Abstract:
A relief vent assembly for a fuel storage tank includes a vent body defining a chamber to provide a substantially axially smooth and unencumbered path of flow for pressurized fluid to vent out from the tank. Such a path of flow allows the pressurized fluid to remain laminar throughout approximately the entire path through the chamber, maintaining a high flow rate. The vent assembly includes a crossbar that supports the rod of a lid that covers a distal margin of the vent body. The crossbar is disposed substantially at the distal margin of the vent body to prevent any premature turbulent flow of the pressurized fluid, which would slow the flow rate. A widening tapered bore of the chamber increases the flow area and serves to offset the area occupied by the crossbar.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to fuel storage tanks and relief vents for such tanks. More particularly, the present invention concerns a relief vent assembly for a fuel storage tank that allows for rapid discharge of pressurized fluid through the vent and out of the tank when the pressure within the tank exceeds a selected level that is greater than the pressure outside the tank. 
       BACKGROUND 
       [0002]    Fuel storage tanks, such as shallow tanks commonly used to hold fuel for a backup electrical generator, include a relief vent assembly that allows pressurized fluid to escape from the tank when a buildup of pressure within the tank exceeds a selected level that is greater than the pressure outside the tank. Often, these tanks are located above the ground and frequently include an inner tank that holds the fuel and an outer tank that acts as a safety vessel by containing the fuel from the inner tank should the structure of the inner tank be compromised. As such tanks normally hold fuel in liquid form, they tend not to be designed to hold a highly pressurized fluid. Thus, the relief vent assembly allows a buildup of pressurized fluid, when such condition arises, to discharge from the tank and reduce stress on the structure of the tank. 
         [0003]    Typically, such an increase in pressure within the tank is due to an increase in heat in the area surrounding the tank, often by a fire. In order to prevent damage from rapid expansion of the pressurized fluid pushing against the structure of the tank, the vent assembly must allow this pressurized fluid to be discharged safely from the tank. Preferably, this venting occurs at a flow rate high enough to ensure that the pressure within the tank can be maintained at a manageable level. 
         [0004]    Inasmuch as the vent assembly includes a passage from inside the tank to the outside atmosphere, a lid is customarily included such that, under normal operating conditions, the lid keeps the vent closed and maintains the inside of the tank substantially closed off from the atmosphere for various reasons. Accordingly, in addition to allowing pressurized fluid to vent out from the tank, the vent assembly should also prevent foreign matter from entering the tank. A short stroke lid is often used to accommodate the frequently limited space constraints around the fuel tank as well as to prevent foreign matter from entering the tank, including such things as contaminants or unauthorized devices used to syphon fuel from the tank. 
         [0005]    Conventionally, a gravity closing vent has been used with these types of fuel tank systems. Such a vent provides satisfactory performance in some respects, although those of ordinary skill in the art will recognize that a gravity closing lid must be in a vertical orientation in order to function properly, limiting design options for placement on a tank. Additionally, prior art gravity closing vent assemblies have presented a stepped bore with a large and axially centrally located crossbar for supporting the lid. This crossbar introduces turbulence to the flow of the fluid in the chamber of the vent before the fluid has passed substantially through the vent, causing the fluid flow to slow down and limiting the maximum flow rate through the vent and out of the tank. Slowed flow rate is undesirable, as it can impede evacuation of pressurized fluid from the tank during emergency vent situations. 
         [0006]    High flow rates of the pressurized fluid are advantageous, as a quick evacuation of pressurized fluid is desired in emergency situations. Furthermore, the popular certification organization Underwriters Laboratories (“UL”) requires, in order to receive certification, that a vent be able to provide a flow rate of 110,000 cubic feet per hour at two and a half pounds per square inch of pressure for a four inch open pipe. Some prior art gravity closing vents have been unable to meet this threshold and, consequently, have not qualified for a commercially advantageous UL certification. 
       SUMMARY 
       [0007]    The present invention provides a relief vent assembly for a fuel storage tank that allows pressurized fluid to rapidly discharge out from the tank when the pressure within the tank exceeds a selected level that is greater than the pressure outside the tank. The relief vent assembly provides a flow path through a chamber of the vent body that is substantially smooth and unencumbered, ensuring that the flow of pressurized fluid remains laminar throughout approximately the entire path. This prevents the fluid from becoming turbulent, which would detrimentally slow the flow rate through the chamber and out of the vent. The vent includes a crossbar that supports a rod of a lid that covers a distal margin of the vent body when the vent is closed. The crossbar is disposed substantially at the distal margin of the vent body to prevent any premature turbulent flow of the pressurized fluid, providing improved flow out of the tank. 
         [0008]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description of the preferred embodiments. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
         [0009]    Various other aspects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and the accompanying drawing figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    A preferred embodiment of the present invention is described in detail below with reference to the attached drawing figures, wherein: 
           [0011]      FIG. 1  is a perspective view on a reduced scale of an electrical power generation assembly constructed in accordance with the principles of the present invention, broadly including a generator, an engine, and a fuel tank assembly with an outer tank shown in solid lines and an inner tank disposed within the outer tank shown in broken lines, wherein both the outer and inner tanks include a relief vent assembly; 
           [0012]      FIG. 2  is an exploded perspective view of the relief vent assembly of  FIG. 1 , depicting in detail the multiple components of the vent assembly from a generally top front vantage point; 
           [0013]      FIG. 3  is an exploded perspective view of the relief vent assembly of  FIG. 1 , depicting in detail the multiple components of the vent assembly, similar in many respects to  FIG. 2 , but illustrating the components from a generally bottom front vantage point; 
           [0014]      FIG. 4  is an enlarged, fragmentary, partial cutaway perspective view of the relief vent assembly, depicting in detail the multiple components thereof; 
           [0015]      FIG. 5  is a fragmentary, partial side sectional view of the relief vent assembly shown in  FIG. 4 , depicting the multiple components thereof and the shape of the chamber, with the assembly depicted with the lid in a closed position; 
           [0016]      FIG. 6  is a fragmentary, partial side sectional view of the relief vent assembly shown in  FIG. 4 , depicting the multiple components thereof and the shape of the chamber, similar in many respects to  FIG. 5 , but with the assembly depicted with the lid in an open position; 
           [0017]      FIG. 6   a  is an enlarged, fragmentary, partial side sectional view of a portion of the relief vent assembly shown in  FIG. 6 , depicting in detail an externally threaded portion of the vent body received within a correspondingly threaded flange of the tank; 
           [0018]      FIG. 7  an enlarged, fragmentary, partial cutaway perspective view of an alternative embodiment of the relief vent assembly, depicting in detail the multiple components thereof, similar in many respects to  FIG. 4 , but with the screen element positioned adjacent the base of the crossbar; 
           [0019]      FIG. 8  is a fragmentary, partial side sectional view of the alternative embodiment of the relief vent assembly shown in  FIG. 7 , depicting the multiple components thereof and the shape of the chamber, with the assembly depicted with the lid in a closed position; 
           [0020]      FIG. 9  is a fragmentary, partial cutaway perspective view of a prior art vent assembly, depicting in detail the multiple components thereof; 
           [0021]      FIG. 10  is a fragmentary, partial side sectional view of the prior art relief vent assembly shown in  FIG. 9 , depicting the multiple components thereof and the stepped bore of the chamber, with the assembly depicted with the lid in a closed position; and 
           [0022]      FIG. 11  is a fragmentary, partial side sectional view of the prior art relief vent assembly shown in  FIG. 9 , depicting the multiple components thereof and the stepped bore of the chamber, similar in many respects to  FIG. 10 , but with the assembly depicted with the lid in an open position. 
       
    
    
       [0023]    The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the preferred embodiment. 
       DETAILED DESCRIPTION 
       [0024]    The present invention is susceptible of embodiment in many different forms. While the drawings illustrate, and the specification describes, certain preferred embodiments of the invention, it is to be understood that such disclosure is by way of example only. There is no intent to limit the principles of the present invention to the particular disclosed embodiments. 
         [0025]    With initial reference to  FIG. 1 , a backup generator assembly  20 , depicted by way of example, broadly includes a diesel engine (not shown) located in a housing  22  that powers an electrical generator  24 , as will be readily understood by one of ordinary skill in the art. A control box  26  is mounted to engine housing  22  to facilitate control of operating parameters for backup generator assembly  20 . Fuel for the engine (not shown) is stored in a tank assembly  28 . 
         [0026]    Tank assembly  28  broadly includes an inner tank  30  that contains liquid fuel and an outer tank  32  that contains inner tank  30 . As is known in the art, the inclusion of multiple tanks in the arrangement of tank assembly  28  allows outer tank  32  to act as a safety vessel, containing the liquid fuel in the event of any structural damage to inner tank  30 . The depicted tanks  30  and  32  are shallow, above-ground tanks, although the principles of the present invention may also be applied to other types of liquid fuel tanks. 
         [0027]    Inner tank  30  is substantially sealed and includes a relief vent assembly  34  that allows pressurized fluid to vent from tank  30  when a buildup of pressure within tank  30  is such that the pressure within tank  30  exceeds a selected level that is greater than the pressure outside tank  30 . Relief vent assembly  34  provides for rapid evacuation of pressurized fluid from tank  30  during emergency situations, such as a significant increase in pressure within tank  30  due to an increase in heat in the area surrounding tank assembly  28 , as may be caused by a fire. 
         [0028]    Outer tank  32  includes a relief vent assembly  36  that functions similarly to vent assembly  34  and allows pressurized fluid to vent from tank  32  when there is pressurized fluid in outer tank  32 . In the embodiment depicted, vent assembly  34  and vent assembly  36  are structurally identical, although such conformity is not necessary, as will be readily appreciated by one of ordinary skill in the art. While only vent assembly  34  will be described in greater detail below, it is to be understood that the details of construction for vent assembly  34  also apply to vent assembly  36  in the embodiment of tank assembly  28  depicted in  FIG. 1 . 
         [0029]    With reference now to  FIGS. 2-6   a,  vent assembly  34  is depicted in greater detail, showing details of construction of the component parts thereof. Vent assembly  34  broadly includes a vent body  38 , a shiftable lid  40 , and a rod  42 . Only vent assembly  34  of inner tank  30  will be described in greater detail herein, with the understanding that the details of construction of vent assembly  34  also apply to vent assembly  36  of outer tank  32 . 
         [0030]    Vent body  38  is generally annularly shaped and includes an axially proximal margin  44  and an axially distal margin  46 . Axially proximal margin  44  of vent body  38  is configured for threaded receipt within a receiving flange  48  fixed to the top wall of tank  30 . In the illustrated embodiment, flange  48  presents a diameter of approximately four inches, although other size flanges and associated vent bodies could be similarly used without departing from the teachings of the present invention. Flange  48  protrudes outward from tank  30  and includes internal threads  50 . Axially proximal margin  44  of vent body  38  includes a threaded portion  52  that threadably secures vent assembly  34  within flange  48 . Threaded portion  52  extends from an axially proximal end  52 a up to an axially distal end  52   b.  While the illustrated embodiment depicts flange  48  protruding upwardly from the top of tank  30 , alternative dispositions for a flange (such as on the side of a tank) are within the ambit of the present invention, as will be appreciated by one of ordinary skill in the art upon review of this disclosure. 
         [0031]    Vent body  38  includes a radially inner wall surface  54  and a radially outer surface  56 . Inner wall surface  54  includes a constant diameter portion  58  that extends axially upwardly from proximal margin  44 . Inner wall surface  54  also includes a tapered bore portion  60  that extends axially upwardly from constant diameter inner wall portion  58  to distal margin  46  of vent body  38 . Tapered bore portion  60  of inner wall  54  presents a diameter that increases smoothly and continuously from the diameter of constant diameter portion  58  to a larger diameter at axially distal margin  46 . 
         [0032]    Radially outer surface  56  includes a noncircular portion  62  that is configured such that a tool can be used to twist vent body  38  to secure vent body  38  to flange  48  of tank  30 , as will be readily appreciated by one of ordinary skill in the art. Depicted noncircular portion  62  comprises a plurality of flat faces  64 , some of which can be engaged with a wrench, although it is clearly within the ambit of the present invention to include more or fewer flat faces (or even shapes that are other than polygonal) for an alternative noncircular portion. 
         [0033]    A thread  66  of threaded portion  52  of vent body  38  includes a radially innermost thread root  68  and a radially outermost thread crest  70 . As shown particularly in the enlarged view of  FIG. 6a , the radial distance between constant diameter inner wall portion  58  and thread root  68  is less than the radial distance between thread root  68  and thread crest  70 . This thin wall section of vent body  38  defines a diameter of constant diameter inner wall portion  58  of vent body  38  that is nearly as large as the diameter of flange  48  itself, providing a relatively large area through which pressurized fluid can flow through vent body  38  and out of vent assembly  34 . 
         [0034]    Returning now to radially inner wall surface  54  of vent body  38 , a radially extending groove  72  is defined in wall surface  54 . Groove  72  is disposed between constant diameter portion  58  and tapered bore portion  60 , such that constant diameter portion  58  is below groove  72  and tapered bore portion  60  is above groove  72 . A screen  74  is disposed within groove  72  to prevent the introduction of foreign matter through vent body  38  and into tank  30 , as will be readily appreciated by one of ordinary skill in the art upon review of this disclosure. Accordingly, screen  74  helps to both prevent contamination and deter theft of the contents of tank  30 . 
         [0035]    Axially distal margin  46  of vent body  38  includes a generally flat top face  76 . Top face  76  includes an axially extending groove  78  defined therein and extending in a circle. A seal  80  is disposed at least partially within groove  78  to cooperate with lid  40 , as described in greater detail below. To this end, at least a portion of seal  80  extends out of groove  78  and above top face  76  of vent body  38 . 
         [0036]    Vent body  38  also includes a crossbar  82  that spans the diameter of vent body  38  along distal margin  46  thereof. Crossbar  82  includes an axially distal portion presented by a top surface  84  and an axially proximal portion presented by a bottom surface  86 . Top surface  84  of crossbar  82  is coplanar with top face  76  of vent body  38 . The disposition of crossbar  82  adjacent axially distal margin  46  of vent body  38  provides a largely unencumbered area within the chamber of vent body  38  such that fluid can flow through vent body  38  (from proximal margin  44  to distal margin  46 ) with minimal interference, as will be described in greater detail below. As shown particularly in  FIG. 2 , crossbar  82  also includes a generally centrally disposed enlarged portion  88  with an axial hole  90  defined therethrough. Hole  90  extends from top surface  84  to bottom surface  86 . 
         [0037]    Lid  40  generally surmounts vent body  38  and is shiftable between a closed position (shown in  FIG. 5 ) and an open position (shown in  FIG. 6 ). Lid  40  includes an outside top surface  92  and an inside bottom surface  94 . A portion of inside bottom surface  94  cooperates with seal  80  to substantially close vent assembly  34 . A centrally disposed threaded recess  96  extends upwardly from bottom surface  94  of lid  40 . Threaded recess  96  is coaxial with hole  90  through crossbar  82  when lid  40  is disposed in surmounting relationship with vent body  38 . 
         [0038]    Rod  42  generally supports and defines the path of travel for lid  40  by cooperating with structure of vent body  38 . In particular, rod  42  extends downwardly from bottom surface  94  of lid  40  and through hole  90  in crossbar  82 , such that crossbar  82  radially supports rod  42 . Depicted rod  42  comprises a bolt that includes a shaft  98 , a head  100  at the proximal end of shaft  98 , and a threaded portion  102  at the distal end of shaft  98 . In assembled vent assembly  34 , rod  42  extends upwardly within vent body  38 , through hole  90  in crossbar  82 , and into threaded recess  96  in lid  40 . Threaded portion  102  of rod  42  is thereby threadably secured to lid  42 , as shown particularly in  FIGS. 5 and 6 . 
         [0039]    With continued reference to  FIGS. 5 and 6 , a spring  104  is axially aligned with and disposed around shaft  98  of rod  42 . In assembled vent assembly  34 , one end of spring  104  engages bottom surface  86  of crossbar  82  and the other end of spring  104  engages an engagement surface  106  of head  100  of rod  42 . As will be readily appreciated by one of ordinary skill in the art upon review of this disclosure, the extension force of spring  104  biases lid  40  toward the closed position (shown in  FIG. 5 ). 
         [0040]    The general operation of vent assembly  34  should be apparent to one of ordinary skill in the art from the foregoing description and, therefore, will be described here only briefly. Fuel is stored in inner tank  30  and vent assembly  34  is secured to flange  48  of tank  30 . Under normal operating conditions, the fuel in tank  30  is stored in liquid form and vent assembly  34  maintains separation between the contents of tank  30  and the outside environment with lid  40  in the closed position (shown in  FIG. 5 ). Upon a condition of a buildup of pressurized fluid within tank  30 , such as may occur during an increase in heat in the area surrounding tank  30 , some of the pressurized fluid discharges from tank  30  through vent assembly  34 . 
         [0041]    As the pressure within tank  30  increases, a force is exerted on bottom surface  94  of lid  40 , which compresses spring  104 , and moves lid  40  from a closed position to an open position (shown in  FIG. 6 ). When lid  40  is open, the pressurized fluid vents from inside tank  30  to the outside environment, relieving pressure buildup within tank  30 . The structure of relief vent assembly  34  provides a flow path through vent body  38  that is substantially smooth and unencumbered. 
         [0042]    The structure of the present invention ensures that the flow of pressurized fluid remains laminar and prevents the venting fluid from becoming turbulent, which would slow the flow rate through vent body  38  and out of vent assembly  34 . Maintaining a laminar flow of the venting fluid provides a more rapid evacuation of the pressurized fluid from tank  30 , which is particularly advantageous during emergency situations, such as when the pressure buildup is rapid and/or significant, as when a fire increases the heat in the area surrounding tank assembly  28 . 
         [0043]    In the illustrated embodiment, crossbar  82  is disposed adjacent axially distal margin  46  of vent body  38 , within the area of tapered bore  60  that presents the largest diameter across the chamber of vent body  38 . In this arrangement, the diminution of cross sectional area of the chamber due to the inclusion of crossbar  82  is compensated for by the enlarged diameter of the chamber due to tapered bore  60 . Additionally, the disposition of crossbar  82  at distal margin  46  of vent body  38  ensures that laminar fluid flow of the venting pressurized fluid is undisturbed by the structure of crossbar  82  until such laminar flow is at distal margin  46  and ready to discharge out of vent body  38 . 
         [0044]    Such arrangement prevents the introduction of turbulence to the flow within the chamber of vent body  38 , which would detrimentally slow the flow of the fluid through vent body  38  and lessen the discharge flow rate out of vent body  38 . This configuration provides a sufficiently high discharge flow rate that vent assembly  34  of the present invention meets the UL certification threshold of discharging 110,000 cubic feet per hour at two and a half pounds per square inch of pressure for a four inch open pipe that some prior art units have been unable to meet. 
         [0045]    With reference now to  FIGS. 7-8 , another embodiment of a vent assembly  234  is depicted secured to threaded flange  48  of tank  30 . Many of the elements and details of construction of alternative vent assembly  234  are very similar in many respects to those of vent assembly  34  discussed above. Therefore, for the sake of brevity and consistency, similar elements between vent assembly  34  and alternative vent assembly  234  are numbered in similar fashion, but differing by an order of two hundred. Additionally, only the differences between the embodiments will be discussed in detail, as the vast majority of the elements and functions will be the same between these illustrated embodiments, as will be readily apparent to one of ordinary skill in the art from the description above. Vent assembly  234  broadly includes a vent body  238 , a shiftable lid  240 , and a rod  242 . 
         [0046]    Vent body  238  is generally annularly shaped and includes an axially proximal margin  244  and an axially distal margin  246 . Axially proximal margin  244  of vent body  238  is configured for threaded receipt within receiving flange  48  of tank  30 . Axially proximal margin  244  of vent body  238  includes a threaded portion  252  that threadably secures vent assembly  234  within flange  48 . 
         [0047]    Vent body  238  includes a radially inner wall surface  254  and a radially outer surface  256 . Inner wall surface  254  includes a constant diameter portion  258  that extends axially upwardly from proximal margin  244 . Inner wall surface  254  also includes a tapered bore portion  260  that extends axially upwardly from constant diameter inner wall portion  258  to distal margin  246  of vent body  238 . Tapered bore portion  260  of inner wall  254  presents a diameter that increases smoothly and continuously from the diameter of constant diameter portion  258  to a larger diameter at axially distal margin  246 . Radially outer surface  256  includes a noncircular portion  262  that is configured such that a tool can be used to twist vent body  238  to secure the same to flange  48  of tank  30 , as will be readily appreciated by one of ordinary skill in the art. 
         [0048]    Axially distal margin  246  of vent body  238  includes a generally flat top face  276 . Top face  276  includes an axially extending groove  278  defined therein and extending in a circle. A seal  280  is disposed at least partially within groove  278  to cooperate with lid  240 , as described in greater detail below. To this end, at least a portion of seal  280  extends out of groove  278  and above top face  276  of vent body  238 . 
         [0049]    Vent body  238  also includes a crossbar  282  that spans the diameter of vent body  238  along distal margin  246  thereof. Crossbar  282  includes an axially distal portion presented by a top surface  284  and an axially proximal portion presented by a bottom surface  286 . Top surface  284  of crossbar  282  is coplanar with top face  276  of vent body  238 . The disposition of crossbar  282  adjacent axially distal margin  246  of vent body  238  provides a largely unencumbered area within the chamber of vent body  238  such that fluid can flow through vent body  238  (from proximal margin  244  to distal margin  246 ) with minimal interference, as described in greater detail with respect to the first embodiment above. Crossbar  282  also includes a generally centrally disposed enlarged portion  288  with an axial hole  290  defined therethrough. Hole  290  extends from top surface  284  to bottom surface  286 . 
         [0050]    Returning now to radially inner wall surface  254  of vent body  238 , a radially extending groove  272  is defined in wall surface  254 . In distinction to groove  72  of the first embodiment discussed above, groove  272  is disposed within tapered bore portion  260  and generally adjacent bottom surface  286  of crossbar  282 . A screen  274  is disposed within groove  272  to prevent the introduction of foreign matter through vent body  238  and into tank  30 , as will be readily appreciated by one of ordinary skill in the art upon review of this disclosure. Accordingly, screen  274  helps to both prevent contamination and deter theft of the contents of tank  30 . In this configuration, screen  274  is disposed closer to distal margin  246  and outlet end of vent body  238  than is screen  74  of the first embodiment discussed above. More particularly, screen  274  of this alternative embodiment is disposed as close to crossbar  282  as practicable, as shown particularly in  FIG. 8 . 
         [0051]    Lid  240  generally surmounts vent body  238  and is shiftable between a closed position (shown in  FIG. 8 ) and an open position (not shown, but readily appreciated by one of ordinary skill in the art from the above description). Lid  240  includes an outside top surface  292  and an inside bottom surface  294 . A portion of inside bottom surface  294  cooperates with seal  280  to substantially close vent assembly  234 . A centrally disposed threaded recess  296  extends upwardly from bottom surface  294  of lid  240 . Threaded recess  296  is coaxial with hole  290  through crossbar  282  when lid  240  is disposed in surmounting relationship with vent body  238 . 
         [0052]    Rod  242  generally supports and defines the path of travel for lid  240  by cooperating with structure of vent body  238 . In particular, rod  242  extends downwardly from bottom surface  294  of lid  240  and through hole  290  in crossbar  282 , such that crossbar  282  radially supports rod  242 . Depicted rod  242  comprises a bolt that includes a shaft  298 , a head  300  at the proximal end of shaft  298 , and a threaded portion  302  at the distal end of shaft  298 . In assembled vent assembly  234 , rod  242  extends upwardly within vent body  238 , through hole  290  in crossbar  282 , and into threaded recess  296  in lid  240 . Threaded portion  302  of rod  242  is thereby threadably secured to lid  242 , as shown particularly in  FIG. 8 . 
         [0053]    A spring  304  is axially aligned with and disposed around shaft  298  of rod  242 . In assembled vent assembly  234 , one end of spring  304  engages bottom surface  286  of crossbar  282  and the other end of spring  304  engages an engagement surface  306  of head  300  of rod  242 . As will be readily appreciated by one of ordinary skill in the art upon review of this disclosure, the extension force of spring  304  biases lid  240  toward the closed position (shown in  FIG. 8 ). 
         [0054]    The general operation of alternative vent assembly  234  should be apparent to one of ordinary skill in the art from the foregoing description and is substantially the same as the operation of vent assembly  34 , described in greater detail above. Therefore, for the sake of brevity, a redundant operational description is not presented here, but rather attention is directed to the discussion of operation of vent assembly  34 , above, with the understanding that alternative disposition of groove  272  and screen  274  do not materially change the fundamental operation of alternative vent assembly  234  from that of vent assembly  34 . 
         [0055]    Turning briefly now to  FIGS. 9-11 , a prior art gravity closing vent assembly  334  that does not maintain laminar flow of the venting fluid is depicted on a tank  330 . Prior art vent assembly  334  includes some components that are somewhat similar to those of vent assembly  34  discussed above. Therefore, in the interest of clarity, similar elements between vent assembly  34  and prior art vent assembly  334  are numbered similarly, but differing by an order of three hundred. Prior art vent assembly  334  broadly includes a stepped bore vent body  338 , a shiftable lid  340 , and a rod  342 . 
         [0056]    Prior art vent body  338  is generally annularly shaped and includes an axially proximal margin  344  and an axially distal margin  346 . Axially proximal margin  344  of vent body  338  is configured for threaded receipt within a receiving flange  348  of a tank  330 . Axially proximal margin  344  of vent body  338  includes a threaded portion  352  that threadably secures vent assembly  334  within flange  348 . 
         [0057]    Prior art vent body  338  includes a radially inner wall surface  354  and a radially outer surface  356 . Inner wall surface  354  includes a first constant diameter portion  358  that extends axially upwardly from proximal margin  344  and a second constant diameter portion  360  that extends axially downwardly from distal margin  346 . The diameter of first portion  358  is less than the diameter of second portion  360 , and a horizontally extending circular lip  362  is formed at the intersection of the portions  358 ,  360 , making inner wall surface  354  axially discontinuous. 
         [0058]    Outer surface  356  is circular and does not include a portion that could be turned with a wrench to facilitate securement of prior art vent body  338  within flange  348 . Further, the radial wall thickness of first constant diameter portion  358  is relatively thick compared to the depth of the threads on threaded portion  352 , which may add structural rigidity, but limits the area through which pressurized fluid can flow through vent body  338  and out of prior art vent assembly  334 . 
         [0059]    Axially distal margin  346  of prior art vent body  338  includes a generally flat top face  376 . Top face  376  includes an axially extending groove  378  defined therein and extending in a circle. A seal  380  is disposed at least partially within groove  378  to cooperate with lid  340 , in a manner that will be readily understood upon a review of the foregoing description. To this end, at least a portion of seal  380  extends out of groove  378  and above top face  376  of vent body  338 . 
         [0060]    Prior art vent body  338  includes a crossbar  382  that spans the diameter of vent body  338  along an axially interior portion thereof. Crossbar  382  includes a top surface  384  and a bottom surface  386 . Both top surface  382  and bottom surface  386  of crossbar  382  are disposed axially between proximal margin  344  and distal margin  346  of vent body  338  so that crossbar  382  is axially centrally disposed within vent body  338 . More specifically, bottom surface  386  of crossbar  382  is radially aligned with horizontally extending circular lip  362 . 
         [0061]    Crossbar  382  also includes generally centrally disposed enlarged portion  388  with an axial hole  390  defined therethrough. Hole  390  extends from top surface  384  of crossbar  382  to bottom surface  386  of crossbar  382 . Crossbar  382  does support rod  342  of lid  340 , as explained in greater detail below, but the axially central disposition of crossbar  382  within vent body  338  between proximal and distal margins  344 ,  346  creates turbulence within the fluid as the fluid flows through vent body  338  and out of vent assembly  334 . This turbulence slows the flow of the fluid and reduces the flow rate of the pressurized fluid out of vent assembly  334 . 
         [0062]    Lid  340  generally surmounts vent body  338  and is shiftable between a closed position (shown in  FIG. 10 ) and an open position (shown in  FIG. 11 ). Lid  340  includes an outside top surface  392  and an inside bottom surface  394 . The axial thickness of lid  340  between top surface  392  and bottom surface  394  is substantial so that lid  340  is sufficiently heavy to be biased toward the closed position by the force of gravity acting on lid  340 . A portion of inside bottom surface  394  cooperates with seal  380  to substantially close vent assembly  334 . A centrally disposed threaded recess  396  extends upwardly from bottom surface  394  of the  340 . Threaded recess  396  is coaxial with hole  390  through crossbar  382  when lid  340  is disposed in surmounting relationship with vent body  338 . 
         [0063]    Rod  342  generally supports and defines the path of travel for lid  340  by cooperating with structure of prior art vent body  338 . In particular, rod  342  extends downwardly from bottom surface  394  of lid  340  and through hole  390  in crossbar  382 , such that crossbar  382  radially supports rod  342 . Depicted rod  342  comprises a bolt that includes a shaft  398 , a head  400  at the proximal end of shaft  398 , and a threaded portion  402  at the distal end of shaft  398 . In assembled prior art vent assembly  334 , rod  342  extends upwardly within vent body  338 , through hole  390  in crossbar  382 , and into threaded recess  396  in lid  340 . Threaded portion  402  of rod  342  is thereby threadably secured to lid  342 , as shown particularly in  FIG. 10 . 
         [0064]    Some aspects of the general operation of prior art vent assembly  334  will be apparent to one of ordinary skill in the art from the foregoing description and, therefore, will not be described in detail here. It is emphasized, however, that prior art vent assembly  334 , while satisfactory in some respects, includes structural differences that limit the flow rate of pressurized fluid through vent body  338 . For example, the relatively thick radial wall thickness of threaded portion  352  restricts the area of vent body  338  through which pressurized fluid can flow, limiting the maximum possible flow rate. Additionally, the axially central disposition of crossbar  382  between proximal and distal margins  344 ,  346  and the inclusion of horizontally extending circular lip  362  of the stepped bore of vent body  338  both create turbulence within the fluid as the fluid flows through vent body  338  and out of vent assembly  334 . This turbulence slows the flow of the fluid and further reduces the maximum possible flow rate of the pressurized fluid out of vent assembly  334 . 
         [0065]    The preferred forms of the invention described above are to be used as illustration only, and should not be utilized in a limiting sense in interpreting the scope of the present invention. Obvious modifications to the exemplary embodiments, as hereinabove set forth, could be readily made by those skilled in the art without departing from the spirit of the present invention. 
         [0066]    The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and access the reasonably fair scope of the present invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention set forth in the following claims.