Abstract:
A magnetic safety valve for installation through a tank wall incorporates a piston movable within a valve body. The valve is held normally-closed by two opposite-pole magnets, one in the inner end of the piston, and one in the valve body. A vacuum produced by a pump connected to the valve will act upon the outer end of the piston, producing a force tending to move the piston outward. When the vacuum-induced outward force on the piston exceeds the attractive force between the two magnets, it pulls the piston outward and away from the valve body magnet, unseating the inner end of the piston from the valve body, and allowing outward fluid flow through the valve. A second valve seat may be provided for engagement with an outer portion of the piston to prevent uncontrolled fluid flow out of the tank in the event of valve damage.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit, pursuant to 35 U.S.C. 119(e), of U.S. Patent Application No. 61/468,966, filed Mar. 29, 2011, and said earlier application is incorporated herein by reference in its entirety for continuity of disclosure. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates in general to valves for regulating flow from fluid storage tanks, and in particular to valves adapted to close in the event of significant physical damage. 
       BACKGROUND 
       [0003]    A need exists for the prevention of uncontrolled flow of fluids from storage tanks to the environment as a result of piping breaches, equipment failures, or acts of vandalism. This is the case for tanks used to store many different types of fluids, including various chemicals, acids, and fuel oils, to name only a few. One common example is a storage tank containing fuel oil for an oil-fired furnace in an adjacent house or other building. 
         [0004]    To access the contents of such storage tanks, a manual shut-off valve is typically installed at the bottom of the tank, and piping is run from this valve to a pump for feeding the stored fluid to a furnace or other appliance. There have been many instances where piping from such valves has been sheared off either accidentally or deliberately. In recent years, deliberate damage to fuel oil shut-off valves has become a particular problem in some areas due to theft of the high-value copper tubing running from the fuel storage tank to the furnace. In some cases, even the manual shut-off valve itself can be either broken off or damaged to the point that all of the fluid flows out of the tank. Equipment failure, whether caused by a structural break or a seal failure, can also result in uncontrolled flow of fluid out of the tank into the environment. Such incidents can have drastic and severe environmental impacts costing very large amounts of money to rectify or remediate. 
       BRIEF SUMMARY 
       [0005]    The present disclosure teaches a magnetic safety valve which when installed through the wall of a storage tank is disposed entirely inside the tank except for an external valve stem (i.e., valve operator). The valve incorporates a piston that is movable within the valve body, and a preset pressure differential is required across the piston to activate or open the valve. The valve is held in a normally-closed position by two opposite-pole magnets, one incorporated into the inner end of the piston (also referred to as the piston magnet), and one incorporated into the valve body (also referred to as the valve body magnet), and in sufficiently close proximity so as to be magnetically attracted to each other. In preferred embodiments, the position of the valve body magnet relative to the valve body is longitudinally adjustable, such that the magnetic force between the two magnets when the valve is closed (i.e., corresponding to the minimum valve-opening force or cracking pressure) can be adjusted. In alternative embodiments, however, the valve body magnet could be in a fixed position relative to the valve body, such that the valve will have a fixed cracking pressure. 
         [0006]    Upon start-up, the fluid feed pump (or other connected appliance) will produce a vacuum, which acts upon the outer end of the piston, producing a suction force tending to pull the piston outward (i.e., toward the exterior of the tank) away from the valve body magnet. When the vacuum builds up to a value (the “cracking pressure”) at which the outward force on the piston exceeds the magnetic force between the two magnets, it pulls the piston outward and away from the valve body magnet, thus unseating the inner end of the piston from its seat within the valve body, and allowing fluid flow outward through the valve. The movement of the piston reduces the magnetic force attracting the two magnets to each other, but a residual attractive force remains. 
         [0007]    When the pump (or appliance) is shut off, the vacuum drops in the piping between the valve and the pump (or appliance), such that the residual attractive force between the magnets exceeds the outward force (if any) acting on the piston. As a result, the piston is drawn inward toward the valve body magnet, until it engages the rear seat and thus returns the valve to the normally-closed position, stopping the flow of fluid. 
         [0008]    Siphoning is another way that can cause uncontrolled fluid flow out of a tank. If a tank is placed above ground and if the piping from the tank extends down to a surface or appliance at a lower elevation, a liquid column exists. This liquid column in the piping presents an additional potential hazard. If the piping is sheared off at the appliance, the liquid column flows out of the piping, resulting in creation of a vacuum, which will open the valve. This problem is addressed in one embodiment of the disclosed valve by providing a second (or outer) valve seat in the valve body for engagement by the outer end of the piston. Because the outward fluid flow in this scenario is uncontrolled (i.e., much more than what is usually called for by the appliance or pump), this creates a large pressure differential across the rear and front of the piston head. Thus the excess flow pushes against a flat surface on the backside of the piston. This differential pressure and fast liquid flow causes the piston to shuttle forward and engage the second (outer) valve seat. This feature may be alternatively referred to as the valve&#39;s excess flow prevention feature. 
         [0009]    The in-tank magnetic safety valve also incorporates means for mechanically opening the valve, to provide a means of bleeding air from the system when it is initially installed. The mechanical valve-opening means is also used to push the piston rearwards if the excess flow prevention feature of the valve has been activated. After this is done, the valve is returned to the activated position, and a safety locking mechanism for the normally-closed position is engaged. 
         [0010]    The in-tank magnetic safety valve is also designed in such a way that should the valve itself be sheared off flush to the tank structure it will still prevent uncontrolled flow of fluid from the tank. This is due to the valve seat (or seats) and magnets being positioned inside the tank structure. As the magnets hold the valve in a normally-closed position and are protected from damage, the loss of fluid from the tank is prevented. The addition of the excess flow prevention feature of the valve may also be employed in this condition. As the valve is being sheared off, the piston is dragged forward by the departing piece before breaking the front of the piston off. This action engages the outer O-ring seal on the piston against the tapered outer valve seat in the main body, shutting off fluid flow. 
         [0011]    The in-tank magnetic safety valve of the present disclosure accommodates any damage or irregularity between the in-tank magnetic safety valve and the source of vacuum, whether due to a piping break, filter damage, manual valve failure, or other cause. Because the valve requires a vacuum to open, any leakage caused by damage between the valve and the pump will result in a loss of vacuum. This loss of vacuum will cause the valve to revert to its normally-closed position or will prevent it from being activated at all. If a failure occurs at the lowest point in the system and the liquid column drains out, this causes a rapid change in differential pressure across the valve piston. This in turn causes the piston to move outward and contact the outer valve seat in the main body, thus sealing off the flow from the tank. 
         [0012]    The in-tank magnetic safety valve also incorporates means for adjusting the spatial relationship between the magnets. The height of the fluid column will determine the final setting of the spatial relationship of the magnets; i.e., a tall tank will have a higher head pressure than a short tank. One of the magnets in the valve is installed inside an externally threaded holder. The rear of the valve body has internal threads that this magnet holder screws into. By screwing this magnet holder in or out, the spatial distance relationship between the magnets can be changed. By bringing the magnets closer together, magnetic attraction is increased and the valve will be able to hold back higher head pressures (as would be in the case for taller tanks). In the case of a shorter tank, the magnets are adjusted away from each other, thereby reducing magnetic attraction between them. 
         [0013]    If installed in the bottom of a tank, the valve is adjusted until it will hold back a pressure equal to at least 150% of the fluid column acting against the smaller (inner) end of the piston in the valve. This reduces the amount of vacuum build-up that the pump or appliance needs to exert against the larger (outer) side of the piston in order to open the valve. 
         [0014]    The valve can also be installed into the top wall of a tank with a drop tube installed onto the inner end of the valve and extending downward within the tank to a selected distance (for example, but not limited to, about 1.5 inches) above the bottom of the tank. This is done so that the valve, when activated, will not draw debris and or water off the bottom of the tank. The drop tube acts as a stilling well, and any debris drawn up by the vacuum will typically drop out of the fluid column and therefore will not be drawn into the valve. The vacuum set point for a top-mounted valve will typically be set much lower than it would be for a bottom-mount situation, because a top-mounted valve does not have to hold back a fluid head. Typically, a top-mounted valve will be set to open at a vacuum of about 1″ of mercury (Hg). 
         [0015]    In this patent document, the adjectives “inner”, “inward”, “outer”, and “outward”, as used with reference to various components, are to be understood relative to a tank in which a valve in accordance with the disclosure has been or is to be mounted. For example, the inner end of the piston would be disposed further toward the interior of the tank than the outer end of the piston (which would be closer to the tank wall). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Embodiments within the scope of the present disclosure will now be described with reference to the accompanying figures, in which numerical references denote like parts, and in which: 
           [0017]      FIG. 1  is an exploded view of the components of one embodiment of a magnetic safety valve in accordance with the present disclosure. 
           [0018]      FIG. 2  is a cross-section through the valve body magnet holder of the assembled valve shown in  FIG. 6 . 
           [0019]      FIG. 3  is a cross-section through the inner end of the piston of the assembled valve shown in  FIG. 6 . 
           [0020]      FIG. 4  is a cross-section through the main body of the piston of the assembled valve shown in  FIG. 6 . 
           [0021]      FIG. 5  is a view of the outer section of the valve body illustrating the position of the valve stem after actuation to mechanically open the valve. 
           [0022]      FIG. 6  is a cross-section through a magnetic safety valve assembled from the components illustrated in  FIG. 1 . 
           [0023]      FIG. 7A  is a cross-section through a magnetic safety valve as in  FIG. 6 , installed in a bottom wall of a fluid storage tank, showing the valve in its normally-closed position. 
           [0024]      FIG. 7B  is a cross-section through a magnetic safety valve as in  FIG. 7A , showing the valve in an open position resulting from outward movement of the piston in response to a suction force acting on the piston. 
           [0025]      FIG. 7C  is a cross-section through a magnetic safety valve as in  FIG. 7A , showing the valve in an open position resulting from actuation of the valve stem into the position illustrated in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    The accompanying Figures illustrate one non-limiting embodiment of a magnetic safety valve  100  in accordance with the present disclosure. Valve  100  includes a main valve body comprising an outer valve body  10  and an inner valve body  50 . Outer valve body  10  has an outer section  12  and an inner section  15 , with inner section  15  having an externally threaded section  15 A for mounting valve  100  in an opening through the wall of a storage tank. A bore  11  extends through outer valve body  10 , and an outer region of bore  11  is adapted (such as by internal threading  11 A as illustrated) to facilitate connection to piping P leading to a pump or other appliance. A transverse bore  19  is provided through the wall of outer section  12  of outer valve body  10  for receiving a valve actuating assembly  20 . 
         [0027]    In the illustrated embodiment, valve actuating assembly  20  comprises an actuating handle  22  connected to a cylindrical shank  24  rotatably disposable within transverse bore  19 , in conjunction with O-rings  24 A or other suitable seal means. Extending from shank  24  is a valve stem  26  having a relatively flat and generally rectangular cross-section, plus a threaded cylindrical lower end  26 A which is received in a threaded pocket  19 A provided in bore  11  opposite transverse bore  19  as see in  FIG. 6 . Valve actuating assembly  20  preferably incorporates security means to prevent or deter accidental or maliciously intentional actuation of valve  100 . The illustrated embodiment provides such security means by forming handle  22  to include a locking lug  23  which, when valve  100  is in its normally-closed position, will be disposed between a stop member  13  fixed to outer section  12  of outer valve body  10 , and a locking screw  14  removably secured in a receiving hole  14 A in outer section  12  of outer valve body  10 . Preferably, removable locking screw  14  will be configured to require a special tool for removal. As most clearly seen in  FIG. 1 , handle  22  is preferably formed with an abutment  22 A for abutting stop member  13  to prevent over-rotation of valve stem  26  when valve  100  is being manually opened. 
         [0028]    As best seen in  FIG. 1 , an inner portion of bore  16  within inner section  15  of outer valve body  10  has an internally-threaded region  16 A for engagement with mating threads on inner valve body  50  (as will be described later herein). Outboard of threaded region  16 A, bore  16  defines a frustoconical valve seat  17  decreasing in diameter as it progresses outward. 
         [0029]    Valve  100  further includes a piston assembly  30  comprising an inner piston section  35  and a camming member  38  separated by a contiguous central piston section  36 . Inner section  35  of piston assembly  30  is formed with an inner tip segment defining a magnet pocket  34  for receiving a piston magnet  40 A, plus an adjacent frustoconical sealing surface  33  increasing in diameter as it progresses outward. The segment of inner piston section  35  outward of the inner tip segment has an inward-oriented annular surface  35 C surrounding the inner tip segment, plus a generally frustoconical perimeter surface  35 A which decreases in diameter toward central piston section  36 . Grooves  35 B or openings of other suitable shape are formed in perimeter surface  35 A to permit fluid flow. Perimeter surface  35 A is also formed to receive an O-ring  37  or other suitable seal means. 
         [0030]    Central piston section  36  is generally cylindrical in the illustrated embodiment, with one or more longitudinal grooves  36 B being formed in its perimeter surface (to permit outward flow of fluid exiting grooves  35 B in inner section  35  of piston assembly  30 ), with ribs  36 A thus being formed between adjacent grooves  36 B. Central piston section  36  is not restricted to the illustrated configuration, as persons skilled in the art will appreciate that piston sections of different configurations but functionally equivalent to central piston section  36  may be readily devised without special knowledge or skill. 
         [0031]    In the embodiment shown in the Figures, camming member  38  has a generally rectilinear (and typically but not necessarily square) opening  39 , for receiving valve stem  26 . As best appreciated with reference to  FIGS. 7A ,  7 B, and  7 C, the dimensions of valve stem opening  39  in camming member  38  are such that camming member  38  can move longitudinally relative to valve stem  26  (within a range of travel determined by the longitudinal dimension of valve stem opening  39 ) when valve stem  26  is oriented transverse to the direction of flow through the valve (i.e., when in its normal operating position as shown in  FIGS. 1 ,  7 A, and  7 B). However, rotation of valve stem  26  (by corresponding rotation of valve stem handle  22 , as shown in  FIG. 5 ) will cause valve stem  26  to engage camming member  38  so as to cause outward movement of piston assembly  30 , as may be seen in  FIG. 7C . 
         [0032]    Inner valve body  50  is a generally cylindrical sleeve having an externally-threaded outer end  56 , for mating engagement with internally-threaded region  16 A of inner section  15  of outer valve body  10  (after insertion of piston assembly  30  within bore  16  of outer valve body  10 ). Inner valve body  50  has a through-bore  52 , an inner end region  52 A of which is internally threaded, and an outer region of which defines a frustoconical valve seat  54  increasing in diameter as it progresses outward. Through-bore  52  is formed to receive an O-ring  58  or other suitable seal means near the inner end of valve seat  54 . 
         [0033]    Valve  100  also includes an inner magnet holder  60  comprising an outer section  61  defining a magnet pocket  62  for receiving a valve body magnet  40 B (the polarity of which is opposite to that of piston magnet  40 A), plus an externally-threaded inner section  63  having one or more longitudinally-oriented flow channels  64 . The number, size, and configuration of flow channels  64  will be a design choice to suit desired flow rates. Threaded inner section  63 , with valve body magnet disposed within magnet pocket  62 , may be screwed into threaded inner end region  52 A of inner valve body  50 . 
         [0034]    In the illustrated embodiment, flow channels  64  are shown as round holes, which can also be engaged by a suitable tool to rotate inner magnet holder  60  within inner valve body  50  to adjust the longitudinal position of valve body magnet  40 B relative to inner valve body  50 , and thereby to adjust the intensity of the magnetic attractive force acting between piston magnet  40 A and valve body magnet  40 B for a given longitudinal position of piston magnet  40 A relative to inner valve body  50 . This enables valve  100  to accommodate different head pressures in the tank; i.e., inner magnet holder  60  may be screwed closer to piston  30  to account for higher pressures, or screwed away from piston  30  for lower pressures. Persons skilled in the art will readily appreciate, however, that this functionality can alternatively be provided by means other than the above-described threaded engagement of inner magnet holder  60  and inner valve body  50  (for example, ring retainers, press-fits, etc.). 
         [0035]    In the illustrated embodiment, valve  100  includes a filter element  70 , comprising a fluid inlet tube  72  having an inner end  78  and a plurality of orifices  74  to permit fluid flow into inlet tube  72 , with inlet tube  72  being wrapped with a fine-mesh screen  73  to prevent entry of large particulate matter or debris into valve  100 , as this may cause piston  30  to stick in the open or closed position. Filter element  70  is preferably designed to be a low-maintenance, full-flow type of filter. Screen  73  is preferably a 100 mesh screen, which will only allow particle sizes through that will not bind between the piston and bore  16  of outer valve body  10 . Filter element  70  is preferably designed to provide full flow capabilities, even if 90% of screen  73  is plugged. Filter element  70  has an externally-threaded end  76  for engagement with internally-threaded region  52 A of inner valve body  50  (after insertion of inner magnet holder  60  into inner valve body  50 ). In preferred embodiments, threaded end  76  of filter element  70  butts up against inner magnet holder  60  and locks it in place to retain the valve&#39;s magnetic pulling-force settings. However, many different types of filter media and retaining methods may alternatively be used to achieve desired results. 
         [0036]    Filter element  70  will not be required in cases where valve  100  is mounted into the top wall of a fluid storage tank, using a drop tube to draw fluid into the valve from a lower region of the tank. In such installations, the drop tube may be fitted with a suitable threaded fitting for engagement with internally-threaded region  52 A of inner valve body  50  (or the assembly may be adapted for other means of connecting the drop tube). 
         [0037]    In one embodiment of valve  100 , outer valve body  10  has ½″ (12.7 mm) NPT male threading ( 15 A) and female threading ( 11 A), but this is by way of example only. Valve  100  can be smaller or larger as specific conditions may dictate, and can incorporate any type of threading or alternative mounting or attachment system (e.g., flanged connections). 
         [0038]    Outer valve body  10  is preferably constructed from a corrosion-resistant metal. However, alternative materials including but not limited to different metals and plastics may be used without departing from the scope of the present disclosure. 
         [0039]    The operation of valve  100  may be readily understood with reference to  FIGS. 7A ,  7 B, and  7 C, which show valve  100  mounted in a tank wall TW, with piping P connected to outer section  12  of outer valve body  10  by means of a suitable piping connection PC. In  FIG. 7A , valve  100  is in its normally-closed position by virtue of the attractive magnetic force acting between piston magnet  40 A and valve body magnet  40 B, with inner seal surface  33  on piston  30  in sealing engagement with O-ring  58  on frustoconical inner valve seat  54 , thus preventing fluid flow through valve  100 . 
         [0040]    In  FIG. 7B , a vacuum produced by a pump or other appliance connected to piping P acts on the piston  30  to produce an outward-acting force (represented by the “Suction” arrow) which pulls piston  30  outward and out of sealing engagement with inner valve seat  54 , thus allowing fluid flow through valve  100 , with fluid from inside the tank flowing into valve  100  via fluid inlet orifices  74  in filter element  70  (as represented by the curved flow arrows in  FIG. 7B ). Valve  100  is calibrated (such as by adjusting the longitudinal position of valve body magnet  40 B) such that the vacuum force will draw piston  30  outwardly away from inner valve seat  54  so as to allow fluid flow therethrough, but not so far as to bring outer O-ring seal  37  on piston  30  into sealing engagement with outer valve seat  17  in outer valve body  10 . 
         [0041]    When valve  100  is open as shown in  FIG. 7B , fluid entering valve  100  from filter element  70  flows, in sequence, through flow channels  64  in inner section  63  of inner magnet holder  60 , through bore  52  in inner valve body  50 , through flow grooves  35 B in inner section  35  of piston assembly  30 , through flow grooves  35 B in central piston section  36 , and finally outward through bore  16  in inner section  15  of outer valve body  10  into piping P. 
         [0042]    The manual cam-actuated valve actuating assembly  20  provides means for mechanically opening valve  100  and allowing liquid to flow out of the tank. Locking screw  14  is removed from hole  14 A in outer valve body  10 , and valve stem  26  is rotated 90° counter-clockwise until abutment  22 A on valve stem handle  22  comes to rest against stop member  13 . As valve stem  26  is rotated, it engages camming member  38  so as to urge piston  30  outward as shown in  FIG. 7C , disengaging seal surface  33  from O-ring seal  58 , and thus allowing fluid flow through valve  100 . 
         [0043]    Valve actuating assembly  20  also provides means for reopening valve  100  when the excess flow prevention feature of the valve has been activated (i.e., when O-ring seal  37  on piston  30  has been forced by fluid pressure into sealing contact with valve seat  17  in outer valve body  10 , thus preventing unrestricted fluid flow out of the tank). In that configuration of valve  100 , valve stem  26  will be closely adjacent to the inner side of opening  39  of camming member  38 , such that rotation of valve stem  26  by 90 degrees (as in  FIGS. 5 and 7C ) will push piston  30  inward and away from valve seat  17 . This allows fluid to flow and brings magnets  40 A and  40 B back into closer proximity with each other. Rotating valve stem  26  back to the position shown in  FIG. 1  then returns valve  100  to its magnetically normally-closed position as shown in  FIG. 7A  (i.e., with sealing surface  33  on the inner end of piston  30  in sealing engagement with O-ring  58  on inner valve body  50  and thus preventing fluid flow). 
         [0044]    Opening valve  100  by means of valve actuating assembly  20  causes fluid to flow into the system and allows air to be bled out of the system. When all air is bled out of the system, valve stem handle  22  is rotated clockwise until locking lug  23  engages stop member  13 . This allows piston  30  to be pulled inward by the magnetic force attracting piston magnet  40 A to valve body magnet  40 B, until sealing surface  33  engages O-ring  58  on valve seat  54 . Locking screw  14  is then re-installed to ensure that valve  100  cannot be inadvertently opened. 
         [0045]    It is to be understood that the present disclosure is not limited to valves incorporating valve actuating assemblies specifically as illustrated and described herein. Persons skilled in the art will appreciate that alternative valve actuating assemblies providing functionality substantially equivalent to that of the illustrated valve actuating assembly can be readily devised in accordance with known technology, and valves incorporating such alternative valve actuating assemblies are intended to be within the scope of the present disclosure. 
         [0046]    The various O-rings or other seals incorporated into valve  100  may be made of a suitable material selected having regard to the nature of the liquid in the tank. In certain applications, these seals may be provided in the form of Viton® fluoroelastomer O-rings. 
         [0047]    Piston  30  may be made from acetal homopolymer, a chemical- and oil-resistant plastic (commonly known commercially as Delrin®) that provides low friction and good impact resistance. However, persons skilled in the art will appreciate that piston  30  could alternatively be made from various other plastics or metals without departing from the present disclosure, with the selected material being dependent on the particular liquids to be contained. 
         [0048]    The frustonically-tapered outer surface  35 A on piston  30  is larger than tapered sealing surface  33  on the innermost end of piston  30 , such that a smaller surface area is presented to the head pressure in the tank. The correspondingly larger end with tapered surface  35 A (and correspondingly larger O-ring  37 , relative to O-ring  58 ) is situated towards the vacuum or outer part of valve  100 . The smaller inner end of piston  30  provides a small surface area for the head pressure from the liquid in the tank to react against. The larger outer piston surface  35 A with O-ring  37  provides a comparatively large surface area for the vacuum from the pump to react against. This difference between the inner and outer piston areas reduces the amount of vacuum required to move piston  30  forward and to open valve  100  to fluid flow. This same difference in sizes assures that piston  30  will shuttle outward and that O-ring  37  will sealingly engage tapered surface  17  in the event of valve damage that might otherwise result in uncontrolled fluid flow out of the tank. 
         [0049]    A shear point or weakened area is preferably provided at the juncture of central piston section  36  and camming member  38 . This is provided so that if outer valve body  10  is sheared off at the tank wall TW, an outer portion of piston  30  will also shear off, but will leave the main portion of piston  30  intact. Thus valve  100  will still be able to magnetically close and or shuttle forward to stop the flow of liquid out of the tank. 
         [0050]    Piston magnet  40 A preferably comprises a plated rare earth (e.g., neodymium) magnet, but alternatively may comprise any other type of magnet providing suitable functionality. In the illustrated embodiment, piston magnet  40 A is press fit into the magnet pocket  34  with the South pole of piston magnet  40 A facing inward (toward inner valve body  50 ). It should be noted, however, that the present disclosure is not limited to the use of magnets to move piston  30 ; other known means such as mechanical springs may be used in lieu of magnets in alternative embodiments. 
         [0051]    Inner magnet holder  60  is preferably (but not necessarily) made from acetal homopolymer (Delrin®). 
         [0052]    Valve body magnet  40 B preferably comprises a plated rare earth (e.g., neodymium) magnet, but alternatively may comprise any other type of magnet providing suitable functionality. However, this also will not limit the scope of the present disclosure, as a holder can be used in inner valve body  50  to vary the amount of force that a mechanical spring can exert against piston  30  to push it inward against valve seat  54  and the associated O-ring  58 . Valve body magnet  40 B is shown press-fit into the magnet pocket  62  of inner magnet holder  60  with the North pole of valve body magnet  40 B facing outward toward piston  30 . Thus the North pole of valve body magnet  40 B attracts the South pole of piston magnet  40 A. (The polarity of the magnets in the preceding discussion is of course arbitrary; in alternative arrangements, the South pole of valve body magnet  40 B could attract the North pole of piston magnet  40 A.) 
         [0053]    It will be appreciated by persons skilled in the art that various modifications and alternative embodiments of magnetic safety valves may be devised without departing from the scope and teachings of the present disclosure, including modifications that may use equivalent structures or materials hereafter conceived or developed. It is to be especially understood that the disclosure is not intended to be limited to any particular described or illustrated embodiment, and that the substitution of a variant of a described or illustrated element or feature, without any substantial resultant change in functionality, will not constitute a departure from the scope of the disclosure. It is also to be appreciated that the different teachings of the embodiments described and illustrated herein may be employed separately or in any suitable combination to produce desired results. 
         [0054]    In this document, any form of the word “comprise” is to be understood in its non-limiting sense to mean that any item following such word is included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one such element. Any use of any form of the terms “connect”, “engage”, “couple”, “attach”, or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the subject elements, and may also include indirect interaction between the elements such as through secondary or intermediary structure. Relational terms such as “parallel”, “perpendicular”, “flat”, “coincident”, “intersecting”, and “equidistant” are not intended to denote or require absolute mathematical or geometrical precision. Accordingly, such terms are to be understood as denoting or requiring substantial precision only (e.g., “substantially parallel”) unless the context clearly requires otherwise.