Abstract:
A spring capture assembly is provided for securing a compression spring of a spring-biased mechanism, such as a spring-biased pressure relief valve, to permit disassembly of the mechanism without risk of damage or injury associate with rapid resiling of the spring from a compressed state. The assembly includes a tool, a housing having an opening for admitting passage of the tool and capturing the spring at one end, a spring retainer, and a compression spring mounted within the housing and captured at one end by said housing and toward an opposite end by the spring retainer. The tool is adapted for mating with the spring retainer and the housing to compress the spring therebetween. The spring capture assembly may be incorporated into a pressure relief valve for venting pressure and/or vacuum from a pressure vessel. Provided also is a method for disassembling a spring-biased mechanism including a spring capture assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 13/155,846, filed Jun. 8, 2011, the entire contents of which being fully incorporated herein by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates generally to a spring-capturing assembly in a spring-biased mechanism, such as a valve including a spring-biased poppet, and more particularly to a pressure relief valve for a pressure vessel for containing a pressurized fluid, such as an over-the-road tank trailer, that includes such a spring-capture assembly, which allows for safe and easy disassembly of the valve in the field for cleaning or other purposes. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    As known to those skilled in the art, an over-the-road tank trailer is a mobile pressure vessel, typically pulled behind a truck or tractor, for containing a fluid during transportation from one point to another. Such contained fluids can be pressurized fluids or unpressurized fluids, however, the un-pressurized fluids may become pressurized due to heating of the tank by the sun which in turn heats the fluid contained in the tank causing it to be pressurized. Also, during an emergency situation, such as upon the over-the-road tank trailer becoming heated in a fire, the fluid contained in the tank can become heated and pressurized. 
         [0004]    A common prior art pressure relief vent for an over-the-road tank trailer includes a housing mounted on the top of the tank trailer including a valve seat that is normally engaged by a poppet forced into sealing engagement with the valve seat by a compression spring mounted in the housing and providing downwardly-acting force on the poppet. The underside of the poppet is exposed to the pressurized fluid in the tank and the pressurized fluid in the tank provides an upwardly acting force on the underside of the poppet. As is still further known to those skilled in the art, the compression spring is preloaded such that the downwardly acting force provided by the spring on the poppet is sufficient to maintain the poppet in sealing engagement with the valve seat up to a set pressure in opposition to any upwardly acting force applied to the underside of the poppet by the pressurized fluid. As is still further known, the compression spring must be chosen such that upon the fluid in the over-the-road tank trailer becoming over-pressurized to the flow pressure the compression spring will compress sufficiently upwardly to permit the poppet to be lifted up off of the valve seat by the force created by the over-pressurized fluid a distance sufficient to provide a space or opening, typically an annular space or opening, between the valve seat and the poppet sufficiently large to permit the over-pressurized fluid to flow therethrough at a desired flow rate. 
         [0005]    As is still further known, compression springs are characterized by what is known as a spring constant, which reflects the distance the spring will compress upon the application thereto of a given force. Accordingly, as is still further known, the spring constant for the compression spring of a pressure relief vent is the difference between the flow pressure and the set pressure in pounds per square inch times the area of the poppet in square inches, divided by the distance in inches between the valve seat and the poppet required to provide the above-noted flow rate. A general characteristic of compression springs, as is known, is that the higher the spring constant the stiffer the spring. 
         [0006]    As is still further known, applicable regulations require that the pressure relief vent for an over-the-road tank trailer be mounted on the tank trailer as close as possible to the top center of the tank trailer so that the pressure relief vent is exposed to the vapor space inside the tank trailer, with such vapor space, as is known, being the space between the fluid contained in the tank trailer and the top of the tank trailer. As is further known the height of the pressure relief vent is determined largely by the height or length of the compression spring. 
         [0007]    Since the pressure relief vent must be mounted on the top center of the over the road tank trailer, it is desirable that the height of the pressure relief vent be as small as possible to permit the over-the-road tank trailer with the pressure relief vent mounted on top to safely pass under overhead structures such as bridges and the like with adequate clearance while maintaining the required flow rate. This means that the length or height of the compression spring of the pressure relief vent must be as small as possible and yet the compression spring, as noted above, must be sufficiently stiff to maintain the poppet in sealing engagement with the valve seat at the set pressure and which spring must be sufficiently un-stiff that it will compress sufficiently at the flow pressure to permit the poppet to be moved away from the valve seat a distance sufficient to provide the above-noted flow rate. Obviously, as known to those skilled in the art, these two spring requirements are in conflict with each other because, generally speaking and as is further known, the higher or longer the compression spring the lower the spring constant and the shorter the spring the higher the spring constant. Accordingly, to obtain a relatively shorter height valve, stiffer springs are generally desired. 
         [0008]    A certain prior art valve is disclosed is commonly assigned U.S. Pat. No. 5,203,372, the entire disclosure of which is hereby incorporated herein by reference. This valve is adapted to include a poppet having a predetermined shape for forming an escaping stream of over-pressurized fluid into a jet stream that provides a reaction force that acts against the underside of the poppet to assist the over-pressurized fluid in lifting the poppet off of the valve seat upon occurrence of over-pressurization. This increased upward force in turn allows for use of a relatively stiffer, and shorter, spring, and advantageously provides a valve with a relatively lower height. 
         [0009]    Because of the relatively high degree stiffness of the springs in such valves, a mechanical press is typically required to compress the spring during routine cleaning of the valve, namely the surfaces of the poppet in communication with the pressurized fluid, e.g, between hauls of different pressurized fluids. Thus, it is typically necessary to remove the valve from the tank, climb down from the truck, and transport the valve to a hydraulic or other mechanized press (which is heavy ground-mounted equipment). This is inconvenient and time-consuming. Further, because of the stiffness of the spring, it would be impractical to provide a valve that could be disassembled manually, without the use of a mechanized press, because as soon as the housing would be disassembled, the stiff spring would rapidly decompress and tend to turn the decoupled housing parts into projectiles, which could result in damage to the valve or other equipment, and poses a risk of serious harm to service technicians. It is noted that a similar concern exists in spring-biased mechanisms other than valves that also require use of relatively stiff springs, and where manual disassembly is desirable. 
         [0010]    What is needed is a safety assembly adaptable to a broad range of spring-biased mechanisms that would allow for safe disassembly of the spring-biased mechanism without safety risks associated with decompression of the spring during disassembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention will now be described by way of example with reference to the following drawings in which: 
           [0012]      FIG. 1  is a perspective view of a pressure-relief valve in accordance with an exemplary embodiment of the present invention; 
           [0013]      FIG. 2  is a cross-sectional view of the pressure relief valve of  FIG. 1 , taken along line A-A of  FIG. 1 ; 
           [0014]      FIG. 3  is an exploded view of the pressure relief valve of  FIG. 1 ; 
           [0015]      FIGS. 4A and 4B  are elevational and cross-sectional views of the valve of  FIG. 1 , shown mated with a spring compression tool, and before compression of the spring; 
           [0016]      FIGS. 5A and 5B  are elevational and cross-sectional views of the valve of  FIG. 1 , shown with a nut advanced against a housing in position to compress the spring; 
           [0017]      FIGS. 6A and 6B  are elevational and cross-sectional views of the valve of  FIG. 1 , shown mated with a spring compression tool, and after compression of the spring, and showing the frame and spring assembly removed from the tank mount; 
           [0018]      FIGS. 7A and 7B  are cross-sectional views of the valve of  FIG. 1  shown mated with an alternative embodiment of a spring compression tool; 
           [0019]      FIG. 8  is a cross-sectional view of an alternative embodiment of the valve of  FIG. 1 , shown with a spring retainer having an externally-threaded stud, mated with a tool having complementary internal threads, and a fixed shoulder; 
           [0020]      FIG. 9  is a cross-sectional view of an alternative embodiment of the valve of  FIG. 1 , shown with a spring retainer having an externally-threaded stud, mated with a tool having complementary internal threads, and a tool supporting a threaded nut; 
           [0021]      FIG. 10  is an exploded view of a pressure-relief and vacuum venting valve in accordance with an alternative exemplary embodiment of the present invention; 
           [0022]      FIGS. 11A and 11B  are elevational and cross-sectional views of the valve of  FIG. 10 , shown mated with a spring compression tool, and before compression of the spring; 
           [0023]      FIGS. 12A and 12B  are elevational and cross-sectional views of the valve of  FIG. 10 , shown with a nut advanced against a housing in position to compress the spring; 
           [0024]      FIGS. 13A and 13B  are elevational and cross-sectional views of the valve of  FIG. 10 , shown mated with a spring compression tool, and after compression of the spring, and showing the frame and spring assembly removed from the tank mount; 
           [0025]      FIG. 14  is a cross-sectional view of an alternative embodiment of the valve of  FIG. 10 , shown with a spring retainer having an externally-threaded stud, mated with a tool having complementary internal threads, and a fixed shoulder; and 
           [0026]      FIG. 15  is a cross-sectional view of an alternative embodiment of the valve of  FIG. 10 , shown with a spring retainer having an externally-threaded stud, mated with a tool having complementary internal threads, and a tool supporting a threaded nut. 
       
    
    
     SUMMARY 
       [0027]    The present invention provides a safety assembly in the form of a spring-capture assembly, a pressure relief valve including a spring-capture assembly, and a method for disassembling a spring-biased mechanism, such a pressure relief valve. The spring capture assembly permits disassembly of the spring-biased mechanism, e.g., for cleaning or maintenance purposes, without risk of damage or injury associated with rapid resiling of the spring from a compressed state. Accordingly, a relatively stiffer spring may be used without fear of injury, which advantageously allows for a shorter height in over-the-road tank trailer valves, and permits manual valve disassembly in the field by a service technician atop a tank trailer, using no more than common hand tools. 
         [0028]    A spring capture assembly for a spring-biased mechanism includes a tool having an elongated member and a distal end, and a housing having an opening for admitting passage of the tool. The assembly further include a spring retainer configured to mechanically interlock with the tool, e.g. via complementary threads. A compression spring is mounted within the housing and captured at one end by the housing and toward an opposite end by the spring retainer. The tool may include a fixed shoulder, such that rotation of the tool relative to the spring retainer, with the tool mated to the spring retainer and the shoulder abutting the housing, advances the spring retainer onto the tool and acts to compress the compression spring between the spring retainer and the housing. Alternatively, the tool may include a nut supported on threads instead of a shoulder. In such an embodiment, rotation of the nut relative to the elongated member, with the tool mated to the spring retainer and the nut abutting the housing, withdraws the tool relative to the housing and acts to compress the compression spring between the spring retainer and the housing. 
         [0029]    Provided also is a pressure relief valve for venting a pressure vessel containing a pressurized fluid. The valve includes a mount having a lower portion adapted for mounting to the pressure vessel, a passageway for venting fluid therethrough, and an upper portion defining a first mating structure circumscribing the passageway. The valve further includes a valve seat supported on the mount about the passageway, and a poppet matable with the valve seat to occlude the passageway and disrupt a flow of fluid therethrough. Further still, the valve includes a housing having a first portion defining a second mating structure complementary to the first mating structure, and an opening for admitting passage of a tool, and a spring retainer having a mating structure mechanically interlockable with the tool, and a flange. The valve further includes a compression spring mounted within the housing and captured at one end by the housing and at an opposite end by the flange of the spring retainer. The compression spring biases the poppet from an open position spaced from the valve seat toward a closed position in abutting relationship with the valve seat. The tool is an elongated member having a distal portion dimensioned to pass through the opening of the housing. The tool has a distal portion having a distal end matable with the mating structure of the spring retainer to compress the compression spring between the spring retainer and the housing. 
         [0030]    Also provided is a method for disassembling a spring-biased mechanism having a spring capture assembly for capturing a compression spring of the mechanism. The method includes manually grasping an elongated tool having a distal end, inserting the distal end of the tool through a housing of the spring capture assembly, mating the distal end of the tool with a spring retainer of the spring capture assembly, manipulating the tool to draw up the spring retainer and compress the compression spring between the spring retainer and the housing; and disassembling the spring-biased mechanism. 
         [0031]    The spring-capture assembly allows for safe disassembly of a valve (or other spring-biased mechanism) without the safety risks associated with decompression of the spring during disassembly. 
       DETAILED DESCRIPTION 
       [0032]    The present invention provides a safety assembly in the form of a spring-capture assembly. The spring-capture assembly is adaptable to a broad range of spring-biased mechanisms, including a pressure relief valve. The spring-capture assembly allows for safe disassembly of the valve (or other spring-biased mechanism) without the safety risks associated with decompression of the spring during disassembly. As applied to a pressure relief valve, the spring-capture assembly advantageously permits a multi-piece valve construction that can be manually disassembled safely for poppet/valve cleaning purposes in the field, namely, by a service technician on the top of an over-the-road tank trailer, using common hand tools, without the need for a mechanized press or other heavy ground-based equipment. 
         [0033]    Referring now to  FIGS. 1-3 , an exemplary pressure-relief valve including an exemplary spring-capture assembly is shown. This exemplary valve is useful in venting over-pressurized pressure vessels such as, for example, an over-the-road tank trailer. As shown in  FIG. 1 , the valve  100  is of a multi-piece, readily-disassemblable construction including an upper housing  10  and a lower mount  60 . 
         [0034]    The mount  60  may have various forms, and its lower portion  62  may be substantially conventional in nature. By way of example, the lower portion  62  of the mount  60  may be adapted for sealably mounting to a pressure vessel, such as an over-the-road tank trailer, by welding or mechanical fasteners, and defines a generally centrally-located passageway  64  for venting fluid therethrough. Of particular note, and in accordance with the present invention, the mount  60  includes an upper portion  66  defining a first mating structure  68  that generally circumscribes (or surrounds) the passageway  64 . The first mating structure  68  may have any suitable configuration provided that it is capable of serving to mate with and readily releasably secure thereto, e.g. through the use of no more than common hand tools and without a need for a mechanized press or other ground-based equipment, the housing  10 . As best shown in  FIGS. 2 and 3 , in this exemplary embodiment, the first mating structure  68  comprises external threads  69 . By way of example, the first mating structure could alternatively include internal threads. Though other mating structures could be used, complementary threads are preferred for mating the mount and housing  10 , because the threads allow for mating with relatively more or relatively less compression of the spring, which adjusts the set pressure (at which spring force is overcome to cause venting). 
         [0035]    A valve seat  80  is supported on upper portion  66  of the mount  60  in position so as to circumscribe, and not to occlude, the passageway  64 , in position to mate with a poppet. By way of example, the valve seat  80  may be provided as a suitable elastomeric O-ring extending around the passageway  64 , as shown in  FIGS. 2 and 3 . 
         [0036]    The housing  10  has a lower portion  12  defining a second mating structure  14  complementary to the first mating structure  68  of the mount  60 . The second mating structure  14  may have any suitable form, provided that it provides a secure, but readily releasable, mounting to the mount  60  that resists axial separation of the housing  10  and mount  60 . In this exemplary embodiment, the second mating structure comprises internal threads  16  complementary to the external threads  69  of the mount  60 . 
         [0037]    Further, the housing  10  defines an opening  18  for admitting passage of a tool, for purposes discussed below. The opening  18  is located generally toward the center (“centrally located”) of the housing, or toward the center of a spring, as discussed below, and as shown in  FIGS. 2 and 3 . Further still, the housing  10  is provided with openings  20  for venting pressurized fluid (such as air, gas, or vapor, collectively referred to herein as “fluid”). 
         [0038]    In this embodiment, the valve  100  further includes a rain shield  30 , and a hole plug  34  dimensioned to fit snugly yet removably within the opening  18  of the housing  10  so as to substantially occlude the opening, and thus thwart entry of rainwater or other contaminants. 
         [0039]    The valve  100  further includes a movable poppet  40  matable with the valve seat  80  to occlude the passageway  64  and disrupt a flow of fluid therethrough. The poppet  40  includes a central portion  42  for abutting the valve seat and selectively occluding the passageway  64 . Though optional, in this example, the poppet  40  includes a stick-resistant layer on its underside, to avoid bonding with the valve seat  80 . In this example, the poppet includes a formed body  44  constructed of stainless steel, and the stick-resistant layer is provided as a unitary body  48  of PTFE liner machined to conform to the poppet. 
         [0040]    The valve  100  further includes a compression spring  50  mounted within the housing  10 . The compression spring  50  is positioned within the housing such that its first end  52  abuts and/or is braced against the housing  10 , and its second (opposite) end  54  is braced against the poppet  40 . When assembled, the compression spring  50  is preloaded, such that it exerts downwardly acting force, indicated by arrow Z in  FIG. 2 , against the poppet  40 , to urge the poppet  40  into sealing engagement with the valve seat  80  on the mount. 
         [0041]    In accordance with the present invention, the valve  100  further includes a spring retainer  70  configured to be matable with the tool to compress the spring  50  within the housing  50 , so as to relieve downward force otherwise exerted by the spring  50  on the poppet  40 . In the exemplary embodiment shown, the spring retainer  70  is configured with an opening  72  having internal threads  74  for mating with the tool. In an alternative embodiment, the spring retainer may have other structures, such as a post bearing external threads for mating with the tool, or a hook, loop, latch or other structure for mating with the tool to permit upward (as shown in the figures) pulling on the spring retainer  70  to compress the spring  50 . In this exemplary embodiment, the spring retainer includes a generally radially-extending flange  76  dimensioned to capture the second end  54  of the spring  50 , and the spring retainer is positioned between the spring and the poppet  40 . Alternatively, the spring retainer  70  could have other structure, grasp the spring other than at its end, and be positioned to capture the spring at a point other than between the compression spring and the poppet. 
         [0042]    Thus, the spring  50  is captured between the spring retainer  70  and the housing  10 , and in a normal condition, the spring  50  biases the poppet  40  from an open position spaced from the valve seat  80  (to permit venting of fluid via the passageway  64 ) toward a closed position in abutting relationship with the valve seat  80  (to thwart venting of fluid via the passageway  64 ). 
         [0043]    It will be understood that the compression spring  50  is chosen to have a stiffness sufficient to cause the spring  50  to exert sufficient downwardly-acting force to maintain the poppet  40  in sealing engagement with the valve seat  80  up to a set pressure of the valve  100 . 
         [0044]    In use, the exemplary valve shown in  FIGS. 1-3  is operable to effectively seal a pressure vessel until fluid contained in the pressure vessel has become over-pressurized sufficiently in excess of the set pressure of the valve  100  to produce an upwardly-acting force that acts against the central underside portion of the poppet  40  (upon liner  48 ) with sufficient force to overcome the downwardly-acting force applied against the poppet  40  by the compression spring  50  and thus to lift the poppet  40  up off of the valve seat  80 . Upon the poppet  40  being lifted up off of the valve seat, the over-pressurized fluid escapes or is vented outwardly through the openings  20  in the housing  10 . 
         [0045]    Further, in accordance with the present invention, the valve may be easily and safely disassembled, e.g., by a field technician atop an over-the-road tank trailer using simple, lightweight common hand tools such as a soft mallet, screwdriver and/or a combination or other wrench, by virtue of the valve&#39;s inclusion of a spring capture assembly  90  in accordance with the present invention, as is illustrated with reference to  FIGS. 4A-7B . It should be noted, after the tool is used to capture the spring and relieve spring biasing on the poppet, the associated spring tension placed by the spring on the threads of the mount and housing is relieved, and thus the mount and housing are loosely coupled and may be easily decoupled by hand. Such disassembly is required periodically for service and/or cleaning, e.g., between fillings of the pressure vessel with different fluids. 
         [0046]    Referring now to  FIGS. 3-7B , it is illustrated that the exemplary spring capture assembly  90  includes at least the housing  10 , spring  50 , spring retainer  70 , and a tool  80  configured to mate and cooperate with the spring retainer  70  to compress the spring  50  within the housing  10 . 
         [0047]    The tool  80  is an elongated member having an elongated body  82  having a distal portion  84  dimensioned to pass through the opening  18  of the housing  10 . The distal portion  84  has a distal end  86  matable with the spring retainer  70 . The spring retainer and tool may include any suitable complementary structure for mating purposes, provided that the spring retainer and tool are mechanically interlockable to resist substantial relative motion away from each other in an axial direction of the tool, as the tool is used to draw up the spring retainer and compress the spring between the spring retainer and the housing. Preferably, the tool  80  further includes a handle  89  extending generally transversely to the elongated body  82 , and thus such a tool  80  is generally L-shaped ( FIGS. 4A-6B ) or T-shaped ( FIGS. 7A-7B ). 
         [0048]    In the exemplary embodiment shown in  FIGS. 1-7B , the centrally-located opening  72  of the spring retainer  70  is provided with internal threads  74 . Accordingly, the distal end  86  of the tool  80  comprises external threads  88  complementary thereto. In the embodiment shown in  FIGS. 4A-6B , the proximal end  90  of the tool  80  also comprises external threads  88  supporting a complimentarily threaded nut  92 . 
         [0049]    In an alternative embodiment, the tool  80  does not include such external threads on its proximal end, or a nut, but instead includes a radially-extending shoulder  94  for abutting the housing that acts as a stop, as shown in  FIGS. 7A and 7B . Unlike the nut, the shoulder  94  is fixed relative to the body  82 , such that the tool  80  can not be advanced any further into the housing  10  after the shoulder abuts the housing  10 . 
         [0050]    In use, the tool  80  is operable is operable to mate with the spring retainer  70  and draw up the spring retainer  70  to compress the compression spring  50  between the spring retainer  70  and the housing  10 . By way of example, the embodiment of the tool  80  shown in  FIGS. 4A -6B  may be used as follows to disassemble a valve having a spring capture assembly  90  for capturing a compression spring biasing a poppet of the valve. First, the hole plug  34  is removed from the opening  18  of the housing  10 , if necessary, to clear the opening. Then, the elongated tool  80  having a distal end  86  is manually grasped. Next, the method involves inserting the distal end  86  of the tool  80  through the housing  10  of the spring capture assembly  90 . Next, the method involves mating the distal end  86  of the tool  80  with the spring retainer  70  of the spring capture assembly  90 , e.g. by threading together the spring retainer  70  and tool  80 , as shown in  FIGS. 4A and 4B . Further, the method involves manipulating the tool  80  to draw up the spring retainer  70  and compress the compression spring  60  between the spring retainer  70  and the housing  10 . 
         [0051]    Subsequently, the housing  10  may be disengaged from a pressure vessel, as shown in  FIGS. 6A and 6B . By way of example, this may involve rotating the housing  10  relative to a mount  60  of the pressure vessel to decouple complementary mating structures on the mount and on the housing. This may be accomplished using a crescent or other wrench to loosen the housing from the mount, and/or by using a soft mallet and screwdriver to tap against lugs on the housing. It will be noted that because the spring is securely captured by the spring capture assembly  90 , opposed axial forces on the mating structures of the housing  10  and the mount  60  are relieved, eliminating binding of the mating structures that would make decoupling difficult. Further, the spring will not resile rapidly and cause the housing  10  to “pop off” from the mount  60 , thus avoiding injury to personnel during disassembly. Further still, it will be noted that after the housing/spring capture assembly  90  has been removed from the mount  60 , the poppet  40  is retained loosely on the mount  60 , simply resting on the valve seat (assuming that the tank trailer has already been depressurized), as shown in  FIG. 6B . Accordingly, a technician may simply manually lift the poppet  40  from the valve seat  80  and clean its underside, if necessary, and/or replace the valve seat  80 , if necessary. Notably, this can be accomplished using only common hand tools, and while a technician is atop a tank trailer, without the need for ground-based presses or other heavy equipment. 
         [0052]    For embodiments in which the spring retainer  70  includes internal threads  74  and the distal end  86  of the tool  80  includes external threads, mating the distal end of the tool with the spring retainer comprises threading the tool  80  through the spring retainer  70 , as shown in  FIGS. 4A and 4B . 
         [0053]    In an embodiment in which the tool  80  includes a shoulder  94  for abutting the housing  10 , manipulating the tool involves threading the tool  80  through the spring retainer  70  until the shoulder  94  abuts the housing  10  (see  FIG. 7A ), and then continuing to thread the tool through the housing while the shoulder abuts the housing (see  FIG. 7B ). The continued threading causes the spring retainer to be drawn upwardly on the threads of the tool, and the compression spring  50  to be compressed as a result, as best shown in  FIG. 7B . Thus, rotation of the tool relative to the spring retainer with the tool mated to the spring retainer and the shoulder abutting the housing advances the spring retainer onto the tool and acts to compress the compression spring between the spring retainer and the housing. 
         [0054]    In an alternative embodiment in which the tool does not include a shoulder but instead includes external threads on its proximal end  89  that support a complimentarily threaded nut (see  FIGS. 4A-6B ), manipulating the tool involves threading the tool  80  into the spring retainer  70  (see  FIGS. 4A and 4B ) and then advancing the nut  92  on the tool until the nut  92  abuts the housing  10  (see  FIG. 5A and 5B ) and draws up the spring retainer  70  to compress the compression spring (see  FIGS. 6A and 6B ). The advancing of the nut  92  causes the elongated member  82  to be drawn upwardly relative to the housing (while the spring retainer remains in a substantially constant position on the member), and the compression spring  50  to be compressed as a result. Thus, rotation of the nut relative to the elongated member with the tool mated to the spring retainer and the nut abutting the housing withdraws the tool relative to the housing and acts to compress the compression spring between the spring retainer and the housing. 
         [0055]    In another alternative embodiment, the spring retainer  70  comprises external threads  71  on a stem  73  integral with the spring retainer  70 , and the distal end of the tool  80  comprises complementary internal threads  83 . In one such embodiment, the tool  80  further comprises a shoulder  94  for abutting the housing (similar to that shown in  FIGS. 7A and 7B ), as best shown in  FIG. 8 . In such an embodiment, manipulating the tool  80  involves threading the tool  80  onto the stem  73  of the spring retainer  70  while the shoulder abuts the housing  10 , as best shown in  FIG. 8 . 
         [0056]    In yet another alternative embodiment, the spring retainer  70  similarly comprises external threads  71  on a stem  73  integral with the spring retainer  70 , and the distal end of the tool  80  comprises internal threads complementary thereto  83 . However, in this alternative embodiment, a proximal end of the tool comprises external threads supporting a complimentarily threaded nut  92  for abutting the housing (similar to that shown in  FIGS. 4A and 6B ), as best shown in  FIG. 9 . In such an embodiment, manipulating the tool involves threading the tool onto the spring retainer and advancing the nut on the tool until the nut abuts the housing and draws up the spring retainer to compress the compression spring. 
         [0057]    After cleaning/service, the poppets may be replaced on the valve seat  80 /mount  60 , the housing  10  may be secured to the mount  60  (e.g., by threading them together), and then the tool  80  can be rotated or otherwise decoupled from the spring retainer  70  to restore spring-bias to the valve/mechanism, and to return the valve/mechanism to service. The tool  80  may then be withdrawn from the housing  10  and the hole plug  34  may be replaced in the housing&#39;s opening  18 . 
         [0058]      FIGS. 10-13B  show an alternative exemplary embodiment of a valve in accordance with the present invention. This embodiment is similar to that shown in  FIGS. 1-7B , but is configured as both a pressure relief and vacuum venting valve. Many of the components are identical or virtually identical to those shown in  FIGS. 1-7B . However, as best shown in  FIGS. 10 and 11B , in this embodiment, the poppet  40   a  is modified to define at least one vent opening  110  in communication with the passageway, and the valve further includes a second poppet  120  dimensioned to close the vent opening(s)  110  in the poppet  40   a,  a stem  122  extending from the second poppet  120  and passing though a support opening  112  in the first poppet  40   a,  a stop  124  mounted on a distal end  126  of the stem  120 ; and a spring  130  compressed between the first poppet  40   a  and the stop  124 , the spring biasing the second poppet  120  from an open position spaced from the first poppet  40   a  toward a closed position in abutting relationship with the first poppet  40   a.  The second poppet may carry a suitable valve seat  140 , such as a suitable elastomeric O-ring, to facilitate sealing of the second poppet  120  with the first poppet  40   a.    
         [0059]    Accordingly, in the event that the pressure within the pressure vessel is sufficiently lower than the ambient pressure outside the pressure vessel, the pressure differential will cause the second poppet  120  to move (against the bias of spring  130 ) from the closed position toward the open position to admit ambient air to enter the pressure vessel through passageway  64  via the opening  110  in the first poppet  40   a.  When the pressure differential has been sufficiently reduced, the spring  130  will urge the second poppet  120  into the closed position, thereby thwarting the continued flow of fluid via the passageway  64 . 
         [0060]    Referring now to  FIGS. 11A-13B , it is illustrated that the exemplary alternative spring capture assembly  90  includes at least the housing  10 , spring  50 , a spring retainer  70 , and a tool  80  configured to mate and cooperate with the spring retainer  70  to compress the spring  60  within the housing  10 . 
         [0061]    Optionally, as in the embodiment shown in  FIGS. 11A-13B , the spring retainer  70  is modified relative to that discussed above to include at least one axially extending leg  78  positioned to abut the poppet (which optionally is also modified to accommodate the leg as best shown in  FIG. 9B ) and space a portion of the spring retainer from the poppet  40   a  to permit fluid to pass therethrough for venting purposes. Further, the spring retainer  70  may include openings  75  to permit fluid to pass therethrough for venting purposes, as best shown in  FIG. 10 . 
         [0062]    The tool  80  may be identical to the tools described above. Alternatively, either embodiment described above may be modified to provide that the distal end  84  of the tool&#39;s body  82  is centrally hollow to admit passage of at least a portion of the second poppet&#39;s stem  122 , the stop  124 , and optionally a portion of the spring  130 , as will be appreciated from  FIG. 11B . 
         [0063]    Alternative embodiments are shown in  FIGS. 14 and 15 . Such alternative embodiments are similar to those discussed above with reference to  FIGS. 8 and 9  in that the spring retainer  70  comprises external threads  71  on a stem  73  integral with the spring retainer  70 , and the distal end of the tool  80  comprises complementary internal threads  83 . In one such embodiment, the tool  80  further comprises a shoulder  94  for abutting the housing, as best shown in  FIG. 14 , and manipulating the tool  80  involves threading the tool  80  onto the stem  73  of the spring retainer  70  while the shoulder abuts the housing  10 . In yet another alternative embodiment, the spring retainer  70  similarly comprises external threads  71  on a stem  73  integral with the spring retainer  70 , and the distal end of the tool  80  comprises internal threads complementary thereto  83 . However, in this alternative embodiment, a proximal end of the tool comprises external threads supporting a complimentarily threaded nut  92  for abutting the housing, as shown in  FIG. 15 . In such an embodiment, manipulating the tool involves threading the tool onto the spring retainer and advancing the nut on the tool until the nut abuts the housing and draws up the spring retainer to compress the compression spring. 
         [0064]    In use, the tool  80  is operable to mate with the spring retainer  70  and draw up the spring retainer  70  to compress the compression spring  50  between the spring retainer  70  and the housing  10  in a manner similar to those described above. By way of example, the tool  80  shown in  FIGS. 9A-11B  may be used as follows to disassemble the valve by threading the tool  80  into the spring retainer  70  (see  FIG. 9B ), tightening the nut  92  down against the housing  10  (see  FIG. 10B ), and then continuing to advance the nut  92  on the tool  80  to draw up the spring retainer  70  and compress the spring  50  to secure the spring between the spring retainer  70  and the housing  10 , and relieve downward force on the poppet  40   a,  at which point the housing  10  may be safely and easily decoupled from the mount  60 , as best shown in  FIG. 11B . This exposes the poppets for service and/or cleaning, as best shown in  FIG. 11B . 
         [0065]    After cleaning/service, the poppets may be replaced on the valve seat  80 /mount  60 , the housing  10  may be secured to the mount  60  (e.g., by threading them together), and then the tool  80  can be rotated or otherwise decoupled from the spring retainer  70  to restore spring-bias to the valve/mechanism, and to return the valve/mechanism to service. The tool  80  may then be withdrawn from the housing  10  and the hole plug  34  may be replaced in the housing&#39;s opening  18 . 
         [0066]    While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.