Note: Descriptions are shown in the official language in which they were submitted.
~57(~g~
STORAGE TANKS HAVING FORMED JACKET FOR SECONDARY CONTAINMENT
-
This invention relates to storage tanks. More particularly,
the invention relates to underground storage tanks which have
secondary containment means.
Background of the Invention
Commercial and industrial storage tanks are widely used for
storing a great variety of liquids. Some of these liquids are
highly corrosive and/or are flammable. The service life of a
storage tank will vary, depending upon environmental conditions,
including the liquid being stored. Eventually, however, the tank
will become corroded and develop leaks. This can result in a
significant danger to the environment and health of nearby
residents. For example, storage tanks are commonly used for storing
gasoline at service stations. Gasoline, of course, is highly
flammable and is capable of posing a significant health and safety
haæard if not properly contained. Federal as well as local
regulations govern the structure of such storage tanks.
Heightened public awareness of the danger posed by storage
tanks (particularly underground gasoline storage tanks) has led to
additional govern~ental regulations. Recent proposed regulations
will soon require most storage tanks to have secondary containment
means and possibly a fail safe design feature to guard against
accidental soil, water, and air contamination. Secondary
containment means must be capable of containing leaked liquid from
the storage tank. Rigid double walled tanks have been suggested as
one alternative. While effective for containment purposes, such
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~:Z 57(~
tanks, as presently available, are costly to build and difficult to
install because of their weight. Such tanks are built by basically
forming two rigid tanks utilizing different sized, reusable molds
and then placing one tank inside the other.
Single and double walled tanks made from fiberglass reinforced
resinous material are built using a number of distinct time
consuming steps. In all known methods, a cylindrical-shaped,
reusable mold is used to build tank halves which are subsequently
assembled. Initially, layers of fiberglass followed by a resinous
coating are applied to the mold or chopped fiberglass/resin streams
are simultaneously directed onto the mold and subsequently cured.
Sufficient applications of the fiberglass and resin are made until a
wall thickness is obtained which has the desired strength. Next,
support rib molds of cardboard, four to six inches wide, are placed
completely around the cylinder at approximately sixteen inch
intervals. Fiberglass and resin are then applied over the cardboard
molds and onto adjacent areas of the cylinder so as to become an
integral part of the inner tank shell. The mold is finally removed.
The cylindrical-shaped wall, including the ribs and one end of the
tank, are produced in this stage of the method. The above steps are
repeated to obtain a second half-tank. The two half-tanks are then
joined together by appropriate sealing means. The resultant single
walled tank is capable of being installed in the ground andl in
fact, is of the type which has been extensively used for the past
twenty years.
In more recent years, double walled tanks have been built and
used. Essentially, these tanks are built by the same method as the
single walled tanks. An inner, rigid tank is formed in the above
-- 2 --
~L~57(~9~
described manner. Next, a larger diameter reusable mold is used to
build a horizontal half-tank. The fiberglass/resin is applied in a
known manner to the mold and cured to form the half-tank. A second
horizontal half-tank is formed. Next, the completed inner tank is
placed into the larger diameter half-tank. The ribs on the inner
tank are properly d~mensioned -to act as spacer ribs between the two
tanks. The second larger diameter half-tank is placed over the
inner tank, joined and sealed at the seams with its matching half-
tank. The resultant product is a double walled storage tank system
comprised of essentially two rig id tanks, one inside the other .
A second method of making double walled fiberglass, reinforced,
resinous tanks is similar to the above method and is just as time
consuming and costly. In this method, the mold has a design wherein
the ribs are formed as the f iberg lass and res in material is applied .
After forming the inner tank of which the ribs are an integral part
thereof, the mold is removed. The interior porticn of the tank next
has a fiberglass/resin layer applied over the rib indentations to
result in a smooth cylindrical-shaped interior. A second half-tank
is formed in the same manner and the two halves joined. A
cylindrical-shaped outer tank is then formed in horizontal halves.
The formed inner tank and outer tank halves are assembled as in the
f irst method described above to form a double walled storage tank
system based on two rig id tanks with support ribs therebetween.
As is readily apparent, building a double walled storage tank
system by known methods is very labor extensive and costly. Recent
concerns about leaked tanks has heightened the need for an efficient
and economical manner of building double walled storage tank system.
A jacketed storage tank system, as disclosed in my U.S. Patent No.
-- 3 --
~2S7(~
4,523,454 also provides secondary containment means and avoids the
problems associated with the rigid double walled systems.
Additionally, the aforementioned jacket system features a fail-safe
design due to the fact it provides continuous monitoring means
whereby the integrity of both the primary and secondary containment
means are checked to insure that leakage of either containment means
is known when it first occurs.
There has now been discovered methods whereby new and used
storage tanks can be provided with secondary containment means in a
convenient, yet economical manner. Further, used storage tanks are
refurbished to a standard equivalent to that possessed by a new tank
and then upgraded to have a secondary containment feature.
Summary of the Invention
A method of adding secondary containment capability to storage
tanks comprises the steps of (a) applying a gas pervious material to
a storage tank, (b) applying a layer of a fibrous reinforcing
material onto the storage tank, and (c) applying a resinous material
onto the reinforcing material. When the resinous material is cured,
a con~ainment means is formed which covers at least about the lower
40~ of the surface area of the storage tank, thereby providing
secondary containment for any liquid which may leak from the storage
tank. The space between the storage tank and newly formed secondary
containment means can be monitored for any leakage.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 iS a side view in partial section of a storage tank
having a fibrous reinforced resinous material as a jacket completely
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~25~
surrounding the tank.
FIG. 2 is a end view of the storage tank of FIG. 1 taken along
lines ~-2.
FIG. 3 iS a side view of a typical fiberglass reinforced
resinous storage tank having support ribs surrounding the tank and a
jacket of a fibrous reinforced resinous material surrounding the
storage tank.
FIG. 4 is a side view of storage tank of this invention
illustrating the use of monitor means.
FIG. 5 is a side view of storage tank of this invention
illustrating another monitor means.
FIG. 6 is a partial view in section of a tank fitting for pipes
used in a storage tank of the invention, said tank having monitor
means.
FIG. 7 is a partial view in section of another tank fitting
used in a storage tank of this invention wherein a jacketed
pipeline connected to the storage tanlc and jacketed storage tank can
both be continuously monitored.
FIG. 8 iS a partial view in section of a storage tank having a
jacket over only a part of its surface area.
FIG. 9 iS a partial view in section of a manhead sleeve
especially useful with the storage tank of FIG. 8.
FIG. 10 is another partial view in section of a manhead sleeve
having attachment means for a bladder.
Detailed Description of the Invention
While the description to follow describes the invention in
terms of its use with underground storage tanks, it should be
-- 5 --
570~6
understood the invention has applicability for other uses as well.
~lowever, the invention lends itself particularly well to underground
storage tanks used for storing liquid gasoline and, therefore, this
preferred use is described in the following paragraphs.
With reference to FIG.l, there is shown an underground storage
tank 10. Storage tanks lO of the type shown in FIG. 1 are well
known and are widely used, especially in the gasoline service
station industry. They are typically made of metal or, more
recently, a fiberglass reinforced resin material. Either type of
tank has ùse in this invention. A typical metal storage tank is
shown in FIG.l. Sufficient openings are found in the storage tank lO
to allow for various access lines to communicate with the interior
of the tank. As shown, lines 11, 12, and 13 are a fill pipe,
dispensing line and vent pipe, respectively.
The fill pipe ll provides as its obvious function the means by
which gasoline can be pumped into the inner tank from an outside
source, e.g. a tank truck. As illustrated in FIG. l, fill pipe ll
comprises a line 14 through which gasoline flows to the inner tank
lO and a space 15 within the fill pipe which acts as a vapor
recovery line. As gasoline is pumped into the inner tank, gasoline
vapors which are formed are sucked through the space 15 back to ~he
tank truck for recovery. This reduces the amount of gasoline vapors
which would otherwise be vented to the atmosphere or remain in the
inner tank preventing the tank from being filled completely with
gasoline. As used throughout here, the term "fill pipe" connotes
the pipe by which gasoline is pumped to the tank; it can be a single
pipe, but more often has vapor recovery means associated with it and
is often referred to as a vapor recovery fill line. As shown in
-- 6 --
~.2~ 6
FIG. 1, line 14 extends into the inner tank 10 with its end near the
bottom.
Dispensing line 12 is used for withdrawing gasoline and
delivering it to the consumer through gasoline dispenser 16. While
not illustrated in FIG. 1, a pump is positioned within the inner
tank, dispensing line or gasoline dispenser for pumping gasoline to
the dispenser. The bottom of the dispensing line 12 is in close
proximity with the bottom of the inner tank 10. The vent pipe 13 is
optional, though preferred, and merely provides means by which
gasoline vapors resulting primarily from a filling operation can be
vented to the atmosphere~ The opening to the atmosphere is normally
substantially off ground level for safety reasons. All the
aforementioned pipes and lines are securely attached to the rigid
inner tank. Outer jacket 17 provides the secondary containment
enjoyed by the tanks of this invention while closed space 18
provides a means by which leakage of the inner tank and jacket can
be detected.
A gas pervious material is applied to the storage tank before
the jacket is formed. The purpose of the separating agent is to
insure that a subsequently applied fibrous reinforcing material and
resinous material which form the jacket will not adhere to the inner
storage tank. It is necessary that the cured jacket and the storage
tank have a space between the t~o. Such space is closed and
provides true secondary containment capability. Additionally, any
sudden stress in the rigid storage tank which may cause a crack
therein is less likely to be transmitted to the jacket 17 because of
the structural independence of the storage tank and jacket. Still,
another function of the closed space 18 is to provide a means by
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~257~
which the space therein can be monitored for possible tank or jacket
leaks.
Gas pervious materials 19 used herein are foraminous or porous
and can take on various physical shapes and structures. Examples of
such materials are mattings, nets, screens, and meshes. Specific
examples are jute, polyurethane foam, polyester foam, fiberglass
matting, cotton matting, nylon matting, corrugated cardboard, and
asbestos. A heat seal or sealing material, e.g. a polymeric coating
or film such as Mylar or a polyethylene, is used on one surface of
the gas pervious ~aterial when needed to prevent substantial
saturation with a subsequently applied resinous material as
discussed in the following paragraphs. Other separating means
include stored liquid, e.g. gasoline-soluble and water-soluble solid
materials. These materials are especially useful when used in
conjunction with certain types of monitor means as discussed in the
following paragraph.
Jacket 17 is a fibrous reinforced resinous material. It is
formed by first applying a layer of fibrous reinforcing material on
separating agent 19 found on storage tank 10. The fibrous
reinforcing material can take on many different physical shapes and
structures variously referred to as mattings, nets, screens, meshes,
and chopped strands. Examples of fibrous materials include
fiberglass, nylon, and other synthetic fibrous materials. The
fibrous material, if in a sheet form, can be laid onto the storage
tank as a continuous matting.
Once the fibrous reinforcing material is applied, a resinous
material is next applied to the reinforcing material and thereafter
cured. Several different resinous materials are known for the
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~57(~9~
purpose of reinforcing fibrous material. Such materials include
polyesters, e.g. vinylesters, isophthalic polyesters, polyethylene,
polypropylene, polyvinylchloride, polyurethane, and polyepoxide.
The listed resinous materials used in the construction of this
jacket are not all inclusive, but only illustrative of some of the
resinous materials which can be used. Alternatively, the fibrous
material can be applied in the form of chopped strands with the
resinous materials described in the previous paragraph. That is,
the chopped strand and resinous material can be sprayed from
separate nozzles of the same spray gun and the jacket formed
therefrom on the separating agent as the resin cures. Other kno~n
methods of forming a fibrous reinforced resin substrate can be used.
The shape of the resultant jacket is such that it encases the
rigid inner storage tank to form a closed space 18, but is not a
structural part of it. The jacket itself is capable of containing
any liquid which is stored in the storage tank and which has leaked
therefrom. The strength of the jacket varies depending upon the
needs of the user. Thus, the jacket can have sufficient structural
integrity to withstand external load forces normally encountered by
underground storage tanks without suffering cracking or collapsing.
As used herein, cracking is defined to means the jacket structurally
tears apart to the extent a liquid will at least seep there through.
51ight surface deformations can be tolerated; however, deflections
of greater than about two inches from the norm would be considered a
collapseO Alternatively, the jacket can be positioned close enough
to the rigid storage tank that the rigid tank itself ensures that
the jacket maintains its shape. In such a case, the jacket is semi-
rigid or flexible. Preferably, the jacket is rigid and will not
_ g _
~2~
noticeably crack or collapse when external load forces are
encountered during normal use.
In a preferred embodiment of the invention, a thinned walled
tank and jacket are used. The thin walls and consequent less total
weight of the system can be used when a thin layer of gas pervious
material is positioned between the two. As a result of the close
proximity of the jacket and rigid tank, the sys-tem's total strength
or its integral structural strength is sufficient to withstand
normal external load forces. the thickness of the gas pervious
material is less than about 0.25 inches, preferably, less t'nan about
0.125 inches.
The jacket is capable of holding over 100% by volume of the
liquid stored in inner storage tank 10, more preferably from about
101% to about 150% by volume of the liquid stored in the inner tank.
FIG. 3 illustrates a typical fiberglass reinforced resinous
storage tank 20. Such tanks are formed with supporting ridges 21
circumferentially surrounding the tank. The ribs act as supports so
that the weight of the tank, including the contents therein are
evenly distributed and add strength needed to withstand earth load
stresses. This unique construction has necessitated special
fabrications with prior art vaulted storage tanks based on two rigid
shells. Such vaulted storage tanks have required first that special
supports be positioned between supports ribs 21 to keep the outer
rigid shell from collapsing from the earth load stresses. An
advantage of this invention is that the fibrous reinforcing material
can be laid over the gas pervious material-covered ridges 21 and the
resinous material applied without any special steps to accommodate
the ridges 21. The subsequently formed jacket 22 which conforms
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~57C~6
substantially to the contour of the rigid tank is not only capable
of holding any leaked liquid but also is capable of withstanding
external load forces without breaking. The steps of applying the
fiberglass reinforcing material and the resinous material are the
same as described above with respect to the metal storage tank of
FIG. 1
With reference to FIG. ~, gas pervious material 23 is an open
cell polyurethane foam. The space between the jacket 17 and the
storage tank 10 can be monitored. As sho~n in FIG. 4, an access
tube 24 extends from ground level through the jacket so as to be in
communication with the closed space. Any of well known and
commercially available monitor means can be used. For example, the
closed space can be filled with a detecting liquid. This detecting
liquid can be placed in the closed space by the manufacturer of the
tank due to the fact the closed space between the storage tank and
jacket occupies a small volume, e.g. about 25-100 gallons detecting
liquid is sufficient for use with a 20,000 gallon storage tank. At
the end of the access tube is a sight glass 25. Whenever leakage
occurs, a change in the level or color of a detecting liquid will
occur and will be readily observed in the sight glass. Instead of
the sight glass and visual observation of a change in level or color
of detecting liquid, non-visual leak detection means such as
pressure transducers or float controls can be used to detect a
change in level.
Alternatively, the closed space can be placed either under a
non-atmospheric pressure, i.e. a positive or negative air pressure.
Detection means associated with the closed space is capable of
detecting any change in pressure resulting from the leak in the
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~57~
jacket or the storage tank. As shown in FIG. 5, there is provided a
means 26 for maintaining the closed space under a positive or
negative pressure. Conventional air pump or vacuum pump, together
with an associated pressure regulator can be used. A pressure
change sensor 27 is a part of the detection means. A pressure
gauge serves this purpose adequately. Gptionally, an alarm system
can be electronically linked with the pressure sensor to audibly or
visually warn of a pre-set significant pressure change. Gas
pervious material 28 maintains a spaced relationship between the
inner tank and the jacket when a vacuum is used as well as serves as
the separating agent. Preferably, an access tube 29 with
strategically spaced holes extends from the air or vacuum pump 26 to
the lower portion of the closed space. When tube 29 extends over
the end portion of the storage tank, it serves the dual function of
strengthening the jacket at that point and providing a means to
monitor for leaked liquid at a low point where it could ultimately
seek.
Another embodiment of the detection means utilizes an analyzer
capable of detecting the liquid being stored. Thus, the detection
means comprises the analyzer which is in communication with the
closed space. Preferably, a vacuum means for withdrawing gaseous
material from the closed space is used for the purpose of obtaining
a sample. Thus, in FIG. 5, element 27 could be an analyzer capable
of detecting selected liquids instead of a pressure change sensor.
Still another detection means utilizes a probe which extends
through an access tube so as to monitor for leakage, preferably at
or near the bottom of the closed space. The probe is capable of
detecting pre-selected liquids or gases.
- 12 -
~5~0~3~
In the embodiment of this invention wherein used storage tanksare utili~ed, an additional step must be taken. Such tanks which
have been used and removed from the ground typically will have
weakened areas in the form of holes~ cracks, or pits. The first
step is to locate the weakened areas and repair said area. A visual
observation of the tank quite often will reveal where the weakened
areas occur. A pit is readily repaired with welding or with a
reinforced resinous material. Resinous materials which are useful
here are those which will adhere to the storage tank and which are
resistant to fuel stored in the tank. It is possible the weakened
area will extend completely through the wall of the storage tank or
eventually will corrode to such a point. In such an instance it is
necessary that when liquid contacts the resinous repair material
that the material itself is not dissolved or corroded away. A wide
range o different resinous materials can be used which have known
qualities of adhering to storage tanks and which are resistant to
stored liquids such as fuel. Particularly preferred are the
polyester and epoxy type resins, which may be reinforced with
fiberglass or other known resin fibrous materials.
Once all weakened areas are repaired, it is possible to test
the repaired storage tanks in any of several different manners. For
example, either a vacuum or air pressure can be applied to the
interior of the tank. The failure to maintain the pressure is an
indication that a leak is still present. Filling the storage tank
with a liquid under pressure and observing for any leaked liquid
through the tank is also another obvious manner of testing. Once
the tank has been repaired, a vacuum of at least about 3 inches of
mercury is applied. Preferably, a vacuum of from about 3 inches to
- 13 -
~57Q9~
about 10 inches of mercury i5 applied. This will show not onlywhether the storage tank still contains leaks, but whether it is
structurally sound and capable of being completely refurbished.
That is, once the leaks in a used tank have been repaired and the
aforemen~ioned vacuum applied, the structural soundness of the tank
is established. In the absence of such soundness, the tank will
collapse. Of course, when this happens, the tank must be scrapped
without continuing further with the steps of this invention or
special structural work undertaken. A tank which has been
refurbished and certified as structurally sound is provided with a
jacket in the manner previously described.
FIGS. 6 and 7 show alternative fittings useful with the storage
tanks whereby the closed space between the storage tank and jacket
and the closed spaced associated with a jacketed pipeline system can
be monitored. In FIG. 6 a fitting 30 is provided for the point at
which dispensing line 12 enters the storage tank 10. The fitting
which is a cylindrical shaped housing has a large enough inside
diameter to fit around the dispensing line 12. The Eitting is
welded to the storage tank by welds 31. Jacket 17 is securely
adhered to the fitting by adhesive means or clamping means so as to
form a fluid tight closed space 18. A -threaded fitting 32 used to
secure dispensing line 12 to the storage tank allows for easy field
installation of the storage tank in that once the tank is properly
positioned, the necessary pipeline can be installed in a
conventional fashion. Closed space 33 is formed by the dispensing
line 12 and a flexible jacket 34, which is a part of a jacket
pipeline system. Separate monitor means of the type discussed above
can be used to monitor for both storage tank and access pipeline
- 14 -
~57~9~
leakage, i.e. fill, dispensing, and vent line leakage. Thus, accesstube 35 is used for monitoring closed space 18 for storage tank
leakage.
The fi-tting 36 shown in FIG. 7 allows one monitor means be used
to monitor for storage tank leakage and pipeline leakage. Thus,
fitting 36 is similar to fitting 30 discussed above except openings
37 are provided for communication with closed space 18. The
advantage derived from fitting 36 is that it allows for the
continuous monitoring of a total underground storage tank and
delivery system by one monitor means. Any abnormal reading from the
monitor means alerts an attendant to a problem. A further checking
can pin point the location of the leak.
All the leak detection means discussed above can be
electronically linked with an alarm system to audibly or visually
warn of a pre-set significant change in the closed spaces. The leak
detection means and secondary containment means allow for an early
warning of a deterioration of either the primary or secondary
containment means thereby permitting the necessary repair work to be
done before any significant soil or water contamination has
occurred.
In FIGS. 1 and 2, the storage tank 10 is encased by jacket 17.
However, it is possible to obtain partial containment by forming a
jacket on at least about 40~ of the surface area of the storage
tank. For this partial secondary containment feature, the bottom
portion of the storage tank (where leaks are most likely to form)
has the separating agent and jacket formed thereover. Preferably,
at least about 40% and, more preferably, at least about 90~ of the
surface area of the storage tank has a jacket formed over it. As
- 15 -
~%5~9~
shown in FIG~ 8, jacket 38 covers essentially the bottom half ofstorage tank 39. Jacket 38 is sealed at edges 40 to form a closed
space 41 between said jacket and storage tank 39. The obvious
advantage of this system is a cost-savings, while still obtaining
adequate containment of that part of the storage tank which is most
likely to leak. Gas pervious material 41, positioned in the closed
space between jacket 38 and storage tank 39, performs the same
function as the gas perv ious material described with reference to
FIGS~ 1~ 2, 4, and S.
FIGo 9 illustrates an inner manhead sleeve especially useful
with the type of storage tank shown in FIG. 8. It prov ides a means
by which 100~ total containment is achieved. The inner manhead
sleeve 47 comprised of side walls which is in a cylindrical shape
form dimensioned to fit within a manhead 46 of the type commonly
found on certain storage tanks 44. An inner cover 48 fits over an
upper flange of the side walls 47 and an outer cover 49 fits over
the inner cover 48 and is attached to the manhead 46 by bolts 50 and
nuts 51. A gasket 52 ensures a liquid-tight seal. A second gasket
53 ensures a liquid-tight seal betweén the storage tank's interior
and the closed space defined by the outer cover 49, manhead 46, and
inner manhead sleeve 47. Spot welds are used to attach the inner
manhead sleeve 47 to the manhead 46. Inner manhead sleeve 47 is
dimensioned to fit within the manhead 44, as aforementioned, and to
form a closed space which is in communication through hole 54 with
the closed space 45 between the inner tank 44 and jacket 43.
Sealing material 55 between the inner manhead sleeve and the inner
storage tank 44 is to seal the closed space 45 from the storage
tank' s interior. Primary containment of the stored liquid is
-- 16 --
~;25~09~
provided by the inner storage tank 44, inner manhead sleeve 47, and
inner cover 48. Total secondary containment is provided by the
jacket 43, manhead 46 and outer cover 49. Leak detection means of
the type described above can readily monitor the closed space
provided by the aforementioned secondary containment system.
FIG. 10 il]ustrates another inner manhead sleeve useful with
storage tanks, the design of which is shown in FIG. 8. Again 100~
total containment is achieved. Inner manhead sleeve 56 fits within
manhead 46 so as to leave a closed space therebetween. Spot welds
are used to accomplish this. Inner cover 57, outer cover 58,
gaskets 5~, and bolts 61 and nuts 62 perform the same functions as
in FIG. 9. Access opening 60 is to provide a means by which a
dispensing line can enter. As an added measure of safety, bladder
66 is positîoned within the inner storage tank to act as the primary
containment means. Lo~er flange 63 on inner manhead sleeve 56 is
used as a means by which a ring clamp, together with bolts 64 and
nuts 65, can hold the bladder. Closed space 67 is used to monitor
for leakage. The advantage achieved by this system is the ability
to provide for true total secondary containment of the stored liquid
and to provide for a structure which permits effective leak
monitoring~ Additionally, by providing for a means by which access
lines can pass through the manhead, the total storage system is
adequately contained and can be adequately monitored.
While not shown in FIG. 10, a vacuum means could be used to
monitor for leakage. Because bladder 66 of FIG. 10 may not be
completely gasoline impervious, the vacuum means will withdraw
gasoline and water due to natural condensation. The water can be
removed by any known separation method and the gasoline returned to
- 17 -
~2s7~fi
the bladder's interior. Optionally, a shut-off valve can be
provided to prevent the bladder from being overfilled. Also, the
same concept can be used to recover gasoline which may leak from one
tank and seep through the jacket of a second tank. Such gasoline
would be removed by the vacuum means and directed to the interior of
the second.
The invention herein has been described with particular
reference to the drawings. It should be understood other variations
of the invention are within the scope of coverage.
- 18 -
