Note: Descriptions are shown in the official language in which they were submitted.
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~ ~
6 73818-19
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 ~
73818-19
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~ ~
16
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~
18 73818-19
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
73818-19
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~
21 73818-19
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~
73694-1
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.
