Abstract:
A fusible bung for sealing an opening in a threaded flange on a liquid container. The bung is formed as a unitary body of polymeric material that includes cylindrical, concentric interior and exterior walls separated by a vent passage and interconnected by a unitary venting fuse. The exterior wall is threaded for mounting of the bung and includes an annular shoulder and separate sealing ring for providing a gas-tight seal to the container flange. The interior wall is supported by the exterior wall via the venting fuse, which is formed during molding of the bung as a thin-walled section of the polymeric material which melts and ruptures at elevated temperatures. The central region within the interior wall can include either a unitary cover member or can have a threaded bore to receive a separate relief valve.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to fusible bungs for tanks and other receptacles for containing fluids. More particularly, it relates to a bung for relieving gas or air pressure in such a receptacle in response to elevated temperature.  
         BACKGROUND OF THE INVENTION  
         [0002]    There are many types of tanks for storing or transporting industrial liquids such as paint and solvents which require safeguards against excessive air or gas pressure in the tank. Such a condition, for example, may arise when a tank containing liquid and air is subjected to increasing ambient temperature.  
           [0003]    As disclosed and claimed in my U.S. Pat. No. 5,573,135 granted Nov. 12, 1996, it is already known to provide tanks with a manually removable pressure relief bung in the top of the tank and/or in a manhole cover and/or in a mixer mounting cover which will relieve the tank pressure to the atmosphere through vent holes in the bung. In this, the vent holes will be fully opened in about one full turn of the bung in less time than the minimum time required to release the mixer cover or the manhole cover or the bung itself from the tank. Accordingly, when the pressure relief bung is opened before either the mixer cover or the manhole cover is disconnected from the tank, the risk of either cover being blown off the tank is greatly diminished.  
           [0004]    There is a need for providing some tanks of the type described above with a bung which will function to relieve pressure in the tank in response to temperature. It is desirable in some applications to provide pressure relief in response to excessive temperature by means combined with manually removable pressure relief bung as described in the aforementioned U.S. Pat. No. 5,573,135. Alternatively, in some applications it may be desirable to provide a bung which relieves excessive tank pressure in response to temperature as its sole function.  
           [0005]    In some applications it is desirable to provide such tanks with a bung with means for relieving excessive gaseous pressure from the tank independently of the temperature at the bung. As disclosed in U.S. Pat. No. 5,240,027, it is already known to provide a bung with both pressure responsive and temperature responsive relief devices for containers such as storage tanks and the like.  
         SUMMARY OF THE INVENTION  
         [0006]    The invention provides a fusible bung for use in connection with tanks and other liquid containers, including both portable and non-portable containers. In accordance with one aspect of the invention, the fusible bung includes first and second walls and a fusible link. The first and second walls preferably comprise concentric, cylindrical exterior and interior walls, respectively, with the first wall having threads or some other fastening feature by which the bung can be mounted to the tank. A vent passage is located between the two walls and is closed off at one end by the fusible link. The walls and fusible link can all be formed as a unitary body of polymeric material such as HDPE. The bung can also include a sealing ring located at the exterior wall so that, when attached to an opening in the tank, the bung provides a gas-tight seal of the opening. Upon experiencing elevated temperatures that could create increased pressures within the tank, the fusible link softens and/or melts to the point of rupture so that the gas pressure within the tank can be relieved through the vent passage.  
           [0007]    The central region within the interior wall can be closed off by a cover member that can be unitary with the second wall. Alternatively, the interior wall can include a threaded bore for receiving a separate relief valve, such as a pressure and/or vacuum relief valve. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    Preferred exemplary embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein:  
         [0009]    [0009]FIG. 1 is a top plan view of a first embodiment of the fusible bung of this invention.  
         [0010]    [0010]FIG. 2 is a cross-sectional view of the first embodiment in a typical installation.  
         [0011]    [0011]FIG. 3 is an exploded view of a second embodiment of the fusible bung of this invention in a typical installation, and  
         [0012]    [0012]FIG. 4 is a side elevation view of the fusible bung of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    Referring now to the drawings, illustrative embodiments of the invention are shown in a fusible bung constructed as a unitary body of polymeric material such as high density polyethylene (HDPE). In a first embodiment, the fusible bung is adapted to relieve container pressure at a predetermined temperature. In a second embodiment, the fusible bung incorporates a pressure relief valve and is adapted to relieve container pressure at a predetermined pressure value or at a predetermined temperature. It will be appreciated as the description proceeds that the fusible bung of this invention may be utilized in a wide variety of applications and may be realized in different embodiments.  
         [0014]    The fusible bung of this invention is especially adapted for use as a pressure relief device for liquid containers such as portable liquid mixing tanks of the type described above with reference to U.S. Pat. No. 5,573,135. The entire disclosure of that patent is hereby incorporated by reference.  
         [0015]    As shown in FIGS. 1, 2 and  4 , the fusible bung  10  is adapted for threaded connection with a threaded bung flange  12  which is suitably formed in or mounted to a top wall or cover  14   a  of a tank  14 . In the illustrative embodiment, the bung  10  is formed of a polymeric material, preferably a high density polyethylene (HDPE) material. The bung is preferably formed by injection molding as a unitary body. In the illustrative embodiment, the bung  10  is adapted to sealingly close the opening  13  of the bung flange  12  which is provided in the cover  14   a.    
         [0016]    The fusible bung  10  comprises a cylindrical exterior wall  18  which has an open lower end  22  for communication with the opening  13  formed by the bung flange  12 . A male thread  24  on the outside of the cylindrical wall  18  is adapted to engage the threaded bung flange  12 . Bung  10  also comprises a cylindrical interior wall  18   a  which is closed at its upper end by a cover member  16  disposed within the interior wall  18   a  and closing the upper end thereof. The interior wall  18   a  is shorter than the wall  18  and provides a vent passage  15  which extends from the tank opening  13  to a venting fuse  20  for venting the tank  14  to the atmosphere. The venting fuse  20  comprises a thin, annular ring which is unitary with the walls  18  and  18   a  and constitutes a fusible link which will be described in detail below.  
         [0017]    At the upper end of the fusible bung  10 , the outside diameter of the cylindrical wall  18  is enlarged and forms an annular shoulder  26  which extends radially outwardly. The shoulder  26  is provided at its outer periphery with a set of four tool receiving notches  28  which are equally spaced around the circumference of shoulder  26 . Each tool receiving notch has an axially extending side wall  32  with a flat bottom  34 . The set of notches  28  are adapted to collectively receive a set of four drive teeth of a wrench for tightening and loosening the fusible bung in its threaded connection with the bung flange  12 .  
         [0018]    As shown in FIG. 2, a preformed flat-sided sealing ring  36  of generally rectangular cross section is disposed in an annular recess  38  extending around the exterior of wall  18  adjacent the outer end of the thread  24 . When the bung  10  is tightened into the bung flange  12 , one flat side of the sealing ring  36  is seated against an annular inner rib  42  of the shoulder  26 . The opposite flat side of the sealing ring  36  is thus seated against the annular outer surface of the bung flange  12 .  
         [0019]    Preferably, the sealing ring  36  is held captive on the bung by a mechanical interlock provided by the annular rib  42  and the annular recess  38  on the outside of wall  18 . This mechanical interlock is formed by inserting the preformed sealing ring  36  into the mold cavity in which the fusible bung is molded. The preformed sealing ring  36  has an annular groove corresponding to the annular rib  42  and also has corners with a radius corresponding to the annular recess  38 .  
         [0020]    As shown in FIGS. 2 and 4, the fusible bung  10  is provided with a set of four safety vents  46  (only three shown). These vents are equally spaced on the wall  18  and each vent is elongated circumferentially. The vents are located axially relative to the threads on the bung so that venting of the tank begins within about ¼ turn of opening rotation of the fusible bung. This safety vent structure is described in complete detail in the above cited U.S. Pat. No. 5,573,135.  
         [0021]    The venting fuse  20 , referred to above, will now be described in greater detail. The venting fuse is unitary with both the inner cylindrical wall  18   a  and the outer cylindrical wall  18 . It comprises an annular ring which has a thin axial dimension relative to the axial dimension of the wall  18  and relative to the axial dimension of the wall  18   a . The thickness of the venting fuse  20  is 0.04″ whereas the axial length of the interior wall  18   a  is 0.625″ and that of the exterior wall  18  is greater. The axial thickness of the fuse  20  is less than about {fraction (1/15)} of the axial length of the exterior cylindrical wall  18  and interior cylindrical wall  18   a . The venting fuse  20  is thus adapted to melt more quickly than the walls  18  or  18   a  in response to an ambient temperature above the melting temperature of the HDPE. Accordingly, if the ambient temperature rises above the melting point of HDPE, the venting fuse  20  will melt and rupture while the walls  18  and  18   a  remain intact. The time lapse between the occurrence of the melting temperature and rupture of the fuse will vary in accordance with the ensuing temperature and pressure values. When a rupture of the venting fuse  20  occurs the gaseous pressure in the tank is vented to the atmosphere.  
         [0022]    In general, the venting fuse  20  must rupture and thereby relieve tank pressure before it reaches a value at which any other pressure sustaining element of the tank is ruptured. The tank pressure will increase as the ambient temperature increases. When the ambient temperature reaches the melting point of the fuse  20 , there will be a time delay before the fuse ruptures and relieves tank pressure. The amount of time delay will depend upon the values of both temperature and pressure.  
         [0023]    Tests were conducted on samples of the fusible bung of this invention for studying the effect of the dimensions of the venting fuse  20  and the internal pressure of the test vessel on the temperature at which the internal pressure is relieved by the fusible bung. As shown in Table I below, the same test was performed on five different specimens numbered 1-5. All of the specimens were of the same structure except that each specimen had a fuse of dimensions different from the other specimens. In the test procedure, each specimen was installed on a pressure vessel which was disposed inside a test oven adapted to maintain a preset temperature of fixed value above the melting point of HDPE (about 270° F.) for each test specimen. The pressure vessel was connected to an air compressor for maintaining a pre-determined pressure inside the test vessel throughout the test. In the conduct of the test for each test specimen, the oven temperature was allowed to increase from room temperature toward the preset temperature until the venting fuse ruptured and relieved the pressure in the test vessel to the ambient air pressure. For each test specimen, the total time lapse from start to pressure relief was recorded.  
         [0024]    The small margins between the relief temperatures of the specimens indicated that the venting fuse dimensions do not have a significant effect on the relief temperature of the fusible bung provided that it is thin enough relative to its supporting structure so that it melts and ruptures before its supporting structure. It was observed that the gauge pressure of the test vessel dropped instantaneously upon the occurrence of pressure relief. The test specimens all showed signs of rupture across about two-thirds of the circumference of the venting fuse on the inner part of the fuse surrounding the interior wall of the fusible bung. The actual pressure outlet was an opening on the ruptured circumference of each venting fuse.  
                                                                                                     TABLE I                           Determination of Relief Characteristics of the Fusible Bung using       Various Fuse Dimensions and Pressures            TEST   Fuse Dimensions (in.)   PRESSURE   PRESET   RELIEF   TOTAL TIME TO            Specimens   Y (thickness)   X (width)   (PSI)   TEMP.   TEMP. (° F.)   RELIEF (MINUTES)                    1   0.02   0.25   6   350   338   38       2   0.02   0.312   6   350   340   37:25        3   0.015   0.312   6   350   336   34:07*       4   0.04   0.312   6   350   345   —       5   0.02   0.312   8.5   350   343   35                          
 
         [0025]    Based on the test results shown in Table I above, the dimensions of the venting fuse of specimen number 4 was used as the standard dimensions of the venting fuse in each of the test specimens in the additional testing described below.  
         [0026]    Tests were conducted on specimens numbered 6-10 (see Table II below) to study the role of temperature and pressure on the venting characteristics of the fusible bung of this invention. In the testing of these specimens, the oven temperature was raised to various pre-determined temperature ranges and maintained within the limits of the specified range. In the test procedure, the internal pressure of the test vessel was manually controlled periodically to reset the pressure to a predetermined constant value. The trends in Table II show that as the temperature range was increased beyond the melting point of HDPE (about 270° F.) there was a decline in the relief times and the test vessel pressure dropped faster after relief.  
                                                                   TABLE II                           Determination of Relief Times of the Fusible Bung       at Various Temperature and Pressures                Tested                           Temp.           Range       Time to           (T1° F.-   Pressure   Reach T1   Relief Time       Test #   T2° F.)   (PSI)   (Minutes)   (Minutes)   Comments                    6   290-295   6   27:30   23   Instant Drop                           of Pressure       7   290-295   8.5   26   19:50   Instant Drop                           of Pressure       8   275-280   6   25:40   25   Gradual Drop                           of Pressure       9   275-280   6   25:40   27:40   Gradual Drop                           of Pressure       10   260-265   6   22   46:30   Slowest Drop                           of Pressure                  
 
         [0027]    A test was conducted on the specimen number 11 (see Table III below) to determine whether the fusible bung would relieve pressure at a temperature below 220° F. According to U.S. Department of Transportation (DOT) regulations, the fusible bung, for certain applications, should not relieve pressure below 9 psi at a temperature of 220° F.  
         [0028]    The results of this test, as shown in Table III, shows that the test specimen withstood up to 9 psi at 220° F. for a prolonged period of time.  
                                         TABLE III                           Determination of Fusible Bung Characteristics at 220° F.                Tested                           Temp.           Range       Time to           (T1° F.-   Pressure   Reach T1   Relief Time       Test #   T2° F.)   (PSI)   (Minutes)   (Minutes)   Comments               11   220-225   9   18   2:02   Elevated                       (No Relief)   Groove Layer                  
 
         [0029]    A test was conducted on test specimens  12 ,  13  and  14  (see Table IV below) to determine the performance of the fusible bung at room temperature and under conditions of high pressure. In this test, the pressure regulator was set to the test pressure level. These results show that the venting fuse is capable of functioning at room temperature under pressures up to at least 84 psi and possibly even up to 102 psi, although leaking in the seal area did occur at this upper pressure in another, similar test.  
                                         TABLE IV                           Hydrostatic Test of the Fusible Bung                Pressure   Torque   Room   Duration           Test #   (PSI)   (ft-lbs)   Temp. (° F.)   (Minutes)   Results               12   102   30   75   31   No Leaks-                           Deformed                           Groove Layer       13   81   —   70   25   No Leaks-Slight                           Elevation of                           Groove Layer       14   84   30   75   31   No Leaks-Slight                           Elevation of                           Groove Layer                  
 
         [0030]    The illustrative embodiment of the invention as described above exhibits sufficient structural integrity so that it can withstand operation within the normal range of pressure and temperature without melting of the venting fuse  20  before the temperature becomes excessive. On the other hand, the venting fuse does melt and produces venting of the tank within an accepted time period after the ambient temperature reaches the melting point of the fuse.  
         [0031]    A second embodiment of the fusible bung of this invention is shown in FIG. 3. This embodiment of the invention differs from that of FIGS. 1, 2 and  4  in that a pressure vacuum relief valve  50  is combined with the fusible bung to provide for pressure or vacuum relief when the tank pressure reaches a predetermined value above or below the atmospheric pressure. In this embodiment, the structure and operation of the fusible bung is the same as in the first embodiment except for the addition of the pressure vacuum relief valve  50 . Accordingly, only these changes will be described below. The same reference characters will be used for the same parts in both embodiments of the fusible bung and, for modified parts a prime symbol will be added to the reference characters of the embodiment. For added parts, additional reference characters will be used.  
         [0032]    As shown in FIG. 3, the pressure vacuum relief valve  50  is combined with a modified fusible bung  10 ′. The fusible bung  10 ′ is the same as fusible bung  10  except that the interior wall  18   a ′ is formed with a threaded bore  48  (instead of the cover  16  of FIG. 2).  
         [0033]    The relief valve  50  has a valve body  52  provided with external threads  54  which mate with the threaded bore  48  for providing a fluid tight seal between the valve  50  and the fusible bung  10 ′. The valve  50  is of conventional design for providing both pressure and vacuum relief at preset pressures above and below atmospheric pressure. Alternatively, the relief valve could provide either pressure relief or vacuum relief instead of both functions.  
         [0034]    Although this invention has been described with reference to particular embodiments, it is not to be construed in a limiting sense. Many variations and modifications will now occur to those skilled in the art.  
         [0035]    As used in this specification and appended claims, the terms “for example” and “such as,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.