Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A safety Valve t1
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Background of the Invention ,~
The present invention relates to a safety valve or
a safety escape valve for fluid and more particular to a
safety valve for fluid used in a perfectly hermetically
sealed system as in a nuclear power station.
In general a safety valve for fluid has mostly
been provided in conventional equipment so as to discharge
excessive pressure directly to the atmosphere through suitable
ducts when such occurs. ~s a rule a discharge pipe to be
connected to the exit passage of the valve body of a safety
valve of this kind for leading the fluid blown off through
the valve seat to the atmosphere is so designed that the
fluid pressure within the valve chamber constituted in the
valve body at its exit passage side is kept below 10% of the
blow-off pressure. However, with the recent appearance of
nuclear power stations and the ~uestion of pollution problems,
and the like, since it is under no circumstances permissable
to discharge fluid in which radioactive particles are
contained, noxious fluids, etc. to the atmosphere directly,
in order to lock in such fluid, etc. which has hitherto keen
discharged directly to the atmosphere, a wholly hermetically
sealed system becomes necessary.
However, in the case of a safety valve, as the
result of the discharge of an excessive pressure into a
sealed system its valve disc is subjected at the exit passage
side of the valve body to considerable variations in discharge
pressure reaching as high as 15 to 50% of the pressure at
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the inlet passage side, resulting in a tendency to the early
closing of the valve disc.
A safety valve designed as a backpressure equilibrium
type having a bellows seal constitution has been hitherto known,
and which was designed such that even when a backpressure exists
prior to the blow-off of the valve it blows off the fluid at a
predetermined pressure irrespective of the backpressure. However,
with the safety valve of this bellows type, it has been found dif-
ficult to make it function properly against high backpressure as
well as large variations in discharge pressure such as occur dur-
ing blow-off as stated above.
Summary of the Invention
It is a primary object of the present invention to pro-
vide an improved safety valve which can eliminate all of the de-
fects of the conventional safety valves as above said.
It is a further object of the present invention to pro-
vide a safety valve which can rapidly blow off at a predetermined
blow-off pressure and discharge against the pressure prevailing
in the sealed system which is high and is subject to large varia-
tions during the blowing off into the sealed system and at thesame time can easily cease the blow-off within a predetermi.ned
blow-down under stable operation.
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According to the present invention there is provided
a safety escape valve, comprising: a valve body, having an in-
let port, an outlet port and a valve chamber; a nozzle seat,
having a substantially flat valve seat surface, secured within
said valve body in communication with said inlet port; a guide
secured within said valve body; a disc socket; having a depending
annular skirt at one end for deflecting and stabilizing the flow
of fluid, slideably mounted in axial alignment with said guide
and moveable from a fully closed position to a fully opened po-
sition; a valve disc affixed at said one end of said disc socketand adapted to coact with said valve seat surface; a back pressure chamber
formed within said disc socket and said guide; a valve stem associat-
ed with an adjustable spring mechanism, affixed to said valve
body urging said valve disc toward said valve seat surface; an
upper ring adjustably affixed in axial alignment with said guide
and proximate to said annular skirt; a bellows seal disposed for
isolating said back pressure chamber from said spring mechanising;
a stem disc fixed to said stem and said bellows seal in said
back pressure chamber for equalizing the downwards pressure on
the valve disc; and said back pressure chamber being isolated
from said valve chamber except for a passage means terminating
at a point immediately adjacent said depending skirt where the
static pressure remains substantially constant.
The skirt formed by elongating the disc socket accord-
ing to the present invention acts as a kind of flow regulating
element which can guide the fluid in an orderly manner when it
flows through the gap formed between the valve disc and the valve
seat, without causing the eddy current phenomenon there, that
would otherwise ~e caused as in a conventional safety valve, re-
sulting in variations in pressure within the back pressure cham-
ber and making the operation of the valve disc unstable. There-
fore, in the present invention the valve disc operates stably
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due to the non-occurrance of the eddy current phenomena thanks
to the provision of the skirt which opens as well as closes the
valve seat at previously set pressures, respectively.
Brief Description of the Drawings
The above and other objects of the present invention
will be more fully understood by reference to the foll.owing des-
cription of the presently preferred, but nonetheless illustrative
embodiments, in accordance with the present invention, when
taken in conjunct.ion with the accompanying drawings, wherein:-
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Fig. l is a cross-sectional view of the essential
portion of one embodiment of the safety valve according to ~1
the present invention; ii
Fig. 2 is a cross-sectional view of the valve
shown in Fig. l on an enlarged scale to show the par-ts
within the valve chamber at the time of the closing oE the
valve disc;
Fig. 3 is a similar view to Fig. 2, but showing
the state at the time of opening the valve disc;
Fig. 4 is a diagram to show the fluid flow between
the valve disc and the valve seat at the time of opening the
valve disc in a conventional safety valve; and ,
Fig. 5 is a similar diagram to Fig. 4 showing the
case of the present invention.
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Description of the_Pre erred Embodiment
In Fig. l of the attached drawings there is shown
an essential portion of an embodiment of ~e safety valve
according to the present invention, having a valve body l~
which is provided with a flange la adapted to be connected
to a steam pipe line and a flange l_ adapted to join its
exit passage to a discharge conduit not shown.
Welded to valve body l at its inlet passage which
is in communication with flange la)is a nozzle seat 2 which
is proviaed with a flat valve seat surface 2a at its inner
end or upper end as viewed in Fig. l elongating in the
horizontal direction. Coaxially suspended from the upper
end of valve body l is a cylindrical guide 6 so that it is
fixedly secured at its upper flanged end portion to valve
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body 1 and elongates downwards into a valve chamber lc formed
within valve body 1 to an extent that its lower end portion lo-
cates above valve seat surface 2a with a sufficient annular gap
being left therebetween. Shiftably disposed within cylindrical
guide 6 is a cylindrical disc socket 12 which securely mounts
within it at its lower part a valve disc 3 by any conventionally
known means such as by securing valve disc 3 at its upper portion
to annular ribs formed on the inner surface of disc socket 12 with
a nut threaded to the outer surface of valve disc 3 at its upper
end portion. In this manner the valve disc 3 is provided at its
lower end portion, by such a welding, with an annular valve disc
member 3_ made of abrasion resisting metal. The valve disc mem-
ber 3_ is adapted to coact with valve seat surface 2a of nozzle
seat 2 when the former is urged to abut against the latter. Valve
disc 3 is adapted to be usually forced to abut against valve seat
surface 2_ through a stem 5 which is disposed coaxially with cy-
lindrical guide 6 and under the action of a coil spring 4 which
is arranged within a spring case 20 which is secured to valve body
1 so as to surround coil spring 4 through an intervention of a
cooling spool 8. The lower end of spring 4 is supported by a
lower seat 21 fixedly secured to stem 5 and the upper end of
spring 4 is supported by an upper seat not shown which freely pas-
ses the upper portion of stem 5 therethrough and is adapted to be
adjustably secured to the spring case. Thus, stem 5 at its lower
end urges valve dlsc 3 towards valve seat surface 2_ through the
force of spring 4 which may be adjusted by controlling the posi-
tionofthe upper seat relative to spring case 20. Therefore,
valve disc 3 or valve disc member 3a abuts against valve seat sur-
face 2_ to prevent the fluid from flowing from the inlet passage to
the exit passage of the valve body 1 as long as the fluid pressure
within the inlet passage is lower than a previously set force ap-
plied to valve disc 3. As can be seen in Fig. 2, as usual in a
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safety valve of this kind, an upper ring 22 and a lower ring 23
are respectively screwed on theouter surfaces of guide cylinder 6
and nozzle seat 2 for the object of controlling the flow pattern
of the fluid blowing through the gap formed between valve seat
surface 2a and valve disc 3 or valve disc member 3_ when the lat-
ter is urged upwards against the action of spring 4, whereby upper
and lower rings 22 and 23 are respectively associated with lead
pins 24 and 25 screwed in the wall of valve body 1 orthogonally
to the axis of rings 22, 23 to fixedly retain them in a predeter-
mined position relative to guide cylinder 6 and nozzle seat 2,respectively, after their adjustment is completed.
As more precisely shown in Fig. 2, disposed within a
backpressure chamber 9 formed within guide cylinder 6 is a bel-
lows 10 which has, on one hand, its one end or the lower end as
viewed in Fig. 2 welded to a disc 26 which is sealingly secured
to valve stem 5 at its lower portion and above valve disc 3 by
a lock nut 11 and has its other end sealingly welded to a disc
27, on the other hand, which is fixedly secured between the upper
flanged end of guide cylinder 6 and cooling spool 8 with gaskets
7, 7 being interposed therebetween, respectively.
The general construction so far described is substan-
tially similar to that of a conventional safety valve.
The safety valve according to the present invention is
differentiated in construction from the conventional one in that,
in the present invention, as best shown in Figs. 2 and 3, disc
socket 12 is integrally provided with an annular skirt 13 at its
lower end portion so as to form a cylindrical space below valve
disc 3. The skirt 13 depends downwards as viewed in Fig. 2 or 3
to such an extent that it can still cover the lower end inner
peripheral portion of upper ring 22 threadably mounted on guide 6
even when valve disc 3 is lifted from valve seat surface 2_ to
its maximum stroke, i.e. disc socket 12 moves upwards together
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with valve disc 3 against the action of spring 4 to its upper
stroke limit as shown in Fig. 3.
Now, the operation of the safety valve according to the
present invention generally having such a construction will be
fully explained.
Prior to this firstly the behaviour of the fluid flow
at the time of the lift of valve disc 3 will be explained in the
case of a conventional safety valve with reference to Fig. 4,
which shows its pertinent portion on an enlarged scale.
It is assumed that valve disc 3 closes valve seat sur-
face 2_ under the action of spring 4 as shown in Figs. 1 and 2.
As the fluid pressure within the pipe line to which valve disc 3
is exposed at the inlet passage side of valve body 1 is increas-
ed above a previously set closing pressure of valve disc 3, such
as given by coil spring 4, the fluid pressure promptly lifts valve
disc 3 so that it becomes separated from valve seat surface 2_ and
moves to a second position shown in Fig. 3. The fluid flows
through the most throttled portion of nozzle seat 2 to flow
through a gap formed between the under surface of the valve disc 3
and valve seat surface 2a, and is then guided substanti.ally down-
wards to continuously blow off into valve chamber 1_, finally be-
ing discharged into a closed vessel (not shown) from the exit
passage of valve body 1 through the discharge conduit (not shown)
connected to flange 1_.
In this case, valve disc 3 is held in the second posi-
tion by a holding force comprising the reaction of the fluid flow-
ing through the gap formed between valve disc 3 and valve seat
surface 2a and the static pressure prevailing below valve disc 3,
while the fluid passed through a clearance 15 formed between the
outer surface of disc socket 12 and the inner surface of guide cy-
linder 6 enters backpressure chamber 9 formed between the outer
surface of bellows 10 and the inner surface of socket 12 so as to
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apply force against the rear surface of valve disc 3, tending
to urge va]ve disc 3 downwards against the holding force as above
said. As long as the holding force is greater than the sum of
the force applied to the rear surface of valve disc 3 and the force
exerted by spring 4, valve disc 3 continues to remain open so as
to discharge the fluid. If the force applied to the rear sur-
face of valve disc 3, i.e. the sum of the pressure within back-
pressure chamber 9 and the force of spring 4, exceeds the holding
force, valve disc 3 is forced to close valve seat surface 2a and
therebyshut off the fluid flow. During such an operation, when
the pressure within backpressure chamber 9 varies or exceeds the
holding force, valve disc 3 is quite unable to maintain its open
state. Therefore, in order to prevent such a phenomena it is ne-
cessary to reduce the influence of the backpressure.
As explained previously, since in a conventional safety
valve, disc socket 12 is provided with no skirt, as shown in Fig.
4, the fluid passing through the flow gap formed between the under
surface of valve disc 3 and valve seat surface 2_ is forced to have
its flow direction changed by upper ring 22 so that valve disc
3 is subjected to a variable lift. In this case, owing to colli-
sion of the fluid passing through the gap formed between valve
disc 3 and valve seat surface 2_ with upper ring 22 the dynamic
energy of the flow is transformed into a static pressure. The
fluid at a high pressure tnus passes through clearance 15 formed
between the shifting surfaces of disc socket 12 and guide 6 to
accumulate in backpressure chamber 9. Consequently, in a conven-
tional safety valve of the equilibrium type having a bellows-
seal construction, in order to remedy such unfavourable conditions
due to a high and variable backpressure, a large hole is usually
3Q formed in the wall of guide 6 for the purpose of equalizing the
pressures within backpressure chamber 9 and valve chamber 1_.
However, with such a construction, if the valve has originally
been designed on the assumption that the pressure within the
~ac~pressure chamber 9 will be hig~l, when the pressure within backpressure
chamx~-9 becomes 1~, a lar~e blow-dcwn will result. Conversely, if
the valve was originally designed on tne assum~tion that the pressure within
backpressure cha~ber 9 will be 1~, when the pressure within backpressure
chamber 9 varies to beco~e high, annoyances such as chattering of valve
disc 3, etc. may occur. ~lerefore, in the case where the pressure within
the exhaust piFe lines is high or varies ~reatly, it is necessary to el-
iminate the influence of the pressure change within the exhaust pipe ~
lines.
During the blowing off of the fluids th~ fluid flow
along the flow passage from the valve inlet passage of valve
body 1 to the gap formed between valve disc 3 and valve seat sur-
face 2a is not influenced by the pressure within the exhaust
pipe lines. When the flow passing through the gap formed between
valve disc 3 and valve seat surface 2_ impinges upon the wall of
upper ring 4, etc., the flow energy is transformed into a high
pressure. And, if the fluid under such a high pressure is intro-
duced into backpressure chamber 9, it becomes impossible to design
the safety valve for the reasons explained above. In the light
of the above considerations, the safety valve according to thepresent invention is so designed that the energy of the fluid
passed through the yap formed between valve disc 3 and valve seat
surface 2_ is not transformed into pressure, and instead a pres-
sure corresponding to the static pressure only is fed into back-
pressure chamber 9. For this purpose, in the present invention,
as stated above and shown in Fig. 3, the lower end portion of
disc socket 12 is elongated downwards to form an annular depend-
ing skirt 13, having a generally conical inner periphery enlarged
towards the end so as to surround a space below the lower end of
valve disc 3 and valve seat surface 2_ at the lift position of
valve disc 3. Thus, as shown in Fig. 5 on an enlarged scale, in
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the lift position of the valve disc 3, backpressure chamber 9
can be put in communication with the fluid passing through the
gap formed between valve disc 3 and valve seat surface 2_ -
through an annular gap 30 formed between the outer periphery
of skirt 13 and the inner periphery of the lower end portion of
upper ring 22. In this case, as shown in Fig. 5, the inner peri-
phery of the lower end portion of upper ring 22 is so positioned
that the margin of the flow lines o the fluid blown out along
the lower edge of skirt 13 can elongate substantially in the di-
rection shown by the arrows. Thus, it will be appreciated that
skirt 13 according to the present invention acts as a flow regula-
tion plate to prevent the pressure within backpressure chamber 9
from being made unstable as has hitherto usually occurred in con-
ventional safety valves, because, since such instability is caused
by the pressure variation to which the fluid is sub]ected due to
the eddy current phenomenon caused by collision of the fluid
against upper ring 22 when it flows thereagainst as shown in Fig.
4 by the swirling arrows, skirt 13 can effectively suppress the
occurrence of such a phenomenon by its flow controlling action
as shown in Fig. S by the arrows.
It is to be understood that although certain forms of
this invention have been illustràted and described, it is not to
be limited thereto except so far as such limitations are inclined
in the following claims:
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