Note: Descriptions are shown in the official language in which they were submitted.
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Description
CYLINDER VALVE HAVING A DEVICE FOR REDUCING OR CLOSING OFF THE FLOW
IN THE EVENT OF A RISE IN TEMPERATURE
Background of the invention
[0001] The invention relates to a tap for a pressurised gas container. More
precisely, the invention relates fo a tap for a pressurised gas container
fitted with a shut-off valve. While the invention is appropriate for
applications involving various types of gases, it is particularly suitable for
oxidising gases sensitive to adiabatic compression, more particularly for
oxygen applications.
Prior art
[0002] The speeds involved in a tap for a high pressure (above 200 bar) gas
container are very high. For gases such as helium the speeds can be
much greater than the speed of sound. With such speeds some plastic
seats or inserts in the regulator valve cannot resist the adiabatic
compression shock and can burn in the presence of an oxidising gas. It is
therefore useful to restrict the pressure and slow the speed of the gas to
absorb the shock wave when opening the main valve of the tap for
withdrawing gas.
[0003] ln the prior art filters were provided between the main valve and the
regulator valve but these filters have the disadvantage of slowing the gas
flow when the container is nearly empty. In addition, filters can become
clogged. As a result, they suffer shocks every time they are opened and
can generate particles. At high pressure, which can be of the order of 300
bars or more, when the gas cylinder is full, known filters pose no problems
and do not interfere with the flow. However, filters cause a constant
pressure drop, and at low pressures, below 50 bars, pressure
disturbances begin and become particularly detrimental at 10 bars. These
known filters that cause a constant pressure drop therefore choke the gas
expansion curve at low pressure.
[0004] Other, less damaging, solutions have been developed for when the
container pressure decreases.
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[0005] For example, Patent EP 1500854 Al discloses a container tap provided
with a non-sealing shutter located between an on/off valve and a regulator
tap. The shutter is normally positioned across the flow area. When the
valve is opened, the pressurised gas rapidly forces the shutter to a
position across a restricted flow area so as to reduce the shock wave
applied to the regulator valve. After the pressure equalizes across both
sides of the shutter, the latter returns to its normal position across the
full
flow area.
[0006] Patent US 7,225,810 62 discloses a container tap with a shutter similar
to
that in the previous document and operating in the same way.
[0007] These shutters certainly provide an interesting solution; however, they
have the disadvantage of complexity linked to a reliability constraint, as
well as a disadvantage in that they do flot definitely prevent combustion
when the valve is opened. Indeecl, in the presence of impurities in the tap
pathway and, especially in the presence of oxygen under high pressure,
combustion can still occur and cause serious safety problems. Indeed, in
the event of combustion, times can escape from the tap and cause bums,
damage to nearby equipment and/or cause &es.
Summaty of the invention
The technical problem
[0008] The invention aims to provide a container tap that overcomes at least
one
of the problems mentioned above. More particularly, the invention has the
objective of proposing a container tap that reduces the risk of fire and
burns when operating the tap, especially with strong oxidising gases such
as oxygen.
Technical solution
[0009] The invention relates to a tap for pressurised gas container,
comprising a
housing with a gas inlet, a gas outlet and a gas pathway connecting the
inlet to the outlet, a shut-off valve for shutting off and/or reducing the gas
path; wherein it further comprises a device for reducing or closing the path
in response to a rise in temperature, the device being arranged in the
housing downstream of the shut-off valve.
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[0010] Such a tap is designed to operate at greater than or equal to 50 bars
pressure, preferably to 100 bars, more preferably even at 200 bars.
[0011] According to an advantageous embodiment of the invention, the tap
includes a regulator valve located downstream of the device for reducing
or closing the passage, preferably in the tap housing. The regulator valve
can be integrated into the tap body. The latter may consist of several
assembled components.
[0012] According to another advantageous embodiment of the invention, the
device for reducing or closing the passage is configured to reduce or close
the gas flow when the temperature in the gas flow exceeds 100 C,
preferably 120 C, more preferably 150 C.
[0013] According to a further advantageous embodiment of the invention, the
device for reducing or closing the passage is mechanical. This device is
indeed preferentially purely mechanical.
[0014] According to a further advantageous embodiment of the invention, the
device for reducing or closing the passage comprises a shape memory
alloy element that can be deformed when its temperature exceeds a
preset level.
[0015] According to a further advantageous embodiment of the invention, the
shape memory alloy element has a memory effect only when the
temperature is raised.
[0016] According to a further advantageous embodiment of the invention, the
device for reducing or closing the passage is configured so that the
deformation of shape memory alloy element operates directly to reduce or
close the passage.
[0017] According ta yet another advantageous embodiment of the invention, the
shape memory alloy element comprises a deformable portion with a
circuler edge designed to make contact with a fixed surface, preferably
formed directly in the housing, so as to reduce or close the passage.
[0018] According to a further advantageous embodiment of the invention, the
deformable portion of the shape memory alloy element is dome-shaped.
[0019] According to a further advantageous embodiment of the invention, the
diameter of the circuler edge increases when the temperature exceeds the
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preset level, preferably more than 10% above 100 C, 120 C or aven
150 C.
[0020] According to a further advantageous embodiment of the invention, the
shape memory alloy element comprises a generally elongated part
attached to the deformable portion, the generally elongated part ensuring
the fixing of the element to the housing.
[0021] According to a further advantageous embodiment of the invention, the
generally elongated portion comprises a male thread mating with a
corresponding female thread in the housing.
[0022] According to a further advantageous embodiment of the invention, the
device for reducing or closing the passage comprises a cylindrical cavity
with a first region with a first diameter receiving the deformable portion of
the shape memory alloy element and a second region with a second
diameter inside the first and upstream of the first region, so that the gas
must flow around the circuler outer edge of the dome-shaped part.
[0023] According to yet another advantageous embodiment of the invention, the
deformable part of the shape memory alloy element is dome-shaped with
a circuler outer edge, located in the cavity so that the hollow of the dome is
directed towards the second region of the cavity.
[0024] According to yet another advantageous embodiment of the invention, the
cavity comprises a third region adjacent to the first region and opposite to
the first, with a means for fixing the shape memory alloy element,
preferably by a female thread.
Claimed benefits
[0025] The invention can take advantage of the increase in temperature caused
by combustion when the on/off valve is opened, so to ensure closure or at
least an automatic quasi-closure in a very short time. Given the fact that
combustion in such a tap cannot be excluded, even in the presence of
devices such as those described in the "Prior Art section, the tap in the
invention provides a significant safety advantage.
[0026] The use of one (or more) shape memory alloy elements enables the
response time to be very short and, above all, compatible with a very
oxidising gas under very high pressure, such as oxygen. Indeed,
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automatic gas flow closure systems involving a fuse element are known,
including anti-blowback functions in welding torches. Such a solution is
obviously not applicable to a container tap where oxygen at a pressure of
about 200 bars predominates.
[0027] Furthermore, the fact of using one (or more) shape memory alloy
elements
with an edge designed to corne into direct contact with a fixed surface so
as to close off or reduce the passage is particularly interesting both
because it is easy to implement as well as being reliable.
Short description of the diagrams
[0028] Figure 1 is a plan view of a container tap according to the invention.
[0029] Figure 2 is a sectional view of the shell of the tap in Figure 1,
sectioned at
2-2.
[0030} Figure 3 is a sectional view of the tep closure device in the avent of
a
temperature rise in the tap of Figure 1, albeit with another design of shape
memory alloy element, the device being in the open position.
[0031] Figure 4 is a sectional view of the tap closure device in the avent of
a
temperature rise in the tap of Figure 1, albeit with another design of shape
memory alloy element, the device being in the closed position.
Description of the embodiments
[0032] The container tap 2 for pressurised gas comprises a housing 4 with a
gas
inlet 8, an outlet (flot shown) and a passage 10 connecting the inlet to the
outlet. The housing comprises a male thread 6 to be screwed onto the
neck of a gas cylinder.
[0033] The tap further comprises a shut-off valve 26 illustrated in Figure 2.
The
latter is a sectional view of the tap in Figure 1, sectioned at 2-2. The duct
for the passage of gas can also be seen. The shut-off valve 26
comprises an element movable in translation and rotation, and provided
with a sealing ring mating with a seat formed in the valve housing. This
movable element is actuated by a handwheel 24 accessible from the
outside of the valve and located on the side of the housing,
[0034] Downstream of the on/off valve 26 is a device which is arranged to
close
the passage of gas when the temperature exceeds a critical threshold.
This device comprises a chamber 14 and a shape memory alloy element
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16. The latter includes a head portion capable of changing its shape
significantly. More particularly, the head of the shape memory alloy
element comprises a circular outer edge designed to change its size in
order to seal with the cavity 14 in which it is housed. ln the avent that the
temperature of the head of the shape memory alloy element lises beyond
a critical levai, it will change shape se that the diameter of its outer edge
increases so that it cornes into contact with the inner surface of the cavity
14 and automatically closes off the gas passage.
[0035] ln Figure 1 the shape memory alloy element is in the closed position,
that
is to say the outer edge of that part of it intended to make contact with the
cavity forms a seal with the said cavity.
[0036] Shape memory alloys (SMA) are among alloys with several new properties
among metallic materials: the ability to remember an initial form and retum
to it aven after deformation; the ability to switch between two previously
stored forms when the temperature varies around a critical temperature;
and a super-elastic behaviour allowing elastic elongations greater than
those of other metals. Among the main shape memory alloys there are a
variety of nickel and titanium alloys as the main components in
approximately equal proportions. Althoug h "nitinol" ("Nickel-Titanium Naval
Ordnance Laboratory") is actually the name of one of these "quasi-
equiatomic nickel-titanium" alloys this name has become commonly used
in the literature to describe ail of these alloys, which have very similar
properties. To a lasser extent soma brass and copper-aluminium alloys
also have shape memory properties.
[0037] The active portion, in this case the head of the shape memory alloy
element is designed to deform so that the diameter of its outer edge
increases by at least 5%, preferably 10 %, more preferably 15%. Such
super-elastic behaviour enabling elastic elongations can be achieved by a
judicious choice of materials and suitable design of the active part of the
element. The critical temperature can vary depending on the choice of
material. ln the case of container taos, which typically operate at amblent
temperatures of between 0 C and 30 C, the critical threshold will be set, at
least approximately, to about 100 C, 120 C or aven 150 C. The closure
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valve must remain open over a broad temperature range, such as between
-40 C and +70 C to cover the temperature extremes in which the valve is
likely to need to function normally.
[0038] Particularly in the case of oxygen and when opening the tap's on/off
valve
26, the pressurisation of the gas passage between the said valve and the
regulator valve 12 may give rise to transient adiabatic compression,
generating temperature increases and initiating combustion inside the
valve housing. Such combustion may be made possible by the presence
of residues or impurities in the valve.
[0039] In the event of combustion, flames can escape from the tap,
particularly
because of the large flow of oxygen. The presence of a self-closing device
or, at least, one that reduces the gas flow to the tap provides a certain
degree of safety in this problem area that, up till now, has had no real
solution. lndeed, in the event of combustion starting when the valve 26 is
opened, the shape memory alloy element will quickly heat up and exceed
the critical threshold. lt will then, in a very short time directly linked to
its
thermal inertia, deform and corne into contact with the inner wall of the
cavity. This contact closes off the passage of the gas, in this case oxygen,
and thus stops the flames.
[0040] It should be noted that the contact between the outer edge of the
active
part of the shape memory alloy element and the inner surface of the cavity
cannot be made completely gas-tight, especially in ternis of the surface
state of the active part and the state of the corresponding internai surface
of the cavity. The device may therefore be a device for reducing or
decreasing the gas flow but not a device for closing it off completely.
[0041] The cavity 14 discharges upstream into a filter 20 located in a fitting
22.
The gas passing through the cavity 14 will therefore meet a first pressure
drop generator from the narrowing formed by the filter and a second
narrowing directly downstream at the regulator valve seat. The pressure
drops created by these elements will increase the shock wave in the gas
when the on/off valve is opened. This shock wave will be created in the
cavity 14. Positioning the active part of the closure device in this cavity
and
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adjacent to the filter and the regulator valve seat allows the response time
of the device to be minimised and, thus, its effectiveness is increased.
[0042] With reference to the point made earlier about a device reducing the
flow
area, it should be noted that, depending on the application and its
parameters, such a device significantly reducing this, for example by least
70%, preferably 80%, still more preferably 90%, the flow area could also
increase the safety of the tap by limiting, in a known manner, the
propagation of flames outside the tap.
[0043] Figure 3 illustrates the closure device of Figure 1, albeit with a
design of
shape memory alloy element that differs at the active part or head of the
element. This latter 16 includes a first active domed portion 161 and a
second generally cylindrical portion 162. The cavity 14 is generally
cylindrical with a first region 141 of a fixed first diameter and wherein the
active portion 161 of the element is located. The cavity 14 also includes a
second region immediately adjacent to the first region 142 and in fluid
connection therewith. The second region has a smaller diameter than the
first. The dome-shaped portion 161 of element 16 is oriented so that its
open end faces the second region 142 of the cavity 14. The cavity 14 is
supplied with gas radially at the second region 142. The gas thus flows
bypassing the rear portion and the outer edge of the dome-shaped portion.
[0044] The cylindrical portion 162 of element 16 ends with a male thread 163
inserted into a tomate thread formed in a third region 143 of the cavity 14.
The three regions 141, 142 and 143 of the cavity 14 are concentric.
[0045] When the on/off valve is opened, in the event of combustion caused by
the adiabatic shock wave, the temperature in the first region 141 of the
cavity 14 will increase. The temperature of the active domed part 161 of
element 16 will increase and will deform to take the shape shown in Figure
4. The dome 161 is flattened and has increased its outer diameter so as to
be in contact with the inner surface of the cavity 14. This super-elastic
deformation thus enables the passage of gas to be stopped and the
combustion to be stopped dead. Further, because the umbrella or dome
shape of this part, oriented sa that its hollow is on the upstream side of the
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gas flow, allows this part to deforrn even further in the direction of closure
from the effect of the shock wave triggered by its deformation.
[0046] Note that the shape memory alloy elements shown in Figures 1, 3 and 4
are purely examples. They can take many forms other than those shown.
List of part number references
[0047] 2: container tap
[0048] 4: housing
[0049] 6: male thread
[0050] 8: gas inlet
[0051] 10: gas outlet
[0052] 12: regulator valve
[0053] 14: cavity
[0054] 141: first region of the cavity 14
[0055] 142 : second region of the cavity 14
[0056] 143: third region of the cavity 14
[0057] 16: shape memory alloy element
[0058] 161: active dome-shaped part of the element 16
[0059] 162 : elongated part of the element 16
[0060] 163: male thread of the elongated part 162 of the element 16
[0061] 20: filter
[0062] 22: reg ulator valve seat and filter support
[0063] 24: handwheel of the on/off valve
[0064] 26: on/off valve
