Apparatus and method for filling carbon dioxide cylinders

A device for filling a high-pressure CO.sub.2 cylinder with liquid CO.sub.2 while venting gaseous CO.sub.2 comprises a two-compartment chamber that is installed in the top opening of the cylinder. A first dip tube connected to one compartment extends to the bottom portion of the cylinder and a second dip tube connected to the other compartment extends to the upper portion of the cylinder. Each compartment has a port for flow into or out of the compartment. Liquid CO.sub.2 introduced into the compartment with the first dip tube will flow into the cylinder and cause gaseous CO.sub.2 to exit through the second dip tube and the other compartment. When liquid CO.sub.2 appears in the exiting stream, the introduction of liquid CO.sub.2 is stopped. In a common embodiment, a conventional CO.sub.2 valve has the first dip tube connected to the bottom thereof. A street tee with one end connected to the second dip tube is screwed into the top opening of the cylinder. The CO.sub.2 valve is screwed into the other end of the tee, the first dip tube extending with annular clearance through the second dip tube into the cylinder.

BACKGROUND OF THE INVENTION 
This invention relates to an apparatus and method of filling carbon dioxide 
(CO.sub.2) cylinders. More particularly, the invention involves filling 
liquefied CO.sub.2 high pressure cylinders by passing liquefied CO.sub.2 
from a low pressure container of liquefied CO.sub.2. 
High pressure cylinders for liquefied CO.sub.2 have a single valved port 
and, by long established practice, are filled at a recharging depot where 
liquefied CO.sub.2 is pumped into each cylinder through its valved port. 
Filling is continued until the weight of CO.sub.2 is equal to two-thirds 
of the weight of water that would fill the cylinder. This customary 
filling limit serves to provide a safe vapor space above the liquefied 
CO.sub.2 in the cylinder. 
In contrast to the common, laborious and costly practice of transporting 
each cylinder from a CO.sub.2 user to a depot, filling it while carefully 
weighing the added CO.sub.2 to avoid overfilling, and transporting the 
recharged cylinder back to the CO.sub.2 user, the invention provides a 
system of supplying CO.sub.2 to cylinders much like the familiar delivery 
of fuel oil to the tanks at several homes. In spite of the extensive 
distribution of CO.sub.2 cylinders and the frequent need to transport each 
to a refilling depot and back again to the user, no practical proposal is 
known for obviating this cumbersome and expensive system of shuttling 
cylinders between CO.sub.2 customers and a recharging depot. 
Accordingly, a principal object of the invention is to provide an apparatus 
and method for filling cylinders at various locations with liquefied 
CO.sub.2 from a large container that is transported to the various 
locations. 
Another important object is to provide an apparatus for filling CO.sub.2 
cylinders which is simple to install and to use. 
A further object is provide apparatus that automatically limits filling 
cylinders with liquid CO.sub.2 to a selected safe level. 
These and other features and advantages of the invention will be apparent 
from the description which follows. 
SUMMARY OF THE INVENTION 
In accordance with this invention, three basic elements have been added to 
the conventional CO.sub.2 valve that is screwed into the threaded port at 
the top of a high-pressure cylinder for liquefied CO.sub.2, namely, a 
street tee and two dip tubes. A first dip tube, usually a copper tube, is 
soldered or otherwise connected to the bottom opening in the conventional 
CO.sub.2 valve. A second dip tube, larger in diameter than that of the 
first dip tube, usually a copper tube, is soldered of otherwise connected 
to the end of the tee that has a male thread matching the female threaded 
opening of the cylinder. 
The CO.sub.2 valve with the first dip tube is inserted into the opposite 
end of the street tie which has a female thread. The first dip tube 
extends through the second dip tube with an annular clearance between 
them. When the CO.sub.2 valve is fully screwed into the top female end of 
the tee, and the bottom male end of the tee is fully screwed into the 
threaded opening of the cylinder, the bottom end of the first dip tube 
will be close to, preferably only about 1 inch above, the bottom of the 
cylinder. By contrast, the second dip tube will extend down only about 
one-third of the internal length of the cylinder. Thus, liquid CO.sub.2 
introduced through the conventional CO.sub.2 valve flows down the 30 first 
dip tube into the bottom of the cylinder while gaseous CO.sub.2 passes up 
the second dip tube and out of the tee through its side opening which may 
be provided with a valve. 
The level of liquid CO.sub.2 in the cylinder will keep rising during the 
filling operation until it reaches the bottom end of the second dip tube. 
Up to that point, gaseous CO.sub.2 has been leaving the cylinder by 
flowing up the second dip tube through the annular space between it and 
the first dip tube and into the street tee from which it exits at the side 
opening of the tee. 
As soon as the level of liquid CO.sub.2 reaches the bottom end of the 
second dip tube, the gaseous CO.sub.2 in the cylinder above the liquid 
develops sufficient pressure to cause liquid CO.sub.2 to flow up the 
second dip tube and out of the tee through its side opening. The escaping 
liquid CO.sub.2 flashes into CO.sub.2 snow which 10 signals that the 
desired liquid CO.sub.2 capacity of the cylinder has been reached and the 
further supply of liquid CO.sub.2 to the cylinder should be terminated. 
Thereupon, the conventional CO.sub.2 valve is closed to stop the flow of 
liquid CO.sub.2 into the cylinder and a valve at the side opening of the 
street tee is also closed to stop the escape of gaseous CO.sub.2 from the 
cylinder. Then the valve connected to the side of the tee has its 
discharge end connected to tubing that can convey gaseous CO.sub.2 to a 
desired use station, such as a beer dispenser or a soda fountain, and the 
valve is opened to permit gaseous CO.sub.2 flow to the use station. 
It is noteworthy that the invention involves the simple assembly of three 
common plumbing elements with the conventional CO.sub.2 valve. Two of the 
three added elements are merely lengths of metal tubing, further 
highlighting the simplicity and low cost of the apparatus of the invention 
that eliminates the continuous, cumbersome and expensive transportation of 
cylinders between CO.sub.2 use sites and CO.sub.2 supply depots. 
However, it should be noted that the composite of the CO.sub.2 valve and 
street tee provides in effect a metal chamber with two 30 compartments: a 
liquid CO.sub.2 feed compartment in the CO.sub.2 valve above a CO.sub.2 
vapor exit compartment in the tee. Therefore, stated more generally, the 
invention involves a metal chamber that can be screwed into the top 
opening of a CO.sub.2 cylinder, the metal chamber having a wall therein to 
provide two compartments. Each compartment has a port to the exterior of 
the chamber and each has a dip tube connected thereto and extending into 
the CO.sub.2 cylinder, the two tubes having different lengths. However, in 
its basic form, the invention comprises means for sealing the top opening 
of a CO.sub.2 cylinder and for holding two dip tubes extending 
therethrough into the cylinder to different levels therein.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The components of the apparatus of the invention in its common form are 
shown disassembled in FIG. 1. A standard CO.sub.2 cylinder valve 10 is 
shown with a single addition thereto of a first dip tube 11 attached to 
the central opening 12 at the bottom of valve 10 which has the usual valve 
stem 13 and knob 14 at the top thereof. The bottom end of valve 10 has a 
male thread 15 matching the female thread of the sole opening at the top 
of the CO.sub.2 cylinder in which valve 10 was screwed prior to this 
invention. Valve 10 has a threaded port 16 for the flow of CO.sub.2 and a 
lateral cell 17 containing a safety disk that will rupture and release the 
pressure in the CO.sub.2 cylinder if the pressure exceeds a predetermined 
safe maximum. 
The other basic components are a street tee 18 and a second dip tube 19 
connected to the opening at the end of tee 18 which has male thread 20 
chosen to match the female thread of the top opening of the CO.sub.2 
cylinder into which tee 18 will be screwed. The top end 21 of street tee 
18 has a female thread matching the male thread 15 of CO.sub.2 valve 10 so 
that valve 10 and tee 18 can be screwed together. 
Tube 11 connected to CO.sub.2 valve 10 is longer and smaller in diameter 
than tube 19 connected to street tee 18. In order to screw valve 10 and 
tee 18 together, the first dip tube 11 is inserted in top end 21 and 
through tee 18 and second dip tube 19 until the bottom of valve 10 is 
against the top end 21 of tee 18. Valve 10 and tee 18 are then screwed 
together and are ready to be installed in a CO.sub.2 cylinder by inserting 
the concentric first and second dip tubes 11,19 through the top opening in 
the CO.sub.2 cylinder until tee 18 reaches the female threaded opening at 
the top of the CO.sub.2 cylinder. Male threaded end 20 of tee 18 is then 
screwed into the top of the CO.sub.2 cylinder to complete the installation 
of the apparatus of the invention. The lateral port 22 of street tee 18 
serves as the discharge opening for the withdrawal of gaseous CO.sub.2 
from the cylinder as will be explained in the description of FIG. 2. 
FIG. 2 is a diagrammatic representation of the apparatus of the invention 
as installed in a high-pressure CO.sub.2 cylinder together with typical 
accessories used with the cylinder. The components of FIG. 1, when 
assembled as the apparatus of the invention, are shown installed in a 
CO.sub.2 cylinder 23. 
First dip tube 11 extends from the bottom of CO.sub.2 valve 10 to close to, 
say 1 to 2 inches from, the bottom of cylinder 23. Second dip tube 19 
surrounding tube 11 extends from the bottom of tee 18 about one-third down 
the inside length of cylinder 23. More precisely, the length of second 
tube 19 is determined by a long established regulation for high-pressure 
CO.sub.2 cylinders. That regulation specifies that the maximum quantity of 
liquefied CO.sub.2 in a cylinder shall not exceed two-thirds of the weight 
of water that will fill the cylinder. This formula ensures a safe vapor 
zone in the cylinder above the liquid CO.sub.2 therein. Too small a vapor 
zone is dangerous because a very high pressure could develop in the 
cylinder to the point of exploding it. 
To introduce liquid CO.sub.2 into cylinder 23, the apparatus of the 
invention makes it possible for liquid CO.sub.2 to flow from a supply 
container into CO.sub.2 valve 10 through port 16. The liquefied CO.sub.2 
flows down valve 10 and first dip tube 11, discharging into the bottom of 
cylinder 23. Gaseous CO.sub.2 evolved from the liquid rises in cylinder 23 
and flows up second dip tube 19 into tee 18 exiting therefrom through 
lateral port 22. When the liquid level in cylinder 23 reaches the bottom 
end of second tube 19, CO.sub.2 vapor in the top of cylinder 23 is 
trapped. If additional liquid CO.sub.2 is introduced into cylinder 23, 
liquid will rise in second tube 19 and flash out of port 22 into dry ice 
snow. The snow is a visual notice that the cylinder has been filled with 
the allowable maximum quantity of liquid CO.sub.2 and that the flow of 
liquid CO.sub.2 into cylinder 23 should be stopped. 
To facilitate the introduction of liquid CO.sub.2 and the withdrawal of 
gaseous CO.sub.2, high-pressure cylinder 23 is connected to known 
accessories. A manifold 24 equipped with pressure gauge 25 and pressure 
relief valve 26 is connected by tube 27 to port 16 of CO.sub.2 valve 10. 
In accordance with this invention, manifold 24 is connected by tube 28 to 
liquid check valve 29 which is connected to supply tube 30. A quick 
coupler 31 is attached to tube 30 to facilitate the connection of a hose 
extending from a low-pressure (usually about 300 pounds per square inch) 
container of liquid CO.sub.2 on a truck driven to the building containing 
the bar or soda fountain where the CO.sub.2 cylinder requires 
replenishment of liquid CO.sub.2. It should be noted that, in the 
arrangement shown, valve stem 13 with knob 14 has been turned to the open 
setting and there never is a need to close it because check valve 29 
automatically prevents back-flow through CO.sub.2 valve 10. It is well to 
note that in the conventional use of CO.sub.2 valve 10 port 16 serves only 
for the withdrawal of gaseous CO.sub.2 from a high-pressure cylinder. 
Pursuant to the invention, port 16 is used to introduce liquid CO.sub.2 
into a cylinder. 
Manifold 32 equipped with pressure relief valve 33 is connected by tube 34 
to lateral port 22 of tee 18. Manifold 32 is connected by tube 35 to ball 
valve 36 which is connected by tube 37 to muffler 38. Tube 39 equipped 
with pressure regulator 40 and connected to manifold 32 serves to convey 
gaseous CO.sub.2 from cylinder 23 to a desired use site such as a soda 
fountain. Manifold 32 may have several ports so that additional tubes like 
tube 39 can convey gaseous CO.sub.2 to different use sites. 
When cylinder 23 requires replenishment of liquid CO.sub.2, a truck 
carrying a low-pressure container filled with liquid CO.sub.2 will park 
near the building in which the cylinder is housed and a hose connected to 
the liquid CO.sub.2 container will be drawn to connect it to quick coupler 
31. The high pressure, say 700 pounds per square inch, in cylinder 23 is 
reduced by opening valve 36 until the pressure drops to a pressure about 
15 pounds below the pressure in the supply container. As soon as the 
pressure in the cylinder drops below that in the supply container, liquid 
CO.sub.2 flows from the hose through components 30,29,28,24,27,16,10 and 
11 into the bottom of cylinder 23. Simultaneously, CO.sub.2 vapor evolved 
from the liquid in cylinder 23 rises and flows up the annular space 
between first and second dip tubes 11,19 and through components 
18,22,34,32,35,36,37 and 38 where the CO.sub.2 vapor is vented to the 
atmosphere. When the level of liquid CO.sub.2 reaches the bottom of second 
dip tube 19, gaseous CO.sub.2 can no longer flow into tube 19 and the 
pressure of gaseous CO.sub.2 trapped in the top of cylinder 23 builds up 
so that liquid CO.sub.2 begins to rise in dip tube 19 and flow through 
components 18,22,34,32,35,36,37, exhausting from muffler 38 in the form of 
dry ice. The appearance of dry ice at muffler 38 is the visual sign that 
cylinder 23 has been filled with the allowable maximum quantity of liquid 
CO.sub.2. Thereupon, the hose is disconnected from quick coupler 31 and 
valve 36 is closed. The accessories shown in FIG. 2 make it possible to 
draw gaseous CO.sub.2 from cylinder 23 through tube 39 at any time 
including while liquid CO.sub.2 is being introduced into cylinder 23. This 
is an additional benefit of the invention; heretofore, the flow of gaseous 
CO.sub.2 to a soda fountain or other use site was interrupted while a 
depleted cylinder was being replaced with a freshly charged cylinder. 
FIG. 2 shows a single cylinder 23 connected by tubes 27,34 to manifolds 
24,32, respectively. However, several cylinders can be connected by 
similar tubes to both manifolds 24,32; multiple cylinders are desirable 
for large users of gaseous CO.sub.2. It has already been pointed out that 
manifold 32 can have several tubes 39 to convey gaseous CO.sub.2 to 
different use stations. Hence, manifolds 24,32, make it possible to supply 
liquid CO.sub.2 simultaneously to several cylinders 23 connected in 
parallel thereto as well as permit the flow of gaseous CO.sub.2 to several 
use stations without any interruption. 
The simplicity of the invention is enhanced by the fact that all of the 
components are common plumbing parts. For example, both dip tubes 11,19 
and all the tubes connected to manifolds 24,32 can be copper tubing. 
Optional muffler 38 is used to deaden the sound of escaping CO.sub.2 
during the filling of cylinder 23 with liquid CO.sub.2. While the flow of 
liquid CO.sub.2 from the low-pressure container on the truck to a cylinder 
requiring replenishment can take place merely because the pressure in the 
supply container is higher than that in the cylinder, a pump mounted on 
the truck may be used to hasten this filling operation. 
Even though the apparatus shown in FIG. 1 is formed of readily available 
components that are not expensive, the functions of that apparatus, 
namely, the simultaneous introduction of liquid CO.sub.2 into, and venting 
of CO.sub.2 vapor from, a cylinder can be achieved with a specially 
designed apparatus. FIG. 3 is a cross-sectional view of one such 
apparatus. A cylindrical metal chamber 45 has a male thread 46 at one end 
47 which matches the female thread of the sole top opening of the CO.sub.2 
cylinder into which chamber 45 will be screwed. A wall 48 extends from end 
47 to the opposite end 49, dividing chamber 45 into two compartments or 
sections 50,51. Ports 52,53 in chamber 45 communicate with sections 50,51, 
respectively. Dip tubes 54,55 connected to sections 50,51, respectively, 
through end 47 of chamber 45 complete another embodiment of the invention. 
Of course, in accordance with the invention, dip tubes 54,55 will have 
distinctly different lengths. Thus, if tube 54 is longer than tube 55, 
liquid CO.sub.2 introduced through port 52 will flow into the cylinder 
while CO.sub.2 vapor will rise through tube 55 and exit through port 53. A 
valve will be connected to each of ports 52,53 for flow control. 
FIG. 4 shows that, fundamentally, the invention requires only a threaded 
plug 56 which can be screwed into the sole female-threaded opening at the 
top of a CO.sub.2 cylinder, and two tubes 57,58 extending through plug 56, 
one tube 57 reaching close to the bottom of the cylinder and the other 
tube 58 reaching down only a minor fraction, say about one third, of the 
height of the cylinder, as illustrated in FIG. 2. Of course, the exterior 
ends of tubes 57,58 would be connected to the usual accessories, such as 
those shown in FIG. 2, to facilitate the flow of liquid CO.sub.2 down 
through tube 57 into the cylinder and the flow of CO.sub.2 vapor up 
through tube 58 and out of the cylinder. A third tube may be included in 
plug 56 to serve as an alternate draw-off tube for gaseous CO.sub.2 in the 
event that liquid CO.sub.2 in tube 58 upon expanding through a regulator 
(not shown) on tube 58 became clogged with dry ice. Such a third tube 
would not need to extend below the threaded end of plug 56. In lieu of the 
third tube, it may be preferable to interpose a street tee (like tee 18 of 
FIG. 1 without dip tube 19) between the top opening of the CO.sub.2 
cylinder and plug 56 as shown in FIG. 4. Thus, the lateral opening of the 
tee would serve, like a third tube, for the withdrawal of gaseous CO.sub.2 
free of liquid. 
To summarize, each of the different structural forms of the apparatus of 
the invention illustrated in FIGS. 1 to 4 provides means for sealing the 
top opening of a CO.sub.2 cylinder and two flow passageways extending 
therethrough into the cylinder to different levels therein. 
Those skilled in the art will visualize variations and modifications of the 
invention as hereinbefore illustrated without departing from the spirit of 
scope of the invention. For example, the conventional CO.sub.2 cylinder 
valve can be replaced in FIG. 1 by an elbow with a dip tube connected to 
the end of the elbow which is screwed into the street tee. In any of the 
embodiments of the invention, the external portion of the tube used for 
venting CO.sub.2 may be provided with an electric heater to eliminate any 
plug of dry ice that might form therein. Such a heater on the external 
portion of tube 58 in FIG. 4 is a practical substitute for the optional 
third tube discussed in relation to FIG. 4. Accordingly, only such 
limitations should be imposed on the invention as are set forth in the 
appended claims.