Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
108384~3
BACKGROUND OF T~ TENTION - -
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Field of the Invention
This invention concerns a sensitive J-tube
instrument and a particular application thereof. More
specifically it concerns an application of the principles
involved to provide a novel manometer that has increased
sensitivity. Also, a particular application is that of
measuring the change in liquid level of a tank of liquid
over a predetermined period of time, which change may
indicate the presence of a leak.
Description of the Prior Art
The testing of underground tanks for leakage
has always been a difficult problem. Heretofore, two
known methods which have been used have had various draw-
backs. A first method required the product to be removed
from the tank and the vent lines to be sealed. Then
the tank was pressurized with air to several pounds per
square inch. The pressure would then be monitored over
a given period of time for indications of a leak.
Obvious drawbacks of that arrangement included the
fact that changes in pressure indicated would not
necessary mean that the tank was leaking but it might
just as well be in the connecting lines or dispensor
from the tank. Furthermore, the removal of products
from the tank was time consuming and costly, and
the pressurizing o~ the tank risked damage thereto.
A second procedure which has been employed
involved the fitting of the fill pipe of the tank
with a four or five foot high standpipe, and then
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the tank would be filled with product to the top of
the standpipe. Any lea~age would then ~e detected
by observing the drop in level of the standpipe. This
method had a bad tendency to stress the tank and could
expand the ends of the tank. Also, since product
had to be added to the tank for this test the tem-
perature would not be stable, and consequently con-
siderable variations would have to be taken into
consideration to make an accurate determination.
Consequently, it is an object of this
invention to provide an instrument and/or method for
determining leaks in large product tanks, such as
underground storage tanks for gasoline or the like.
It involves the principles of this invention which
provides an amplification of the difference in surface
levels of a pair of liquid columns that are connected
by a U-tube.
SUM~ OF THE INVENTION
....
Briefly, the invention concerns a sensitive
J-tube devise for measuring change in the surface level
of a fluid. It comprises a relatively small inside
diameter U-tube containing a predetermined quantity
of a colored indicator-fluid that is immiscible with
said fluid the surface level of which is to be measured.
The said indicator-fluid has a density which is
approximately the same but heavier than said fluid
being measured. The combination comprises a relatively
large inside diameter tube connected to one leg of
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said U-tube and forming therewith the taller leg of
said J-tube. The said large tube i5 long enough to
extend ~rom above the maximum surface level of said
fluid being measured to below the minimum surface level
thereof. It also comprises a three-way valve having
three ports for connection to each of the legs of said
U-tube and to the body of said fluid being measured,
- and it comprises means for connecting said U-tube leg
ports to said U-tube at a location that is above the
maximum height of said indicator-fluid therein. The
- said three-way valve having at least three positions
one for connecting all three of said ports together
and one for connecting only the shorter leg of said
J-tube to the body of said fluid being measured and
one for closing said U-tube leg ports. It also comprises
a reservoir connected into the shorter leg of said J-tube
at a location above the maximum expected height of
said indicator fluid, in order to contain any overflow
without lost of indicator fluid. And it comprises an
elongated support for holding said J-tube device in a
fixed position when a measurement is being taken. It
al~o comprises an elongated handle for actuating said
three-way valve from a location above the surface of
said fluid being measured.
Again briefly, the invention concerns a
method of magnifying the measurements of a change in
surface level of a first fluid by employing a U-tube
containing a second fluid which is immiscible with said
first fluid. The method comprises the steps of connect-
ing a relatively large cross-section area tube to one
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leg of said U-tube at a location that is higher than a predetermined maximum
level of risc of said second fluid in one of the legs of said U-tube. It
also comprises the steps of connecting both legs of said U-tube into
communication with said first fluid at a location above said maximum level
prior to the commencement of a measurement time period, and immersing said
U-tube and said large area tube in said first fluid to equali~e the level of
said first fluid inside of said large area tube with that outside, and
equalize the levels of said second fluid in said U-tube legs. It also
comprises isolating said one leg and the large cross-section area tube
from said first fluid at said commencement of said measurement time period, .
and determining the difference in fluid levels of said second fluid in said
U-tube legs at the termination of said measurement time period.
Once more briefly, the invention concerns a sensitive J-tube
instrument for measuring change in the surface level of a fluid in an
underground tank or the like, comprising a U-tube portion containing an
indicator fluid therein, said indicator fluid being immiscible with said
fluid the change in surface level of which is to be measured, said U-tube
portion having a predetermined inside cross-section area, one leg of said
U-tube portion being connected to a larger inside cross-sectional area tube
to form the taller leg of said J-tube, said larger inside cross-sectional
area tube having a length greater than the maximum difference in surface
levels of said fluid being measured between the maximum and minimum surface
levels during a measurement thereof, and valve means for connecting each
of said U-tube portion legs with said fluid being measured and for
isolating said taller leg, said valve means being connected above the tops
of said indicator fluid.
Again briefly, the invention concerns a methodof measuring a
change in surface level of a fluid, comprising the steps of taking a
relatively small inside cross-sectional area U-tube having an indicator-
fluid therein, connecting a larger inside cross-sectional area tube to one
leg of said U-tube, immersing said tubes into said fluid with said larger
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area tube extending above said surface level, connecting both legs of
said U-tube with said fluid at a location on said tubes which is above
the maximum height of said indicator-fluid therein, said connection being
made while said tubes are immersed, disconnecting said one leg from said
fluid to isolate said leg and said larger area tube from said 1uid at the
beginning of a measuring time period, and determining the difference in
height of the tops of said indicator-fluid levels in said U-tube at the
end of said measuring time period whereby th0 change in surface level of
said fluid is magnified.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects and benefits of the invention
will be more fully set forth below in connection with the best mode contem-
plated by the inventor of carrying out the invention, and in connection
with which there are illustrations provided in the drawings, wherein:
Figure l is a schematic diagram illustrating a J-tube structure
according to one embodiment of the invention;
Figure 2 is a schematic diagram like that of Figure 1 but showing
the fluid level modified in accordance with changes in the level of a
bulk fluid that is having its surface level change measured;
Figure 3 is a longitudinal elevation not according to scale,
illustrating one embodiment of an instrument in accordance with the
invention;
Figures 4 and 5 are schematic diagrams illustrating two
operative positions of the three-way valve that is employed in the
instrument according to Figure 3; and
Figure 6 is a schematic cross-sectional diagram illustrating a
sensitive manometer structure in accordance with the invention.
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DESCRIP~ION OF THE PREFERRED EMBODIMENTS
It has been discovered that a change in
the level of a body of liquid may be amplified by
employing a J-tube instrument according to this
invention. The basic principles are illustrated and
will be explained in connection with the schematic
showings of FIGS. 1 and 2. Both of these figures
illustrate a body of liquid 11 that has a.surface 12,
which may change in height, as indicated in FIG. 2. .
A change in the height of the surface 12 of liquid
body 11 may be because of a leak in the tank (not
shown), or other container for the liquid 11. However,
such change would be slow and small in many instances.
And, particularly where an underground tank of gasoline
or the like is concerned, the change in level is
difficult to detect.
.It will be noted that the instrument includes
a U-tube portion 15, which has a shorter leg 16
connected by the U-shaped bottom with a longer leg
17, on the other side. ..
Connected to the top of the leg 17 of the
U-tube, there is a larger cross-sectional area tube
20 that is long enough to extend up above the maximum
level of surface 12 of the liquid body 11.
There are two valves 23 and 24 that are
connected as indicated, so that the top of leg 16
has valve 23 controlling the opening or closing of
.the interior of this leg through the top, in regard
to connection thereof with the body of fluid 11. The
valve 24 is connected so as to similarly control a
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~luid connection from the inside of the leg 17 of the
U-tube lS to the body of 1uid 11. In this case there
is a schematic indication of a pipe or other fluid conduit
27 from the upper portion of the U-tube leg 17, to
one side of the valve 24. The other side of valve 24
is connected directly into the body of liquid 11,
similarily as is the other side of the valve 23, which
is connected to the top of the leg 16 of the U-tube lS.
In the U-tube 15 there is an indicator fluid
30, which is immiscible with the liquid 11. As will
appear from the explanation which follows, the indicator
liquid 30 may be slightly heavier than the liquid 11.
However, so long as the immiscibility is maintained,
there appears to be no reason why the density of the
indicator liquid 30 might not be the same or even less
than the density of the liquid 11.
It will be observed that the larger tube
20 has an inside cross-sectional area which is indicated
by an arrow across the diameter. It has reference
No. 31 applied thereto. This area is greater than the
inside cross-sectional area of the legs 16 and 17 of the
U-tube. The latter area is indicated by the dimension
d2 which has arrows with reference numeral 32 applied
thereto (in FIG. 1).
It has been discovered that the changes in
the level or height of the surface 12 of the body of
liquid 11, will produce a differential in the levels
of the indicator liquid 30 in U-tube 15.- And, the
ratio of the change in level of surface 12, to the
differential in the levels of the indicator liquid
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30 in the legs 16 and 17, is in accordance with the
ratio of the inside cross-sectional area of the legs
16 and 17 to the inside cross-sectional area of the
tube 20. Consequently, there is a substantial amplification
of the change in the level of the surface 12. Further- ;
more, with the density of the indicator liquid 30
being the same or close to the same density as the
body of liquid 11, the changes in levels are sub-
stantially all on account of the ratios of cross-sectional
areas. As will appear below, this is because the
volumne of liquid which must move during the establish-
ment of a new balance, is the major factor in the change
in liquid levels.
The foregoing relationship was discovered to
exist while employing an indicator liquid that was made
of a mixture of water and methanol, and with the body of
liquid having its surface level measured being gasoline.
An explanation of why the amplification of
liquid level ch~nge takes place, may be made clear
by reference to the schematic diagrams of FIGS. 1 and 2.
Thus, with relation to the various liquid level changes
and the sizes of the J-tube structure, consider the
following. The procedure involves first the immersion
of the J-tube structure, i.e. U-tube 15 and the larger
tube 20 connected to leg 1~ thereof, all into the body
of liquid 11. The immersion is done with valves 23
and 24 both open. Then the liquids in both legs of
the J-tube system are permitted to equalize and the
surfaces of the indicator liquid 30 will be at the
same level. This level is indicated in the diagrams
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by a dashed line 35.
Next, when it is desired to commence a fluid
level measuring time period, the valve 24 will be
closed so as to isolate the liquid inside of tube 20
and the connecting leg 17 of the U-tube 15. ~hereafter,
following some predetermined period of time it may be
found that the fluid level 12 of the body of liquid 11
has fallen to the position of the surface 12 which i8
indicated in FIG. 2. The difference between these levels
is indicated by the symbol in FIG. 2.
The change a h in the level of surface 12 will
cause a difference in pressure on the indicator-liquid
30 in the two legs of the U-tube 15, because of the
fact that the liquids in tube 20 and the leg 17 are
isolated from the body of liquid 11. Consequently, the
indicator liquid 30 will be pushed down in the leg 17
of the U-tube 15, and a corresponding change must take
place in raising the liquid level of the indicator
liquid 30 in leg 16. Since the liquid 11 and indicator
liquid 30 are immiscible, all of the liquid which was
isolated from the body of liquid 11 in the long leg
of the J-tube structure remains isolated and there
must be an equal volume of the liquid displaced on the
leg 16 side of the U-tube as the volume which has
moved down from the tube 20 into the leg 17 of the
U-tube, as the change in liquid levels took place.
Because of the foregoing conditions, the
changes in fluid levels will be directly in proportion
to the ratios of the cross-sectional areas of the
fluid columns involved or to the square of the diameter
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of each of the fluid columns.
The foregoing relationship may be proved
mathematically in the following manner, with reference
to the dimensions indicated on EIGS. 1 and 2, and
assuming that the tube 20 and the legs 16 and 17 are
circular in cross-section. Thus, it will be observed
that:
4 h = h6 + h7 (1)
~hen, h6 can be obtained in terms of h2 from the
fact that the volumne of liquid that has left the large
diameter tube 20 is equal to the volume of liquid that
has entered the small diameter leg 17. The latter is
the distance h2 divided by two. This may be expressed
by the following equations:
7r/4 dl2 h6 = ~r/4 d2 h2/2 (2)
which may be solved for h6 and will result in the
equation:
h6 = (d2/dl )2 h2/2
Then, h7 can be obtained in terms of h2 from
the fact that:
h7 = h4 - (h3 + h2 ) = (h4 - h3 ) - h2 (4)
It will be noted that the quantity h4 - h3
can be expressed in terms of h2 as follows, and involving
the 1uid pressures: the pressure at the depth h3 may
be expressed as h3 = h3 pg (5)
wherein pg = the density of the liquid 11.
Then considering the other side (isolated
portions) of the U-tube columns, the pressure at depth
h4 which is due to the isolate head of liquid 11 above
the indicator fluid level in the leg 17 of the U-tube
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may be expressed as h4 = h4 p (6)
And, since we ha~e a static balance, we can
express the dif~erence in pressure between the depths
h3 and h4 as being equal to the expression h2 Pw ~ wherein
Pw = the density of the indicator liquid 30. Thus:
h4 pg - h3 pg = h2 Pw
or,
h4 - h3 = h2 Pw/pg
Next, it is clear that:
h7 = (h4 - h3 ) - h2 (8)
and substituting in that equation for the quantity
h4 - h3 from the foregoing equation (7) we have
h7 = h2 Pw/pg h2
h2 (Pw/Pg~ 1 ) (9 )
Now, since ~h = h6 + h7 , it may be rewritten
by substitutions from equations (3) and (9) to be
h = (d2/dl) h2/2 + h2(pw/pg 1)
= h2 [1/2 (d2/dl) + Pw/Pg (10)
From this it can be seen that if the densities, i.e.
Pw and pg are substantially equal, the difference in
liquid levels from the beginning to the end of a
measurement time period, i.e. h, will be reflected
at ~he levels of the indicator-liquid 30 surfaces as
one half of h times the ratio of the inside diameter
d2 divided by dl , squared. Or:
~ h = h2/2 (d2/dl)2 (11)
In other words, the change in level 12 of the liquid
11, will be small compared to the change in the level
of the surfaces of the indicator liquid columns of
liquid 30, in the U-tube legs 16 and 17. Thus, the
latter is an amplification of the former, in accordance
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with a ratio that is mostly related to the inside
cross-sectional areas of the larger and smaller columns
when the density of the indicator liquid 30 is nearly
the same as that of the body of liquid ll.
An instrument constructed in accordance with
the invention, which may be employed for measuring
change in the surface level of a fluid, is illustrated
in FIG. 3. This includes the various elements which
will be descri~ed in more detail below. The instrument
will be immersed in a body of liquid 40 which is to
have any change in surface level thereof measured.
There is a relatively small inside diameter
U-tube 41 which has a pair of legs 44 and 45. The U-tube
41 contains a predetermined quantity of an indicator
liquid 48 therein, which is immiscible with the liquid
40. In-addition, the indicator liquid 48 will
preferrably have a color added thereto for aiding
observation o~ the surface levels thereof.
An instrument that was tested, employed as
the indicator liquid 48, a mixture of methanol and
5% water, which was dyed slightly to make it distinguishable
visually from the body of liquid 40 which was gasoline.
Of course, the legs 44 and 45 of the U-tube portion
41, were transparent.
In the instrument illustrated in FIG. 3, a
relatively large inside diameter tube 51 is connected
to the top of the leg 45 of the U-tube 41. The large
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tube 51 is long enough to extend from above the maximum
surface level of the body of liquid 40, during a measure-
ment, to below the minimum surface level thereof. ~;
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There is a three-way valve 52 that is
schematically indicated in FIGS. 4 and 5. This valve
52 has three ports 56, 57 and 58. These ports are
connected to the legs 44 and 45 of the U-tube 41, as
well as to the body of liquid 40, in the manner indicated
by the schematic diagrams of FIGS. 4 and 5.
~ alve 52 is located on the instrument so
that the connections to U-tube legs 44 and 45 are above
the maximum height of the surfaces of indicator liquid
48 therein. Also, it has at least three different
positions, two of which are indicated by the schematic
showings in FIGS. 4 and 5. One position is like that
shown in FIG. 4 which connects the port 57 directly
wilh common internal passages that are indicated
schematically by three arrows 60. Consequently, the
port 57 is connected to port 58 and port 56 together.
Thus, in this position the leg 45 of the J-tube instrument
is connected to the leg 44 and to body of liquid 40.
Therefore the indicator liquid 48 will stabilize
its surfaces at equal levels, so that the indicator
liquid 48 has equal height columns in the legs 44 and 45.
It will be observed that the instrument also
has a reservoir 61 that is connected into the leg 44
of the U-tube 41. This reservoir 61 is provided in order
to contain any overflow of the indicator liquid 48,
in case the response becomes too great.
Also, there is an elongated support member
62 which, has the tubes of the J-tube instrument
attached in any convenient manner. It is for handling
the instrument and to support it when a measurement is
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being taken.
There is an elongated handle 65 which connects
to the three-way valve 52 and extends upward sufficiently
to rise above the surface of the liquid 40 for manual
manipulation of the valve.
It will be appreciated that a measurement
procedure to detect a change in surface level of the
liquid 40 will involve an instrument like that described
above, and a step of immersing the J-tube instrument
into the body of liquid 40. Then the instrument will
be hela at a fixed position to allow equalization of
the columns of indicator - liquid 48 in the legs 44 and
45. This equalization will take place with the valve
52 in the position indicated by FIG. 4.
At the commencement of a measuring time
period the valve 52 will be shifted to the position
indicated in FIG. 5, and consequently the liquid column
on the long side (tube 51 and leg 45) of the J-tube
instrument will be isolated from the liquid 40. After :
a predetermined period of time, any change in the level
of the body of liquid 40 will be reflected by the
amplified change in levels of the surfaces of indicator ~ .
liquid 48, in the manner indicated above. This change
will take place while the valve 52 is in a position .
shown in FIG. 5.
Then, in order to take a reading of the
indicator - fluid surface levels in the U-tube legs
44 and 45,.the situation may be held at then existing
conditions by shifting the valve 52 to a position
(not illustrated) which will close both ports 57 and 58.
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This holds the liquid levels in legs 44 and 45 at the
positions they had reached. Then the instrument may
be raised bodily up out of the liquid 40 in order to
take a reading of the difference in levels of the
surfaces of indicator liquid 48.
It will be appreciated by any one skilled
in the art that the same principles apply to a structure
which may be employed as a sensitive manometer. ~hus,
with reference to FIG. 6 there is illustrated a U-tube
structure 70. The bottom portion contains an indicator-
liquid 73 which may be like the indicator liquid of the
above described modifications.
The indicator liquid 73 is immiscible with
the liquid columns 74 and 75 that are located above
the upper surfaces of the indicator liquid 73. These
liquid columns 74 and 75 are continued in small size
portions 78 and 79 respectively, above the indicator
liquid 73 in the U-tube 70. It will be appreciated
from the description of the foregoing J-tube modification
that the legs 78 and 79 and the bottom of the U-tube
have a predetermined relatively small inside cross-
sectional area.
Connected to the tops of the legs 78 and 79
there are a pair of extensions 80 and 81 respectively,
and these are enlarged so that the inside cross-sectional
areas are greater than that of the legs 78 and 79.
The liquid column 74 and 75 will be filled
to an equal level at the surfaces thereof, when the
indicator liquid 73 stands in balance with its upper
surfaces at the same level. In order to ensure
stability under such conditions, it is preferable
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for the indicator liquid 73 to have a slightly greater
density than the liquid in the ~olumns 74 and 75.
Since the instrument 70 is intended for use
as a manometer, it will be usual to have the extensions
80 and 81 constructed with a reduction of the diametric
size thereof at the top of each. This provides tubes
or passages for application of gas pressures that are
to be measured. It will be appreciated and can be shown,
that in the manometer instrument according to FIG. 6,
a difference in pressure applied to the two liquid
columns 74 and 75, will produce an amplified difference
in the surface heights of indicator liquid surfaces 73.
The same principles as were explained above in connection
with the other modifications of the invention are ,
applicable. Such amplification will be at a ratio whlch
is close to that of the cross-sectional areas of the
larger and smaller portions of each of the two liquid
columns making up the U-tube 70. This, of course,
assumes that the density of the indicator liquid 73
is quite close to the same density as the liquid in
columns 74 and 75 there above.
While particular embodiments of the invention
have been described above in considerable detail in
accordance with the applicable statutes this is not
to be taken as in any way limiting the invention but
_ rely as bei~g desor1ptive thereof.
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