURE 6 is a similar illustration when the pipe has filled to the top thereof;
FIGURE 7 is a similar illustration when the pipe is surcharged by the flow;
FIGURE 8 is a 8C ,hematic illustration of the operation of the inventive device in the open channel flow condition of Figure 5;
FIGURE 9 i8 a similar illustration of the operation of the device when the flow has reached the top of the pipe, as in Figure 6 and FIGURE 10 is a similar illustration of its operation when the pipe is surcharged by the flow, as in Figure 7.
Best M _ for Carrying Out the Invention Referring to the drawings, it will be seem that the portable device 2 has a cylindrical body 4 and is adapted diametrically to be slideably inserted into the entrance section 6 of a sewer pipe 8 from a 131~ ~ 3 ~
manhole 10 therein. If necessary or desired, the body 4 of the device may be subdivided into two or more longitudinal sections (not shown) to facilitate its insertion in the pipe from the manhole; but in any event, the central portion of the device has an annular groove 12 about the circumference thereof, for receiving an inflatable collar 14 with which to fix and seal the device in the pipe. The collar 14 is mounted in the groove 12 prior to the insertion of the device in the pipe, and is e~uipped with an elongated valve stem 16, and a valve 15 thereon, through which gas can be charged into the collar 14 from the manhole 10, for purposes of inflating the collar.
As a tubular venturi metering device, the device 2 has an open-ended bore 18 through the same, and the longitudinal axis of the bore coincides with that of the device itself, so that when the device is installed in the pipe, the axis of the bore is substantially parallel to the axis 20 of the pipe.
The bore 18 also has an axially inwardly tapered entrance section 22 adjacent the upstream end 25 thereof, which converges toward the axis of the bore in the downstream axial direction thereof. In addition, the bore 18 has an axially outwardly tapered exit section 26 adjacent the downstream end 28 thereof, which diverges from the axis of the bore in the aforesaid downstream axial direction thereof.
11 13 ~
The entrance and exit sections are interconnected at the axis of the bore by a polygonal throat 30. The cross-section of the throat 30 is adapted, relative to that of the pipe upstream from the device, transverse the respective axes thereof, so that the throat fills with liquid substantially simultaneously with the upstream section of the pipe, when the liquid depth rises therein, as shall be explained.
However, for the present, suffice it to say that the throat 30 is orthogonal, and in fact, square in cross-section, whereas the entrance and exit sections 22 and 26 of the bore 18 are truncated cones 32 cut by vertical chords 34 at the sides thereof. See Figure 3. The chords 34 are planar and terminate just short of the respective ends 24 and 28 of the device, so that in the end elevational view of Figure 3, the cylindrical exit end 28 of the device is immediately apparent to the viewer, whereas the planar side walls 34 and the part conical top and bottom walls 34 of the exit section 26 lie therebehind.
As seen in Figures 1 - 3, moreover, the device 2 is equipped with a bench 36 on the top of the same, at the exit end 28 thereof, and a level indicator 38 is mounted on top of the bench. The level indicator 38 may be of the bubble-level type, with a crosshair for indicating the level condition. Both the bench 1 3 ~ 0 12 73818-lg 36 an~ the lndicator 38 are on parallels to the top 40 and/or bottom 42 of the throat, so that the lndlcator 38 can be used to level the throat for the meterlng operatlon.
In addltlon, the devlce 2 has a pressure sensor 44 mounted beneath the entrance sectlon 22 at the lower part conlcal wall or surface 32 thereof; and a second pressure sensor 46 ls mounted at or near the top or crest 40 of the throat, at the surface thereof. The pressure sensors 44 and 46 may be elther plezometers or plezoelectrlc pressure trans-ducers.
The pressure sensor 44 ls employed to determlne thestatlc pressure of the llquld ln the upstream sectlon of the plpe when the liquld ls flowlng ln the plpe at a depth less than that adapted to flll the upstream sectlon of the plpe, so that the devlce can be used to meter the flow ln the plpe for the less-than-full condltion thereof. The pressure sensor 46 ls employed to determlne the statlc pressure of the llquld ln the throat 30 of the devlce, so that the devlce can be employed to meter the flow ln the plpe for the full condltlon thereof.
Thls ls commonly done by determlnlng the dlfference between the pressure ln the upstream sectlon of the plpe and the pressure ln the throat of the devlce.
For thls purpose, a slgnal converter 48 ls mounted on .~'`
~ 3 31 ~3~ ~ ~
13 7381~-19 the wall of the manhole lO to receive the pressure slgnals from the sensors 44 and 46 through a two-lead conductor 50 extending therebetween. The converter 48 converts the slgnals to flow rates, and the flow rates are stored ln turn ln an electronlc memory (not shown~ wlthin the converter. The converter 48 may also convert the dlfference between the pressure signals, to meter and store the flow rate of the plpe for both the full condltion and the less-than-full conditlon thereof, as indlca-ted.
The converter 48 may be a conventional bubbler-type mechanlsm, that ls, one in whlch gas bubbles are discharged from the end of a tube (not shown) submerged ln a llquld. The pressure requlred to malntaln a predetermlned bubble rate ls measured uslng a bellows (not shown) or some other such mechan-lsm. The pressure ls proportlonal to the depth of submergence of the end of the tube, and a dlfferentlal between two pres-sures can be determined by measurlng the deflectlon of the dlaphragm (not shown) of the bellows when one pressure is lm-posed on each slde of the dlaphragm. Of course, the statlc pressure at the top of the throat 30 ls amblent alr pressure until the throat fllls wlth llquld.
The flow data may be recorded ln the converter by an lnk pen and a paper chart (not shown~, or by a 14 ~3~
stylus and a pressure sensitive chart (not shown).
Alternatively, the converter may be a conventional electronic mechanism such as a piezoelectric mechanism (not shown) which emits elec-trical signals that are proportional to the pressureexerted on them. Furthermore, a digital integrated circuit mechanism (not shown) may be programmed to intermittently calculate a flow rate, and to store it in an electronic memory, given the static pressure at the entrance section 22 of the device and/or the differential pressure across the device.
In use, the device 2 is inserted into the open end of the entrance section 6 of the pipe and installed in the same in the manner of Figure 1. At the same time, the body of the device i8 rotated to place the level indicator 38 at the top of the same, and to level the device using the indicator. A
source of pressurized gas (not shown) is attached to the valve 15 to introduce gas into the inflatable collar 14, and the collar is inflated between the body of the device and the inside surface of the entrance section of the pipe. When inflated, the collar 14 fixes the device in position and provides a fluid tight seal between the device and the pipe.
Thereafter, the conductor 50 to and from the pressure sensors 44 and 46, i5 routed to the top of the manhole, the converter 48 is attached to it and mounted on the wall of the manhole, and the pressure ~ 3 ~
slgnals to the converter are employed to meter the flow in the pipe for the full condltion, as well as the less-than-full condltlon of the same.
Referrlng now to Flgures 5 - 10, lt will be seen that when a sewer pipe 8 is open to atmosphere and the llquld 51 thereln flows by gravlty in the same, the liqui~ normally flows under open-channel flow condltlons, that ls, condltlons whereln the pipe ls less than filled with the llquld, as ln Flgure 5.
However, on occaslon, the plpe may be flooded because of a downstream constrlctlon, or by some unusual surge of llquld through lt from upstream. In the past, lt was possible, uslng a venturl meterlng devlce 42, to meter the flow under normal open channel flow condltlons. But as the depth of flow rose to the polnt where the llquld fllled that sectlon of the plpe up-stream from the device, it was no longer possible to get an accurate readlng of the liquld flow rate. Thus, when there was flooding, the devlce no longer gave an accurate readlng of the flow rate. Ultlmately, the plpe would become so surcharged wlth llquld that the upstream llquld level ln the plpe would rlse above the top of the plpe. In thls condltlon, the devlce could be employed to meter the flow as a venturl tube type pressure differentlal produclng devlce. However, ln the transltlon stage between (1) the tlme when the flow ~3 ~ `x~ ~
was such that the venturi device performed as a venturi flume, and (2) the time when the pipe was surcharged to the extent that the device performed as a venturi tube, no flow measurement was possible.
According to the present invention, the flow can be metered at all times, even in the transition stage, if the throat is dimensioned so that there is (1) "necking downn of the liquid during open channel flow and (2) zero "necking down" of the liquid when the upstream section of the pipe fills with liquid.
To explain, when a venturi metering device 42 is installed in a sewer pipe 8 or the like, the device operates as a flume so long as the flow 52 is open channel flow. That is,'when the flow 52 reaches the throat 56 of the device, it dips or "necks down" as seen at 54 in Figure 5, and assumes a depth that can be calculated. This depth is termed the "critical depth." The operation of the device as a flume makes it possible, in turn, to determine the flow rate in the pipe, since a relationship exists between the upstream depth of flow and the rate of flow itself.
As the depth of flow in the upstream section of the pipe increases, however, the "necked down" flow in the throat 56 of the venturi device does not increase correspondingly, and there is a point when the upstream section of the pipe fills with liquid 51 while the throat 56 continues to have "necked down"
flow 54 therethrough - - that is, flow with an airgap 17 1 3~
above the same, as in Figure 6. At this point that is, the point when the upstream section of the pipe fills with liquid - it is no longer possible to monitor the depth of flow in the upstream section of the pipe, and therefore, no longer possible to determine the rate of flow through the pipe.
Meanwhile, since the throat 56 is not filled with liquid at this time, the device cannot be employed as a venturi-tube type pressure differential producing device. In fact, it will not be possible to use the device as such until the throat is force-filled with liquid, such as when the pipe becomes so surcharged with liquid that the upstream liquid level in the pipe rises above the top of the pipe. See Figure 7.
This transition stage - - when the device is no longer operating as a venturi flume and yet the pipe is not so surcharged that the device will perform as a venturi tube - - may exist for a considerable length of time.
~0 Referring now to Figures 8 - 10 and the inventive device 40', 42' therein, the cross-section of the throat 30 is dimensioned, relative to that of the upstxeam section of the pipe, transverse the respective longitudinal axes thereof, so as to dictate that the throat 30 will fill with liquid substantially simultaneously with the upstream section of the pipe. That is, the flow 54 through 13~i3~
the throat 30 ls controlled so that the flow no longer tends to "neck: down~' ln lt when the llquid ln the upstream section reaches the top of the plpe. Put another way, the "necking down~ effect 54 ahates to zero at that tlme when the upstream sectlon of the plpe fllls wlth llquid. In thls way, a statlc pressure readlng of the throat, and a statlc pressure readlng of the upstream sectlon of the plpe, wlll give a true readlng of the flow through the plpe slnce the dlfference between the two pressures can be used to determlne the flow ln thls transi-tlon condltlon.
Of course, as ln the prlor art devlces, one can stlllread the statlc pressure of the upstream sectlon of the plpe durlng open channel flow (Flgure 8), and can contlnue to read the throat and upstream pressures ~urlng surcharged flow (Flgure 10), so as to determlne flow under all condltlons, whether open channel flow, transltlon flow, or surcharged flow.
In order to control the flow through the throat ln thls fashlon, however, it is necessary to provide an axlally lnwardly tapered entrance sectlon 22 to the throat, as shown ln Flgures 1 - 4, and the entrance sectlon must converge toward the axls of the bore in vertlcal planes parallellng the axls and ln that axial dlrectlon relatlvely toward the downstream end 28 of the bore. Only when the entrance sectlon converges in thls fashlon can the cross-sectlon of l9 1 ~ ~3~3~
the throat be dimensioned so that the "necking down"
effect abates to zero when the upstream section of the pipe fills with liquid. One may constrict the sides of the entrance section, or one side, but he must also constrict the entrance section in vertical planes parallel to the axis of the bore.
Given the diameter of the sewer pipe and the range of flow rates in the same, the cross~section of the throat can be determined empirically using the following equations:
Qc = ~ (a3/T) x g or v2 = a/2T
2g D1 + v2 = Z + Dc + v2 + hL
2g 2g In the above equations, "Qc" i8 the flow rate in the throat under open channel flow conditions; "a" is the cross-sectional area of flow in the throat and thus the cross-sectional area of the throat itself when the throat is filled with liquid; "T" is the width of the top of the flow in the throat and thus the width of the throat at the top of the same when the throat is filled with li~uid; and "g" is acceleration due to gravity. "D1" is the depth of flow in the upstream section of the pipe; "V2" is the average velocity of flow in the th:roat; llZ~ is the 13 ~ 3 helght to whlch the bottom of the throat ls raised above the bottom of the plpe (l.e., the "slll helght"); ''Dc'' ls the depth of flow ln the throat; "hL" ls the head loss between the up-stream sectlon of the plpe and the throat.
Typlcally, the head loss can be expected to be 5 - 10 percent of the difference in kinetlc energy (velocity head) be-tween the upstream sectlon of the plpe and the throat. Thls is a very small number for practical purposes, and therefore, for slmpliclty, ls ignored ln the example followlng.
To lllustrate the appllcatlon of the equatlons, assume that the plpe diameter ls 8 lnches, that the devlce lt-self has a 1/4 lnch wall thlckness and that because of lts wall thlckness, the plpe dlameter at the mouth of the devlce ls effectlvely 7-1/2 lnches. Assume, moreover, that a devlce wlth an orthogonal throat ls to be used, and that the throat has a wldth of 4 lnches and a slll helght of 1-3/4 lnches. For such an orthogonal throat, Qc = ~ x T x DC/2' and Dl ~ Dc + Z + a/2T - v2 2g ~5`~ 3~
Uslng conventlonal emplrlcal practlce, Dc 15 4 inches or .333 feet.
Qc \/32.16 x .333 x (.333)2/3 Qc = .363 cfs a = .333 x .333 = .111 sf Dl 5 .333 + .146 + .111/t2 x .333) - V~
2g Followlng the same practlce, Dl ls the effective plpe diameter of .625 foot.
.625 = .333 + .146 + .167 - .022 ~ .624 Thus, when a devlce wlth 1/4 lnch thlck walls ls ln-serted lnto an 8 lnch plpe, a throat that ls 4 lnch square and centered ln the devlce wlll cause the throat to flll wlth llquld substantlally slmultaneously wlth the upstream sectlon of the plpe when the llquld depth rlses thereln.
The equatlons are equally appllcable to other throat conflguratlons. In the case of a rectangular conflguratlon, the cross-sectlon can be vertlcally rectangular, but wlth a rlsk of clogging ln small dlameter sewers. On the other hand, wlth large dlameter sewers, a vertlcally rectangular cross-sectlon may in fact be the most deslrable to accompllsh the slmultaneous flll functlon.
The throat need not be orthogonal, nor even poly-gonal. It may, for example, have convexly bowed sldes, and ln fact, sldes formed by the plpe ltself, as ln Flgures 8 - 10.
~3~
Similarly, the body 4 of the device need not be solid.
It nnay be hollow between the outer cylindrical wall and the hore 18 l;hereof; and if desired, when hollow, the cylindrical wall of the same may be perforated (not shown) to allow alr and liquid to escape from within the device.
; 1.
Claims (41)
1. A method of metering the flow of liquid which is flowing by gravity in an elongated pipe that is open to atmosphere, comprising:
installing in the pipe a tubular venturi metering device 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 of 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 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, configuring the cross-sectional area of the throat, 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 depth rises therein, and providing means whereby the static pressure 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 pressures 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.
installing in the pipe a tubular venturi metering device 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 of 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 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, configuring the cross-sectional area of the throat, 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 depth rises therein, and providing means whereby the static pressure 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 pressures 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.
2. The method according to claim 1, further comprising leveling the bottom of the throat of the device before the respective determinations are made.
3. The method according to claim 1, wherein the throat has a polygonal cross-section, transverse the longitudinal axis of the bore of the device.
4. In combination, 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 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 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 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 depth rises therein, and there being second means for determining the static pressure of the liquid in the throat of the device and 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 pressures 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.
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 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 depth rises therein, and there being second means for determining the static pressure of the liquid in the throat of the device and 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 pressures 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.
5. The combination according to claim 4 wherein the axially inwardly tapered entrance section of the bore of the device has a top, bottom and sides which taper axially inwardly of the axis of the bore in the aforesaid downstream axial direction thereof.
6. The combination according to claim 4 wherein the wall of the axially inwardly tapered entrance section of the bore has a trapezoidal section in that vertical plane coinciding with the axis of the bore.
7. The combination according to claim 4 wherein the bore also has an axially outwardly tapered exit section adjacent the downstream end thereof, which diverges from the axis of the bore in the aforesaid downstream axial direction thereof.
8. The combination according to claim 7 wherein the wall of the axially outwardly tapered exit section of the bore has a trapezoidal section in that vertical plane coinciding with the axis of the bore.
9. The combination according to claim 4 wherein the first pressure determination means include a first pressure sensor which is disposed on the device adjacent the upstream end of the bore.
10. The combination according to claim 9 wherein the first pressure sensor is disposed adjacent the bottom of the upstream end of the bore.
11. The combination according to claim 4 wherein the second pressure determination means include a second pressure sensor which is disposed on the device adjacent the throat of the bore therein.
12. The combination according to claim 11 wherein the second pressure sensor is disposed adjacent the top of the throat.
13. The combination according to claim 4 further comprising means for leveling one side of the device in the pipe.
14. The combination according to claim 13 wherein the leveling means are operable to level the bottom of the throat in the bore of the device.
15. The combination according to claim 4 wherein the throat has a polygonal cross section, transverse the longitudinal axis of the bore.
16. The combination according to claim 4 wherein the pipe and the device have cylindrical cross-sections transverse the respective longitudinal axes thereof, and the seal forming means include an inflatable tube which is circumposed about the device between it and the pipe.
17. The combination according to claim 16 wherein the inflatable tube is seated in an annular groove formed about the outer periphery of the device.
18. The combination according to claim 4 wherein there is a manhole to the sewer pipe, and the metering device is inserted in that portion of the pipe through which the flow enters the manhole.
19. The combination according to claim 4 further comprising means for determining the flow in the pipe under the full and less-than-full conditions thereof, from the pressure of the liquid in the throat and the upstream section of the pipe.
20. Apparatus for metering the flow of liquid which is flowing by gravity in an elongated pipe that is open to atmosphere, both for the condition wherein the pipe is less than filled with the liquid, and the condition wherein the pipe is filled with the liquid, comprising, in combination, a cylindrical member having end portions disposed at substantially the same elevation and an inner surface forming a tubular venturi-type device which in turn has an entrance section and a throat section, means circumposed about the cylindrical member and operable to form a fluid tight connection between the member and the internal wall of the pipe when the member is substantially coaxially inserted therein, whereby the liquid in that section of the pipe upstream from the member is constrained to flow through the entrance and throat sections of the venturi-type device, means for sensing the pressure of the liquid at the crest of the throat section of said tubular venturi-type device, and means for sensing the pressure of the liquid at the invert of the entrance section of said tubular venturi-type device.
21. The apparatus according to claim 20 wherein the fluid-tight connection forming means include an inflatable tube seated in an annular groove about the circumference of the cylindrical member.
22. A device for metering fluid flow comprising a cylindrical member having open ends, at least a portion of the outer surface of said cylindrical member configured substantially to fit inside the contour of an entrance pipe to a sewer manhole, a single tubular venturi-type member having an entrance section a throat section and an exit section mounted in said cylindrical member in such a manner that all of the liquid that flows through the open ends of said cylindrical member must pass through said tubular venturi-type member, means for securing said cylindrical member in said entrance pipe attached to said cylindrical member whereby a seal is established between the inside contour of said entrance pipe and an annular portion of the outer surface of said cylindrical member, means attached to the invert of the entrance section of said tubular venturi-type member to sense the pressure of the liquid therein, means attached to the crest of said throat section to sense the pressure of the liquid therein, conductor means attached to each of said pressure sensor means to conduct pressure signals therefrom, and means attached to said conductor means to convert said pressure signals into flow rates and store in said flow rate data.
23. A device for metering liquid flow in a substantially cylindrical entrance pipe to a sewer manhole, said entrance pipe flowing either partially filled or filled with liquid, said device comprising, in combination, a cylindrical member, the inner surface of which forms a tubular venturi-type member having an entrance section and a throat section therein, the outer surface of which member is dimensioned substantially to fit the inside contour of said substantially cylindrical entrance pipe, means for securing said cylindrical member in said entrance pipe and for forming a closed connection between the outer surface of said cylindrical member and the inner surface of said substantially cylindrical entrance pipe, means attached to the invert of the entrance section of said tubular venturi-type member to sense the pressure of the liquid therein, means attached to the crest of the throat section of said venturi-type member to sense the pressure of the liquid therein, conductor means attached to each of said pressure sensor means to conduct pressure signals therefrom, and means attached to said conductor means to convert said pressure signals into flow rates and store said flow rate data.
24. An apparatus for measuring flow in a closed conduit, comprising:
a venturi-type member for disposition in the closed conduit in a manner as to accept the flowing material in a flowpath therethrough and otherwise substantially block the conduit;
said venturi-type member formed having a constricting inlet section in the direction of flow, terminating within said member in a throat section, said throat section defined as a passage continuing from said constricting inlet section and extending substantially parallel to the axis of the said member;
access means to permit sensing of the pressure in the region of said constricting inlet section and in said throat;
said throat configured in said member such that it fills at about the same time as the conduit fills upstream upon increasing flow in the closed conduit.
a venturi-type member for disposition in the closed conduit in a manner as to accept the flowing material in a flowpath therethrough and otherwise substantially block the conduit;
said venturi-type member formed having a constricting inlet section in the direction of flow, terminating within said member in a throat section, said throat section defined as a passage continuing from said constricting inlet section and extending substantially parallel to the axis of the said member;
access means to permit sensing of the pressure in the region of said constricting inlet section and in said throat;
said throat configured in said member such that it fills at about the same time as the conduit fills upstream upon increasing flow in the closed conduit.
25. The apparatus of claim 24, wherein said access means further comprises:
a first pressure-sensing point in said constricting inlet section and a second pressure-sensing point in said throat, said first sensing point located adjacent the end of and the bottom of said constricting inlet section opposite from said throat and said second sensing point located adjacent the upper portion of said throat.
a first pressure-sensing point in said constricting inlet section and a second pressure-sensing point in said throat, said first sensing point located adjacent the end of and the bottom of said constricting inlet section opposite from said throat and said second sensing point located adjacent the upper portion of said throat.
26. An apparatus for measuring flow in a closed conduit, comprising:
a tubular venturi-type member for disposition in the closed conduit in a manner as to accept the flowing material in a flowpath therethrough and otherwise substantially block the conduit;
said tubular venturi-type member formed having a constricting inlet section in the direction of flow, terminating within said member in a throat section, said throat section defined as a passage continuing from said constricting inlet section and extending substantially parallel to the axis of the said member;
access means to permit sensing of the pressure in said constricting inlet section and in said throat;
said throat being positioned relative to said constricting inlet section such that it fills at the same flowrate as the conduit fills upstream upon increasing flow in the closed conduit.
a tubular venturi-type member for disposition in the closed conduit in a manner as to accept the flowing material in a flowpath therethrough and otherwise substantially block the conduit;
said tubular venturi-type member formed having a constricting inlet section in the direction of flow, terminating within said member in a throat section, said throat section defined as a passage continuing from said constricting inlet section and extending substantially parallel to the axis of the said member;
access means to permit sensing of the pressure in said constricting inlet section and in said throat;
said throat being positioned relative to said constricting inlet section such that it fills at the same flowrate as the conduit fills upstream upon increasing flow in the closed conduit.
27. The apparatus of claim 26, wherein said access means further comprises:
a first pressure-sensing point in said constricting inlet section and a second pressure-sensing point in said throat, said first sensing point located adjacent the end of and the bottom of said constricting inlet section opposite from said throat and said second sensing point located adjacent the upper portion of said throat.
a first pressure-sensing point in said constricting inlet section and a second pressure-sensing point in said throat, said first sensing point located adjacent the end of and the bottom of said constricting inlet section opposite from said throat and said second sensing point located adjacent the upper portion of said throat.
28. The apparatus of claim 26, wherein:
said constricting inlet section has a trapezoidal section in a plane parallel to the axis of said flowpath;
said throat has a substantially constant cross-section; and an outlet section extending from the opposite end of said throat from said constricting inlet section, said outlet section expanding from the flowpath axis as said outlet section extends from said throat, said outlet section having a trapezoidal cross-section in a plane parallel to said axis of said flowpath.
said constricting inlet section has a trapezoidal section in a plane parallel to the axis of said flowpath;
said throat has a substantially constant cross-section; and an outlet section extending from the opposite end of said throat from said constricting inlet section, said outlet section expanding from the flowpath axis as said outlet section extends from said throat, said outlet section having a trapezoidal cross-section in a plane parallel to said axis of said flowpath.
29. The apparatus of claim 28, wherein said access means further comprises:
pressure-sensing means connected to said first and second sensing points to allow the apparatus to measure flow in open-channel flow, full pipe flow, and a transition zone therebetween.
pressure-sensing means connected to said first and second sensing points to allow the apparatus to measure flow in open-channel flow, full pipe flow, and a transition zone therebetween.
30. The apparatus of claim 29, further comprising:
sealing means disposed on the exterior of said tubular member selectively engageable to the closed conduit.
sealing means disposed on the exterior of said tubular member selectively engageable to the closed conduit.
31. The apparatus of claim 30, further comprising:
leveling means on said member to level it in said closed conduit;
said sealing means disposed in a recess on the outer periphery of said tubular member and selectively inflatable to engage a pipe for sealing therewith.
leveling means on said member to level it in said closed conduit;
said sealing means disposed in a recess on the outer periphery of said tubular member and selectively inflatable to engage a pipe for sealing therewith.
32. The apparatus of claim 31, further comprising:
pressure-transmission means connected to said first and second pressure-sensing means to transmit pressure readings to a location remote from said member;
calculation means to accept input from said pressure-transmission means and to calculate flow through said member.
pressure-transmission means connected to said first and second pressure-sensing means to transmit pressure readings to a location remote from said member;
calculation means to accept input from said pressure-transmission means and to calculate flow through said member.
33. A method for measuring flow in a closed conduit, comprising the steps of:
placing in the closed conduit a closed conduit venturi-type member with a constricting inlet section leading to a throat section so that the flow in the closed conduit passes through the member;
configuring the throat section relative to the constricting inlet section such that the closed conduit fills upstream of the member at about the same time as the throat fills on increasing flowrate;
measuring the static pressure in said throat and said constricting inlet or in both said throat and said restricting inlet;
determining the flow in said flowpath for open-channel flow and full pipe flow.
placing in the closed conduit a closed conduit venturi-type member with a constricting inlet section leading to a throat section so that the flow in the closed conduit passes through the member;
configuring the throat section relative to the constricting inlet section such that the closed conduit fills upstream of the member at about the same time as the throat fills on increasing flowrate;
measuring the static pressure in said throat and said constricting inlet or in both said throat and said restricting inlet;
determining the flow in said flowpath for open-channel flow and full pipe flow.
34. An apparatus for permitting measuring flow in a closed conduit in which a liquid is flowing generally parallel to the longitudinal axis of said closed conduit due to gravity, comprising:
at least first and second cross-sectional shapes along the conduit's axis, the second cross-sectional shape being down-stream from the first cross-sectional shape in the direction of flow and being constricted including vertically between top and bottom elevations thereof relative to said first cross-sectional shape such that the cross-sectional shapes fill with liquid simul-taneously as the flowrate of liquid in the closed conduit increases.
at least first and second cross-sectional shapes along the conduit's axis, the second cross-sectional shape being down-stream from the first cross-sectional shape in the direction of flow and being constricted including vertically between top and bottom elevations thereof relative to said first cross-sectional shape such that the cross-sectional shapes fill with liquid simul-taneously as the flowrate of liquid in the closed conduit increases.
35. The method of claim 33 wherein said step of configuring includes configuring the elevation of the top of both the inlet section and the throat section such that the highest point of the throat section is not higher than any top elevation of the inlet section.
36. An apparatus for use in a critical-flow meter for a closed conduit, comprising:
at least one closed conduit throat section constricted, including vertically between top and bottom elevations thereof, relative to the closed conduit upstream of the throat section, effective to cause simultaneous filling of said throat section and the closed conduit upstream of said throat as the flowrate through said throat increases.
at least one closed conduit throat section constricted, including vertically between top and bottom elevations thereof, relative to the closed conduit upstream of the throat section, effective to cause simultaneous filling of said throat section and the closed conduit upstream of said throat as the flowrate through said throat increases.
37. The meter of claim 36, wherein:
said throat section is constricted in at least one vertical plane parallel to the direction of flow.
said throat section is constricted in at least one vertical plane parallel to the direction of flow.
38. The meter of claim 36, wherein:
said throat section has a finite length in the direction of flow.
said throat section has a finite length in the direction of flow.
39. A flow measuring apparatus for closed conduits, comprising:
a flow restriction so disposed in the closed conduit that said restriction fills on increasing volumetric flowrate at the same volumetric flowrate as the closed conduit adjacent said restriction;
static pressure measurement means to allow sensing the static pressure in at least said restriction.
a flow restriction so disposed in the closed conduit that said restriction fills on increasing volumetric flowrate at the same volumetric flowrate as the closed conduit adjacent said restriction;
static pressure measurement means to allow sensing the static pressure in at least said restriction.
40. A method of measuring flow in a closed conduit, comprising:
placing a restriction in the closed conduit of such configuration so that it fills on increasing volumetric flowrate at the same volumetric flowrate as the conduit upstream;
measuring the static pressure in at least said restric-tion for the purpose of computing the flowrate.
placing a restriction in the closed conduit of such configuration so that it fills on increasing volumetric flowrate at the same volumetric flowrate as the conduit upstream;
measuring the static pressure in at least said restric-tion for the purpose of computing the flowrate.
41. The method of claim 40, further comprising:
measuring the static pressure immediately upstream of said restriction.
measuring the static pressure immediately upstream of said restriction.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/051,325 US4799388A (en) | 1986-03-31 | 1987-05-19 | Apparatus and technique for metering liquid flow |
| US051,325 | 1987-05-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1315130C true CA1315130C (en) | 1993-03-30 |
Family
ID=21970615
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000545117A Expired - Fee Related CA1315130C (en) | 1987-05-19 | 1987-08-21 | Apparatus and technique for metering liquid flow |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JP2520656B2 (en) |
| CA (1) | CA1315130C (en) |
-
1987
- 1987-08-21 CA CA000545117A patent/CA1315130C/en not_active Expired - Fee Related
- 1987-08-24 JP JP62210029A patent/JP2520656B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPS63293418A (en) | 1988-11-30 |
| JP2520656B2 (en) | 1996-07-31 |
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