EP2910284A2

EP2910284A2 - Valve closure mechanism and an air blast valve using said valve closure mechanism

Info

Publication number: EP2910284A2
Application number: EP15152126.7A
Authority: EP
Inventors: Jonathan Schneider
Original assignee: Beth El Zikhron Yaaqov Industries Ltd
Current assignee: Beth El Zikhron Yaaqov Industries Ltd
Priority date: 2014-02-24
Filing date: 2015-01-22
Publication date: 2015-08-26
Also published as: IL231140A0; SG10201500395UA

Abstract

A valve closure mechanism having a moveable plate (28) that is displaceable relative to at least one fixed plate (26, 27), each of the plates having perforations (30, 31) that are mutually offset between one plate and another, so that in an open position of the valve the perforations in each plate allow air to pass therethrough and in a closed position of the valve the moveable plate makes abutting contact with the at least one fixed plate such that at least some of the perforations in each plate are sealed by the plate complementary thereto.

Description

FIELD OF THE INVENTION

This invention relates generally to air blast protection systems and particularly to air blast protection valves for use with such systems.

BACKGROUND OF THE INVENTION

Protected spaces for people and/or equipment for group protection or military command posts and structures on the one hand have to be ventilated, while on the other hand they have to resist the impact of blast waves that could harm people, equipment and air filtration system components.
In order to protect against blasts, air entry and exit openings are fitted with blast protection valves that are able to protect against the most extreme situation. These provide effective protection for people and equipment against the impact of explosions caused during warfare or civil emergencies, including protection during repeated occurrences of both phases of the blast wave: the positive pressure phase and the negative suction phase. The valve has a closure element typically having the general shape of a convex plate that is designed to block the vast majority of the blast wave from entering the protected space and from drawing crucial amounts of air out of the protected space. To this end, the closure element is adapted to engage suitable valve seats within the housing on both sides, i.e. upstream and downstream, of the closure element.
The valve housing typically forms a channel for the air entering the protected space. During normal operation the moving air passes between the blast valve plate and the valve housing. During a blast, the high acceleration of the blast wave impacts the blast plate at high force and causes the closure of the air passage within milliseconds or fractions of milliseconds.
Often the gap allowing the air passage is symmetrical to a longitudinal axis of the valve. For example, the valve closure element may be designed as a flat plate, or as a structured plate for example spherical or semi-spherical or hybrids of such shapes, with an annular air gap surrounding the valve closure element and typically concentric therewith. The valve closure element has to be very strong to absorb the blast energy without deformation, while nevertheless having small mass in order to reduce inertia and allow short closing times.
The closure element is mounted for axial movement along the longitudinal axis of the valve so as to allow free passage of air at rated airflows with a minimum of air resistance, while closing the air passage extremely fast in case of a blast wave. This mounting is achieved by elastic elements that allow the closure element to reach the valve seats upstream and downstream and return to the initial position, so as to be ready to take the next blast, without damage or fatigue for all elements of the system. In most cases the elastic elements are springs, such as compressing springs or tension springs or a combination of both types of spring.
In the case of a strong blast wave, a fast positive pressure front accelerates the closure element, pushing it against the valve seat downstream which blocks the air flow and prevents the blast wave entering the protected space. The characteristic negative pressure segment of the blast wave, the suction phase, follows immediately and pulls the closure element back to the valve seat upstream and seals the protected space in the opposite direction from negative pressure impact. After the positive and negative pressure phases, the closure element is automatically returned to its original open position by means of the elastic elements.
The elastic elements are typically mounted upstream or downstream the closure element or around the periphery thereof. In such case, these elements are themselves subject to the direct or indirect impact of the blast wave. This is undesirable for two reasons. First, the air blast can damage or cause stress to the elastic elements; and secondly, the elastic elements obstruct the air stream and can increase the pressure loss.
Fig. 1 illustrates the general design of a shelter protected from blast waves and air contamination. At the air intake is one or many blast protection valves 1 installed through the wall. Incoming air into the shelter can come only through these valves. The air flow is drawn through piping 2 to air purification filters 3 that release filtered air through ducting 4 to a blower 5, which pressurizes the protected space within the shelter. An air exit valve 6 regulates the air over-pressure in the protected space to a desired pressure; and it likewise is of the form of a wall-mounted device similar to the blast protection valves 1.
Figs. 2 to 5 show a conventional blast protection valve. Air enters via an entry aperture 8 into a housing 9 having an exit aperture 10 and flows through an annular gap between the housing 9 and a valve plate 12 (constituting a closure element). Air flows inside the housing around the periphery of the blast valve plate 12 to the exit aperture 10. The valve plate 12 is resiliently displaceable within the air stream via tension springs 11 one end of which is attached to a periphery of the valve plate 12 and the opposite end of which is anchored to an internal side wall the housing 9. In such a configuration, the springs 11 partially obstruct air-flow, thus increasing the pressure drop across the valve and reducing its efficiency. Furthermore, the very high impact of the air blast acts directly on the side-wall of the springs 11, such that repeated operation of the valve causes damage to the valve, such as distortion and reduces its elasticity.
Air ventilation or air filtration systems employing air blast protection valves are designed to provide a defined amount of airflow to a protected space according to a given standard. Total air throughput dictates the number of valves of given rating required. Larger valves are able to handle a higher air-flow and therefore allow the rated air-flow to be handled using fewer valves.
Financial considerations require that installation and running costs be optimized. Since installations may comprise up to hundreds of air blast protection valves, the required number of valves has a significant impact on investment costs. On this basis alone, it would appear to be desirable to minimize the number of blast protection valves in the system. This, in turn, suggests that valves of higher flow-rate be used and these are inevitably larger and more expensive.
As against this, a consideration of running costs requires that minimum energy be wasted owing to unnecessary pressure drop across the blast protection valves. This consideration leans toward increasing the number of valves so as to decrease the pressure drop across each valve.
It is thus apparent that the ideal solution is the optimum tradeoff between rated airflow and pressure drop. Clearly, for valves of a given rated air-flow, the required number of valves as well as their running costs may be reduced by increasing valve efficiency and this requires that pressure drop across each valve be reduced.
US 2006/0065316 and US Patent No. 6,824,117 disclose non-return valves having a generally tubular valve body that includes an elongate passageway with inlet and outlet at opposing ends. A valve membrane is of a generally conical-shaped diaphragm formed integrally with the valve body and the diaphragm has a collapsible opening or aperture located at or adjacent the cones apex.
WO 1999/027283 discloses a safety valve comprising a guide body provided with an axial perforation and a valve body, movable inside the perforation. The valve body has a frustoconical head able to bear against the walls of a conical middle section of said axial perforation. The valve body is movable axially under the action, on the one hand, of the pressure of the inflating air and, on the other hand, of pressure means.
CA 2,238,593 discloses an inflating valve that includes inner and outer pieces which have first and second peripheral flanges for cementing together and a central plug and a central tubular spout to be sealingly fitted together. A frusto-conical shaped first web portion is formed between the plug and the first peripheral flange to project inward from the first peripheral flange and is provided with a plurality of passage holes for communication with the tubular spout. A second web portion of frusto-conical shape is formed between the tubular spout and the second peripheral flange to abut against the first peripheral flange and can be flexed at its wider end so as to separate the tubular spout from the plug.
Thus this valve has a pair of interacting conical valve elements, but they are disposed with their respective flanges abutting each other and their apices mutually opposed similar to the arrangement shown in Fig. 2. They are not disposed one inside the other.
Thus valves having conical seating are well-known as are valves having conical sealing elements or diaphragms that may be resiliently urged toward the conical seating in order to seal the air passage between the seating and the diaphragm. However, there appears to be no suggestion in the prior art to provide a valve mechanism, particularly for a gas valve, having at least one pair of axially displaceable perforated plates having perforations that are mutually offset, so that when the two plates abut one another the perforations in each plate are sealed by the complementary abutting plate.
There appears likewise to be no suggestion to provide such a valve mechanism with stacked conical plates whose surfaces abut one another when the valve is closed.
US Patent No. 7,527,663 discloses a ventilation system providing NBC protection for a shelter with constant slight excess pressure, having an air inlet and outlet and an explosion protection valve. A pre-filter is disposed between two rigid plates that have mutually offset perforations, one of which is moveable toward the other under the force of an explosion. When the two plates are mutually apart, air can flow through the perforations of both plates but under the force of an explosion, the perforations in each plate are sealed by the opposing plate owing to the fact that the respective perforations in both plates are non-overlapping.
In such arrangement there is no abutting contact between the two plates since they are separated by the pre-filter; and since only two plates are provided it can absorb only the positive phase of a blast wave and not the negative phase, which applies force in the opposite direction. Furthermore, it is used as an air inlet valve but cannot be used as an air exit valve which, under normal operating conditions, must be slightly open in order to provide the desired overpressure in the shelter.
More particularly there appears to be no suggestion in the art to provide a valve mechanism for an air blast valve having a pair of fixed outer perforated closure elements rigidly supported within a housing and defining a respective inlet and outlet of the valve; and at least one intermediate perforated closure element resiliently supported between the fixed elements and adapted for axial movement therebetween.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a valve mechanism that lends itself to improved performance in an air blast valve.
It is a further object of the invention to provide an improved air blast valve using such a mechanism so as to exhibit a higher efficiency than hitherto-proposed valves of comparable rating.
A further object is to provide an air exit valve with the ability to regulate the overpressure within a space.
It is another object of the invention to reduce the space occupied by the air blast valve.
These objectives are realized in accordance the invention by a valve mechanism and air blast protection valve having the features of the respective independent claims.
An air blast valve according to one embodiment of the invention utilizes a set of three perforated conical elements that are stacked one inside the other, such that the two outermost conical elements are in permanently fixed positions and the intermediate element has lower mass and is axially and/or radially moveable relative to both of the outer plates and capable of retention in defined working positions between the outermost elements by resilient elements.
The holes of the perforated cones are arranged in such a way that depending on the mutual alignment between the cones they can allow air passage or block air passage. If the intermediate element abuts either of the fixed elements, the air passage is blocked, while in a neutral position of the intermediate element where it is axially separated from both of the fixed elements, air can pass from the inlet to the outlet of the valve with pressure drops of less than 500 Pa.
In accordance with some embodiments, the pressure drops can be adjusted e.g. to 135 Pa or 300 Pa meeting the requirements of particular standards or needs.
There is a relational function between size of the perforations, angle of the cone and the stroke i.e. the distance traveled by the middle plate. Thus, the wider the cone, the larger will be the angle between the central axis and the wing, and the smaller will be the stroke of the middle plate and the size of the perforations. Circular perforations having a diameter between 3 to 25 mm have been used to particularly good effect.
It is a further feature that the rigidity of the middle cone may be reduced owing to the fact that the travelling distances between working (i.e. open) position and closed position are so small that the force applied thereto by the high acceleration forces of the blast wave is not sufficiently high to deform the intermediate cone during the stopping process. This arises from several factors that work simultaneously toward the same effect:

1. The stroke can be as small as a few mm only. This allows closing times of less than 1 ms and certainly much less than 0.1 second.
2. Owing to the small travel distances, the resilient elements face no deformation and destruction by the impact of the blast wave.
3. A lightweight intermediate element closes faster, and so can already be in the closing position where it has the mechanical support of one of the rigidly fixed elements before the main forces of the blast become effective.
4. A lightweight intermediate element generates less friction on the guiding elements. So it acts and closes faster. Furthermore the fixation on defined working positions can be achieved with less force and smaller and lighter springs.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 shows a pictorial view of a shelter system with a blast protection valve;
Fig. 2 is an isometric view of a prior art blast protection valve at the air entrance to the shelter;
Fig. 3 is a partial sectional view of Fig. 2;
Fig. 4 is a front elevation of Fig. 3 showing the springs and the blast plate;
Fig. 5 is a vertical cross-sectional view of the valve as seen through arrow A-A in Fig. 4;
Figs. 6a and 6b are pictorial representations showing different ways to mount an air blast valve according to a first embodiment of the invention having a conical closure mechanism to the wall of a protected shelter;
Fig. 7 shows an isometric view showing mainly the outer side of the valve;
Fig. 8 shows an isometric view showing mainly the inner side of the valve;
Fig. 9 is a cross-sectional view of the valve showing a detail of the closure mechanism according to a first embodiment;
Figs. 10a, 10b and 10c are partial cross-sectional views of the valve showing schematically a detail of the closure mechanism according to a second embodiment and the relative displacements of the valve elements in different operating positions;
Fig. 10d is an enlarged partial sectional view of the valve showing in greater detail the relative displacements of the valve elements when the valve is slightly open;
Figs. 11a, 11b and 11c are partial sectional views of the valve elements in the different operating positions of Figs. 10a, 10b and 10c, respectively;
Figs. 12a, 12b and 12c show enlarged details of the valve elements in the respective operating positions depicted in Figs. 11a, 11b and 11c;
Figs. 12d, 12e and 12f show details of a valve according to another embodiment having a flexible closure member that opens under gravity;
Figs. 13a and 13b are partial sectional views of a valve according to another embodiment of the invention in the open position;
Figs. 14a and 14b are partial sectional views of the valve shown in Fig. 13a in the closed position;
Figs. 15a, 15b and 15c are partial cross-sectional views of an air blast valve having a closure mechanism according to a further embodiment and the relative displacements of the valve elements in different operating positions;
Figs. 16a, 16b and 16c are partial cross-sectional schematic views of an air blast valve having a closure mechanism according to yet another embodiment and the relative displacements of the valve elements in different operating positions;
Figs. 17a, 17b and 17c are respective partial cross-sectional pictorial views of the air blast valve of Figs, 16a, 16b and 16c showing a detail of the perforations;
Fig. 18a is a partial cross-section through an air blast valve having an elongated diaphragm formed of multiple segments; and
Fig. 18b is an enlarged detail of the arrangement in Fig. 18a showing the joining of adjacent segments.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description of some embodiments, identical components that appear in more than one figure or that share similar functionality will be referenced by identical reference symbols.
Fig. 6a shows pictorially a detail of an air blast protection valve 20 mounted on a sleeve 21 in the shelter wall 22. The sleeve 21 is an anchored pipe passing through the shelter wall and having a flange on which the valve is mounted. The sleeve is shown in Fig. 1, only an edge thereof being visible in Figs. 6a and 6b. Fig. 6b shows a corresponding air entry valve where the valve is mounted in opposite orientation. The valve has a sufficiently narrow profile that it can be completely accommodated within the thickness of the wall without any overhang into the shelter thus saving space. This is one of the benefits of the invention.
Figs. 7 to 10c show an air blast valve 25 that may be dimensioned for mounting on the flange of a standard 8-inch wall sleeve and has an air outlet capacity of 800 m³/h. The valve 25 includes a pair of rigid perforated fixed elements 26 and 27 defining a respective inlet and outlet of the valve, and an intermediate perforated closure element 28 resiliently supported for axial movement between the fixed elements. Preferably, the intermediate perforated closure element is formed of plate material that is resistant to corrosion and temperature and has a thickness between 0.5 and 3 mm. The fixed elements 26, 27 and the intermediate closure element 28 are generally concave in shape and have similar cross-sectional profiles so that the intermediate closure element 28 may be urged into tight abutting contact with either of the rigid fixed elements. Specifically, in one position as shown in Figs. 10a and 11a, an inner concave surface of the intermediate closure element 28 abuts an outer convex surface of one of the rigid elements; while in the other position as shown in Figs. 10c and 11c, an outer convex surface of the intermediate closure element 28 abuts an inner concave surface of the other rigid element. The intermediate closure element 28 has perforations 30 that are mutually offset relative to perforations 31 in both of the fixed elements so that when the intermediate closure element is subjected to an air blast whereby it is urged into abutting contact with either one of the fixed elements, the respective perforations in the fixed element and in the abutting intermediate closure element are mutually sealed thereby preventing air flow, while when the intermediate closure element is axially separated from both of the fixed elements, air can pass between the inlet and the outlet.
A spring 32 constituting a resilient biasing element is coupled to the intermediate closure element for maintaining the at least one intermediate closure element in an axially displaced position from both of the fixed elements in an open position of the valve shown in Figs. 10b and 11b. An air blast in either direction forces the intermediate closure element 28 against the resilient bias force of the spring 32 thus urging it into abutting contact with the respective downstream fixed element, thereby sealing the valve and preventing air flow. As is known, air blasts have two mutually opposite intake and exhaust phases whereby in short successive the intermediate closure element is urged against both of the fixed elements, in both cases preventing passage of air through the valve and thus blocking the air blast from permeating into the shelter. Fig. 10d is an enlarged partial sectional view of the valve when used as an air exit valve. In the equilibrium position, the intermediate closure element 28 is slightly displaced from the outermost fixed element 26 so that the valve is slightly open and releases air from the shelter at a lower pressure than the air inlet pressure. This creates a slight over-pressure in the shelter that prevents contaminants in the atmosphere outside the shelter from entering the shelter.
If the valve is mounted in a vertical axial position, the opening can be assisted by gravity whereby the middle plate can move into the intermediate position at least partly under its own weight. It will be borne in mind that this occurs only when the pressure of the air blast has diminished and it becomes safe for the valve to re-open. Since there is no longer high air pressure acting against the spring, the spring is free to return to its equilibrium position where the middle plate is intermediate the two outer plates. The weight of the middle plate may assist this process.
Figs. 12d, 12e and 12f show details of a valve 25 according to such an embodiment having a casing 29 open at one end and supporting a flexible closure member 28 that operates under gravity alone. The valve 25 includes a pair of rigid perforated fixed elements 26 and 27 defining a respective inlet and outlet of the valve as shown by the arrows. In this embodiment, the inlet element 26 is part of the casing 29. The closure member 28 may be a perforated rubber flap or diaphragm that is hingedly attached at one edge to an inside edge of the casing intermediate the elements 26 and 27 so as to be capable of vertical pivotal movement between the fixed elements 26 and 27. When an air blast enters the valve through the fixed element 26 constituted by the wall of the casing, the closure member 28 is urged into abutting and sealing contact with the fixed element 27, the respective perforations in the fixed element 27 and in the abutting intermediate closure member 28 being mutually sealed thereby preventing air flow. In the negative suction phase of the air blast, the closure element 28 is urged into abutting contact with the fixed element 26 assisted in this case by gravity. In normal operating conditions, the intermediate closure member 28 is axially separated from both of the fixed elements, allowing air to pass between the inlet and the outlet.
If formed of rubber, the intermediate closure member 28 may be 2-8 mm in thickness and, in order to enhance the effect of gravity, it may be reinforced with a material of higher density than the plate itself such as metal fibers, wire or a perforated metal sheet, such as steel. However, the intermediate closure member 28 does not itself need to be flexible so long as it is able to swing into sealing abutment with the fixed plates. So it could be formed of thin metal sheet having a thickness in excess of 1mm.
It should also be noted that the intermediate closure member 28 can be formed of a single material or a sandwich structure. Furthermore, although the arrangement shown in Figs. 12d to 12f operates as a standalone module, several such modules can be cascaded in parallel for higher air flows within a unitary valve system.
The operating position is achieved mainly by gravity of the intermediate closure member 28 thereby providing the overpressure required by the locally applicable shelter standard. In some embodiments, the valve is used as air exit valve and should regulate the overpressure to 250 Pa. At the hinge point the flexibility of the material will affect the operating position. Furthermore, stopper elements such as notches may be provided to keep the plate in a preferred position even if some fluctuations of the air flow occur. However in the blast situations they should neither increase the closure time nor reduce the closure effect and tightness of the seal.
In an embodiment of the invention reduced to practice, the valve elements were conical in shape with identical or nearly identical apex angles. However, it will be appreciated that other hollow or concave cup-shaped cross-sections may be used. It will also be understood that while the fixed elements 26, 27 are rigid, the intermediate closure element 28 may be sufficiently flexible to adapt to the contour of the fixed elements 26, 27. This allows for the shape of the intermediate closure element 28 to be similar to that of the fixed elements, without being necessarily identical. Alternatively, the intermediate closure element 28 may be rigid and shaped for abutting contact with the fixed elements. It should also be noted that only those portions of the surfaces of the intermediate closure element 28 and of the elements 26, 27 that either have perforations or serve to seal perforations of an abutting element need be complementary in shape. Other portions of these elements, particularly the ends that support the spring 32, may be solid and if so there is no requirement that the surfaces of adjacent elements abut. When used in an air blast valve, the intermediate closure element 28 may have a downstream surface of generally spherical shape able to withstand a yield stress >150 MPa.
Having described the operating principle of the valve 25, its fixation to the wall of the shelter and the spring mechanism will now be described. The two fixed elements 26 and 27 are provided with a peripheral flange 33 having through-holes 34 that allow the flange to be bolted to the wall sleeve. For the sake of explanation, we will refer to the element 26 as the outermost element and to the element 27 as the innermost element, although it will be understood that this nomenclature is arbitrary since the valve can be mounted in either direction. A guide bolt 35 is fixedly supported at a first end by the outermost fixed element 26 using a nut 36 and a counter nut 37 and slidably supports the intermediate closure element 28 via a bearing 38. A spring housing 39 shown in Fig. 9 may be mounted on the guide bolt 35 to accommodate the spring 32 and extends through an aperture (not shown) in the innermost element 27 so as to allow axial displacement of the intermediate closure element 28 relative thereto. An adjustable seat 40 is slidably supported on the guide bolt 35 and may be urged toward the first end thereof by tightening a nut 41 so as to adjust the tension in the spring 32, which is supported by the adjustable seat 40 and secured by a bolt 42. This sets the resilient bias force in the equilibrium position shown in Fig. 10b when the intermediate closure element 28 abuts neither of the fixed rigid elements 26, 27 thus allowing air to flow through the valve.
Fig. 10a shows a first closed position of the valve where an air blast enters at through the outermost element 26 at sufficiently high force to overcome the resilient bias force of the spring 32. The resultant force acting on the intermediate closure element 28 urges it toward and into abutting contact with the innermost element 27, thus closing the valve and preventing the air blast from passing therethrough. This action compresses the spring 26, which expands and releases the intermediate closure element 28 back to its equilibrium open position when the force of the air blast dissipates.
Fig. 10c shows the opposite situation where the exhaust phase of the valve acting in the opposite direction flows initially through the perforations in the innermost element 27 and urges the intermediate closure element 28 toward and into abutting contact with the outermost element 26, thus closing the valve and preventing the air blast from passing therethrough. This action also stretches the spring 32 as shown in Fig. 10c, which compresses and releases the intermediate closure element 28 back to its equilibrium open position when the force of the air blast dissipates. Movement of the intermediate closure element 28 in either direction induces axial displacement of the spring housing 39 through the aperture in the innermost element 27, thus allowing the intermediate closure element 28 to reach the full extent of its stroke, which is preferably less than ±10 mm.
In the arrangement shown in Figs. 10a to 10c, the spring 32 is supported between the closed end of the spring housing 39 and the adjustable seat, which is anchored to the guide bolt 35 towards it second end, remote from the outermost element 26. The spring 32 in this case compresses when the intermediate closure element 28 is urged by the air blast toward the innermost element 27 and stretches when it is urged by the air blast toward the outermost element 26. The equilibrium position is adjusted so that the intermediate closure element 28 is clear of both the fixed elements. When the valve is used an air inlet valve, the intermediate closure element 28 is preferably, substantially mid-way between the two in the equilibrium position so that it closes the valve when subjected to a similar closure force in either direction, while maintaining substantially equal closure times. When the valve is used an air exit valve, the intermediate closure element 28 is much closer in the equilibrium position to the outermost element 26 as shown in Figs. 10d. The distance between the two rigid fixed elements 26, 27 is small, typically about 11 mm, so that the required axial displacement of the intermediate closure element 28 to close the valve in either direction is so small that, when subjected to high acceleration by the air blast, it reaches abutting contact with the respective rigid element before the air blast is able to cause damage or distortion.
In order for the air blast to be capable of overcoming the resilient bias of the spring 26, it must engage sufficient surface area of the intermediate closure element 28. In other words, there needs to be a sufficient amount of material surrounding the perforations to meet the force of the air blast and allow it to urge the closure element 28 to the respective downstream fixed element. If the perforations occupy too much of the space, this will militate against effective closure of the valve. Conversely, if there are insufficient perforations, this will limit the airflow capacity of the valve in the open position. A balance needs to be met depending on the desired airflow capacity and the maximum force of the air blast to be withstood. Thus, a large valve provides higher airflow but offers high resistance, while a small valve offers poor airflow but low resistance.
In an embodiment reduced to practice, the total area of the perforations in each element exceeds significantly 50% of the open area of the connecting 8 inch wall sleeve. The area of the opening of an 8-inch diameter wall sleeve is π. (4 × 25.4)² mm² i.e. about 32,530 mm². The sum of holes in each of the three elements 26, 27, 28 have an open area that is larger than 16,265 mm².
It should be noted that while the guide bolt 35 of the valve mechanism is shown attached to the outermost element 26 and extends into the hollow center of the valve, it can equally well be supported by the innermost element 27 and extend outward as shown in Fig. 9. In such case, the spring housing 39 extends through an aperture in the outermost element 26 and the spring 32 is supported between the closed end of the spring housing 39 and the adjustable seat, which is anchored to the guide bolt 35 towards it second end, in this case remote from the innermost element 26. The spring 32 in this case stretches when the intermediate closure element 28 is urged by the air blast toward the innermost element 27 and compresses when it is urged by the air blast toward the outermost element 26. It should also be noted that while the spring 32 is shown as a single spring, there may be applications where owing to manufacturing tolerances and impact to sliding forces, more than one spring can be used with the effect that with preloaded springs having different stiffness coefficients the working points can be adjusted more easily and more stably.
Figs. 11a, 11b and 11c and 12a, 12b and 12c are partial sectional views of the valve elements in different operating positions showing air flow in both directions. These positions correspond to those shown and in Figs. 10a, 10b and 10c respectively. Thus, Figs. 11a and 12a depict a first closed position where the closure element 28 is in abutting contact with the innermost fixed element 27. Figs. 11b and 12c depict an open position where the closure element 28 is in its equilibrium position intermediate the two fixed elements 26 and 27 and Figs. 11c and 12c depict a second closed position where the closure element 28 is in abutting contact with the outermost fixed element 26.
The air blast valve 25 is able to withstand blast waves with pressures of 1 to 70 bar and prevents air penetration into protected spaces to a leakage degree of 300 Pa·s or better.
Although the above-described closure mechanism employs a central guide bolt 35, a sliding bearing 38 and tension spring 32, it should be understood that this is by way of non-limiting example only and other changes to the valve mechanism may be made as follows:

▪ The resilient retention of the intermediate closure element 28 can be achieved using other elastic elements such as leaf springs, wave washers or tubular springs made of elastomers.
▪ Although a single spring 32 is shown in the figures, more than one spring may be employed.
▪ The resilient bias may be achieved using springs disposed at other locations. For example, radially acting springs may be used as disclosed in IL 209387 entitled "Air Blast Projection Valve" in the name of the present Applicant and published February 28, 2013. Such an action is shown in Fig. 3 and includes a plurality of elastically deformable elements each having a respective first end that is anchored to a surface of a housing. A plurality of inelastic coupling elements are each anchored at a respective first end to a second end of at least one of the elastically deformable elements and are anchored at a respective second end toward a periphery of a closure element. The inelastic coupling elements are adapted to convert axial movement of the closure element caused by an air stream acting on the closure element in either direction to a reduced axial movement of the respective elastically deformable element or elements anchored thereto.
▪ The apex angle of the cone elements and the closure element can vary over a wide range. Indeed, what is important is that the closure elements be coaxial and mutually aligned such that they fit exactly one inside the other with abutting contact between the mating surfaces thereof. In some embodiments the closure elements may be cylindrical as will now be described. In other embodiments (not described), the closure elements may be polyhedral. They may be, but are not required to be, axially symmetrical about a longitudinal axis.

Figs. 13a and 13b are partial sectional views of a valve 45 according to a second embodiment of the invention in the open position and Figs. 14a and 14b show similar views of the valve in the closed position. The principle of the closure mechanism still relies on the displacement of two perforated plates 26, 28 that are relatively displaceable so that in the closed position of the valve, perforations in each plate are sealed by the complementary plate. However, in this embodiment the moveable plate 28 is the side wall of an inner cylinder 46 (constituting a first element) that is coaxially disposed within an outer cylinder 47 (constituting a second element) whose side wall is the fixed plate 26, the respective side-walls of the two cylinders being in abutting contact. The inner cylinder 46 is axially displaceable relative to the outer cylinder 47 against the bias force of a compression spring 32 that urges the inner cylinder 46 into a position where its perforations 30 are aligned with the perforations 31 in the outer cylinder 47 such that the respective perforations overlap thereby allowing air to flow through both perforations. A leaf spring 50 is mounted internally on an end surface of the outer cylinder and acts as a buffer between the two cylinders. The air blast enter inlet apertures 51 at an end of the outer cylinder against the bias force of the spring 32, so as to displace the inner cylinder 46 to the position shown in Figs. 14a and 14b where the respective perforations 30 and 31 are in anti-phase, thus sealing the valve. Thus, in this embodiment the plates 26 and 28 are in constant abutting relationship but their respective perforations are brought into and out of mutual alignment based on relative axial displacement of the two plates.
Preferably, the moveable and fixed plates have an equal number of perforations 30 and 31 that are regularly spaced apart by the same interval spacing in order to ensure that in the open position all the perforations in both plates allow air to pass through. This requirement will not be realized if one plate has fewer perforations than the other. In any case, the perforations must be spaced and dimensioned so that in the closed position all the perforations in each plate are sealed by the complementary plate.
The two cylinders could also be configured to rotate relative to each other to the same effect. For example, two concentric cylinders may be articulated so that force acting linearly on the inner cylinder rotates it relative to the outer cylinder thereby bringing the perforations out of mutual alignment. The requirement to transduce linear motion to rotation of the valve elements renders such an action less attractive for applications having stringent closure times. But the valve mechanism according to the invention may be used in other less stringent applications where increased operating times are less critical.
In either case, although in the embodiment shown in Figs. 14a and 14b the inner cylinder 46 is moveable and the outer cylinder 47 is fixed, it will be appreciated that it is also possible for the inner cylinder 46 to be fixed and for the outer cylinder 47 to be moved either axially or rotationally relative thereto.
Although the air blast valve is shown in Fig. 6a as an air exit valve, it may equally well serve as the air inlet valve. However, higher stringencies apply to the exit valve since, as will be understood to those versed in the art of safety shelters, the air pressure in the shelter must be maintained at slightly above atmospheric pressure in order to inhibit the entry of contaminated air. In practice, this requires that the air exit valve release air from the shelter at a lower rate than the air inlet admits fresh filtered air. Thus when the invention in any of its embodiments is used as an air exit valve in such a shelter as shown in Fig. 1, the moveable plate must be biased so that in its equilibrium intermediate position it is closer to the downstream fixed plate than to the upstream fixed plate. This reduces the rate at which air escapes from the shelter through the exit valve and also shortens the stroke through which the moveable plate must move in order to seal the valve completely. An air exit valve according to the invention meets the overpressure regulation at defined airflows, e.g. 300 Pa @ 800 m³/h and 135 Pa@ 300 m³/h as set by the Israel Standards Institute.
Figs. 15a, 15b and 15c are partial cross-sectional views showing details of an air blast valve 55 having a closure mechanism according to another embodiment also based on a pair of concentric cylinders, but which in this case are both fixed. Thus, an inner cylinder 56 having perforations 31 is coaxially mounted within an outer cylinder 57 having perforations 31. The two cylinders are dimensioned to leave an air gap 60 between the respective side-walls of the two cylinders. The side-walls of the two cylinders are analogous to the two fixed rigid plates of the two embodiment described above with reference to Figs. 9-10 and 13-14, respectively. However, unlike the embodiment shown in Figs. 13-14 where the end surfaces of the two cylinders are likewise perforated to allow the passage of air, in the embodiment of Figs. 15a, 15b and 15c only the side-walls of the two cylinders are perforated, their respective perforations being mutually aligned.
Disposed in the air gap 60 between the two fixed cylinders 56 and 57 is a moveable closure element in the form of a tubular rubber diaphragm 58 that is likewise perforated, but whose perforations 30 are out of overlapping alignment with the perforations 31 of the inner and outer cylinders. In an equilibrium position of the valve, the diaphragm 58 is stretched taut intermediate the side-walls of the two fixed cylinders 56 and 57, thus allowing air passage via the perforations 31 of the two fixed cylinders and the perforations 30 of the moveable diaphragm 58. An air blast entering through the side-wall of the outer cylinder 57 forces the diaphragm 58 into abutting contact with the side-wall of the inner cylinder 56. Since the perforations 30 of the moveable diaphragm do not overlap with the perforations 31 of the two cylinders, the perforations 31 are sealed by the rubber of the intermediate diaphragm 58, thus closing the valve 55 and preventing air passage. In the negative suction phase, the diaphragm 58 is forced by the air blast into abutting contact with the side-wall of the outer cylinder 57 to the same effect. Although for the sake of clarity only a single diaphragm is shown in the figures, in practice more than one diaphragm may be employed in order to achieve a desired spring force.
In this embodiment, the two cylinders 56 and 57 constitute fixed plates and the diaphragm 58, which in this case is pliable, is the moveable plate such that a closure force applied to the moveable plate brings it into abutting relationship with the fixed plates in an analogous manner to that described above with reference to Figs. 7-10. This embodiment has been described with regard to two rigid outer plates and a flexible inner plate. However, the opposite may equally be employed where in one phase of the air blast a first flexible plate is urged into abutting contact with one side of a rigid plate while in the opposite phase of the air blast a second flexible plate is urged into abutting contact with the opposite side of the rigid plate. In such an embodiment there are, in effect, two flexible diaphragms that seal the valve during opposite phases of the blast.
Figs. 16a, 16b and 16c are partial cross-sectional schematic views of an air blast valve 65 having a closure mechanism according to a further embodiment, which is similar in principle to that shown in Figs.15a to 15c. For ease of explanation, identical reference numerals are employed. In this embodiment, frusto-conical valve elements are used and the diaphragm is in the form of a frusto-conical cap that is disposed within the air gap 60 and is closed at its apex 66 so at to envelop the inner conical element 56. The principle of operation is similar to that of Figs.15a to 15c in that the ends of the valve are sealed and air enters the perforations 30, 31 in the side walls. During the positive pressure phase of an air blast, high pressure air urges the diaphragm 58 from an equilibrium position shown in Fig. 16a intermediate the inner and outer elements 56, 57 into abutting contact with the inner element 56 as shown in Fig. 16b and in the negative suction phase, the diaphragm 58 is urged into abutting contact with the outer element 57 as shown in Fig. 16c.
In practice, it has been found that owing to the pressure wave, the diaphragm 58 widens or contracts and this affects its length. Specifically, upon contracting inwardly as shown in Fig. 16b its length increases, while the widening of the diaphragm 58 as shown in Fig. 16c causes its length to decrease. This is not shown in Figs. 16a, 16a and 16c, which are merely schematic representations. However, it is shown in Figs. 17a, 17b and 17c from which it emerges that matching perforations 31 on the inner element 56 and the outer element 57 are not radially aligned since the location of the complementary perforations in the diaphragm move axially depending on the phase of the air blast. In these figures, the material is depicted by the white space and the perforations appear grey. Thus, relative to the closed position shown in Fig. 17b where the diaphragm 58 is axially lengthened and the closed position shown in Fig. 17c where the diaphragm 58 is axially foreshortened, the perforations 30 in the diaphragm are axially displaced toward the apex 66 of the valve i.e. the left of the picture. This is shown by cross-hatching the material bounding matching perforations 31 that are shown as unfilled rectangles in both pictures, it being seen that the perforation 31 of the outer cone 57 in Fig. 17c is somewhat closer to the apex 66 than the matching perforation 31 of the inner cone 56 in Fig. 17b. This axial misalignment of the matching perforations 31 in the two cones 56, 57 ensures that they are both sealed by the diaphragm 58 notwithstanding the axial foreshortening or lengthening thereof.
Figs. 18a and 18b are partial cross-sections through an air blast valve having an elongated diaphragm 58 formed of multiple segments of which there are shown two segments 70 and 71 mounted end to end. As best shown in Fig. 18b, each segment 70, 71 is supported at opposite ends by respective buttresses 75, 76 that are mounted between the opposing surfaces of the two fixed cylinders or cones 56, 57. The buttresses 75, 76 may be formed of plastics by injection molding or other techniques and may be shaped as shown in Fig. 18b to provide interlocking contact. In the figure, only one buttress is shown for each segment since the opposite end of the segment is not shown in the figure. Each diaphragm segment is thus simply supported at its ends like a bridge and is free to deflect upward and downward between its fixed end points. Obviously, even when fully deflected, the diaphragm segments 70, 71 cannot make abutting contact with the upper and lower surfaces of the two fixed cylinders or cones 56, 57 immediately proximate the buttresses 75, 76. This does not affect or impede the operation of the valve provided that there are no perforations in at least one of the diaphragm segment and the upper and lower fixed cylinders in those areas of incomplete abutting contact. For the sake of clarification, this will be explained with reference to two columns of perforations 31a and 31b in the upper cylinder 57 shown in Fig. 18b where upward deflection of the segment 71 is shown schematically by a line 77. At the buttress 76, there is zero deflection of the segment 71; there is incomplete deflection at the first column of perforations 31a such that they are not sealed by the segment and there is full deflection at the second column of perforations 31b such that they are completely sealed by the segment 71. This forms a sealed air pocket 78 between the incompletely deflected end of the segment 71 and the surface of the upper cylinder 57. Even though the perforations 31a are not completely sealed, air entering these perforations is unable to escape from the sealed air pocket 78.
Finally, although the invention has been described with reference to an air blast valve, it is to be understood that this is merely one application of the inventive concept, which may be summarized as follows:

a) a closure mechanism, particularly for a fluid valve, having at least one pair of axially displaceable perforated plates having perforations that are mutually offset, so that when the two plates abut one another the perforations in each plate are sealed by the complementary abutting plate;
b) the closure mechanism as in a) where one of the plates is rigid and the other is optionally pliable;
c) the closure mechanism as in b) wherein in the open position of the valve, the moveable plate is displaced from the rigid plate by such a short distance, typically less than 10 mm, that even when subject to high closure forces no damage is done to the pliable plate prior to its abutting the rigid plate and being cushioned thereby.

It should also be noted that while several different embodiments have been described, features that are described in detail in one embodiment may be employed in different embodiments. For example, radially acting springs may be employed in all those embodiments where axial displacement of the moveable plate is required.
Likewise, in all embodiments where cylindrical or conical valve elements are used, it is reiterated that this is by way of example and other geometrical shapes may be used provided that they are coaxial and mutually aligned. They may, but need not, be axially symmetrical about a longitudinal axis. Thus, the embodiment of Figs. 13 and 14 could employ coaxial polyhedral valve elements adapted for mutual sliding movement such that they fit exactly one inside the other with abutting contact. Likewise, the embodiments of Figs. 15 to 18 which are described with regard to cylindrical and conical valve elements may employ coaxial polyhedral valve elements. In this case, corresponding diaphragms are preferably provided for each face of the polyhedron so as to render the valve substantially insensitive to the direction of the air blast. Nevertheless, depending on the number of faces in the polyhedron, some faces need not participate in the closure operation relying instead on the efficacy of adjacent faces and their respective diaphragms. In other words, if polyhedral elements are used, it is not essential that all faces be perforated.
Where specific design parameters such as diameter of perforations, length of valve stroke and so on are mentioned in connection with one embodiment, it is to be understood that they are not limited to that embodiment. Thus, combinations of features are contemplated as fall within the scope of the appended claims.
It should further be noted that features that are described with reference to one or more embodiments are described by way of example rather than by way of limitation to those embodiments. Thus, unless stated otherwise or unless particular combinations are clearly inadmissible, optional features that are described with reference to only some embodiments are assumed to be likewise applicable to all other embodiments also.

Claims

A valve closure mechanism having a moveable plate (28) that is displaceable relative to at least one fixed plate (26, 27), each of said plates having perforations (30, 31) that are mutually offset between one plate and another, so that in an open position of the valve the perforations in each plate allow air to pass therethrough and in a closed position of the valve the moveable plate makes abutting contact with the at least one fixed plate such that at least some of the perforations in each plate are sealed by the plate complementary thereto.
The valve closure mechanism according to claim 1, wherein the at least one fixed plate (26, 27) is rigid and a closure force is applied to the moveable plate to bring it into abutting contact with the at least one fixed plate.
The valve closure mechanism according to claim 1 or 2, wherein in an open position of the valve, the moveable plate is displaced from the at least one rigid plate by a distance that permits a closure time of less than 0.1 second.
The valve closure mechanism according to any one of claims 1 to 3, wherein:
the moveable plate is disposed intermediate a pair of outer rigid plates, and

each of the outer rigid plates has perforations that are mutually offset relative to the perforations in the moveable plate;

whereby the valve is closed when the moveable plate (28) abuts either of the outer rigid plates (26, 27).
The valve closure mechanism according to any one of claims 1 to 3, wherein:
a pair of moveable plates are disposed on opposite sides of a rigid plate, and

each of the moveable plates has perforations that are mutually offset relative to the perforations in the rigid plate;

whereby the valve is closed when either of the moveable plates (28) abuts the rigid plate (26).
The valve closure mechanism according to claim 4, wherein:
a first one of the rigid plates (26) is an outer wall of a valve casing (29),

a second one of the rigid plates (27) is disposed within the casing, and

the moveable plate (28) is hingedly attached at one edge thereof to the casing and pivotably displaceable between the plates (26, 27).
The valve closure mechanism according to claim 6, wherein the moveable plate (28) comprises rubber optionally reinforced with a material of higher density than the moveable plate or sheet metal.
The valve closure mechanism according to any one of claims 1 to 5, including a resilient biasing element (32) coupled to one of the or each rigid plates for maintaining the moveable plate in a displaced position from the or each rigid plate in an open position of the valve.
The valve closure mechanism according to any one of claims 1 to 8, wherein the moveable plate (28) is sufficiently flexible to adapt to a contour of the at least one fixed plate (26, 27).
The valve closure mechanism according to claim 8 or 9, when dependent on claim 8, wherein the resilient biasing element includes at least two preloaded springs (32) having different stiffness coefficients.
The valve closure mechanism according to any one of claims 8 to 10 when dependent on claim 8, wherein the resilient biasing element is adjustable in order to set the resilient bias force in an equilibrium position where the intermediate plate (28) abuts neither of the fixed plates (26, 27) thus allowing air to flow through the fixed plate and the fixed plates.
The valve closure mechanism according to any one of claims 1 to 5, wherein:
the moveable plate (28) is a side wall of a first polyhedral or cylindrical element (46) and the fixed plate (26) is a side wall of a second polyhedral or cylindrical element (47) that is coaxial with the first element and mutually aligned therewith and is displaceable relative thereto with the respective side-walls of both elements in abutting contact,

a resilient biasing element (32) is articulated to the plates for maintaining an air gap (60) between the moveable plate and the fixed plate whereby the perforations (30) in the moveable plate and the perforations (31) in the fixed plate allow air passage through the valve, and

force applied to the first element against a bias force of the resilient biasing element (32) moves the moveable plate into abutting contact with one of the fixed plates with no overlap between the perforations (30) in the moveable plate and the perforations (31) in the respective fixed plate thereby preventing air passage through the valve.
The valve closure mechanism according to claim 12, wherein the first and second elements are either (i) relatively linearly displaceable in a direction that is parallel to a common longitudinal axis of the two elements, or (ii) are relatively rotatably displaceable about a common longitudinal axis of the two elements.
The valve closure mechanism according to claim 11 or 12, wherein either (i) the first element (46) is moveable and the second element (47) is fixed or (ii) the first element (46) is fixed and the second element (47) is moveable.
The valve closure mechanism according to any one of claims 1 to 5, wherein:
the fixed plate (26) includes a side wall of a polyhedral or cylindrical outer element (57) and a side wall of a polyhedral or cylindrical inner element (56) that is accommodated within the outer element, said elements being coaxial and mutually aligned and being dimensioned to maintain an air gap between the respective side-walls of both cylinders,

the moveable closure element (28) is at least one flexible diaphragm (58) that is disposed within said air gap and is configured so that in an equilibrium position the or each flexible diaphragm is stretched taut thereby allowing air to pass through the perforations (30) in the diaphragm and perforations (31) in the respective side-walls of the two elements, and

force applied to the diaphragm in either direction moves the diaphragm into abutting contact with the respective side-wall of one of the elements wherein the perforations (30) in the diaphragm do not overlap with the perforations (31) in said side-wall thereby preventing air passage through the valve.
The valve closure mechanism according to any one of claims 1 to 5, wherein:
the fixed plate (26) includes a side wall of a hollow element (57),

the moveable closure element (28) includes first and second flexible diaphragms (58) each disposed on opposite sides of said hollow element and spaced apart from respective first and second surfaces of the side wall, the flexible diaphragms (58) being configured so that in an equilibrium position each flexible diaphragm is stretched taut thereby allowing air to pass through the perforations (30) in the diaphragm and perforations (31) in the side-wall of the hollow element, and

a positive phase of an air blast forces the first diaphragm into abutting contact with the first surface of the side-wall and a negative phase of the air blast forces the second diaphragm into abutting contact with the second surface of the side-wall such that in both phases the perforations (30) in the diaphragms do not overlap with the perforations (31) in the side-wall thereby preventing air passage through the valve.
The valve closure mechanism according to any one of claims 1 to 5, wherein:
the at least one fixed plate (26) includes a side wall of an outer tapering element (57) and a side wall of an inner tapering element (56) that is accommodated within the outer tapering element, said inner and outer tapering elements being coaxial and mutually aligned and being dimensioned to maintain an air gap between the respective side-walls of both tapering elements,

the moveable plate (28) is at least one flexible diaphragm (58) that is closed at one end so at to envelop the inner conical element (56) and is configured so that in an equilibrium position the or each flexible diaphragm is stretched taut thereby allowing air to pass through the perforations (30) in the diaphragm and perforations (31) in the respective side-walls of the two tapering elements, and

force applied to the diaphragm in either direction moves the diaphragm into abutting contact with the respective side-wall of one of the tapering elements wherein the perforations (30) in the diaphragm do not overlap with the perforations (31) in said side-wall thereby preventing air passage through the valve.
The valve closure mechanism according to claim 17, wherein matching perforations (31) in the side-walls of the inner and outer tapering elements (56, 57) are axially misaligned to accommodate lengthening or foreshortening of the diaphragm according to whether it is urged into abutting contact with the inner tapering element (56) or the outer tapering element (57), respectively.
The valve closure mechanism according to any one of claims 1 to 5 or 8 to 18 when dependent on any one of claims 1 to 5, including:
a plurality of elastically deformable elements each having a respective first end that is anchored to a surface of a housing; and

a plurality of inelastic coupling elements each anchored at a respective first end to a second end of at least one of the elastically deformable elements and anchored at a respective second end toward a periphery of the moveable plate;

the inelastic coupling elements being adapted to convert axial movement of the moveable plate caused by an air stream acting on the moveable plate in either direction to a reduced axial movement of the respective elastically deformable element or elements anchored thereto.