CA1162129A - Safety valve - Google Patents
Safety valveInfo
- Publication number
- CA1162129A CA1162129A CA000359097A CA359097A CA1162129A CA 1162129 A CA1162129 A CA 1162129A CA 000359097 A CA000359097 A CA 000359097A CA 359097 A CA359097 A CA 359097A CA 1162129 A CA1162129 A CA 1162129A
- Authority
- CA
- Canada
- Prior art keywords
- valve
- disc
- seat surface
- guide
- socket
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16K—VALVES; TAPS; COCKS; ACTUATING-FLOATS; DEVICES FOR VENTING OR AERATING
- F16K17/00—Safety valves; Equalising valves, e.g. pressure relief valves
- F16K17/02—Safety valves; Equalising valves, e.g. pressure relief valves opening on surplus pressure on one side; closing on insufficient pressure on one side
- F16K17/04—Safety valves; Equalising valves, e.g. pressure relief valves opening on surplus pressure on one side; closing on insufficient pressure on one side spring-loaded
- F16K17/08—Safety valves; Equalising valves, e.g. pressure relief valves opening on surplus pressure on one side; closing on insufficient pressure on one side spring-loaded with special arrangements for providing a large discharge passage
- F16K17/087—Safety valves; Equalising valves, e.g. pressure relief valves opening on surplus pressure on one side; closing on insufficient pressure on one side spring-loaded with special arrangements for providing a large discharge passage with bellows
Landscapes
- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Safety Valves (AREA)
Abstract
Abstract of the Disclosure A safety valve of the equilibrium type having a bellows seal constitution comprising a valve body, a nozzle seat secured to the valve body and having a valve seat surface at its free end, a cylindrical guide secured to the valve body generally opposite to the nozzle seat, a disc socket shiftably contained within the guide, a valve disc secured to the disc socket so as to coact with the valve seat surface, a spring means mounted to the valve body to force the valve disc towards the valve seat surface, and an upper ring adjustably mounted to the guide has its disc socket elongated towards the valve seat surface so as to make the fluid flowing through the gap between the valve disc and the valve seat surface orderly when the valve disc is lifted.
Description
ll~Z9 A safety Valve t1 ;~
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 ~Z~9 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.
~16;Zl~
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 lLZ9 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:-21'~3 j,, ~, 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.
.~ il 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 116Z1~9 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 l~fi2'1Z9 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 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 21~
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 lZS~
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:
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 ~Z~9 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.
~16;Zl~
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 lLZ9 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:-21'~3 j,, ~, 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.
.~ il 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 116Z1~9 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 l~fi2'1Z9 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 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 21~
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 lZS~
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:
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A safety escape valve, comprising: a valve body, having an inlet 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 align-ment with said guide and moveable from a fully closed position to a fully opened position; a valve disc affixed at said one end of said disc socket and adapted to coact with said valve seat surface; a back pressure chamber formed within said disc socket and said guide; a valve stem associated 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 bellows seal disposed for isolating said back pressure chamber from said spring mechanism; a stem disc fixed to said stem;
and said bellows seal in said back pressure chamber for equal-izing 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 substan-tially constant,
and said bellows seal in said back pressure chamber for equal-izing 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 substan-tially constant,
2. A safety escape valve as claimed in claim 1, wherein; said passage means comprises a clearance between said disc socket and said disc guide.
3. A safety escape valve as claimed in claim 1, fur-ther comprising: a lower ring disposed about said nozzle seat having a substantially flat surface in planar alignment with said valve seat surface.
4. A safety escape valve as claimed in claim 1, 2 or 3, wherein: said annular wing is juxtaposed in substantial alignment with said upper wing when said disc socket is in said fully opened position.
5. A safety escape valve as claimed in claim 1, 2 or 3, wherein: an annular gap is formed between the outer peripheral surface of said annular wing and the inner peripheral surface of said upper ring.
6. A safety escape valve as claimed in claim 1, 2 or 3, wherein: said annular wing extends below said upper ring when said disc socket is in said fully closed position.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5867580A JPS56156568A (en) | 1980-05-06 | 1980-05-06 | Safety valve |
| JP58675/1980 | 1980-05-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1162129A true CA1162129A (en) | 1984-02-14 |
Family
ID=13091146
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000359097A Expired CA1162129A (en) | 1980-05-06 | 1980-08-27 | Safety valve |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS56156568A (en) |
| CA (1) | CA1162129A (en) |
| DE (1) | DE3041124C2 (en) |
| NL (1) | NL191953C (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3556565B2 (en) * | 2000-04-14 | 2004-08-18 | 川重冷熱工業株式会社 | High precision safety valve |
| CN103511693B (en) * | 2013-09-29 | 2015-08-26 | 北京航天动力研究所 | Backpressure regulation formula steam security valve closed by a kind of valve stem seal type |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3702142A (en) * | 1970-07-27 | 1972-11-07 | Dresser Ind | Safety valve having back pressure compensator |
-
1980
- 1980-05-06 JP JP5867580A patent/JPS56156568A/en active Granted
- 1980-08-27 CA CA000359097A patent/CA1162129A/en not_active Expired
- 1980-08-29 NL NL8004936A patent/NL191953C/en not_active IP Right Cessation
- 1980-10-31 DE DE19803041124 patent/DE3041124C2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE3041124A1 (en) | 1981-11-19 |
| NL191953C (en) | 1996-11-04 |
| JPS56156568A (en) | 1981-12-03 |
| JPS634065B2 (en) | 1988-01-27 |
| NL8004936A (en) | 1981-12-01 |
| NL191953B (en) | 1996-07-01 |
| DE3041124C2 (en) | 1988-01-21 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |