Patent Publication Number: US-2021188539-A1

Title: Vent assembly

Description:
This invention relates to vent assemblies and, in particular, to a vent assembly, for example a vertical vent assembly, for a flow conduit. 
     Many installations require vent assemblies. An example of such an installation is a tank in which volatile liquids are stored. In such tanks, the headspace above the liquid may become saturated with vapour. It is often beneficial to allow the vapour to vent to atmosphere in a free or controlled manner. To do so it is known to use a vent assembly. The vent assembly may be coupled to, or provided with, a flow conduit to fluidly connect the source of vapour to the assembly. 
     It is known to provide vent assemblies with flame arresters. 
     Flame arresters are provided with flame arrester elements which are arranged to prevent the transmission of a flame. Flame arresters may be static or dynamic with the static type being those which are arranged to prevent flame transmission by virtue of the provision of quenching gaps in the flame arrester element. Suitable materials for flame arrester elements include crimped ribbon which is spooled to provide plural parallel passageways. Other materials are also known for the fabrication of flame arrester elements. 
     Flame arresters are typically formed as in-line flame arresters where the flame arrester is provided with two pipe connections, one on each side (ISO 16852 s 3.22) and end-of-line (EOL) flame arresters where the flame arrester is fitted with one pipe connection only (ISO 16852 s 3.21). Where provided, vent assemblies tend to utilise EOL flame arresters although in-line flame arresters are known. 
     As stated above, many tanks are fitted with vent pipes to prevent an overpressure developing within the tank. Vent pipes typically extend vertically from the tank or from pipework attached to the tank. If the tank is arranged to store flammable or volatile material it is usual and often necessary to fit the vent pipe with an EOL flame arrester. An example of such a tank is an above ground fixed storage tank for the storage of flammable or volatile liquids. Other constructions are also provided with EOL flame arresters. 
     Vent assemblies, and especially those provided with EOL flame arresters, are typically located at an elevated position. In order to prevent precipitation and other debris from falling into the flow conduit, and/or on to the flame arrester element, which might clog the flame arrester element or increase the pressure drop across the flame arrester element, it is usual to provide a weather hood. A weather hood is usually a cowl or inverted cup-shaped member mounted above the flow conduit or flame arrester element and with a transverse dimension (e.g. a diameter) larger than that of the flow conduit or flame arrester element so as to shield the flow conduit or flame arrester from precipitation and falling or blown debris. 
     As will be appreciated, for a weather hood to effectively shield the flow conduit or flame arrester element from precipitation, it is necessary to provide a weather hood which is sufficiently sized and closely located to the vent pipe to provide an effective shield. 
     As will be further appreciated as fluid flows out of a vertically-oriented vent assembly or EOL flame arrester the fluid flows vertically upwards. The provision of an effective weather hood will alter the vertical passage of the outflowing fluids and cause that fluid to experience a downward flow (or at least a vector component of a downward flow). 
     In situations where vent pipes are connected to tanks holding volatile, noxious and/or flammable materials it is usual to determine a safe working zone around the pipe. Clearly, it would be beneficial to have as small as safe working zone as possible so that the surrounding area need not be cordoned off or otherwise subject to exclusion. 
     FR2304365 discloses a flame arrester with a weather hood mounted in a housing shaped to cause a certain flow to egressing fluids. The housing will result in a significantly restricted flow. Moreover, although the flame arrester is provided with a weather hood it is understood that due to the construction it will not be effective in all precipitation conditions and precipitation will be allowed to contact the flame arrester element and/or the flow conduit. 
     The present invention seeks to at least partially mitigate the issues found in the prior art. 
     In a first aspect of the invention there is provided, a vent assembly in accordance with Claim  1 . 
     In a further aspect of the invention there is provided a vent assembly comprising a housing, a flow conduit and a weather hood, the flow conduit having a proximal end for being fluidly connected to a source of material and an open distal end, the housing having a base portion, a side wall portion, and a top portion, the flow conduit comprising a baffle to direct fluid flowing from the flow conduit towards the weather hood and through the housing in a vertical direction and towards the top portion of the housing. 
     The baffle acts to reverse the flow of fluid which would otherwise be directed downwardly under the action of the weather hood on the fluid egressing the conduit. 
     Advantageously the vent assembly will encourage or direct an upward flow of fluid from the flow conduit at least a portion of which would otherwise flow downwardly due to the presence of a weather hood. The open top encourages quick and effective venting from the housing so that there is not a substantial build-up of outflow gases within the housing. Clearly, if the fluid flowing out from a conduit is moving in a vertical and/or upwards direction the safe working zone is likely to be closer to the venting location than if the fluid flowing out from the pipe is moving in a downwards direction. 
     The baffle may direct fluid flowing from the flow conduit in a vertical direction and towards the top portion of the housing and, in embodiments, to the periphery of the top portion of the housing. 
     The base portion of the housing may be at least substantially closed, or may be at least substantially open (i.e. fluidly non-occluded). In embodiments, the base portion may comprise one or more drainage ports. The drainage ports may be, for example simple apertures or may be formed by or between an array of internally radiating supports, the space between adjacent supports providing said drainage ports. The drainage ports are useful because they prevent the build-up of liquids (e.g. precipitation) which would otherwise be retained by the housing. The base portion, and/or at least those parts of the base portion which are substantially open may comprise a gauze material, which may function as a bird screen. 
     Because the baffle causes an upward flow of fluid, the bottom portion of the housing may be open. This is advantageous because it reduces weight, provides drainage and/or provides for a throughflow of air from the bottom toward the top portion of the housing. 
     In embodiments, the side wall portion may extend from the periphery of the base portion. The drainage ports may be located at or towards the periphery of the base portion. The base portion of the housing may comprise an array of internally radiating supports, between adjacent supports are provided said drainage ports. The drainage port or some or all of the drainage ports may be provided with one-way valves. The side wall portion is preferably planar, for example extending in a direction parallel to a principal flow direction of fluid egressing the distal end of the flow conduit. The side wall portion may define a shape of constant cross-section. Advantageously, such a side wall portion, and the associated housing, is easy to construct and install. 
     The top portion of the housing may be an open top or it may be covered, at least in part by a perforate member such as a gauze or mesh. The top portion may function as a bird screen. This will help to prevent leaves or other debris from falling into the housing. The gauze or mesh may be heated, for example, using a steam jacket or other appropriate means, so that frost, ice or snow which is on or in the gauze or mesh can be melted. 
     The weather hood may be provided by a solid portion, which may extend across a portion of the open top. The solid portion may present a convex surface to fluid flowing from the flow conduit. If present, the solid portion may be attached to the side wall and may be symmetrically located in relation to the side wall. In an embodiment, the solid portion may have a depending wall formed at or towards its periphery. The weather hood has a periphery larger than the distal end of the flow conduit, for example the weather hood has a minimum transverse dimension which is larger than a maximum transverse dimension across the flow conduit, for example at the distal end of the flow conduit. 
     The weather hood may have a first flow conduit facing face and a second environment facing face. In embodiments, the flow conduit facing face of the weather hood may be substantially flat, and the environment facing face of the weather hood may be substantially flat. In other embodiments, the flow conduit facing face of the weather hood may be convex and the environment facing face of the weather hood may be concave or may be flat. 
     The weather hood may further comprise a drainage channel or tube in communication with the environment facing face. Plural drainage channels or tubes may be provided. 
     The weather hood may be attached to the side wall of the housing, e.g. connected by one or more spokes, arms and/or support bars. The or a space between said spokes, arms and/or support bars may be provided with a perforate member. The weather hood may be symmetrically located in relation to the side wall. 
     The weather hood may have a depending wall formed at or towards its periphery. The weather hood, for example the depending wall of the weather hood, may be provided with a secondary baffle, which may be outwardly directed. The secondary baffle may extend outwardly around the weather hood, for example around the entire depending wall of the weather hood. The internal angle defined between the depending wall and the secondary baffle may be acute. 
     Advantageously, in use, the secondary baffle both provides means to direct flow, for example by deploying the Coanda effect, and/or provides a reservoir for the receipt of fluid, for example precipitation. The terminal edge of the baffle (i.e. the distal edge) may provide a weir over which collected water can overflow. The terminal edge of the baffle may comprise a lip or an edge portion. 
     The secondary baffle may be connected to the depending wall at a juncture. Preferably the juncture of the secondary baffle and the depending wall is smooth and curved which, advantageously will help with flow. 
     The secondary baffle may comprise one or more drainage apertures for drainage of rain water that flows into the housing. Advantageously, this allows water from environmental conditions to flow away from the flow conduit to prevent damage. 
     As will be appreciated the vent assembly having a flow conduit, baffle, weather hood, and housing defines a flow path for fluid egressing from the flow conduit into the atmosphere, in which the flow path vents to the atmosphere in a substantially vertical, upward direction. 
     The baffle preferably extends about the entire periphery (e.g. circumferentially) of the flow conduit. 
     In embodiments, the baffle extends outwardly around the entire side wall and the internal angle defined between the flow conduit and the baffle may be acute. For example, the baffle may taper outwardly from the flow conduit towards, to or beyond the distal end of the flow conduit. 
     The flow conduit may comprise a simple pipe with a constant cross section or may comprise a body which flares outwardly or inwardly towards the distal end from a tubular portion of constant cross section. 
     The flow conduit may be provided with a flange. The flange may be provided at or adjacent the distal end of the flow conduit. The baffle may be secured to the flow conduit at the flange. Alternatively, the baffle may be secured to a side wall portion of the flow conduit, located between the proximal and distal ends of the conduit. 
     The baffle may be provided with or comprise one or more baffle drainage ports. The or each baffle drainage port may be, for example simple apertures, for example formed as a gap or space between the flow conduit and the baffle or may be formed by or between an array of internally radiating supports, the space between adjacent supports providing said baffle drainage ports. The baffle drainage ports are useful because they prevent the build-up of liquids (e.g. precipitation) which would or could otherwise be retained by the baffle. Alternatively, the baffle may provide a weir over which retained liquids can flow. 
     In embodiments, the vent assembly may further comprise a flame arrester assembly. The flame arrester assembly may be one known to those skilled in the art. The flame arrester assembly, comprising a flame arrester element, may be located at or proximate the distal end of the flow conduit. Additionally or alternatively, the vent assembly may be provided with one or more of a pressure relief valve (PRV), vacuum relief valve (VRV) or a pressure and vacuum release valve (PVRV). 
     A further aspect of the invention provides a vent assembly comprising a flow conduit having a principal flow axis, a housing and a weather hood, wherein the weather hood is mounted above a distal end of the flow conduit for preventing precipitation and/or debris from falling into the flow conduit, the weather hood comprising a top portion and an optional peripheral wall extending towards but outboard of the flow conduit, the flow conduit and/or the weather hood having a baffle. 
     The baffle may be arranged to direct fluid flowing out of the flow conduit, in a direction substantially parallel to said principal flow axis. 
     In this specification, a direction substantially parallel means a direction with at least a vector component in a direction parallel to the flow axis. 
    
    
     
       In order that the invention may be more fully understood it will now be described, by way of example only, and with reference to the accompanying drawings, in which: 
         FIG. 1A  is a vent assembly of the prior art; 
         FIG. 1B  is a further vent assembly of the prior art; 
         FIG. 2  is a schematic sectional view of a first embodiment of a vent assembly according to the invention; 
         FIG. 3  is a schematic sectional view of a second embodiment of a vent assembly according to the invention; 
         FIG. 4  is a schematic sectional view of a third embodiment of a vent assembly according to the invention; 
         FIG. 5A  is an isometric view of a fourth embodiment of a vent assembly according to the invention; 
         FIG. 5B  is a sectional view of the fourth embodiment of a vent assembly according to the invention; 
         FIG. 6  is a schematic sectional view of a fifth embodiment of a vent assembly according to the invention; 
         FIG. 7  is a schematic sectional view of a sixth embodiment of a vent assembly according to the invention. 
     
    
    
     Referring first to  FIG. 1A , there is shown a flame arrester A and a housing B of the prior art. The flame arrester A and the housing B in combination comprise a flow conduit  1 , a flame arrester assembly  3 , and a weather hood  12 . The housing B further comprises an annular suction passage  11 . The housing B has a flow cross-section which tapers upwards in the manner of an injector or a diffuser, which opens into an outlet open at the top. 
     A flow path FP 1 ′ of fluid venting into the atmosphere (out-breathing mode) from the flame arrester A and housing B is illustrated with the series of arrows. 
     In use, the weather hood  12  protects the flame arrester assembly  3  from atmospheric conditions such as direct precipitation. The annular suction passage  11  allows for fresh air to enter the housing B. The housing B and the weather hood  12  are closely matched in shape so as to seek to provide a ‘jet effect’. This is may impede performance of the flame arrester A by providing a flow restriction. Moreover, rain water may enter the flame arrester assembly  3  in extreme weather conditions. During heavy rain, rain water will enter into the top open and hit the outer surface of the weather hood  12  and then travel down along the outer surface. Due to the effect of gravity, the velocity of the flowing water significantly increases at the lower edge of the weather hood. The flowing water will hit the inner surface of the housing  7  and at least some of water will enter into the flame arrester element  3  and further, the piping work  1 . 
     Referring now to  FIG. 1B  there is shown a prior art vent assembly comprising a flow conduit provided with a flame arrester and a weather hood. The flow direction of gas venting via the vent assembly is indicated at FP 1 ″. As will be appreciated, the weather hood causes a generally downward flow of egressing fluid. 
     Referring now to  FIG. 2 , there is shown a vent assembly  200  according to the first embodiment of the invention. The vent assembly  200  comprises a flow conduit  10 , a weather hood  12 , and a housing  13 . A so called ‘end-of-line’ (EOL) flame arrester  1  is optionally provided. The flame arrester  1  comprises a flame arrester assembly  11 . 
     The flow conduit  10  comprises a proximal end  10 A for connection to a source of material to be vented (for example a tank having associated venting pipework) and a distal end  10 B. In this embodiment, the flow conduit  10  is cylindrical in shape and flares outwardly towards the distal end but may be any other suitable shape. The proximal end  10 A is configured to be secured to the end of a line, e.g. to a tank or to a pipe (not shown) via suitable means, e.g. flanges and bolts. 
     The flame arrester assembly  11  may be any suitable flame arrester assembly known to those skilled in the art. The flame arrester assembly  11  will typically comprise a flame arrester element (not shown), which is permeable to permit fluid to flow in either direction, into or out of the vent assembly  200 . The flame arrester  1  may be secured to a flange (not shown) provided at the distal end  10 B of the flow conduit  10 . 
     The weather hood  12  comprises a planar top or shield portion  12 A from the periphery of which depends a peripheral skirt portion  12 B. Extending from the distal or terminal edge of the peripheral skirt portion  12 B is an optional peripheral baffle  12 C. The peripheral baffle  12 C extends endlessly around the circumference of the skirt portion  12 B of the weather hood  12  and extends away from the skirt portion  12 B so as to define an acute included angle therebetween. The juncture  12 D of the peripheral baffle  12 C and skirt portion  12 B is preferably curved. The peripheral baffle  12 C may be integrally formed with the weather hood  12  or may be provided on a separate part and be secured to the weather hood  12  using appropriate securing means. In embodiments, the peripheral baffle  12 C may be absent. In this case, the transverse dimension of the shield portion  12 A is greater than the transverse dimension of the flame arrester assembly  11  to such an extent that it provides a shield in all weather conditions. If the peripheral baffle  12 C is present it will typically be provided with a short skirt (not shown) depending from its terminal edge to prevent or inhibit overflowing water from running along the under-surface of the baffle  12 C. Additionally or alternatively a drainage channel or pipe may be provided, extending from the juncture  12 D to the outside of housing  13 . 
     The weather hood  12  is mounted to the vent assembly  200  and is sized to cover the flow conduit  10  and the flame arrester element (not shown) of the flame arrester assembly  11  (if present). In this embodiment, the weather hood  12  may be formed from steel or other suitable alloys or other materials, such as polymers which are corrosion resistant and/or lightweight. 
     Turning now to the housing  13  this provides an enclosure for the distal end  10 B of the flow conduit  10 , the flame arrester  1  (if present) and, in particular, for the flame arrester assembly  11  (if present) and the weather hood  12 . The housing  13  comprises a base portion  13 A, a side wall  13 B, and an optional top portion  13 C. 
     The base portion  13 A comprises a base plate  131 A which is provided with a central aperture  131 B, which is sized and shaped to accommodate the flow conduit  10 . The flow conduit  10  extends through the base portion  13 A. The side wall  13 B of the housing  13  upstands from the base portion  13 A. The base plate  131 A of the base portion  13 A comprises a plurality of drainage ports  15  at or located towards the periphery of the base plate  131 A, although they may be located at any position of the base plate  131 A. In this embodiment, the drainage ports  15  are apertures within the base portion  13 A of the housing  13 . Alternatively, the base portion may comprise plural spokes or arms which extend from the flow conduit to the side wall portion, drainage ports being provided between adjacent spokes or arms. The space between one or more adjacent spokes or arms may be occluded with a mesh or gauze material. In another embodiment, the base plate  131 A may be a perforate plate or screen. 
     In this embodiment, the top portion  13 C (which is optional) comprises a gauze or mesh screen  131 C so as to allow the free flow of fluid into and out of the housing  13  whilst providing a barrier to matter which might otherwise fall into the housing  13 . 
     Importantly, the vent assembly  200  further comprises a baffle  12 E. The baffle  12 E extends endlessly around the flow conduit  10  at a location between the flame arrester assembly  11  and the base portion  13 A of the housing  13 , and preferably at a location between the peripheral baffle  12 C and the base portion  13 A of the housing  13 . The baffle  12 E may be a separate part that is secured, e.g. seamlessly, to the flow conduit  10  using appropriate securing means, e.g. welding or nuts and bolts with any necessary gaskets. 
     The baffle  12 E may be provided with one or more drainage apertures (not shown) to allow any otherwise-collected water from draining therefrom. The or each drainage aperture may be provided with a flow director to ensure that gas or vapour egressing the distal end  10 B of the flow conduit  10  is all directed upwardly by the baffle  12 E and is unable to vent via the drainage ports. Alternatively, the drainage port may be connected via a tube or other flow channel to the outside of the vent assembly. The tube may have a non-rectilinear form so as to inhibit the flow of gas, for example a U-tube. 
     The outer circumference of the baffle  12 E is not larger than the outer circumference of the peripheral baffle  12 C, i.e. the maximum transverse dimension of the peripheral baffle  12 C is wider than the maximum transverse dimension of the baffle  12 E. 
     The vent assembly  200  may be further provided with supporting elements (not shown), e.g. spokes, to support the weather hood  12  on the flame arrester  1  and within the housing  13 . The flame arrester  1  and the housing  13  may be secured together by any suitable means, e.g. nuts and bolts. 
     The weather hood  12  is configured to protect the distal end  10 B of the flow conduit  10 , and the flame arrester assembly  11  from precipitation and debris ingress into the vent assembly  200 . As stated above, the top portion  13 C of the housing  13 , where provided, inhibits the passage of solid matter into the housing  13 . 
     The flow path FP 2  of fluid venting into the atmosphere (out-breathing mode) from the vent assembly  200  is illustrated with a series of arrows. 
     The flow path FP 2  is defined by the flow conduit  10 , the weather hood  12 , and the housing  13 . Fluid may flow freely in either direction, into and/or out of the vent assembly  200  depending upon the pressure difference within the vent assembly  200  in comparison to the atmosphere. It will be appreciated that fluid flowing from the conduit  10  via the flame arrester assembly  11  (if present) and the weather hood  12  has a substantially downward flow direction. The provision of the housing  13  and/or the baffle  12 E causes the substantially downward flow exiting the weather hood  12  to revert into a substantially upward flow to exit the housing  13 . The provision of a mesh or gauze top portion  131 C of the housing  13  does not impede or hinder the egress of fluid from the housing  13  so that a head of fluid is not able to develop within the housing  13 . 
     In use, and in out-breathing mode, fluid flows from its source (not shown) along the flow path FP 2  from the flow conduit  10 , through the flame arrester assembly  11 , and flows along the inner surface of the skirt portion  12 B of the weather hood  12 , along the peripheral baffle  12 C over the curved juncture  12 D, and upwards in a vertical flow direction to vent to the atmosphere. 
     The baffle  12 E further encourages the flow path FP 2  of fluid in an upwards direction. 
     The plurality of drainage ports  15  provide an outlet for precipitation that may ingress into the housing  13  during normal use and would otherwise collect therein. In this embodiment, water that ingresses into the vent assembly  200  will either run to the base plate  131 A via the annular gap between the peripheral baffle  12 C and the side wall  13 B of the housing  13  or it will collect in the curved juncture  12 D of the peripheral baffle  12 C. Once the capacity of the peripheral baffle  12 C is reached water will overflow to drain out of the housing  13  via the drainage ports  15 . The peripheral baffle  12 C may comprise a lip or an edge portion (not shown) to prevent water from flowing along the inner surface of the peripheral baffle  12 C toward the flame arrester assembly  11 . Alternatively, the water collected by the peripheral baffle  12 C may be drained out via a drainage channel or tube (not shown) connected from the  12 D to the outside of the housing  13 . In this way, the weather hood  12  protects the flame arrester assembly  11  from damage caused by rain water and other foreign objects that may ingress into the vent assembly  200  through the top portion  13 C of the housing  13  by providing a pathway for the water and other entrained debris to flow from the housing  13 . 
     It will be appreciated that the baffle  12 E extends away from the conduit  10  in an upward direction and so may also collect ingressing or draining water. Water collected by the baffle  12 E may overflow the baffle  12 E and thence exit the housing  13  via the drainage ports  15 . 
     It is also possible to provide, as the weather hood  12  a flat plate with an optional short peripheral and depending wall  12 B. Outboard of the peripheral wall the weather hood may be secured to the housing using struts or spokes with the intervening spaces covered with a mesh or gauze, or a perforate plate. 
     In an alternative, the weather hood  12  may form part of, and be secured to, the housing  13 , for example the weather hood  12  may be secured to the side wall  13 B of the housing  13  by radial struts or supports. The space between the side wall  13 B and weather hood  12  (for example, between the radial supports or struts) may optionally be covered with a mesh or gauze to prevent debris from falling into the housing  13 . In such a case, the top portion  13 C may be completely open. 
     In embodiments, the top portion  13 C may be formed from a material that may be heated, for example to melt snow or ice, which may otherwise cover the vent assembly  200  and prevent or inhibit fluid venting. 
     In the case of a higher pressure within the vent assembly  200  than the surrounding atmosphere, in which fluid flows out of the vent assembly  200  (‘out-breathing’ mode), the fluid follows path FP 2  from its source (not shown), to the flow conduit  10 , through the flame arrester element (not shown) of the flame arrester assembly  11 , under the skirt portion  12 B of the weather hood  12 , through the housing  13 , and out through the top portion  13 C of the housing  13 . The configuration of the vent assembly  200  of the present invention is designed to vent fluid into the surrounding atmosphere in a vertical or at least substantially vertical direction. 
     In the case of a lower pressure within the vent assembly  200  in comparison to the atmosphere, it is also the case that atmospheric air may enter the vent assembly  200  and flow in the opposite direction to that described for flow path FP 2  (‘in-breathing’ mode). Air may also be introduced via the base portion. 
     The location and shape of the baffle  12 E, the skirt portion  12 B of the weather hood  12  and the housing  13  are configured to dictate the flow path FP 2  of fluid exiting the vent assembly  200 . Fluid vents from the vent assembly  200  to the atmosphere in a predominantly upward, vertical direction, to exit the vent assembly  200 . This vertical flow is advantageous for safety purposes because it reduces the zoned (hazard) area underneath the vent assembly  200 . 
     Referring now to  FIG. 3 , there is shown a vent assembly  300  according to a second embodiment of the invention. The vent assembly  300  comprises a flow conduit  30 , a weather hood  32 , and a housing  33 . A flame arrester  3  is optionally provided. The flame arrester  3  comprises a flame arrester assembly  31  and a housing portion  30 H. The flame arrester  3  is connected to pipework to be vented (not shown) via the flow conduit  30 . As before, the terminal portion of the flow conduit  30 , the flame arrester assembly  31 , and the housing portion  30 H (which provides a weather hood  32 ) are enclosed within the housing  33 . 
     The flame arrester assembly  31  comprises a flame arrester element (not shown) and one or more element supports (not shown). 
     The housing portion  30 H is provided by an upturned cup portion  30 C defined by a weather hood  32  and a peripheral wall  32 B depending from the weather hood  32 . The flow conduit  30  terminates in the housing portion  30 H. The flame arrester assembly  31  is located between a terminal portion of the flow conduit  30  and a facing portion of the peripheral wall  32 B. 
     Extending outwardly and upwardly from the peripheral wall  32 B of the housing portion  30 H is a peripheral and continuous peripheral baffle  32 C. The peripheral baffle  32 C may comprise a short wall or skirt portion (not shown) depending from its terminal edge to inhibit water from flowing along the under surface of the baffle  32 C. 
     The vent assembly  300  further comprises a baffle  32 D. The baffle  32 D is secured to the flow conduit  30  using any suitable securing means. The outer circumference of the baffle  32 D is not larger than the outer circumference of the peripheral baffle  32 C, i.e. the minimum transverse dimension of the peripheral baffle  32 C is larger than the maximum transverse dimension of the baffle  32 D. 
     The flow conduit  30  is substantially cylindrical in this embodiment, although may be any other appropriate shape. The housing  33  is connected to the flow conduit  30  using suitable means. 
     The housing  33  is as shown and described above in relation to the embodiment of  FIG. 2  and comprises a base portion  33 C, a side wall  33 B, and a top portion  33 A. The base portion  33 C comprises a plurality of drainage ports  35 , which may be any appropriate structure and shape. The drainage ports  35  may be located at any point of the base portion  33 C, for example at or towards the flow conduit  30  or at or towards the periphery of the base portion  33 C. The top portion  33 A is preferably mesh or gauze and may or may not be heated 
     The flame arrester element (not shown) of the flame arrester assembly  31  is permeable to fluid flowing in either direction, into or out of the vent assembly  300 . The flame arrester element (not shown) is exposed at the base wall  31 B of the flame arrester assembly  31 , and therefore the base wall  31 B is permeable to fluid. The side wall  32 B of the flame arrester assembly  31  is impermeable to fluid. 
     In use, the weather hood  32  protects the flame arrester assembly  31  from water and debris that may ingress into the vent assembly  300 . 
     A flow path FP 3  is shown for the flow of fluid out of the vent assembly  300 . The flow path FP 3  is defined by the flow conduit  30 , the housing portion  30 H, the baffle  32 C, the baffle  32 D and the housing  33 . In this embodiment, and in out-breathing mode, the fluid flows along the flow path FP 3  from the flow conduit  30 , to the housing portion  30 H in a substantially vertical direction. Upon entering the housing portion  30 H, the fluid flow path changes to a downwards direction. The fluid flows along the flow path FP 3  through the flame arrester assembly  31  in a downwards direction. The fluid is directed upwardly to exit the housing  33  and into the surrounding atmosphere in a substantially vertical direction by the action of the housing and the baffle  32 D. As the fluid flows upwardly, it passes between the terminal edge of the peripheral baffle  32 C and the facing wall of the housing  33 . 
     The peripheral baffle  32 C provides a reservoir for the collection of precipitation. Once the volume defined by the baffle is filled the water will overflow and contact the housing from where it will drain via drainage ports  35 . As stated previously, the baffle  32 C may be provided with a short depending skirt portion and/or may be provided with drainage ports and/or channels. 
     Referring now to  FIG. 4 , there is shown a vent assembly  300 ′ according to a third embodiment of the invention. As this vent assembly  300 ′ is similar to that previously described in relation to  FIG. 3 , the same numeric indicators will be used but distinguished by use of a prime (′). 
     The operation of the vent assembly  300 ′ is substantially the same as for vent assembly  300  of  FIG. 3 . In contrast to the vent assembly  300 , the vent assembly  300 ′ comprises an optional baffle  32 C′ with a curved juncture  32 E, and a baffle  32 D′ with a curved juncture  32 F. The curved juncture  32 E comprises an elongate portion which protrudes from the face of the flame arrester assembly  31 ′ by a distance, d. The baffle  32 C′ extends endlessly around the circumference of the flow conduit  30 ′. 
     Advantageously, the curved juncture  32 E of the baffle  32 C′ of the weather hood  32 ′ provides an enhanced flow path FP 3 ′ for fluid to exit the vent assembly  300 ′. The flow of fluid follows the flow path FP 3 ′ provided in part by the peripheral baffle  32 C′ to direct the fluid to vent in a substantially vertical direction. Fluid flows from the flow conduit  30 ′ and through the flame arrester assembly  31 ′ where the fluid contacts the surface of the baffle  32 C′ to be directed in a substantially upward and vertical direction, out of the housing  33 ′ and into the atmosphere. 
     Furthermore, the peripheral baffle  32 C′ provides a similar weather drainage mechanism. Rain water collects in the curved juncture  32 E of the baffle  32 C′, which is prevented from entering the flame arrester assembly  31 ′. The baffle  32 C′ creates a weir system, as described above for  FIG. 2  and also shown in  FIG. 3 , which overflows once full to allow water to drain out of the drainage ports  35 ′. As before, the peripheral baffle  32 C′ may comprise a short skirt or wall depending from a terminal edge to prevent fluid flowing along the under-surface of the baffle  32 C′. 
     Referring now to  FIGS. 5A and 5B , there is shown a vent assembly  500  according to a fourth embodiment of the invention. The vent assembly  500  comprises a flow conduit  50 , a weather hood  52  and a housing  53 . A flame arrester  5  comprising a flame arrester assembly  51  is optionally provided. The housing  53  is provided to house the terminal end of the flow conduit  50  and the flame arrester assembly  51  (if present). 
     The flow conduit  50  comprises a lower flange  50 A at a proximal end thereof, a frusto-conical shaped body  50 B and an upper flange  50 C at a distal end thereof. The lower flange  50 A is configured to be secured to a source of material to be vented (for example a tank having associated venting pipework) in order to afford fluid connection therebetween. Any suitable attachment means may be used, e.g. bolts. 
     If present, the flame arrester assembly  51  comprises a flame arrester element  51 B, a first element support  51 A and a second element support  51 C. The flame arrester element  51 B is sandwiched between the first element support  51 A and the second element support  51 C. The flame arrester element  51 B is permeable to fluid flowing in either direction, into or out of the vent assembly  500 . 
     In this embodiment, the weather hood  52  comprises a top portion  52 A and an optional skirt portion  52 B depending from the periphery of the top portion  52 A. The top portion  52 A is disc-like and is substantially circular in plan. The top portion  52 A of the weather hood  52  is located within the vent assembly  500  to substantially cover, in plan, the flame arrester element  51 B of the flame arrester assembly  51 . It will be appreciated that the particular configuration and size of the weather hood  52  in embodiments is a matter of choice for the designer in order to achieve the shielding of the distal end of the flow conduit and/or flame arrester assembly from precipitation and to allow or ensure the appropriate flow of fluid. The skirt portion  52 B may not be present, and instead, may be replaced with a perforated plate extending from the periphery of the weather hood  52  and towards the side wall  53 B of the housing  53 . The housing  53 , flame arrester assembly  51  (if present) and weather hood  52  are secured to the upper flange  50 C of the conduit  50  in part by common bolts  56 . 
     As before, the weather hood  52  has a transverse dimension (e.g. a diameter) d 1  and the flame arrester assembly  51  has a transverse dimension (e.g. a diameter) d 2 . In this embodiment, the diameter d 1  of the weather hood  52  is greater than the diameter d 2  of the flame arrester assembly  51 , the ratio of d 1 :d 2  is approximately say 1.3:1 to 1.9:1 or 2:1. Whilst it is possible for the transverse dimension d 1  of the weather hood  52  to be less than the transverse dimension d 2  of the flame arrester assembly  51  in this invention, it is not preferred. 
     There is further provided a baffle  60  which may be provided with drainage apertures (not shown) located proximate the flame arrester assembly  51  (if present). The drainage apertures (not shown) allow any collected water from draining therefrom. 
     The baffle  60  is frusto-conical in shape and provides an upstanding wall around the flame arrester assembly  51 . The baffle  60  extends upwardly and away from the distal end of the flow conduit  50  and/or the flame arrester assembly  51 . The baffle  60  may be secured to the upper flange  50 C of the conduit  50  in common with the flame arrester assembly  51  and weather hood  52 , that is, using common bolts  56  and nuts  57 . It is also possible for the baffle  60  to be secured at a level that is lower than the flame arrester assembly  51 . 
     The baffle  60  extends endlessly around the circumference of the side wall  52 B of the weather hood  52  and extends away from the side wall  52 B so as to define an acute angle with respect to a longitudinal flow axis along the conduit  50 . The acute angle may be between 10 and 45 degrees, preferably between 15 and 30 degrees. 
     The distal edge of the baffle  60  has a transverse dimension (e.g. a dimeter) d 3  which is greater than d 2  but is preferably less than d 1  such that the weather hood  52  shields the baffle  60  from impinging precipitation. In embodiments, the distal portion of the baffle  60  may extend outwardly and at an angle to the body of the baffle  60 . 
     The vent assembly  500  includes a plurality of bolts  56  and corresponding nuts  57 . The bolts  56  extend through apertures  58  provided in the upper flange  50 C, through matched apertures in the first element support  51 A and second element support  51 C of the flame arrester assembly  51  to secure those components together. Advantageously, nuts  57  are provided to secure the bolts  56  such that the flame arrester element  51 B is securely retained between the first element support  51 A and second element support  51 C. At least some of the bolts  56  have extensions which extend upwardly and engage with apertures formed in the weather hood  52  and are secured by nuts  57  to secure the weather hood  52  to the other components of the vent assembly  500 . In embodiments, wherein the housing  53  comprises an at least partially solid top portion which extends across the top of the housing  53  (not shown), the bolts  56  may extend through the top portion of the housing  53  to further secure the housing  53  to the flame arrester assembly  51 . 
     The top portion  52 A of the weather hood  52  and the baffle  60  are separated by the bolts  56  within the vent assembly  500  and are spaced apart to provide a peripheral vent V. 
     The housing  53  provides an enclosure for the flame arrester assembly  51  and the weather hood  52 . The housing  53  comprises a base portion  53 A and a side wall  53 B. In this embodiment, whilst no plated or other membered top portion is shown although it is understood that the vent assembly  500 , and in particular the housing  53 , may be provided with gauze or mesh or an at least partially imperforate top portion (not shown). Alternatively, the top portion is completely open, as shown, and the space between the weather hood  52  and the side wall  53 B may be provided with a gauze, mesh or other perforate member. 
     In this embodiment, the side wall  53 B of the housing  53  is cylindrical in shape. The side wall  53 B covers the flame arrester assembly  51  and the weather hood  52  when viewed from the side, i.e. horizontally. 
     The base portion  53 A is disc shaped and surrounds the flow conduit  50 , which is situated in the centre of the base portion  53 A. The base portion  53 A comprises a plurality of drainage ports  55 . In this embodiment, the drainage ports  55  comprise apertures  53 H, which are formed in the base portion  53 A to define spokes  53 S. The base portion  53 A may additionally comprise a gauze, e.g. a wire gauze covering. Alternatively, the base portion  53 A may comprise a perforate plate. 
     Alternatively, the base portion  53 A may comprise plural spokes or arms which extend from the conduit  50  to the side wall  53 B, drainage ports  55  being provided between adjacent spokes or arms. The space between one or more adjacent spokes or arms may be occluded with a mesh or gauze material. 
     The flow path FP 5  is shown for the flow of fluid into and out of the vent assembly  500 . The flow path FP 5  is defined by the flow conduit  50 , the weather hood  52 , the baffle  60  and the housing  53 . Fluid may flow freely in either direction, into and/or out of the vent assembly  500  depending upon the pressure difference within the vent assembly  500  in comparison to the atmosphere. 
     The flow path FP 5  is shown for fluid leaving the vent assembly  500  (out-breathing mode). In use, the fluid flows from the flow conduit  50  and through the flame arrester assembly  51 . The flow path FP 5  changes direction to flow upwardly and outwardly under the weather hood  52  and is directed upwardly by the baffle  60  and into the housing  53 , which further changes the direction of fluid flow within the flow path FP 5  as the fluid contacts the side wall  53 B of the housing  53 . The fluid in the flow path FP 5  vents in a substantially vertical direction out of the housing  53  of the vent assembly  500 . 
     The weather hood  52  is configured to protect the distal end of the flow conduit  50  and/or the flame arrester assembly  51  from water and debris that may ingress into the vent assembly  500 . In normal operation, water and debris, e.g. rain water may freely enter housing  53 . The drainage ports  55  provide a means for the water and debris to exit the housing  53 . Advantageously, this prevents blockage of or damage to the flame arrester assembly  51 , so that it can continue to function effectively. Also, because of the relatively large size of the drainage ports  55 , a perforate top portion (not shown) to the housing  53  may not be required (because leaves and so on can fall through the apertures  53 H) although may also be provided. 
     Advantageously, the optional side wall  52 B of the weather hood  52  is appropriately shaped so as to provide a means to allow rain water to flow along the surface of the side wall  52 B and be directed out of the housing  53  through the apertures  53 H. If any rain water does flow into the baffle  60  towards the flame arrester assembly  51  then this may egress through the drainage apertures (not shown) in the base of the baffle  60 . 
     The provision of apertures  53 H and spokes  53 S is advantageous because it reduces the overall weight of the housing  53 . 
     In an alternative, the weather hood  52  may form part of, and be secured to, the housing  53 , for example the weather hood  52  may be secured to the side wall  53 B of the housing  53  by radial struts or supports. The space between the side wall  53 B and weather hood  52  may be covered with a mesh, gauze or perforated plate to prevent debris from falling into the housing  53 . 
     Alternatively, the side wall  52 B of the weather hood  52  may further comprise a baffle (not shown), which extends circumferentially around the skirt portion  52 B of the weather hood  52  so as to define an internal acute angle. In other embodiments, the side wall  52 B of the weather hood  52  may not be present, instead the top portion  52 A of the weather hood  52  may be extended to the side wall  53 B of the housing  53  in a form of a perforated plate. 
     Referring now to  FIG. 6 , there is shown a vent assembly  500 ′ according to the fifth embodiment of the invention. As this vent assembly  500 ′ is similar to that previously described in relation to  FIGS. 5A and 5B  the same numeric indicators will be used but distinguished by use of a prime (′). The vent assembly  500 ′ comprises a flow conduit  50 ′, a weather hood  52 ′, and a housing  53 ′. A flame arrester  5 ′ comprising a flame arrester assembly  51 ′ is optionally provided. The housing  53 ′ houses components of the vent assembly  500 ′. 
     In this embodiment, the top portion  52 A′ of the weather hood  52 ′ of the vent assembly  500 ′ is a convex dome shape. The centre of the convex dome  52 C of the top portion  52 A′ faces, and is nearest to, the flame arrester assembly  51 ′. The top portion  52 A′ need not be a convex dome shape, and may be any other suitable convex shape. The top portion  52 A′ of the weather hood  52 ′ may be closed by a plate member  52 D to prevent precipitation from collecting within the concave surface of the weather hood  52 ′. The plate member  52 D may be provided with a peripheral wall depending therefrom. 
     The housing  53 ′ may optionally comprise a top portion  53 A′, which is located above the weather hood  52 ′. As before, drainage apertures  55 ′ are provided to allow drainage of liquids collected within the housing  53 ′. 
     The dimensions of the weather hood  52 ′ may be selected so as to shield the flame arrester assembly  51 ′ from precipitation. Additionally, the baffle  60 ′ may be provided with drainage apertures  61  so as to drain any fluid collected by or within the baffle  60 ′ before it contacts the flame arrester assembly  51 ′. It will be appreciated that the conical angle of the baffle  60 ′ may be selected or optimised according to the top portion  52 A′ of the weather hood  52 ′. 
     The flame arrester assembly  51 ′ (if present), weather hood  52 ′, baffle  60 ′ and housing  53 ′ may be secured as previously described. 
     The flow path FP 5 ′ is shown, in which fluid flows from the flow conduit  50 ′, through the flame arrester assembly  51 ′, through the housing  53 ′ to vent into the atmosphere in an upward, vertical direction. 
     Advantageously, the housing  53 ′ of this embodiment may significantly improve the flow path FP 5 ′ due to reduced flow restriction. The convex shape of the weather hood  52 ′ guides the flow path FP 5 ′ to vent out to the atmosphere enabling the flow path FP 5 ′ to follow a path with no sharp turns involved, which facilitates the flow capacity of the vent assembly  500 ′. 
     In an alternative, the weather hood  52 ′ may form part of, and be secured to, the housing  53 ′, for example the weather hood  52 ′ may be secured to the side wall  53 B′ of the housing  53 ′ by radial struts or supports. The space between the side wall  53 B′ and weather hood  52 ′ may be covered with a mesh or gauze or a perforate plate to prevent debris from falling into the housing  53 ′. 
     Referring now to  FIG. 7 , there is shown a vent assembly  500 ″ according to the sixth embodiment of the invention. As this vent assembly  500 ″ is similar to that previously described in relation to  FIG. 6  the same numeric indicators will be used but distinguished by use of an additional prime (′). 
     In this embodiment, the weather hood  52 ″ does not (but may) comprise a plate member (shown as  52 D in  FIG. 6 ). The top portion  53 A″ is located around the periphery of the weather hood  52 ″, and extends circumferentially towards the side wall  53 B″ of the housing  53 ″. The top portion  53 A″ may comprise apertures and/or is permeable to fluid. In embodiments, if the transverse diameter (od) of the weather hood  52 ″ is larger than that of baffle  60 ″, then the top portion  53 A″ may be a wire gauze or a perforated plate to be used as a bird screen. Otherwise, the top portion  53 A″ may comprise two parts, the part proximate to the side wall being a bird screen and the other part (adjacent the central part of the weather hood) being a solid horizontal plate. 
     The weather hood  52 ″ has a convex dome shape. The weather hood  52 ″ is further provided with a drainage tube  71 . The drainage tube  71  comprises an inlet  71 A and an outlet  71 B. The inlet  71 A of the drainage tube is preferably located below the centre of the convex dome  52 C′. The outlet  71 B of the drainage tube is located in the side wall  53 B″ of the housing  53 ″, so that the drainage tube  71  extends from, and fluidly connected to, the centre of the convex dome  52 C′ to the outer surface of the side wall  53 B″ of the housing  53 ″ to provide an open passage. The inlet  71 A is located above the plane of the outlet  71 B. 
     The drainage tube  71  may be formed from any suitable material that will not rust or otherwise degrade or deteriorate in the outdoor environment and which is chemically compatible with the venting gases. 
     In use, precipitation that would otherwise collect near the centre of the convex dome  52 C′ may drain away from the terminal end of the flow conduit  50 ″ and the flame arrester assembly  51 ″ (if present) through the drainage tube  71  via the inlet  71 A to flow towards and out of the outlet  71 B and into the external environment. Advantageously, precipitation that enters the housing  53 ″ through the top portion  53 A″ may also flow out of the housing through the drainage ports  55 ″. 
     There may be more than one drainage tube  71  provided. The drainage tube  71  may also be an open structure such as a channel along which fluids will flow. Advantageously, the drainage tubes  71  may be used to support the weather hood  52 ″ within the housing  53 ″. For example, the drainage tubes  71  may be formed from a suitably strong material to act as struts or spokes, to secure the weather hood  52 ″ to the housing  53 ″ and above the flame arrester assembly  51 ″. 
     Alternatively, the outlet  71 B of the drainage tube  71  may be located and terminate on or adjacent the wall of the baffle  60 ″ to drain via aperture  61 ″ or between the baffle  60 ″ and the side wall  53 B″ so that rain water drains from the weather hood  52 A″, through the drainage tube  71  and through the drainage ports  55 ″. 
     In circumstances where condensate or moisture forms on the inner surface of the weather hood  52 ″ (or indeed on any of the weather hoods described above) it is possible to have a drain or drainage channel  80  extending from the under surface of the weather hood  52 ″ to the baffle. The drain may comprise a wire or rod (i.e. a solid elongate object along which fluid will flow) or a pipe or channel (i.e. a body in and along which fluid can flow) which extends from the lowermost portion of the weather hood  52 ″ and, preferably extends to a facing portion of the baffle  60 ″, thereby to prevent any condensate from falling in to the flow conduit. 
     In any or all of the aforementioned embodiments, the drainage port may be of any suitable size, shape or arrangement and, for example, the drainage ports may comprise one way valves to allow egress of fluid from the housing but prevent ingress of fluid. Alternatively, in any of all of the aforementioned embodiments, the drainage ports may comprise apertures, for example large apertures, to facilitate air flow into the housing. The apertures are located in the base portion of the housing. The housing may be of any suitable shape and size, for example, the base portion may be planar or a convex or concave shape. 
     In any or all of the aforementioned embodiments, the components comprising the flame arrester assembly may be interchanged with any flame arrester assembly components known to those skilled in the art, for example, a crimped ribbon element, annular plate discs, perforated plate, wire gauze and so on. Moreover, the flame arrester element may be removed. Additionally or alternatively, the vent assembly may comprise a PRV, VRV, PVRV, pressure relief vent. 
     The various components of the invention may be made from suitable materials such as metal, for example steel, stainless steel, or any other suitably strong materials including plastics that are compatible with venting gases, and so on. In all embodiments, the flame arrester element may be formed from a porous matrix, for example a crimped ribbon. Other flame arrester elements known to the skilled person may be deployed. 
     It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention. 
     It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.