Liquid cylinder manifold system

Details Liquid cylinder manifold system Liquid cylinder manifold system

2001-04-20

2003-09-09

Michalsky, Gerald A. (Department: 3753)

Fluid handling

Diverse fluid containing pressure systems

Gas pressure storage over or displacement of liquid

C137S210000

Reexamination Certificate

active

06615861

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates generally to cryogenic fluid dispensing systems, and, more particularly, to a manifold system for cryogenic fluid dispensing systems that use multiple liquid cylinders as the source of cryogenic fluid.
Cryogenic liquids, that is, liquids having a boiling point generally below −150° F. at atmospheric pressure, are used in a variety of applications. Many of these applications require that the cryogen be supplied as a high pressure gas. For example, high pressure nitrogen and argon gases are required for laser welding while high pressure nitrogen, oxygen and argon gases are required for laser cutting. Such cryogens are typically stored as liquids, however, because one volume of liquid produces many volumes of gas (600-900 volumes of gas per one volume of liquid) when the liquid is permitted to vaporize/boil and warm to ambient temperature. To store an equivalent amount of gas requires that the gas be stored at very high pressure. This would require heavier and larger tanks and expensive pumps or compressors.
Industrial applications such as laser welding and cutting require that the cryogenic gases be provided at pressures in the range of approximately 400-420 psi and flow rates in the range of approximately 1500-2500 SCFH. It is known in the prior art that such high pressures and flow rates may be obtained by connecting a number of cryogenic liquid storage tanks or cylinders together in parallel to form a “bank” of liquid cylinders. A prior art bank of cryogenic liquid cylinders is illustrated in FIG.
1
.
As illustrated in
FIG. 1
, the bank of cylinders features a manifold, indicated in general at
10
, which is connected to insulated cryogenic liquid cylinders
12
a
-
12
d.
More specifically, the manifold
10
includes a liquid header
14
that is connected to the dip tubes
16
a
-
16
d
of cylinders
12
a
-
12
d
via flexible lines
18
a
-
18
d.
Similarly, the head spaces of cylinders
12
a
-
12
b
are connected to a gas header
22
of manifold
10
by flexible lines
24
a
-
24
d.
Liquid is forced out of the cylinders through their dip tubes due to the internal pressurization that occurs when the liquid within the cylinders vaporizes as it is warmed over time.
The bank of cylinders provides cryogenic liquid to a use point, typically including a vaporizer, through liquid header
14
and port
26
. Gas header
22
equalizes the pressures within the cylinders. An economizer circuit
28
permits gas to be withdrawn directly from the head spaces of the cylinders and delivered to the use point when the pressure within the gas header exceeds a predetermined level. As a result, venting of cryogenic vapor is avoided. Greater flow rates at high pressures may be obtained by adding additional manifold sections and cylinders to the bank via fittings
20
a
and
20
b.
Situations may occur, however, where liquid is withdrawn from one of the cylinders faster than the others. In such situations, one cylinder may empty of liquid prior to the other cylinders. Prior art manifolds encounter difficulties in handling such occurrences. More specifically, if liquid cylinder
12
b
empties of liquid prior to the other cylinders, as illustrated in
FIG. 1
, gas from cylinder
12
b
will quickly travel out of dip tube
16
b,
as illustrated by arrows
32
, through liquid header
14
and out of port
26
. As a result, the pressure within the bank will collapse as gas travels from the individual cylinders
12
a
,
12
c
and
12
d
into the gas header
22
, as illustrated by arrows
34
,
36
and
38
, and into cylinder
12
b
, as illustrated by arrows
42
. In other words, the vapor from cylinders
12
a
,
12
c
and
12
d
and gas header
22
escapes through the path of least resistance through the empty cylinder
12
b
, dip tube
16
b
, liquid header
14
and port
26
. When the pressure within the bank of cylinders collapses, the system stops delivering high pressure cryogenic fluid and the operation (such as welding or cutting) is interrupted. It is therefore desirable to provide a manifold that prevents interruptions in the delivery of high pressure cryogenic fluid from a bank of liquid cylinders when the liquid supply in a cylinder is exhausted prior to the other cylinders in the bank.
Furthermore, if the liquid level in one cylinder drops below the liquid level of the other cylinders, system efficiency suffers. That is, when the liquid level within a cylinder becomes low, its internal pressure also drops. As a result, the pressure within the remaining cylinders also drops as vapor from the gas header
22
travels into the cylinder with the low liquid level. The bank of
FIG. 1
therefore requires many cylinders to supply cryogenic fluid at an acceptable pressure and flow rate. In addition, if the pressure within one cylinder drops, liquid in the liquid header
14
may back flow into the low pressure cylinder so that fluid delivery is interrupted. It is therefore desirable to provide a manifold that withdraws liquidly evenly from a number of cylinders and prevents the back flow of liquid into the cylinders.
Prior art systems often combine two banks of cylinders of the type illustrated in FIG.
1
. One bank is designated the “primary” or “service” bank while the other bank is designated the “secondary” or “reserve” bank. These are coupled through an electronic control system which typically flows the primary bank and, when it is exhausted of liquid, changes over automatically to the secondary bank and simultaneously activates an alarm. The electronic control system also typically provides a means by which the function of the two banks may be reversed after the empty cylinders of the primary bank are replaced.
An example of such a manifold control system may be found in U.S. Pat. No. 5,062,443 to Maric. The control system of the Maric '443 patent features first and second conduits that connect with primary and secondary cryogenic fluid supply sources (such as liquid cylinder banks). Each conduit includes both a pressure sensor that senses fluid flow pressure and a solenoid-operated on-off fluid flow control valve positioned downstream of the pressure sensor. An electrical circuit is in communication with the pressure sensors and controls the operation of the valves to switch them on and off so as to permit or prevent fluid flow through the respective conduit.
With both fluid sources available, the electrical circuit of the Maric '443 patent only permits one of the fluid sources to provide fluid flow at one time. When the first fluid source delivers fluid at a pressure below a predetermined minimum value, as detected by the first pressure sensor, the electrical circuit generates a signal to close the solenoid valve in the first conduit and simultaneously opens the solenoid valve in the second conduit so that the fluid flow then commences therein. The exhausted first fluid supply may then be replaced. The electrical circuit will switch back to the first fluid supply and conduit when the pressure within the second conduit drops below the predetermined minimum value. If the exhausted first fluid supply is not replaced and the second fluid supply becomes exhausted, the electrical circuit closes the solenoid valve of the second conduit, the solenoid valve of the first conduit remains closed and an alarm is activated. The system remains on standby until one or more of the fluid supplies is replaced.
While the control system of the Maric '443 patent is effective, the pressure within a conduit may fall below the predetermined minimum value while liquid remains in the corresponding fluid supply. As a result, the system may change over to the other conduit and fluid supply while liquid still exists in the original fluid supply. It is therefore desirable to provide a manifold control system that prevents residual liquid in the original primary or service liquid cylinder bank after change over to the secondary or reserve liquid cylinder bank.
Accordingly, it is an object of the present invention to provide a manifold that prevents interrupt

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