Abstract:
A valve having secondary spring force containment includes a valve body featuring an opening with a valve closure member sized to close the opening. A stem has a first end connected to the valve closure member. A proximal spring seat is positioned adjacent to the valve body, A distal spring seat is mounted on the second end of the stem. A spring is positioned between the proximal and distal spring seats so that the valve closure member is urged into a position where the valve body opening is closed. A hollow rod is attached between the proximal and distal spring seats to provide secondary spring force containment with the stem passing through the hollow rod.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to pressure relief valves and, more particularly, to a pressure relief valve and a secondary spring three containment assembly. 
     BACKGROUND 
     As is known in the art, tanks containing fluids under pressure are often provided with pressure relief valves. Such tanks may exist, for example, on railroad tank cars. Pressure relief valves typically use a compression spring to maintain the valve in a closed condition. When the pressure in the tank exceeds a pre-determined level, the spring force holding the valve in the closed condition is overcome and the valve opens so that fluid from the tank is vented to ambient so as to lower the pressure within the tank. An example of such a pressure relief valve is presented in U.S. Pat. No. 3,131,718 to Mingrone. 
     Pressure relief valves that are spring powered typically have a stem axially aligned with the motion of the valve closure member. This stem typically passes through the center of a coil spring and is typically used to set the compression spring at a correct height (or extension if a tension spring is used to achieve the force for the desired pre-determined venting pressure. In the event that the spring is not compressed before removing the component used to set the spring, such as during disassembly of the valve for service, repair or replacement, the spring can release stored energy in unpredictable directions. In the theoretical scenario of stein breakage or other component failure, the spring force can also be released in the unpredictable directions. 
     A need therefore exists for a device that reduces or eliminates the risk of accidental release of spring forces in a pressure relief valve assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a bottom perspective view of a pressure relief valve constructed in accordance with a first embodiment of the present invention; 
         FIG. 2  is a side elevational view of the valve of  FIG. 1  in a closed condition; 
         FIG. 3  is a cross sectional view of the valve of  FIG. 2  taken along line  3 - 3  of  FIG. 2 ; 
         FIG. 4  is a side elevational view of the valve of  FIG. 1  in an open condition; 
         FIG. 5  is a cross sectional view of the valve of  FIG. 4  taken along line  5 - 5  of  FIG. 4 ; 
         FIG. 6  is a side elevational view of the secondary spring force containment assembly of the valve of  FIGS. 1-5 ; 
         FIG. 7  is a cross sectional view of the secondary spring force containment assembly of  FIG. 6  taken along line  7 - 7  of  FIG. 6 ; 
         FIG. 8  is a top perspective view of the valve of  FIGS. 4 and 5 ; 
         FIG. 9  is a bottom perspective view of a pressure relief valve constructed in accordance with a second embodiment of the present invention; 
         FIG. 10  is a bottom plan view of the valve of  FIG. 9 ; 
         FIG. 11  is a cross sectional view of the valve of  FIG. 10  taken along line  11 - 11  of  FIG. 10  with the valve in a closed condition; 
         FIG. 12  is a cross sectional view of the valve of  FIG. 11  in an open condition; 
         FIG. 13  is a top perspective view of the valve of  FIG. 1   
         FIG. 14  is a top perspective view of the secondary spring force containment assembly of the yak e of  FIGS. 9-13 ; 
         FIG. 15  is a cross sectional view of the secondary spring force containment assembly of  FIG. 14 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     A pressure relief valve constructed in accordance with a first embodiment of the invention is indicated in general at  20  in  FIGS. 1 and 2 . As illustrated in  FIG. 1 , the valve includes a valve body  22 , a base  24  and a canister  26 . The base features a number of fastener openings  28  by which the valve may be secured within the wall of a tank (indicated in phantom at  32  in  FIG. 2 ) with the canister portion  2 . 6  positioned within the interior of the tank and the valve body  22  positioned external to the tank. 
     As illustrated in  FIG. 3 , the valve body houses a valve closure member  34  featuring a cap  36  secured to the member  34  by fasteners  42 . An annular groove is formed between the member  34  and the cap  36  within which an O-ring  44  is positioned. The O-ring  44  circumferentially engages an annular edge  46  formed around the valve opening in the valve body when the valve is in the closed condition (illustrated in  FIGS. 1-3 ). The closure member  34  and the interior walls of the valve body  22  define a chamber  55  that communicates with the interior of the tank via passages  57   a  and  57   b.    
     A valve stem  52  is secured to the valve closure member  34  by threads  54  and passes through an opening formed in the base  24  and through the center of valve compression coil spring  58 . The spring is trapped between a proximal spring seat  62  and a distal spring scat  64 , through which the stem  52  also passes. The spring is secured in a compressed state between the proximal and distal seats by nuts  66  and  68  which engage a threaded distal end portion of the stem  52 . The amount by which spring  58  is compressed, as determined by the position of nuts  66  and  58  on the valve stem  52 , determines the spring force that keeps the valve closure member closed (i.e. in the condition illustrated in  FIGS. 1-3 ). 
     As illustrated in  FIG. 5 , when the pressure within the tank within which the valve is mounted exceeds the pressure setting of the valve, the valve spring  58  is further compressed between the proximal and distal seats  62  and  64  as the valve closure member  34  is moved (by pressure M chamber  55 ) to a position where the O-ring  44  is lifted off of the annular edge  46 . As a result, pressurized fluid travels out of the tank, as indicated by arrows  72  and  74 , through valve body clamber  53  and out of the valve opening past the closure member  34 , as indicated by arrows  76  and  78 . 
     As illustrated in  FIGS. 4 and 5 , the end of the valve body  22  opposite base  24  is provided with a cover  82  to protect the valve closure member. The top end  84  of the stem  52  passes through an opening in the cover  82  when the valve is in the open condition to provide a visual indication of the valve condition to an observer. Furthermore, as illustrated in  FIG. 8 , the cover  82  is provided with vent openings  88  to permit pressurized fluid to pass through when the valve is in the open condition. 
     In accordance with the present invention, the valve  20  of  FIGS. 1-5  is provided with a secondary spring force containment assembly. which will now be described with respect to  FIGS. 6 and 7 . As illustrated in  FIGS. 6 and 7 , the secondary spring force containment assembly, indicated in general at  90 , includes a canister  26  that is circumferentially attached at one end to proximal spring seat  62 . This attachment is made via welding, but alternatively may be made by fasteners. As yet another alternative, the proximal spring seat  62  and the cylinder  26  may be constructed as a single unit. 
     As illustrated in  FIGS. 3 and 5 , the proximal spring seat  62  is shaped to engage the base  24  when the valve is assembled. 
     The bottom of the canister  26  features an open end within which an insert  92  is positioned. More specifically, with reference to  FIG. 1 , the insert  92  features an annular portion  94  from which radial arms  96  extend. The end of each radial arm features a bore that receives a fastener  98  after it passes through a corresponding opening in cylinder  24 . 
     As illustrated in  FIGS. 6 and 7 , the secondary spring force assembly  90  also features a hollow rod  102  that passes through the proximal spring seat  62  and features a distal end secured to distal spring scat  64 , such as by welding or fastening. Alternatively, the hollow rod  102  and distal spring seat  64  could be constructed as a single unit. 
     The proximal end of rod  102  is provided with threads  104  which are engaged by nut  106 . The position of nut  106  on the threaded proximal end of rod  102  compresses spring  58  equal to a force that is less than the force corresponding to the pressure relief setting of the valve  20 . 
     As illustrated in  FIGS. 3 and 5 , valve stem  52  passes through hollow rod  102 , As explained previously, nuts  66  and  68  are tightened to further compress spring  58  so that it provides a closing force for closure member  34  (against annular edge  46 ) that corresponds to the pressure setting of the valve. 
     During disassembly of the valve for service, repair or replacement, when runs  66  and  68  ( FIG. 3 ) are removed, the spring  58  expands to the limit permitted by rod  102  and distal spring seat  64  (as illustrated in  FIG. 7 ). In addition, spring  58  is captured in the manner illustrated in  FIG. 7  should the stem  52  break or otherwise become disengaged from the valve closure member  34 . 
     A pressure relief valve constructed in accordance with a second embodiment of the invention is indicated in general at  120  in  FIGS. 9-13 . As illustrated in  FIGS. 9 and 10 , the valve includes a valve body  122 , a base  124  and a secondary spring force containment assembly  129 . The base features a number of fastener openings  128  by which the valve may be secured within the wall of a. tank with the secondary spring three containment assembly  129  positioned within the interior of the tank and the valve body  122  positioned external to the tank. 
     As illustrated in  FIG. 11 , the valve body houses a valve closure member  134  featuring a cap  136  secured to the member  134  by fasteners  142 . An annular groove is formed between the member  134  and the cap  136  within which an O-ring  144  is positioned. The O-ring  144  circumferentially engages an annular edge  146  formed around the valve opening in the valve body when the valve is in the closed condition (illustrated in  FIG. 11 ). The base  124  of the valve is provided with passages  147   a  and  147   b  to permit drainage of rain water and the like from inside valve body  122 . 
     A valve stern  152  is secured to the valve closure member  134  by threads  154  and passes through the center of valve compression coil spring  158 . The spring is trapped between a proximal spring seat  162  and a distal spring scat  164 , through which the stern  152  also passes. The spring is secured in a compressed state between the proximal and distal seats by nuts  166  and  163  which engage a threaded distal end portion of the stem  152 . The amount by which spring  158  is compressed, as determined by the position of nuts  166  and  168  on the valve stem  152  determines the spring force that keeps the valve closure member closed (i.e. in the condition illustrated in  FIG. 11 ). 
     As illustrated in  FIG. 12 , when the pressure within the tank within which the valve is mounted exceeds the pressure setting of the valve, the valve spring  158  is further compressed between the proximal and distal seats  162  and  164  as the valve closure member  134  is moved (by pressure in the tank) to a position where the O-ring  144  is lifted off of the annular edge  146 . As a result, pressurized fluid travels out of the tank and through the valve opening, as indicated by arrows  172  and  174 . 
     As illustrated in  FIGS. 11-13 , the top of valve body  122  is provided with a brace  180  which is secured in place by fasteners  182 . The top end  184  of the stem  152  passes through an opening in the brace  180  and is provided with a flange  185 . When the valve is in the open condition, the flange  185  is raised from the brace  180  and provides a visual indication of the valve condition to an observer. 
     In accordance with the present invention, the valve  120  of  FIGS. 9-13  is provided with a secondary spring force containment assembly, which will now be described with respect to  FIGS. 14 and 15 . As illustrated in  FIGS. 14 and 15 , the secondary spring force containment assembly, indicated in general at  129 , includes a hollow rod  202  that passes through the proximal spring seat  162  and features a distal end secured to distal spring seat  164 , such as by welding or fastening. Alternatively, the hollow rod  202  and distal spring seat  164  could be constructed as a single unit. 
     As illustrated in  FIGS. 11 and 12 , the proximal spring seat  162  features tabs  163  that engage the base  124  when the valve is assembled. 
     The proximal end of rod  202  is provided with threads  204  which are engaged by nut  206 . The position of nut  206  on the threaded proximal end of rod  202  compresses spring  158  equal to a force that is less than the force corresponding to the pressure relief setting of the valve  120 . 
     As illustrated in  FIGS. 11 and 12 , valve stem  152  passes through hollow rod  202 . As explained previously, nuts  166  and  168  are tightened to further compress spring  158  so that it provides a closing force for closure member  134  (against annular edge  146 ) that corresponds to the pressure setting of the valve. 
     During disassembly of the valve for service, repair or replacement, when nuts  166  and  168  are removed, the spring  158  expands to the limit permitted by rod  202  and distal spring seat  164  (as illustrated in  FIGS. 14 and 15 ). In addition, spring  158  is captured in the manner illustrated in  FIGS. 14 and 15  should the stem  152  break or otherwise become disengaged from the valve closure member  134 . 
     As is clear from the above, the secondary spring containment assemblies described above with respect to  FIGS. 6 and 7  and  14  and  15 , and other embodiments of the present invention, could be used to retrofit previously produced pressure relief valves. 
     While the preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the invention, the scope of which is defined by the appended claims.