US3840056A

US3840056A - Apparatus for filling liquid storage tanks

Info

Publication number: US3840056A
Application number: US00324842A
Authority: US
Inventors: A Bower
Original assignee: Emco Wheaton
Current assignee: Emco Wheaton Inc
Priority date: 1973-01-18
Filing date: 1973-01-18
Publication date: 1974-10-08
Anticipated expiration: 1991-10-08

Abstract

The disclosure relates to a vent device for use in a liquid storage tank comprising first vent passage means having an inlet and an outlet end, second vent passage means having an inlet end and an outlet end, said inlet end of said second vent passage means being spaced from said inlet end of said first vent passage means, and a normally closed flow control means in said second vent passage means for controlling flow of fluid therethrough, said outlet end of said second vent passage means opening into said first vent passage means inwardly from the inlet end thereof whereby fluid passing through said second vent passage means may vent by way of the first vent passage means.

Description

United States Patent [1 1 Bower APPARATUS FOR FILLING LIQUID STORAGE TANKS [52] US. Cl 141/59, 141/290, 141/308 [51] Int. Cl B65b 31/00 [58] Field of Search 141/1, 4, 5, 46, 59, 97,

[56] References Cited UNITED STATES PATENTS 2,904,081 9/1959 Wolf et al. 141/290 3,732,902 5/1973 Muller 141/198 [451 Oct. 8, 1974 3,753,453 8/1973 Madden 141/59 X Primary Examine r-Houston S. Bell, Jr. Assistant Examiner-Frederick R. Schmidt Attorney, Agent, or Firm-Fetherstonhaugh & Co.

[57] ABSTRACT The disclosure relates to a vent device for use in a liquid storage tank comprising first vent passage means having an inlet and an outlet end, second vent passage means having an inlet end and an outlet end, said inlet end of said second vent passage means being spaced from said inlet end of said first vent passage means, and a normally closed flow control means in said second vent passage means for controlling flow of fluid therethrough, said outlet end of said second vent passage means opening into said first vent passage means inwardly from the inlet end thereof whereby fluid passing through said second vent passage means may vent by way of the first vent passage means.

4 Claims, 4 Drawing Figures APPARATUS FOR FILLING LIQUID STORAGE TANKS FIELD OF INVENTION This invention relates to the prevention of spillage and resultant environment pollution caused by spillage of fuel oils and the like during loading of storage tanks. In particular this invention is concerned with the prevention of polluting spillage during the filling of underground fuel tanks such as gasoline storage tanks.

PRIOR ART Environmental pollution is a matter of great concern to the oil industry and steps have been taken to provide vapour recovery systems in tank trucks so that the vapour which is vented from a gasoline storage tank during filling of the storage tank is returned to the tank truck rather than simply discharged directly into the atmosphere. Unfortunately the existing vapour recovery systems tend to increase the amount of spillage which occurs during the filling of storage tanks rather than decrease the spillage. With many systems it is extremely difficult for the operator to prevent spillage occuring after loading of a storage tank even where the operator takes considerable care in an attempt to avoid spillage.

Underground storage tanks are generally gravity fed from a tank truck and when the storage tank is filled beyond capacity liquid remains in the filling hose and fills the vent line. When the connection between the filling hose and the filling tube of the underground tank is broken the liquid within the filling hose and the vent line spills onto the ground where it pollutes the environment by running into streams or sewers or evaporates thus polluting the air.

Often underground fuel tanks such as gasoline storage tanks are filled by tank trucks during off peak hours frequently late at night or very early in the morning with the result that any spillage which occurs is generally dissipated either by evaporation or drainage before the fact that a spillage has occured is widely known with the result that operators of tank trucks are more concerned with completing their filling operations as quickly as possible than they are with preventing spillage.

With the introduction of vapour recovery systems, the spillage problems have been increased because of the fact that after completing the filling operation the vapour recovery hose frequently contains an overflow of fuel which is again spilled when the connection between the vapour recovery hose and the vapour adaptor is broken. Additional spillage results from the fact that the conventional vent line which is provided in most liquid storage tanks also becomes at least partially filled with overflow of liquid from the storage tank when the storage tank is filled from a tank truck. The liquid in the vent line tends to spill out of the open end of the liquid adaptor when the liquid hose is removed. The liquid trapped in the vent line creates a further hazard in that it prevents adequate venting of the fuel tank.

SUMMARY OF INVENTION The present invention overcomes the difficulties of the prior art described above and provides a simple and inexpensive method and apparatus for limiting the amount of liquid which will be filled into a storage tank to provide sufficient space within the storage tank to permit the liquid trapped within any of the lines leading to or from the storage tank as a result of filling to drain into the tank after the filling operation has been terminated.

According to an embodiment of the present invention, there is provided a vent device for use in a liquid storage tank comprising first vent passage means having an inlet end and an outlet end, second vent passage means having an inlet end and an outlet end, said inlet end of said second vent passage means being spaced from said inlet end of said first vent passage means, and normally closed flow control means in said second vent passage means for controlling the flow of fluid therethrough, said outlet end of said second vent passage means opening into said first vent passage means inwardly from the inlet end thereof whereby fluid passing through said second vent passage may vent by way of said first vent passage.

According to a further embodiment of this invention, there is provided in a liquid storage tank having an input opening and a vent opening, the vent opening permitting controlled venting of the gaseous atmosphere from said tank during filling, the improvement of means for preventing the escape of gaseous atmosphere from said tank by way of said vent passage means after filling with liquid to a predetermined level whereby a gas filled enclosure is formed within said tank to prevent complete filling of said tank, and pressure relief means communicating between said gas filled enclosure and said vent passage means, said pressure relief means being closed during filling of said tank and open after filling to permit gas trapped within said enclosure to vent therefrom into said vent passage means and thereby permit any liquid trapped downstream of said vent passage and/or upstream of said input passage to drain into said enclosure.

According to a still further embodiment of the present invention, there is provided a method of filling a liquid storage tank from a tank truck comprising the steps of partially filling the liquid storage tank by gravity filling to establish a pressurized gas enclosure within the storage tank having a capacity at least equal to the volume of liquid which may be trapped in the various lines leading to and from the storage tank and relieving the pressure in said gas filled enclosure after filling has been stopped to prevent the liquid trapped in the various lines to drain into said enclosure.

PREFERRED EMBODIMENT The invention will be more clearly understood after reference to the following detailed specification read in conjunction with the drawings, wherein FIG. 1 is a partially sectioned view of a vent device according to an embodiment of the present invention;

FIG. 2 is a pictorial view illustrating the manner in which an underground tank is loaded according to an embodiment of the present invention;

FIG. 3 is a view similar to FIG. 2 illustrating a further embodiment of this invention; and

FIG. 4 is a view of an underground storage tank illustrating a further embodiment of the invention.

With reference to the drawings, the reference numeral 10 refers generally to a vent device according to an embodiment of the present invention. The vent device includes a housing 12 which has a through passage 14 formed therein. The through passage 14 has an upper portion 16 and a lower portion 18. The lower portion 18 is of a greater diameter than the upper portion 16. An extension pipe 20 is threadably connected at its upper end to the lower end of the upper portion 16 of the through passage so as to project downwardly therefrom in a spaced relationship with respect to the lower portion 18 to form a chamber 22 therebetween. The lower end 24 ofthe extension pipe 20 is spaced a substantial distance below the lower end 26 of the housing 12 so that the lower end 24 of the extension pipe may be positioned within a storage tank 28 at a level a substantial distance below the level of the lower end 26 of the housing, as will be described hereinafter.

The housing 12 is formed with a threaded neck portion 30 at the lower end adapted to be threadably mounted in a collar 32 which is secured to the storage tank 28 in a position surrounding the vent passage 34 of the storage tank 28 so that the housing 30 may be mounted with the extension pipe extending downwardly into the storage tank 28 and with the chamber 22 aligned with the vent opening 34 of the storage tank. The housing 12 also has a first discharge port 36 and a second discharge port 38 at the upper end thereof. The second discharge port 38 is adapted to threadably receive an existing vent line 40 of the type which is usually provided in existing underground gasoline storage tanks and the like. A conduit 42 is threadably mounted in the first discharge port 36 of the housing and extends upwardly therefrom and has a vapour adaptor 44 at the upper end thereof. The conduit 42 is of a sufficient length to dispose the vapour adaptor 44 at or adjacent to ground level when the housing is mounted on an underground liquid storage tank. The vapour adaptor 44 has an annular recess 46 at the upper end thereof adapted to receive the closure cap 48 to close the end thereof. The annular recess 46 is also adapted to be connected to a coupler of a vapour hose of a tank truck or the like.

A passage 50 opens outwardly from the chamber 22 and forms the inlet end of the second vent passage of the vent device 10. A passage 52 communicates with the upper portion 16 of the through passage 14 and forms the outlet end of the second vent passage of the device 10. The first vent passage of the device 10 is formed by the combination of the passage 21 formed in the extension pipe 20 and the upper portion 16 ofthe through passage 14.

The normally closed flow control valve 54 has its input passage 56 connected to the passage 50 of the housing 12 by a conduit 58 and elbows 60. The output passage 62 of the valve 54 is connected to the passage 52 of the housing by a conduit 64, coupling 68 and elbow 66. The valve stem 70 of the valve device is held in a normally closed position by a spring 72. The valve stem 70 is movable to an open position by compressing the upper end of the stem which is projected outwardly from the housing so as to compress the spring 72. When the depressing force is removed from the valve stem, the spring 72 forces the valve stem back to the closed position shown in FIG. I of the drawings. It will be noted that the valve 54 is mounted adjacent the vapour adaptor 44 and the closure cap 48 is formed with an annular flange 49 which will force the valve stem 70 to the open position when the closure cap is in a position closing the end of the vapour adaptor 44. This ensures that the storage tank may vent to the existing vent line 40 when the vapour adaptor is closed.

As previously indicated, FIG. 2 of the drawings diagrammatically illustrates the method and apparatus used in filling and venting an underground liquid storage tank such as a gasoline storage tank. The tank 28 is formed with an input opening and a vent opening 34. A filling tube 82 extends into the input opening 80. The filling tube 82 is adapted to be connected to one end of a liquid hose 84, the other end of which is adapted to be connected to one of the faucet valves 86 of the tank truck 88 from which the liquid storage tank is to be filled. The tank truck 88 is of the well known type which includes a plurality of storage compartments, each having a faucet valve 86 for use in draining the contents thereof into the underground storage tank. The tank truck 88 also has a vapour recovery system, generally identified by the reference numeral 90, which includes a lower conduit 92 which is connected to one end of a vapour hose 94, the other end of which is connectible to the adaptor 44 of the vent device 10 as previously described with reference to FIG. 1 of the drawings. The vapour recovery system also includes a riser conduit 96 which is connected to a manifold 98 which extends along the top of the tank truck and is provided with a plurality of vent passages 100 and return passages l02 which open into the storage compartments of the tank truck. The operation of the vapour recovery system is well known and does not constitute a part of the present invention and is not described herein.

In use, a tank truck is positioned closely adjacent the underground storage tank at a height above the underground storage tank sufficient to permit all of the liquid within the tank truck to drain under the influence of gravity into the underground storage tank as required. The liquid hose 84 is connected to one of the faucet valves 86 and to the filling tube 80. The closure cap 48 is removed from the vapour adaptor 44 and the vapour hose 94 is connected to the vapour adaptor 44. As previously indicated, when the closure cap 48 is removed the valve stem 70 moves to the closed position so as to close the valve 54 and thereby close the second vent passage which is diagrammatically illustrated in FIG. 2 and identified by the reference numeral 102. The first vent passage is also diagrammatically illustrated in FIG. 2 of the drawings and identified by the reference numeral 104.

To fill the underground storage tank, the valve 86 to which the liquid hose is coupled is opened so that liquid drains under the influence of gravity from the tank truck through the liquid hose 84 and filling tube 82 to discharge into the tank 28. As the liquid level rises in the underground tank, the atmosphere within the tank is vented to the first vent passage 104 so as to be directed to the vapour hose line 94 or the existing vent line 40.

The portion of the atmosphere which vents through the vapour hose 94 is directed to the vapour recovery system of the tank truck. The level of liquid within the tank will continue to rise and will eventually close the lower end 24 of the extension pipe 20. When the lower end of the extension pipe 20 is closed, the atmosphere above the level of liquid in the tank is no longer able to escape through the first vent passage. As previously indicated, the second vent passage 102 is effectively closed by the valve 54. The head of liquid in the tank truck will cause liquid to continue to discharge into the underground storage tank pressurizing the atmosphere which is trapped in the enclosure formed above the lower end of the extension pipe and also causing liquid to rise in the first vent passage 104. Unless a float type shut-off valve is provided in the first vent passage 104, the liquid level will rise until it extends into the vapour hose 94 and the riser 96 to a level equal to the level of liquid in the compartment of the tank truck which is being drained. Liquid will also rise in the existing vent line 40 unless a suitable shut-off float valve or the like is provided. Once the level of liquid in the riser 96 and existing vent line 40 is equal to the level of liquid in the compartment of the tank truck which is being drained, the flow of liquid into the underground storage tank will terminate. This arrangement has the advantage that it is not necessary for an operator to maintain a continuous watch on the filling operation to determine the exact point at which the storage tank has been filled to the required capacity. The automatic termination of filling is particularly advantageous when considered in combination with the spillage prevention system of the present invention.

When the flow of liquid to the storage tank has terminated, the faucet valve 86 is closed trapping a substantial volume of liquid in the liquid hose, vapour hose and existing vent line. By selecting an extension pipe 20 of a sufficient length to establish a gas filled enclosure within the underground storage tank of a volume at least equal to the volume of liquid likely to be trapped in the lines described above, it is possible to avoid spillage of the trapped liquid by draining the trapped liquid into the underground storage tank. In order to drain liquid into the storage tank, it is necessary to vent the gas filled enclosure and this is achieved by manually opening the pressure relief valve 54 to open the second vent passage 102. The head of liquid in the liquid hose, vapour hose and existing vent line is sufficient to cause the atmosphere within the gas filled enclosure to vent through either the vapour hose line or the existing vent line and thereby permit the liquid in these lines and the liquid hose to drain into the underground storage tank.

After all of the liquid has drained into the underground storage tank from the liquid hose, vapour hose and vent line, the liquid hose is disconnected from the filling tube and the vapour hose is disconnected from the vapour adaptor. The filling tube and vapour adaptor are then capped. As previously indicated, the lower end of the first vent passage 104 has been closed by the liquid within the tank, with the result that the first vent passage cannot be used in order to provide adequate venting for the underground tank during storage. However, as previously indicated the closure cap 48 opens the valve 54 so that the second vent passage 102 is opened. The input end of the second vent passage 102 is spaced a substantial distance above the input end of the first vent passage 104 and is not closed by the liquid within the storage tank. In fact, as indicated in FIGS. 1 and 2 of the drawings, the input end of the first and second vent passages is disposed at a level above the upper end of the tank so that the entire tank may vent through the second vent passage 102 and the output end of the second vent passage 102 opens into the first vent passage 104 at a level substantially equal to the level of the existing vent line so that the second vent passage may vent into the existing vent line to vent to atmosphere.

It will be noted that the extension pipe 20, as previously indicated, is threadably mounted in the housing 12 and may be removed to be replaced by a longer or shorter drop tube as required in use depending upon the proportions of the underground storage tank. When the proportions of the tank are known, it is a simple matter to calculate the length of the extension pipe required in order to establish the required gas filled enclosure during filling.

Various modifications of the present invention will be apparent to those skilled in the art without departing from the scope of the invention.

A typical modification is illustrated in FIG. 3 of the drawings wherein like numerals have been applied to like parts that appear in FIG. 2. In the embodiment illustrated in FIG. 3 it is possible to simultaneously load two storage tanks 28 from one tank truck 88. One of the problems previously encountered in attempting to simultaneously load two underground storage tanks when a vapour recovery system was in use was that after one storage tank was filled, the overflow from the full tank entered the vapour line of the tank being filled and prevented proper venting of the tank which was not completely filled. Two constructions for overcoming this problem are illustrated in FIG. 3 and both employ a float valve. Float valves are diagramatically shown in the tank truck at the point of connection with the vapour recovery system. The manner in which this float valve operates is illustrated with reference to the line 94a which is connected to the storage tank 28 which is completely filled. In this embodiment, the liquid in the storage tank fills the line 94a to the point where the float 122 of the float valve closes the valve 120 and prevents the passage of the liquid into the vapour recovery system beyond the valve 120. It will be noted that in this embodiment, a valve 120 is not provided at the bottom end of the extension pipe 104. In the embodiment of the invention illustrated with reference to the partially filled tank 28, float valve 120 is mounted at the lower end of the extension pipe 104 and serves to prevent the passage of liquid into the passage 104 when the level in the tank rises above a predetermined level. It will be noted that if the valve 120 was used without the provision of the second vent line 102, normal venting of the full storage tank would not be possible in view of the fact that there would be no direct communication between the space provided above the liquid level and the vent to atmosphere line. It will be understood that when a float valve 120 is provided on the extension pipe 20 it is not necessary to provide a similar float valve 120 at the truck end of the line 94b.

Whereas the embodiments of the invention illustrated in FIGS. 2 and 3 of the drawings show the flow control valve 54 mounted adjacent the vapour recovery line, it will be understood that this system for preventing spillage may be used in association with a storage tank which is not designed for use with a vapour recovery system. FIG. 4 of the drawings illustrates a storage tank in which the control valve 54 is mounted adjacent the upper end of the filling tube 82. The control valve 54 is arranged so as to open the vent line 102 when the closure cap 49 is secured in a position closing the filling tube 82. When the closure cap 49 is removed, the valve 54 is closed to prevent the escape of atmosphere from the tank 28 by way of the vent line 102. The valve 54 will remain closed when the filling tube 82 is coupled to the filling hose of a tank truck. When the storage tank of FIG. 4 is filled by way of the filling tube 82 the level of liquid in the storage tank will rise until it is above the level of the bottom end of the tube 104, after which the level will cease to rise when the pressure within the storage tank 28 balances the pressure of the head of liquid within the tank truck. After the filling has been completed, the filling hose is uncoupled and the closure cap 49 replaced. The closure cap 49 serves to open the valve 54 so as to permit venting of the atmosphere in the storage tank by way of vent line 102 into vent line 40. This permits any liquid which has entered the

vent line

102 and 40 to drain back into the storage tank.

From the foregoing, it will be apparent that the present invention provides a simple and inexpensive method and apparatus for effectively filling underground liquid storage tanks or the like from a tank truck without spillage. The apparatus of the present invention also provides an effective adaptor for use in adapting existing underground liquid storage tanks for use with vapour recovery systems now employed in tank trucks and the like.

What I claim as my invention is:

1. In a liquid storage tank of the type which is gravity filled from a tank truck by a filling line communicating with liquid input passage means opening into the tank, the improvement of a. first vent passage means opening outwardly from said tank to permit venting of air from the tank during the filling of the tank,

b. means for preventing the escape of air from said tank by way of said first passage means after filling of the tank with liquid to a first predetermined level whereby continued further filling of the tank causes the pressure of the air trapped in an enclosure above the liquid level to increase to a pressure sufficient to stop the flow of liquid into the tank at a second level below the full height of the tank,

c. second vent passage means opening outwardly from said tank at a level above said second level of said liquid for venting said enclosure,

(1. valve means in said second vent passage means movable between a first position closing said second vent passage means and a second position opening said second vent passage means,

e. means for moving said valve means to said first position closing said second vent passage means during filling of said tank,

f. said valve means being maintained in said second position opening said second vent passage means to vent said enclosure after filling of said tank to said second level whereby the air trapped above said liquid may be discharged through said second vent passage means to permit any liquid in the filling line and first vent passage means to drain into said tank and g. means for maintaining said valve means in said second position to permit continuous venting of said tank when said first vent passage is sealed after fillmg.

2. A liquid storage tank of the type which is gravity filled from a tank truck by a filling line communicating with liquid input passage means opening into the tank, said tank having a vent opening in an upper wall portion thereof, the improvement of a vent device mounted on said tank and communicating with the interior of said tank through said vent opening, said vent device comprising a. a vent housing assembly,

b. extension tube means projecting from said vent housing assembly into said tank through said vent opening to a level a substantial distance below the upper wall of the tank,

c. a first vent passage opening outwardly from said tank through said extension tube and said vent housing assembly, said first vent passage opening from said extension tube to said tank at a first level a substantial distance below the upper wall of the tank to permit venting of air from the tank until the level of liquid in the tank rises above said first level,

d. second vent passage means opening through said vent housing assembly, said second vent passage means having a first end opening into said tank at a second level a substantial distance above said first level whereby the area of the tank above said first level may be vented after said first vent passage is closed e. valve means in said second vent passage means movable between a first position closing said second vent passage means and a second position opening said second vent passage means,

means for moving said valve means to said first position closing said vent passage means during filling of said tank,

g. said valve means being maintained in said second position opening said second vent passage means to vent the air above the liquid level after filling said tank whereby air trapped above said liquid may be discharged through said second vent passage means to permit any liquid in the filling line and first vent passage means h. means for maintaining said valve means in said second position to permit continuous venting of said tank during storage of the liquid.

3. In a liquid storage tank of the type which is gravity filled from a tank truck by a filling line communicating with liquid input passage means opening into the tank, the tank having a vent opening in an upper wall portion thereof, the improvement of a. a vent housing mounted on said tank, said vent housing having a housing passage extending therethrough, said housing passage having a lower end communicating with the interior of said tank through said vent opening,

b. extension tube means mounted in said housing passage and dividing said housing passage into an upper portion and a lower portion and preventing direct communication between said upper and lower portions, said extension tube extending downwardly from said housing into said tank to a level a substantial distance below the level of said upper wall portion of said tank, said extension tube having a vent passage opening therethrough which communicates with said upper portion of said housing passage and the interior of said tank at a level a substantial distance below the level of said lower portion of said housing passage whereby liquid rising in the tank will close the lower end of said extension tube to prevent venting therethrough while the lower portion of said housing passage remains open to the interior of the tank,

c. second vent conduit means having a first end secured to said vent housing in fluid communication with said lower portion of said housing passage at a level above the lower end of said housing passage and a second end secured to said vent housing in fluid communication with said upper portion of said housing passage,

(1. valve means in said second vent conduit means movable between a first position closing said second vent conduit means and a second position opening said vent conduit means,

e. means for moving said valve means to said first position closing said second vent conduit means during filling of said tank,

f. said valve means being maintained in said second position opening said second vent conduit means after filling of said tank whereby the air trapped above the liquid may be discharged through said second vent conduit means to permit any liquid in the filling line to drain into said tank without overflowing said tank and g. means for maintaining said valve means in said second position to permit continuous venting of said tank during storage of the liquid.

4. In a liquid storage tank as claimed in claim 3 the further improvement of vapour recovery conduit means communicating with said upper portion of said housing passage and extending upwardly therefrom and terminating in a coupling element adapted to be connected to a complementary coupling element of a vapour recovery system of a tank truck, third vent passage means opening from said upper portion of said housing passage and venting to atmosphere, said means for maintaining said valve means in said second position consisting of closure cap means for closing said vapour recovery conduit means when not in use, said valve means being disposed adjacent said coupling element of said vapour recovery conduit to be engaged by said cap means when said vapour recovery conduit is closed by said cap means to open said valve means to provide venting of said liquid storage tank by way of said second vent conduit means and said third vent passage means.

Claims

1. In a liquid storage tank of the type which is gravity filled from a tank truck by a filling line communicating with liquid input passage means opening into the tank, the improvement of a. first vent passage means opening outwardly from said tank to permit venting of air from the tank during the filling of the tank, b. means for preventing the escape of air from said tank by way of said first passage means after filling of the tank with liquid to a first predetermined level whereby continued further filling of the tank causes the pressure of the air trapped in an enclosure above the liquid level to increase to a pressure sufficient to stop the flow of liquid into the tank at a second level below the full height of the tank, c. second vent passage means opening outwardly from said tank at a level above said second level of said liquid for venting said enclosUre, d. valve means in said second vent passage means movable between a first position closing said second vent passage means and a second position opening said second vent passage means, e. means for moving said valve means to said first position closing said second vent passage means during filling of said tank, f. said valve means being maintained in said second position opening said second vent passage means to vent said enclosure after filling of said tank to said second level whereby the air trapped above said liquid may be discharged through said second vent passage means to permit any liquid in the filling line and first vent passage means to drain into said tank and g. means for maintaining said valve means in said second position to permit continuous venting of said tank when said first vent passage is sealed after filling.

2. A liquid storage tank of the type which is gravity filled from a tank truck by a filling line communicating with liquid input passage means opening into the tank, said tank having a vent opening in an upper wall portion thereof, the improvement of a vent device mounted on said tank and communicating with the interior of said tank through said vent opening, said vent device comprising a. a vent housing assembly, b. extension tube means projecting from said vent housing assembly into said tank through said vent opening to a level a substantial distance below the upper wall of the tank, c. a first vent passage opening outwardly from said tank through said extension tube and said vent housing assembly, said first vent passage opening from said extension tube to said tank at a first level a substantial distance below the upper wall of the tank to permit venting of air from the tank until the level of liquid in the tank rises above said first level, d. second vent passage means opening through said vent housing assembly, said second vent passage means having a first end opening into said tank at a second level a substantial distance above said first level whereby the area of the tank above said first level may be vented after said first vent passage is closed e. valve means in said second vent passage means movable between a first position closing said second vent passage means and a second position opening said second vent passage means, f. means for moving said valve means to said first position closing said vent passage means during filling of said tank, g. said valve means being maintained in said second position opening said second vent passage means to vent the air above the liquid level after filling said tank whereby air trapped above said liquid may be discharged through said second vent passage means to permit any liquid in the filling line and first vent passage means h. means for maintaining said valve means in said second position to permit continuous venting of said tank during storage of the liquid.

3. In a liquid storage tank of the type which is gravity filled from a tank truck by a filling line communicating with liquid input passage means opening into the tank, the tank having a vent opening in an upper wall portion thereof, the improvement of a. a vent housing mounted on said tank, said vent housing having a housing passage extending therethrough, said housing passage having a lower end communicating with the interior of said tank through said vent opening, b. extension tube means mounted in said housing passage and dividing said housing passage into an upper portion and a lower portion and preventing direct communication between said upper and lower portions, said extension tube extending downwardly from said housing into said tank to a level a substantial distance below the level of said upper wall portion of said tank, said extension tube having a vent passage opening therethrough which communicates with said upper portion of said housing passage and the interior of said tank at a level a substantial distance below the level of said lower portion of said houSing passage whereby liquid rising in the tank will close the lower end of said extension tube to prevent venting therethrough while the lower portion of said housing passage remains open to the interior of the tank, c. second vent conduit means having a first end secured to said vent housing in fluid communication with said lower portion of said housing passage at a level above the lower end of said housing passage and a second end secured to said vent housing in fluid communication with said upper portion of said housing passage, d. valve means in said second vent conduit means movable between a first position closing said second vent conduit means and a second position opening said vent conduit means, e. means for moving said valve means to said first position closing said second vent conduit means during filling of said tank, f. said valve means being maintained in said second position opening said second vent conduit means after filling of said tank whereby the air trapped above the liquid may be discharged through said second vent conduit means to permit any liquid in the filling line to drain into said tank without overflowing said tank and g. means for maintaining said valve means in said second position to permit continuous venting of said tank during storage of the liquid.