SE532578C2 - Fire Safety valve - Google Patents

Description

25 30 532 578 which requires considerable space in the vicinity of the usual valve arrangements.

SUMMARY An object of the present invention is to provide a simple and relatively inexpensive high pressure fire safety valve. A further object of the present invention is to provide a high pressure fire safety valve which is easily fitted to existing high pressure containers without consuming too much space around the ordinary valve.

The above objects are achieved by valves, containers and methods according to the appended claims. In general terms, according to a first aspect, a high pressure fire safety valve includes a disc which is capable of mechanically withstanding a high pressure difference. The disc has a plurality of holes that penetrate through the disc. Each of the holes has a minimum diameter of less than 100 micrometers. The high pressure fire safety valve further comprises a solid phase sealant which seals each of the holes. The sealant exhibits a phase change to a fl surface state at elevated temperatures. This configuration results in the said plurality of holes constituting straight evacuation channels for the high pressure when sealing substances have undergone the phase transformation.

According to a second aspect, a high pressure gas container comprises a high pressure fire safety valve according to the first aspect.

According to a third aspect, a method of manufacturing a high pressure fire safety valve comprises providing a disc and creating a plurality of holes penetrating through the disc. Each of the holes has a minimum diameter of less than 100 micrometers. The method further comprises sealing said number of holes with a sealant.

The sealant is such that it exhibits a phase transformation to a liquid state at elevated temperatures. In a preferred embodiment, MEMS techniques are used to manufacture the disc.

An advantage of the fire safety arrangements according to the present invention is that they can be designed to be very small and that they can be manufactured in a relatively inexpensive manner.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, together with further objects and advantages thereof, is best understood by reference to the following description taken in conjunction with the accompanying drawings, in which: FIG. 1A is a partial cross-sectional view of an embodiment of a high pressure fire safety valve according to the present invention; FIG. 1B is a view of the embodiment of Fig. 1A when opened; FIG. 2A-D are examples of hollow shapes useful in a high pressure fuel safety valve according to the present invention; FIG. 3 is a flow diagram of steps in an embodiment of a manufacturing method according to the present invention; FIG. 4A-B are embodiments of a high pressure fire safety valve according to the present invention comprising protective elements; FIG. 5 is a cross-sectional view of an embodiment of a high pressure fire safety valve according to the present invention; FIG. 6A is a cross-sectional view of an embodiment of an intermediate coupling useful in embodiments of a high pressure gas container according to the present invention; FIG. 6B is a top view of a high pressure fire safety valve used in the embodiments of Fig. 6A; and FIG. 7 is a cross-sectional view of another embodiment of an intermediate coupling useful in embodiments of a high pressure gas container according to the present invention. 10 15 20 25 30 532 578 4 DETAILED DESCRIPTION Throughout the present representation, similar or directly corresponding features in different figures and embodiments will be noted by the same reference numerals.

Gas is often stored under high pressure. In the present preparation, "high pressure" refers to pressures above 20 bar. However, the advantages of the present invention are greater for pressures above 50 bar and even greater for pressures above 100 bar, since the risk of explosion generally increases with increasing pressure. in high pressure gas technology, most constructions are designed with the forces induced by the high pressure in memory. The components are therefore typically made of high strength materials, such as metals and ceramics. Seals are preferably made by welding to ensure the sealing function with a certain distance of solid material. In seals that cannot be welded, rubber o-rings are typically mounted under high pressure to ensure tightness. Less strong seals based on e.g. adhesion, surface tension, membrane, etc. are not normally considered at all for high pressure applications.

The present invention is based on two insights. The first year that even relatively weak materials can withstand. high pressures if only the surface over which the pressure is applied is small enough. The second year that limitations in discharge rates due to small dimensions of discharge channels can be compensated by instead providing a large number of discharge channels.

If a pressure difference of 200 bar is applied over a very small circular surface with a diameter of 100 micrometers, the total force will only amount to 0.16 N. Most solids will withstand such forces even when relatively thin dimensions are used, even materials that are considered relatively soft or soft, such as paraffin, plastic or solder. The small size of the surface thus turns traditional reasoning upside down. 10 15 20 25 532 573 5 A hole with such a small diameter can thus be sealed with almost any solid material and still withstand as high a pressure as 200 bar.

Such a small hole can also be used for a discharge breathing needle. However, the small diameter will greatly limit the discharge rate. In the area of fire safety arrangements, discharge rate is one of the crucial parameters. However, by providing a large number of small holes, a total discharge rate can be achieved, which may be sufficient in typical gas storage applications.

An example will show the possibilities.

Assume that a nitrogen tank has a volume V of 200 l and a nominal pressure P1, of 200 bar at a nominal temperature I; of 293 K. A total mass m of the gas amounts to 46 kg according to: where Rw is the general gas constant. In the event of fire, the gas container has a maximum permissible temperature TM of 400 K. At maximum temperature, the gas container will have a maximum pressure Pm of 273 bar according to: PW = P, -TW r Assume; now that a maximum temperature increase dT is less than 100 K per minute. When the maximum temperature has been reached, a safety evacuation begins. In order to maintain the pressure at or below the maximum pressure 273 bar, the increase in pressure dP due to an increasing temperature must be compensated by a flow of mass dm which is evacuated from the container. The pressure increase dP can be determined as: dP = P -wzr 72 and the evacuation mass flow as: dP «V R T gas ° max dm: In the present example, the required mass flow is 0.19 kg / s.

A flow of a liquid through an opening depends on both the ratio L / d, ie. lengcl-to-diameter ratio, as on the rounding of the entrance. A flow resistance parameter C, for a flat aperture is typically in the range 0.6 to 0.9. In the present case, we assume a value of Cd = 0.75 for an aperture of 100 micrometers.

A total aperture area A (divided into 100 micrometer apertures) required to achieve the required mass fl is given by: which gives A = 2.3mm2, which corresponds to 290 apertures with a diameter of 100 micrometers.

From this example it is concluded that sufficient evacuation can in a typical case be performed by using 300 openings with a diameter of 100 micrometers each. By reducing the aperture diameter to 50 micrometers, while maintaining the flow characteristics through the aperture, 1360 apertures will be required instead.

Only a few years ago, the manufacture of such small holes in such a large quantity would have been impossible with the manufacturing techniques available at that time, such as conventional mechanical machining. Today, however, with MEMS technicians (eng.

MicroElectroMechanical System) structures of much less than C11 millimeters have been manufactured in large numbers.

From the example above, it can be concluded that the flow properties of the channels used for evacuation play an important role in achieving a sufficient fl velocity rate. Straight evacuation ducts that have as short a fateful wave as possible are advantageous.

In the prior art, there are low pressure inlets which are based on melting of a corroding material to effect a safety evacuation. Two typical examples can be found in the English translation of the summary of Japanese patent application 11-132349 and in the European patent EP 0 784 024. The holes originally sealed by a sealant are also used here for evacuation purposes. However, the evacuation holes are too large to withstand high pressures and therefore cannot be immediately applied for high pressure gas applications.

Fig. 1A illustrates a partial view of a cross section of an embodiment of a high pressure fire safety valve 1 according to the present invention. the illustration is i_r¿e_ drawn with a true relationship between different dimensions, to increase the lockability of the figure. The main differences from the drawing scales are noted below. A disc 10 can mechanically withstand a high pressure difference. The disc 10 then has a thickness t which is sufficient to carry the intended maximum pressure over the high-pressure fire safety valve 1. 'Typically, the disc is made of silicon, glass or metal. The disc 10 has a plurality of holes 12 which penetrate straight through the disc 10. The holes 12 have a minimum diameter d of at most 100 micrometers and preferably at most 50 micrometers.

The holes 12 are filled with a sealing substance 20 in a solid phase, which thereby seals each heel 12. The sealing substance exhibits a phase conversion to a liquid state at a predetermined elevated temperature or temperature range. Examples of possible sealants to be used in the present invention are e.g. metals. Pure metals with a sufficiently low melting temperature can be used. Alloys and in particular solder which has a relatively low melting temperature can be used to advantage. However, other sealing substances, such as paraffin, various polymers, in particular thermoplastic polymers, and various kinds of low-temperature melting glass are also possible to use.

The holes 12 in the present embodiment have a tapered shape, with a larger diameter D at a designated high pressure side 11 than a diameter at a designated low pressure side 13, which in the present embodiment is the smallest diameter d of the hole 12. The tapered shape helps the sealant to seal the holes , by converting some of the applied forces caused by the pressure difference into compression forces within the sealing material and thereby strengthening the seal.

It can be noted that the hole 12 is in fact much smaller than the thickness t of the disc, even much smaller than what is illustrated. In a preferred embodiment, the smallest diameter d for each hole is less than 1/10 of the thickness t of the disc 10. In addition, the distance between two adjacent holes is preferably much larger than the thickness of the disc, also in contrast to the drawn dimensions.

As can be seen from the example given further above, the number of holes can advantageously be large, which thus gives a higher evacuation speed. The majority of holes also show a redundancy if certain heels are not opened correctly. In a preferred embodiment, therefore, there are more than 20 holes, and in an even more preferred embodiment, there are at least 100 holes.

Fig. 1B illustrates the same high pressure fire safety valve 10 when in use. As the heat from the fire increases the temperature of the sealant above the temperature at which it has its phase change, the high pressure on the high pressure side 11 has pushed the phase-changed sealant out of the holes, leaving straight evacuation channels 18 for the gas under high pressure to evacuate through. In order to facilitate both the removal of the phase-transformed sealant and the evacuation of the gas under high pressure, the holes 12 have a line of sight 16 through said disc.

The line of sight 16 should preferably be provided in a direction substantially perpendicular to the disc surface.

The holes can be designed in many different ways. l fi g. 2A illustrates another embodiment, where the hole is a heel with an even cross-section through the entire disc, i.e. a hole with straight, parallel walls. Such holes are easiest to make.

However, in order to support the sealing action of the sealing substance, as mentioned above, it is advantageous if a part with a decreasing diameter is located somewhere along the hole. In the embodiment of Fig. 2B, the hole has a minimum diameter in the middle of the disc. The diameters at the disc surfaces are larger, which will probably improve the gas fate properties somewhat. Another embodiment illustrated in Fig. 2C has an even more rounded shape. l fi g. 2D illustrates an embodiment having an asymmetric hole. Those skilled in the art will appreciate that there are numerous possible shapes and forms of heels which have various advantages when applied in the present invention.

Fig. 3 illustrates a step diagram of steps in an embodiment of a method according to the present invention. A process for manufacturing a high pressure fire safety valve begins in step 200. In step 210 a disc is provided. A plurality of heels are created in step 220, which holes penetrate straight through the disc. Each hole has a minimum diameter of less than 10 10 micrometers. In a preferred embodiment, step 220 is performed at least in part by MEMS technology, as indicated by step 222.

In step 230, said plurality of holes are sealed with a sealant. The sealant exhibits a phase change to a liquid state at elevated temperatures. In a preferred embodiment, the seal is made by utilizing the capillary forces in the narrow holes. Step 230 therefore includes stepwise step 232 in which a sealant has melted to a liquid state. In step 234, said plurality of holes in the disc are brought into contact with a surface of the molten sealant. Through the capillary forces, the sealing substance is sucked up in step 236 into said number of holes. If the capillary forces are not sufficient, a pressure difference can be applied over the disc, which helps to suck or press the sealing substance into said plurality of holes. The disc is removed from the molten sealant and allowed to cool in step 238 without any significant pressure difference across the disc. In this way, the sealing substance solidifies inside the holes, which creates a seal of the holes. The process ends in step 299.

In some applications, aggressive gas can be stored in the container and can be harmful when it comes in contact with one or both of the disc and the sealant. In such cases, the high pressure fire safety valve can also be covered with a thin layer of a substance inert to the aggressive gas on the high pressure side. Three embodiments are illustrated in Figures 4A and 4B. I ñg. 4A, the entire high pressure side of the high pressure safety valve is covered with a thin layer 15 of a material inert to the aggressive gas. The thickness of this thin layer 15 is considerably smaller than the disc thickness. The thin layer 15 should be thin enough to break the high pressure difference when the sealant 20 is removed. The thin layer 15 is preferably applied after the holes have been sealed, i.e. after step 230 (ñg. 3). The techniques for providing the thin layer are preferably adapted to the material used. Examples of materials that could be used as an inert thin layer 15 are various types of polymers or corrosion resistant metals or alloys.

Typical thicknesses can be in the order of a few micrometers for e.g. the polymers and even less, e.g. for metal coatings.

If the material in the thin coating is 15 years expensive, e.g. if noble metals are used, the thin coating 15 can be provided in such a way that only those substances which can be affected by the gas are covered. I ñg. 4B, the sheet material resists the gas, while the sealant does not. The thin coating 15 is therefore limited to surfaces such as the sealant and preferably a small safety region around the sealant.

The high pressure fire safety valve presented above is intended to be mounted on a high pressure gas container. One possibility is to have a dedicated opening in the high-pressure gas container which is sealed by such a valve. In such an arrangement, the possibly additional devices can be placed far from the area around the normal outlet valves and thereby do not compete for the available space. However, such solutions require specially designed high pressure gas containers.

Another solution is instead to use existing high-pressure gas containers. An embodiment of such a high-pressure gas container is schematically illustrated in ñg. A high pressure gas container 30 has a shell 31 with an outlet opening 32. The shell 31 encloses a high pressure gas volume 33. An intermediate coupling 34 is mounted at the outlet opening 32 and a discharge valve arrangement 36 is mounted at the intermediate coupling 34.

The thread of the upper part 38 of the intermediate coupling 34 is of the same type and dimensions as the thread 37 of the high-pressure gas container 30. The intermediate coupling 34 is thus a short extent of the gas flow path 35 between the interior of the high-pressure gas container 30 and the discharge valve arrangement 36. 36 used in conventional systems are still used.

The intermediate coupling 34 also comprises a fire safety valve 1 for high pressure 532 578 12 pressure according to the principles described further above. The high-pressure fire safety valve 1 seals a connection between the balance balance 35 in the intermediate coupling 34 and the environment.

Fig. 6A is a cross-sectional view of an intermediate coupling 34 that may be used in a high pressure gas container, as in Fig. 5. A high pressure gas container 30 is illustrated in broken lines. The intermediate coupling 34 is mounted in a thread 37 on the high pressure gas container 30 with a thread 42 of an inner part 41 of a main body 40 of the intermediate coupling 34. The small inner part 41 is generally tubular and has an outwardly directed shaft 45. An outer part 43 of the main body 40 is mechanically attached (not shown in the figure) to the inner part 41 at at least a number of places around the intermediate 34 to provide mechanical rigidity between the inner and outer parts 41, 43. The outer part 43 has an inwardly directed flange 47 on the same level as the flange 45. A high pressure fire safety valve 1 is received on the flanges 43, 45. Two circular o-rings 44, 46 seal the high pressure fire safety valve 1, and are clamped by an inner clamping ring 48 threaded into the inner part 41 and an outer clamping ring 50 threaded into the outer part 43. The outer clamping ring 50 has an inner passage 51, which in the present embodiment is identical to the thread 37 of the high-pressure gas container 30.

The exhaust valve arrangement 36, which is illustrated by broken lines, is mounted by means of the internal thread 51. The intermediate coupling 34 provides an open wall 35 between the high pressure gas container 30 and the discharge valve arrangement 36. The intermediate coupling 34 also provides a flow safety valve 52 from the high pressure pre-gas.

Disc 10 in the high pressure fire safety valve l, illustrated in a top view in ñg. 6B, in the present embodiment has a flat annulus with a central opening 55. The holes 12 in the high pressure fire safety valve 1 are located in the interior of the annular mold, leaving non-perforated edges 57 at the inner and outer sides of the disc 10. The edges 57 are intended to be cooperating surfaces with the o-rings 44, 46 (fi g. 6A). 10 15 20 25 30 532 578 13 Now back to tig. 6A, when the high pressure fire safety valve 1 opens, i.e. when the area around the high pressure fire safety valve 1 becomes hot enough to melt the sealant in the high pressure fire safety valve 1, gas can flow out through the high pressure fire safety valve 1 by using the fate path 52. In the present embodiment, the high pressure fire safety valve 1 is arranged in a direction 54 which provides a downwardly directed flow of effluent gas, as depicted in Figure 6A.

In other words, the high pressure fire safety valve 1 is in a direction to direct gas flowing out 54 through the high pressure fire safety valve 1 toward the shell 31 of the high pressure gas container 33. The gas flowing out through the high pressure fire safety valve 1 generally has a lower temperature than ambient and in particular lower than the gas heated directly by the fire. In such a way, the gas which flows out can form a protective gas area, which somewhat reduces the continued heating of the high-pressure gas container 33 by the heat from an external fire. The flow itself will also contribute somewhat to a cooling of the high pressure gas container 30. Although a flow towards the high pressure gas container 30 may be preferred, the high pressure fire safety valve 1 can of course be arranged in any direction. Another embodiment of an intermediate coupling 34 is illustrated in Fig. 7. Hair comprises a main body 40 at least one and preferably a number of side channels 60, directed substantially perpendicular to the main path 35. The high pressure fire safety valve 1 is supported against one end 63 via an o-ring 64. The high pressure fire safety valve 1 is pressed and secured by a locking ring 66 attached to a thread 62 in the side channel 60. The high pressure fire safety valve 1 is in this embodiment whole discs and typically smaller in size, but instead several high pressure fire safety valves 1 can is mounted in the same intermediate coupling 34. The high-pressure fire safety valve 1 in this embodiment has its holes in a central area, while the edge of the disc is used for fastening purposes. This embodiment can be designed very compactly, whereby the additional occupied space will be very small, compared with an arrangement without fire safety arrangement.

If the outlet of the intermediate coupling 34 has the same passage as the passage of the gas container, the intermediate coupling 34 can be used together with already existing equipment. Existing gas containers can thus be easily upgraded to include a fire safety arrangement according to the present invention.

The embodiments described above are to be considered as illustrative examples of the present invention. Those skilled in the art will appreciate that various modifications, combinations, and changes may be made to the embodiments without departing from the scope of the present invention. In particular, different partial solutions in the different embodiments can be combined in other arrangements where this is technically possible. However, the scope of the present invention is defined by the appended claims.

Claims (16)

10 15 20 25 30 532 578 15 PATENT REQUIREMENTS A high pressure fire safety valve (1), comprising: a disc (10) capable of mechanically withstanding a high pressure difference; said disc (10) having a plurality of holes (12) penetrating through the disc (10): each of the holes (12) has a smallest diameter (d) of less than 100 micrometers; and a solid phase sealing substance (20) sealing each hole (12) of said plurality of holes; which caustic substance (20) exhibits a phase conversion to a liquid state at elevated temperatures; said plurality of holes (12) constituting straight evacuation channels (18) for the high pressure when the sealing substance (20) has undergone the phase transformation. 2. A high pressure fire safety valve according to claim 1, characterized in that the minimum diameter (d) of each hole is less than 1/10 of a thickness (t) of the disc (10). High pressure fire safety valve according to claim 1 or 2, characterized in that the minimum diameter (d) for each hole is less than 50 micrometers. High-pressure fire safety valve according to one of Claims 1 to 3, characterized in that the sealing substance (20) is selected from the list: metal; lcd; alloy; paraffin; polyrner; and glass. 10 15 20 25 30 532 578 16 High pressure fire safety valve according to any one of claims 1 to 4, characterized in that said number of holes (12) comprises more than 20 holes (12). High-pressure fire safety valve according to any one of claims 1 to 5, characterized in that at least one of the holes (12) has a diameter (D) at a high-pressure side (11) of the disc (10) which is larger than said minimum diameter (d). ). High pressure fire safety valve according to any one of claims 1 to 6, characterized in that said high pressure is higher than 100 bar. High-pressure fire safety valve according to one of Claims 1 to 7, characterized in that each of the holes (12) has a line of sight (16) through the disc. ' High-pressure fire safety valve according to one of Claims 1 to 8, characterized by! of a thin film (15) of a resistant material covering at least parts of the high pressure side (11) of the high pressure fire safety valve (1). A high pressure gas container (30), comprising a high pressure fire safety valve (1) according to any one of claims 1 to 9. 11. ll. High-pressure gas container according to claim 10, characterized in that the high-pressure fire safety valve (1) is mounted in an intermediate coupling (34) mounted between a high-pressure gas volume (33) and a discharge valve (36). High-pressure gas container according to Claim 11, characterized in that in that the high pressure fire safety valve (1) is mounted in a direction for directing effluent gas (54) through the high pressure fire safety valve (1) against a shell (3 1) enclosing the high pressure gas volume (33). 10 15 20 25 30 532 573 17 A method of manufacturing a high pressure fire safety valve (1), comprising the steps of: providing (210) a disc (10); creating (220) a plurality of holes (12) penetrating through the disc (10): each of the holes (12) has a minimum diameter (d) of less than 100 micronets; and sealing (230) said plurality of holes (12) through a sealant which sealant (20) exhibits a phase conversion to a liquid state at elevated temperatures. A method according to claim 13, characterized in that the sealing step (230) comprises the steps of: melting (232) the sealing substance (20); bringing (234) said plurality of holes (12) into the disc (10) into contact with a surface of the molten sealant; absorbing (236) the sealant into said plurality of holes (12) through at least one of capillary caps and a pressure difference across the disc (10); and cooling (238) of the disc (10) without pressure difference across the disc (10). Method according to claim 13 or 14, characterized in that the creation step (220) of a number of holes is performed by techniques (222) for microelectromechanical systems - MEMS. Method according to one of Claims 13 to 15, characterized by a further step of covering at least a part of one side of the fire safety valve (1) with a thin layer (15) of an inert material.