Note: Descriptions are shown in the official language in which they were submitted.
CA 02614234 2008-01-04
RAFFAY&FLECK
PATENT ATTORNEYS
Geffckenstrasse 6
D-20249 HAMBURG
EUROPEAN PATENT ATTORNEYS
EUROPEAN TRADEMARK ATTORNEYS
Job Lizenz GmbH & Co. KG CERT. ENG. VINCENZ v. RAFFAY (-2004)
CERT. CHEM. DR. THOMAS FLECK
Kurt-Fischer-Strasse 30 CERT. PHYS. CASPAR v. EICHEL-STREIBER
TELEPHONE: (040) 47 80 23
D-22926 Ahrensburg FAX: (040) 480 25 02
raffay.fteck(cr,t-online.de
2110/81
Safety Valve for a Compressed Gas Container
The invention relates to a safety valve for a compressed gas container
according to the preamble
of Claim 1.
Such a safety valve is disclosed in EP 0 960 634 A2, namely in the exemplary
embodiment
according to Figure 4 there. Another safety valve designed differently from
the preamble of
Claim 1 is disclosed in the patent DE 199 11 530 C2.
According to the industrial standards for compressed gases, e.g., TTRG381,
compressed gas
containers must be equipped with a cut-out fuse or a similar acting fuse to
reliably prevent excess
pressure in the event of a fire, which could lead to rupture of the container.
This is also true, for example, of compressed gas containers in motor vehicles
to hold, e.g.,
natural gas, hydrogen or other combustible gases for use as a fuel.
The variant of such a safety valve known previously from DE 199 11 530 C3,
which was cited
above, contains a closure body, which is supported in a standby position
directly on the metal of
a housing in which an overflow duct is formed. Then the burst body, which in
this example is a
glass ampoule, is then in turn supported directly on the closure body itsel~
According to the
teaching disclosed in the aforementioned publication, the glass ampoule is
ultimately clamped
between two rigidly connected supports. With this arrangement, the differences
between the
thermal expansion coefficients of the metal of which the closure body and the
housing are made
and the glass material of the burst body result in the risk that the burst
body may rupture during
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cooling and/or heating, e.g., because the metal of the closure body and the
housing expands or
contracts to a greater extent than the glass material of the burst body and
therefore compresses it,
especially during cooling. The problem of different temperatures and thus
different expansions
of the aforementioned materials occurs in particular with compressed gas
containers
accommodated in vehicles and/or safety valves provided on them. Especially
when a motor
vehicle is parked outdoors, it is exposed to temperatures ranging from -50 C
in the winter up to
50 C or more (if in direct sun) in the summer, and temperature may even fall
far below the
aforementioned ambient temperatures during the operation of filling the
pressure vessel. Because
of this wide temperature range of 100 C or more, the different thermal
expansion coefficients of
metal and glass are definitely manifested. In other words, there may be
unintentional triggering
of the safety valve, resulting in an outflow of the gas contained in the
compressed gas container.
However, the same considerations with regard to the thermal expansion
coefficients also apply to
other compressed gas containers and/or the safety valves arranged in them,
which are exposed to
high temperature fluctuations.
Figure 4 in DE 199 11 530 C2 shows another variant of a safety valve which
deviates in its
features from the preamble of Claim 1. In this case, a film forms the closure
for the overflow
duct, this film being punctured by a plunger that is under spring tension when
the burst body
ruptures, thereby connecting the overflow duct to the outlet duct. One problem
with this
approach is that the film can be damaged during installation of the safety
valve and can thus
become permeable, resulting in unintentional leakage of the contents of the
pressure vessel
through the safety valve without rupturing the burst body due to high
temperatures and without
triggering the safety valve. Furthermore, gases under high pressures (often
several hundred bar)
are stored in the compressed gas containers for which the safety valves are to
be used, so that a
simple film is often inadequate to reliably withstand such pressures.
In the EP 0 960 634 A2 cited in the introductory part, a remedy is given for
the disadvantages of
the safety valves according to DE 199 11 530 C3. However, a burst disk that
might trigger the
safety valve is required here.
The object of the present invention is therefore to improve upon a safety
valve for compressed
gas containers of the type defined in the introductory part so that the
advantages of the buffering
of different thermal expansions as described in EP 0 960 634 A2 can be
utilized without the
requirement of a burst disk as an additional safety-relevant part.
This object is achieved by a safety valve having the features of Patent Claim
1.
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Advantageous further embodiments of the invention are characterized in the
dependent Claims 2
through 7.
The inventive safety valve is characterized in that it comprises a sealing
element with which the
closure body cooperates to seal the overflow duct, in addition to having such
a closure body as in
some of the variants disclosed in DE 199 11 530 C2. Unlike sprinkler systems,
for example, in
which a line under pressure is usually sealed directly by a closing body held
in position by a
burst body without another sealing element, this is impossible with compressed
gas containers
filled with gases under high pressure. The pressure in water lines of
sprinkler systems is usually
max. 12 bar. In the compressed gas containers equipped with the inventive
safety valves, gases
with pressures of several hundred bar, e.g., 300 bar, are stored. At these
pressures, reliable
sealing of the overflow line is possible with the help of a sealing element in
the form of an 0
ring. This design variant is also described in one of the embodiments of a
previously known
safety valve described in DE 199 11 530 C2 which was cited above.
O rings are commercially available parts which can be acquired easily and
inexpensively and
offer a good seal with respect to the particular sealing surfaces. The
material of the 0 ring should
be selected so that it is suitable for the corresponding temperature ranges
and does not tend to
stick on the sealing surfaces, for example, which might lead to delayed
triggering of the safety
valve, or in the worst case might even prevent triggering of the safety valve
if the 0 ring holds
the closure body cooperating with it in sealing contact with the sealing
surfaces even if the burst
body has already ruptured.
In addition to the features known from DE 199 11 530 C2, the inventive safety
valve, as shown
in Figure 4 of EP 0 960 634 A2 comprises a spring element which exerts a
spring force on the
burst body acting in the direction of the abutment. This spring element serves
specifically to
absorb the stresses, i.e., forces occurring due to different thermal expansion
coefficients of the
housing and the safety valve and/or the closing body and/or the abutment and
the burst body and
thus serves to prevent the burst body from rupturing inadvertently before
reaching a triggering
temperature and thereby inadvertently triggering the safety valve.
To compensate for loads acting on the burst body due to different thermal
expansion coefficients,
it would essentially also be possible to provide a spring element which
prestresses the burst body
in the opposite direction. However, such an approach would have the
significant disadvantage
that the spring element that prestresses the burst element in the direction of
the closing body
which closes the outlet duct must counteract a maximum pressure to be
expected. In other words,
the spring element would have to apply a force to the burst body which can
withstand, e.g., a
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maximum pressure of 300 bar and test pressures of up to 1000 bar or even more.
The burst body
would thus be exposed to a high force over the entire lifetime of the safety
valve which could
alter the burst body over a long period of time. In particular a burst body
made of glass (e.g., a
glass ampoule) would have a tendency to "yield," under such conditions, i.e.,
the glass would
change its shape. This could ultimately result in leakage and malfunction of
the safety valve,
with all the safety-relevant consequences thereof.
However, the selected direction of the spring force allows only a
comparatively low prestress of
the burst body because the spring force in this direction acts like the force
due to the pressure in
the pressure vessel. In the normal case, only pressure loads amounting to a
fraction of the
maximum load are then acting on the burst body, which leads to a definite
increase in the
lifetime of the burst body and thus also the safety valve.
The closure body shaped as indicated in Claim 1 is ultimately especially
suitable for applying a
sufficiently high pressing force to the 0 ring and thus achieving a reliable
seal of the overflow
duct in the standby position and thus making the burst disk provided in EP 0
960 634 A2
superfluous.
An especially good seal can be achieved if the sealing surface of the sealing
element is designed
with a concave curvature (Claim 2) in particular when the concave curvature of
the sealing
surface corresponds to the curvature of a sealing surface of the 0 ring in at
least one section
(Claim 3).
The variant of this preferred embodiment characterized in Claim 4 offers
especially good spring
support for changes in length due to different thermal expansions and thus a
safety valve, which
is especially stable at temperatures below the triggering temperature, and
does so through a total
of two plate springs arranged in the overflow duct.
In a preferred variant of the invention, the spring element is a spring placed
on a shoulder in the
overflow duct, in particular such a plate spring. This then acts on an end of
the burst body
opposite the abutment to act on it with a spring force in the direction of the
abutment. A plate
spring is a small effective component that does not prevent reliable
triggering of the safety valve.
A fluid-filled glass ampoule clamped between the closure body and the abutment
is preferred as
the burst body. Through an appropriate choice of the thickness of the glass
and the type of fluid,
a defined triggering temperature in a comparatively narrow window can be
preselected for such a
burst body so that safety valves can be implemented with a wide variety of
triggering
temperatures through the choice of a concrete glass ampoule and/or a
corresponding fluid filling.
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Other advantages and features of the inventive safety valve are derived from
the following
description of the exemplary embodiments depicted in the accompanying figures,
in which
Figure 1 shows a view of an inventive safety valve
Figure 2a shows a sectional view along line A-A in Figure 1 of the safety
valve in a first
variant in an enlarged diagram;
Figure 2b shows a detail according to the area labeled as B in Figure 2a on an
enlarged scale
Figure 3a shows a sectional diagram of the second variant of an inventive
safety valve
shown along line A-A in Figure 1
Figure 3b shows in an enlarged diagram the area of the safety valve labeled as
B in Figure
3a according to this embodiment
Figure 4a shows a sectional diagram of a third embodiment of an inventive
safety valve
along line A-A in Figure 1 and
Figure 4b shows an enlarged diagram of the area of the safety valve according
to this
embodiment, labeled as B in Figure 4a.
The figures are drawn schematically and not true to scale. The same or similar
element are
provided with the same or similar reference numerals in the figures.
Figure 1 shows an inventive safety valve 100 in one possible embodiment. The
inventive valve
100 is formed in a housing 1. In the interior of the housing the safety valve
100 has an overflow
duct 2 in the area shown at the bottom of Figure 1, said overflow duct being
optionally connected
to a corresponding tapping duct of a compressed gas container. To do so, the
housing 1 is
provided with an outside thread 6 in the area of the overflow duct with which
it can be screwed
into a corresponding inside thread of a connection of a compressed gas
container and/or a
compressed gas valve. For screw mounting, a hex-head screw 5 on which a
commercial wrench
may be used is provided on the housing 1 of the safety valve 100. On its end
opposite the outside
thread 6 the housing 1 is sealed with a screwed in abutment 7. In a middle
section, the housing 1
has outflow openings 4 in the form of boreholes leading radially into the
housing.
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Figures 2a and 2b, 3a and 3b show two different possible embodiment variants
of an inventive
safety valve in sectional diagrams according to sectional line A-A in Figure
1. The embodiment
variants shown here differ only in the internal design of the safety valve 100
but not from the
outside, so the diagram in Figure 1 is equally valid for both variants.
First the variant shown in Figures 2a and 2b will be described with reference
to these figures.
These figures show again clearly the overflow duct 2, as formed in the
interior of the housing 1
of the safety valve 100. A closure body 20 is provided in the overflow duct 2.
The closure body
20 is wedge shaped in cross section, namely V-shaped in this example and is
rotationally
symmetrical about a longitudinal axis. The closure body 20 abuts on the one
hand against a plate
spring 11 which is supported on a shoulder 14 in the overflow duct 2.
On its side facing away from the plate spring 11, the closure body 20 has a
sealing surface 28
with a concave shape, having a larger diameter at its widest than the 0 ring
9. The smallest
diameter of the sealing surface is smaller than the diameter of the 0 ring 9
so the closure body
with its sealing surface 28 extends into the 0 ring 9 in a wedge shape. The
concave shape of the
sealing surface 28 is adapted in its curvature to the curvature of the sealing
surfaces of the 0 ring
9 at least in some areas so that an optimal seal can be achieved between the
sealing surface 28 of
the closure body and the 0 ring 9. The 0 ring 9 rests on a second plate spring
21 which is in turn
supported on a shoulder 24 in the overflow duct 2.
On the side of the plate spring 11 opposite the closure body 20, the under
side of a fluid-filled
glass ampoule 8 is in contact with the plate spring. The fluid-filled glass
ampoule 8 is supported
at its other end in a blind hole in the abutment 7 axially opposite the
closure body 20.
The diagram in Figures 2a and 2b shows the standby position of the closure
body 20 in which it
reliably seals the overflow duct 2 with respect to an outlet duct 3 in
cooperation with the 0 ring
9, which opens into the outflow openings 4. The shape of the closure body 20
shown in this
exemplary embodiment produces an especially good seal of the overflow duct 2
in the standby
position of the closure body 20.
The plate spring 11 situated between the closure body 20 and the glass ampoule
8 on the
shoulder 14 in the overflow duct 2 exerts a spring force on the glass ampoule
8 in the axial
direction, directed at the abutment 7.
The plate spring 11 can in particular absorb through deformation a stress
occurring due to the
difference in thermal expansion of the metal parts of the housing 1, closure
body 20, abutment 7
and glass ampoule 8 [sic; 8] thereby preventing premature rupture of the glass
ampoule 8
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occurring due to such difference in thermal expansion, and thus premature
triggering of the
safety valve 100.
Due to the arrangement of the plate spring 11 on the side opposite the
abutment 7, no forces
resulting from the gas pressure need be absorbed by the glass ampule 8. In
addition, stresses
created due to differences in thermal expansion can be absorbed by the plate
spring 21, thus
resulting in a further improvement in the compensation of such forces and/or
stresses and thus
ensuring even more reliably that the safety valve 100 will not cause
mechanical stresses due to
differences in thermal expansion coefficient of the glass material of the
glass ampoule 8 and the
material of the housing I of the abutment 7 and/or the closure body 20.
In assembling this variant of the inventive safety valve 100, the glass
ampoule 8 is clamped
between the plate spring 11 and the abutment 7 with a defined force in that
the abutment 7 is
bolted to the housing 1 of the safety valve 11 at a predetermined torque with
the glass ampule 8
inserted.
Figures 3a and 3b show a sectional of a second exemplary embodiment of an
inventive safety
valve 100 which is again shown in its outside view in Figure 1.
This exemplary embodiment corresponds in essential design details to the
exemplary
embodiment shown in Figures 2a and 2b so that reference can be made to the
discussion of
Figures 2a and 2b with regard to the description of this exemplary embodiment.
In contrast with the exemplary embodiment described previously, the variant
shown here has
only one plate spring 21, which is arranged on the side of the closure body 20
facing the
overflow duct 2. A plate spring 14 arranged on the side of the closure body 20
facing the glass
ampoule 8 as provided in the exemplary embodiment according to Figures 2a and
2b is omitted
in the present exemplary embodiment.
Another particular detail of the exemplary embodiment illustrates in Figures
3a and 3b is that in
addition to the closure body 20 an intermediate body 29 is arranged between
the former and the
glass ampoule 8. The exemplary embodiment illustrated in Figures 3a and 3b may
of course also
be modified in the sense that the intermediate body 29 is omitted and/or
becomes part of the
closure body 20.
Finally, Figures 4a and 4b illustrate a third embodiment variant of an
inventive safety valve 100.
In this variant, the closure body 15 introduced into the overflow duct 2 is
shaped somewhat
differently in comparison with the closure bodies 20 in the previous
embodiment variants. This
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closure body 15 also has essentially a wedge shape with an inclined sealing
surface 28 with
which it presses the 0 ring 9 radially against the wall of the overflow duct
2, forming a seal.
Instead of the plate springs 21 arranged on the side of the closure body 20
opposite the glass
ampoule 8 in the preceding exemplary embodiments, the 0 ring 9 in this
exemplary embodiment
is supported on an essentially rigid disk 12 which the closure body 15
protrudes with a protrusion
17 through in a central opening. The 0 ring 9 is also secured by a ring 13,
which is in contact
with the closure body 15 and 0 ring 9.
The spring action on the glass ampoule 8 in the direction of the abutment 7 is
exerted in this
exemplary embodiment exclusively by the plate spring 10 which rests on a
shoulder 16 formed
in the overflow duct 2 and abuts against the glass ampoule 8 on one side and
the closure body 15
on the other side.
In the function of prestressing the glass ampoule 8 and triggering of the
safety element 100, this
variant also operates as described above with regard to the exemplary
embodiment according to
the Figures 2a and 2b so that reference can be made to this description in
this regard.
It is clear from the exemplary embodiments illustrated here that the spring
element (as at least
one plate spring in the exemplary embodiments) can be arranged on the side of
the closure body
facing the burst body as well as on the side of the closure body facing the
overflow duct as well
as on both sides at the same time.
In the embodiment variant show in Figures 2a-2b the plate spring 11 which is
in direct contact
with the side of the glass ampoule 8 opposite the abutment 7 offers another
advantage. Namely it
additionally serve as another "sealing element" that prevents soiling of the
overflow duct 2 whish
is on the other side of same due to particle, foreign substances, gases or the
like penetrating
through the outflow openings 4. This "seal" also prevents corrosion in the
area on the side of the
plate spring 11 opposite the glass ampoule 8 in that it also prevents
corrosive media from
penetrating into this area. The same thing is also true of the exemplary
embodiment according to
Figures 4a and 4b. Again here, the plate spring 10 has the additional effect
described above.
All the embodiment variants of the safety valve 100 shown here are triggered
at a predetermined
temperature (at which expansion of the fluid in the glass ampoule 8 causes the
latter to rupture).
At the triggering temperature, the glass ampoule 8 ruptures, so that the
closure body 15 and/or 20
is displaced in the direction of the outlet duct 3 due to the pressure of the
compressed gas applied
to the overflow duct 2 and thus a connection is created between the overflow
duct 2, the outlet
duct 3 and/or the outflow openings 4.
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In the exemplary embodiments, the thermal triggering unit is additionally
formed by the
abutment 7, the glass ampoule 8, the 0 ring 9, the closure body 15 andlor 20
and the plate
spring(s) 10, 11 and/or 21 and in the case of the exemplary embodiment
illustrated in Figures 3a
and 3b, it is additionally formed by the intermediate body 29 and in the case
of the exemplary
embodiment illustrated in Figures 4a through 4b it is additionally formed by
the ring 13 and the
disk 12.
The preceding description of the exemplary embodiments has shown clearly again
the
advantages of the inventive insertion of a spring element, in particular a
plate spring into a safety
valve 100. In addition, the advantages of the inventive form of the closure
body are apparent.
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List of reference numerals
1 Housing 24 Shoulder
2 Overflow duct 28 Sealing surface
3 Outlet duct 29 Intermediate body
4 Outflow openings 100 Safety valve
5 Hex-head screw
.6 Outside thread
7 Abutment
8 Glass ampoule 9 O ring
10 Plate spring
11 Plate spring
12 Disk
13 Ring
14 Shoulder
Closure body
16 Shoulder
17 Protrusion
Closure body
21 Plate spring
