Patent Publication Number: US-2023132679-A1

Title: Filter Element Assembly

Description:
TECHNICAL FIELD 
     This invention relates to a filter element assembly for removing material that is entrained in a gas stream. The invention also relates to a drainage promoter for a filter element, and a filter element. 
     BACKGROUND 
     Filtration of gas in a compressed gas system is generally required so that the gas is sufficiently clean for a subsequent application or to minimise adverse effects of impurities on components of the system. For example, removal of compressor oil can be required to minimise chemical contamination and accumulation on valves which might lead to malfunction of the valves. 
     There are many known filter elements for use in a filter assembly in gas systems. Such filter elements generally comprise a cylindrical filtration layer or “coalescing layer” and a cylindrical anti-re-entrainment barrier or “drainage layer” surrounding the filtration layer on the outside of the filter element. The filter elements typically also comprise an end cap having a trough in which the coalescing and drainage layers are retained. 
     A gas stream enters the tubular filter element through an inlet port and flows through the cylindrical walls of the filter element, generally radially outward from the inside of the filter element to the outside. When the assembly is used to collect liquid droplets in the gas stream (for example which is carried in the stream as an aerosol), the filtration/coalescing layer will cause liquid droplets to coalesce for collection. The coalesced liquid will be carried by the flow of gas to the drainage layer where the liquid can collect. The drainage layer is configured to ensure that re-entry of the liquid into the gas stream is minimised. In use, the liquid will sink to the bottom of the drainage layer, from which it can drain into a reservoir where it can collect prior to disposal. If the liquid does not drain from the drainage layer into the reservoir at least as quickly as liquid is supplied to the drainage layer, the liquid can tend to collect at the base of the drainage layer, where it forms a ‘wet band’ in which the material of the drainage layer is saturated with the liquid. 
     After prolonged use of the filter element, the depth of the wet band can increase to the extent that gas flowing through the element wall will pass through the wet band. This can increase the resistance to flow of gas through the filter element, and therefore give rise to an increase in pressure drop across the filter element. This can result in increased operating costs. Furthermore, gas flowing through or near a saturated part of the drainage layer can draw droplets of liquid from the drainage layer into the gas flow, thereby re-contaminating the gas as it is discharged from the filter element. It can therefore be seen that significant accumulation of liquid in a wet band can reduce the operating efficiency of the filter element. When the operating efficiency is significantly reduced, the filter element in the filter assembly must be replaced, giving rise to expense and possibly also a requirement for the system in which the assembly is used to be shut down. 
     Filter elements can be arranged so that they are positioned vertically or horizontally when in use. Traditionally, horizontally placed coalescing filter elements have a standard circular outer drainage layer, or a drainage layer with an elongate tab that is made from the same material as the drainage layer and positioned at the bottom of the element when it is in its deployed position (i.e., at the circumferentially bottom position in a horizontally deployed filter element having a cylindrical shape, viewing along the element). 
     Reduction of a wet band which can form during use of a filter element would allow more area of the un-wetted filtration material to be used, which would improve the performance of the filter element. 
     SUMMARY 
     In a first aspect of the present disclosure, there is provided a filter element assembly comprising:
         a. a filter element for location in a housing of a filter, comprising a wall of a filtration medium which defines a hollow space, for a gas stream to flow from the space through the wall to be filtered, the filtration medium including a filtration layer, and a drainage layer located outside the filtration layer in which liquid separated from the gas stream can collect, and first and second end caps at opposite ends of the wall, one of the end caps including a port for a gas stream which communicates with the space within the wall; and   b. a drainage promoter comprising a fin which can be fitted/configured to be connected to the filter element so that it extends along the filter element substantially an entire distance between the first and second end caps, the fin compressing the drainage layer along its length to promote drainage of liquid which has collected in the drainage layer.       

     The filter element and the drainage promoter may be capable of being connected to one another, or configured to be connected, so that the filter element and the drainage promoter can be manipulated by a user as a unitary component for positioning in a housing of a filter. 
     The filter element may be adapted to be disposed, in use, in a horizontal position or orientation. The drainage promoter fin may then be located at a position around a perimeter of the filter element, which is disposed lowermost, in use. Where the filter element is generally circular in shape in cross-section (i.e., a generally cylindrically shaped hollow filter element), the position may be a bottom-most position around a circumference of the element, viewing in a direction along a length of the element in its use position. 
     The drainage promoter fin may compress the drainage layer of the filter element, which may break the surface tension of the drainage layer material and promote quicker, more efficient drainage of liquid from the drainage layer. An enhanced drainage effect may therefore be provided over conventional horizontally oriented filter elements, as well as over such filter elements comprising a drainage layer including an elongate tab formed of the drainage layer material itself. It may also simplify construction of the filter element, in particular its drainage layer, in contrast to drainage layers comprising such a tab. Further, and in at least some disclosed embodiments, the drainage promoter fin may be capable of being fitted to a standard filter element, without requiring modification to the structure of the element. 
     The fin may be elongate and may have first and second ends (which may be axial ends). The fin may comprise a base extending along a length of the fin between the ends. The fin may comprise a tip opposite the base and extending along the length of the fin. The tip may define a free edge of the fin. A length dimension of the fin may be greater than a height dimension, the height measured from the base to the tip. The fin may comprise a longitudinal axis extending along a length of the fin between its ends. The base may press into the drainage layer during use. The tip may be spaced away from the base and may define a discharge location from which liquid flowing from the drainage layer can be discharged from the fin. The fin may have a tapered shape in cross-section, which section may be taken transverse (suitably perpendicular) to a longitudinal axis of the fin. This may help to promote the flow of liquid along the fin, for subsequent discharge. The fin may taper in a direction from its base towards its tip. A cross-sectional width of the fin (taken perpendicular to the longitudinal axis) may decrease in a direction towards its tip. The fin may have a height, which may be measured in a direction from the base to the tip. The height may be substantially constant along a length of the fin. The height may vary along a length of the fin, for example the fin (in particular its base) may be curved and may be generally convex. 
     The fin may be connectable to at least one of the first and second end caps, so that it can be secured to the filter element. The fin may be connectable to both end caps. The fin may extend from one end cap to the other end cap. The fin may be releasably connectable to at least one of the end caps, optionally to both end caps. Providing a releasable connection may allow the drainage promoter fin to be fitted to the filter element following assembly of the filter element, and/or may allow the fin to be used with a further filter element, if the element should become clogged during use and requires replacement. 
     The fin may comprise at least one connection (or engaging) feature for engaging the filter element, to connect the fin to the element. The connection feature may engage an end cap of the filter element. The fin may comprise a first connection feature for engaging one of the end caps, and a second connection feature for engaging the other one of the end caps. The first and second connection features may be spaced apart along a length of the fin. The fin may comprise a first axial end and a second axial end, and the first and second connection features may be provided on, at or near the respective first and second axial ends. 
     The filter element may comprise at least one connection (or engaging) feature, which may cooperate with the connection feature on the fin, for connecting the fin to the element. At least one of the end caps may comprise the connection feature. The first end cap may comprise a first connection feature and the second end cap may comprise a second connection feature. The first and second end cap connection features may each be configured to cooperate with the respective first and second connection features of the fin, to connect the fin to the element. 
     The connection feature of the fin may be a male connection feature and the connection feature of the filter element may be a corresponding female connection feature. The connection feature of the fin may be a female connection feature and the connection feature of the filter element may be a corresponding male connection feature. Where the fin comprises first and second connection features, they may each be a male connection feature, each a female connection feature, or a mixture of male and female connection features may be provided. The first and second connection features of the filter element may therefore each be a female connection feature, each a male connection feature, or a mixture of male and female connection features may be provided, as appropriate. 
     The female connection feature may define an opening or entrance which is shaped to receive the male connection feature. The male connection feature may be a protrusion or projection, such as a pin, boss, shaft, finger, rib or the like. The female connection feature may be a recess, socket, bore, channel, passage or the like. 
     The filter element assembly may comprise a pivoting connection between the fin and the filter element. The pivoting connection may be defined by the connection features of the fin and the filter element. One of the fin and the filter element may define a connection feature in the form of a pivot pin or shaft, and the other one of the fin and the filter element may define a pivot mount or socket shaped to receive the pivot pin, so that the fin can pivot relative to the filter element. 
     The pivot pin and pivot mount may be aligned with, or along, a longitudinal axis of the fin, so that the fin can pivot about the longitudinal axis. The fin may be pivotable between a folded (or installation) position and a deployed (or use) position. The fin may be pivotable generally about or near to its base. When the fin is in the folded position, a tip of the fin may be disposed closer to an outer surface of the drainage layer than when the fin is in its deployed position. A flank of the fin may be disposed proximate the outer surface of the drainage layer when the fin is in its folded position. The ability of the fin to fold in this way may facilitate fitting of the filter element assembly in the filter housing, for example if access to the housing is restricted. The fin may comprise a pivot pin, or a pivot mount at each of its ends, configured to engage a corresponding pivot mount or pivot pin of the filter element. The fin may comprise a pivot pin at both ends, a pivot mount at both ends, or a pin at one end and a mount at the other. 
     The pivot pin may be disposed transverse (e.g., perpendicular) to the longitudinal axis of the fin. A pair of pivot pin portions may be provided, and axes of the pin portions may be aligned. A first pivot pin portion may extend in a first lateral direction away from the fin, and a second pivot pin portion may extend in a second lateral direction away from the fin. The lateral directions may be transverse to the longitudinal axis of the pin and are suitably perpendicular to it. The pivot pin and the pivot mount/socket may be disposed on a pivot axis which is transverse to the longitudinal axis of the fin, suitably perpendicular to it, when the fin is connected to the filter element. The arrangement may be reversed, with pin portions provided by the filter element (suitably an end cap) and a mount on the fin. 
     The fin may be pivotable about the pivot axis between a disconnected position in which the fin can be disconnected from the filter element, and a connected position in which the fin is connected to the filter element. In the disconnected position, a longitudinal axis of the fin may be disposed transverse to a longitudinal axis of the filter element. In the connected position, a longitudinal axis of the fin may be disposed substantially parallel to a longitudinal axis of the filter element. 
     The fin and the filter element may define respective latch features, which may cooperate to provide a latching engagement between the fin and the element. The latch feature on the fin may be spaced along a length of the fin from the pivot pin or pivot mount. The latch feature on the filter element may be provided on one of the end caps. One of the latch features provided by the fin and the filter element may be a resiliently deformable element such as a latch arm, finger, catch or the like, and the other latch feature may be a recess, bore or the like, or an edge surface or face. 
     The filter element assembly may comprise a sliding connection between the fin and the filter element. The sliding connection may be defined by the connection features of the fin and the filter element. The fin may be translatable relative to the filter element between a disconnected position in which it is not connected to the filter element, and a connected position in which it is connected to the filter element. One of the fin and the filter element may define a connection feature in the form of a protrusion or projection, which may form a key, and which may be a tab, finger or the like. The other one of the fin and the filter element may define a connection feature shaped to receive the protrusion in a sliding fit, may form a keyway, and may be a channel, recess, guide or the like. The key and keyway may have to be aligned for engagement of the connection features. The sliding connection may comprise a restraint which may serve to resist further translation of the fin relative to the filter element (in at least one direction), once the fin has been translated a sufficient distance relative to the filter element and adopted its connected position. The restraint may be a shoulder, which may be provided or defined by the fin and/or the filter element, in particular by their connection features. 
     The first end cap may comprise a first connection feature for engaging a corresponding first connection feature on the fin. The second end cap may comprise a second connection feature for engaging a corresponding second connection feature on the fin. The respective first connection features of the filter element and the fin, and the respective second connection features of the filter element and the fin, may require to be aligned in order for the fin to be connected to the element. The connection features of the filter element may be aligned along an axis extending along the filter element substantially parallel to its longitudinal axis. At least one of the end caps may comprise a plurality of connection features, which may be spaced around a perimeter of the end cap. This may be advantageous during assembly of the filter element, facilitating rotational alignment of the end cap connection features, so that the fin can subsequently be fitted to the element. 
     The fin may compress the drainage layer along a majority, or all, of a length of the drainage layer defined or exposed between the first and second end caps of the filter element. This may serve to promote maximum discharge of liquid from the drainage layer, along a length of the drainage layer disposed between the end caps, during use. The fin may be captured between the end caps. The fin may extend at least partly over one or both of the first and second end caps. When the fin is fitted to the filter element, a small gap may be provided between one or both of the end caps and a facing surface of the fin. The facing surface may be in the region of and/or may define the base. The small gap may facilitate sliding connection of the fin to the filter element. 
     The fin may be configured so that it is connected to the filter element in a press-fit, suitably between the end caps. The fin may be resiliently deformable so that it can be press-fitted to the filter element. 
     The drainage promoter may comprise at least one drainage element, such as a finger, rib, arm or the like, the drainage element being coupled to the fin and extending in a direction away from the fin. The drainage element may be resilient and/or elastically deformable. The drainage element may extend in a direction around an outer surface of the drainage layer. The drainage element may compress the drainage layer along at least part of its length, which may serve to further promote the drainage of liquid from the drainage layer. The drainage element may extend part way around a perimeter of the outer surface. The drainage element may be disposed transverse to a longitudinal axis of the fin and may be disposed substantially perpendicular to the fin axis. The drainage element may be curved and may have an inner surface with a curvature which substantially matches a curvature of the outer surface of the drainage layer (e.g., for a circular section filter element). 
     The at least one drainage element may have a base at which it is coupled to the fin and may extend away from the base to a tip, which may define a free end. The at least one drainage element may taper in a direction from the base towards the tip. A width of the at least one drainage element (considered in an axial direction relative to the filter element), and/or a depth (considered in a radial direction relative to the filter element) may reduce in a direction towards the tip. This may help to promote the flow of liquid along the drainage element and on to the fin, for subsequent discharge. 
     At least one first drainage element may extend from the fin, optionally around the outer surface of the drainage layer in a first direction around the perimeter of the filter element. At least one second drainage element may extend from the fin, optionally around the outer surface of the drainage layer in a second direction around the perimeter of the filter element. The second direction may be opposite to the first direction. The first and second drainage elements may extend from respective first and second flanks of the fin. The drainage elements extending in the different directions may be disposed at common axial positions along a length of the fin or may be axially staggered. 
     The first and second drainage elements, extending in the different directions, may be configured to together impart a clamping force on the filter element, for connecting the drainage promoter to the element. This may be facilitated by inherent resiliency, or elastic deformability, of the drainage elements. The drainage elements may be considered to form connection features, for connecting the fin to the filter element, and may alternatively be referred to as connection features. The drainage elements may each extend around the perimeter of the filter element to an over-centre position, relative to a central axis of the filter element. This may provide the clamping force. The first and second drainage elements may therefore together encompass more than half of a circumference of a circular filter element. 
     The first and second drainage elements may together describe a generally cylindrical passage or opening between their inner surfaces, which passage may be shaped to receive the filter element and may have a central axis. The drainage elements may each extend to an over-centre position, relative to the central axis. A space may be defined between the free end of the first drainage element and the free end of the axially adjacent second drainage element. A dimension of the space, measured in a direction perpendicular to the longitudinal axis of the filter element, may be smaller than a diameter (or width as appropriate) of the filter element. This may provide the clamping force. 
     The drainage promoter may be connectable to the filter element at a location between the first and second end caps. The drainage promoter may be connectable to the drainage layer of the filter element. The drainage promoter may comprise at least one connecting component which can engage the drainage layer, to connect the fin to the filter element. The connecting component may be a strap or tie, which may extend from the fin and around at least part of a perimeter of the drainage layer. The strap or tie may be provided separately and may be connectable to the fin to secure it to the filter element, for example by passing through a locating aperture in the fin and around the discharge layer. In a variation, a strap may be connectable to an end cap, by passing around a perimeter of the cap. 
     The strap may comprise a first strap portion extending in a first direction away from the fin and around part of a perimeter of the drainage layer. The strap may comprise a second strap portion extending in a second direction away from the fin and around part of a perimeter of the drainage layer, which second direction may be opposite to the first direction. The first and second strap portions may be adapted to be coupled together to connect the fin to the filter element. The first and second strap portions may comprise respective connection features for coupling them together. One of the strap portions may comprise a male connection feature such as a button or stud, and the other one of the strap portions may comprise a female connection feature such as an aperture, the aperture receiving the button in a press fit. The strap portions may carry other connection features, such as zip-tie structures. The first and second strap portions may together encircle the drainage layer when coupled together. 
     The strap may extend from the fin around substantially the entire perimeter of the drainage layer. The strap may have a free end which is adapted to be coupled to the fin so that the strap encircles the drainage layer, to connect the fin to the filter element. 
     A first strap may be provided at a first axial location along a length of the fin, and a second strap may be provided which is at a second axial location along the length of the fin. The provision of two straps may provide a secure connection of the fin to the filter element. Further such straps may be provided if desired, which may depend on factors including dimensions of the filter element. 
     The drainage promoter may be connectable to the drainage layer of the filter element via connection features of the type described as drainage elements above. The connection features may then optionally have a drainage function as described. The drainage promoter may comprise a first part defining a first part of the fin and at least one drainage/connection element, and a second part defining a second part of the fin and at least one drainage/connection element. The first and second fin parts may be adapted to be coupled together to define the drainage promoter. This may facilitate fitting of the drainage promoter to the filter element, in particular where it is fitted to the drainage layer. 
     Reference is made in this document to a fin which compresses a drainage layer of a filter element along its length. It will be understood that the fin will not necessarily compress the drainage layer along its entire length, and thus that a compressive effect of the fin on the drainage layer may occur along only a part of the length of the fin. The fin may overlap the drainage layer along a part of its length, and a compressive effect may be provided along the part which overlaps the drainage layer, and optionally the entire part which overlaps. 
     In a second aspect of the present disclosure, there is provided a drainage promoter which can be connected to a filter element, the drainage promoter comprising:
         a. at least one fin which can be fitted to the filter element so that it extends along the filter element substantially an entire distance between first and second end caps of the filter element, to compress a drainage layer of the filter element along its length and promote drainage of liquid which has collected in the drainage layer;   b. in which the fin comprises a first connection feature for engaging the first end cap of the filter element, and a second connection feature for engaging the second end cap of the filter element, for connecting the fin to the filter element.       

     The fin may be releasably connectable to the end caps. The first and second connection features may be adapted to cooperate with corresponding connection features on the end caps. The connection features may be male connection features adapted to cooperate with corresponding female connection features on the end caps. The connection features may be female connection features adapted to cooperate with corresponding male connection features on the end caps. One of the connection features may be a male feature and the other a female feature. 
     One of the first and second connection features may be a pivoting connection feature, providing a pivoting connection between the fin and the end cap. This may facilitate pivoting movement of the fin relative to the filter element, between a position where an axis of the fin is transverse to a longitudinal axis of the filter element, and a position where the fin axis is substantially parallel to the filter element axis. At least one of the first and second connection features may define a latch feature, which may provide a latching engagement between the fin and the end cap. 
     The first and second connection features may both be pivoting connection features, providing a pivoting connection between the fin and the end cap. This may facilitate pivoting movement of the fin relative to the filter element, about a pivot axis defined by or parallel to a longitudinal axis of the fin. In this way, the fin may be pivoted between a folded (or installation) position and a deployed (or use) position. 
     The first and second connection features may be adapted to provide a sliding connection between the fin and the end caps. 
     In a third aspect of the present disclosure, there is provided a drainage promoter which can be connected to a filter element, the drainage promoter comprising:
         a. at least one fin which can be fitted to the filter element so that it extends along the filter element substantially an entire distance between the first and second end caps, to compress a drainage layer of the filter element along its length and promote drainage of liquid which has collected in the drainage layer; and   b. at least one connecting component which can engage the drainage layer to connect the fin to the filter element.       

     The drainage promoter may be connectable to the filter element at a location between the first and second end caps. 
     The connecting component may be a strap or tie which extends from the fin and around at least part of a perimeter of the drainage layer. 
     The strap may comprise a first strap portion extending in a first direction away from the fin and around part of a perimeter of the drainage layer. The strap may comprise a second strap portion extending in a second direction away from the fin and around part of a perimeter of the drainage layer, which second direction may be opposite to the first direction. The first and second strap portions may be adapted to be coupled together to connect the fin to the filter element. 
     The strap may extend from the fin around substantially the entire perimeter of the drainage layer and may have a free end which is adapted to be coupled to the fin so that the strap can encircle the drainage layer, and connect the fin to the filter element. 
     The connecting component may take the form of a resilient or elastically deformable rib, finger or the like, which may be coupled to the fin and extend in a direction away from the fin. The connecting component may extend, in use, in a direction around an outer surface of the drainage layer. The connecting component may be disposed transverse to a longitudinal axis of the fin and may be disposed substantially perpendicular to the fin axis. 
     The connecting component may be curved and may have an inner surface with a curvature which substantially matches a curvature of an outer surface of the filter element drainage layer (for a circular section filter element). 
     At least one first connecting component may extend from the fin in a first direction. At least one second connecting component may extend from the fin in a second direction, which may be opposite to the first direction. The first and second connecting components extending in the different directions may be configured to together impart a clamping force on the drainage layer of the filter element, for connecting the drainage promoter to the element. The connecting components may describe a generally cylindrical passage or space between inner surfaces of the components, which passage may be shaped to receive the filter element, the passage having a central axis. The connecting components may each extend to an over-centre position, relative to the central axis. This may provide the clamping force. 
     In a fourth aspect of the present disclosure, there is provided a drainage promoter which can be connected to a filter element, the drainage promoter comprising:
         a. at least one fin which can be fitted to the filter element so that it extends along the filter element substantially an entire distance between the first and second end caps, to compress a drainage layer of the filter element along its length and promote drainage of liquid which has collected in the drainage layer, the fin having first and second axial ends and a longitudinal axis extending along the fin between its axial ends; and   b. at least one drainage element coupled to the fin and extending in a direction away from the fin, transverse to its longitudinal axis.       

     The at least one drainage element may extend, in use, in a direction around an outer surface of the drainage layer. The at least one drainage element may compress the drainage layer along at least part of its length, which may serve to further promote the drainage of liquid from the drainage layer. The at least one drainage element may extend part way around a perimeter of the outer surface. The at least one drainage element may be disposed substantially perpendicular to the fin axis. 
     The drainage promoters of the second to fourth aspects may be connectable to the filter element so that, in use, the filter element and the drainage promoter can be manipulated by a user as a unitary component for positioning in a housing of a filter. 
     The drainage promoters defined in the second to fourth aspects, including the fins forming part of the drainage promoters, may have any of the further features of the drainage promoters defined elsewhere in this document, particularly in or with reference to the filter element assembly of the first aspect. 
     In a fifth aspect of the present disclosure, there is provided a method of improving drainage of liquid from a drainage layer of an existing filter element, the method comprising fitting a drainage promoter according to the third or fourth aspect of the present disclosure to the drainage layer of the filter element. 
     Further features of the method may be derived from the text set out elsewhere in this document. 
     In further aspects of the present disclosure, filter element assemblies may be provided comprising a filter element and a drainage promoter according to any one of the second, third or fourth aspects. 
     The filter element may be for location in a housing of a filter, comprising a wall of a filtration medium which defines a hollow space, for a gas stream to flow from the space through the wall to be filtered, the filtration medium including a filtration layer, and a drainage layer located outside the filtration layer in which liquid separated from the gas stream can collect, and first and second end caps at opposite ends of the wall, one of the end caps including a port for a gas stream which communicates with the space within the wall. 
     In a further aspect of the present disclosure, there is provided a filter element assembly comprising:
         a. a filter element for location in a housing of a filter, comprising a wall of a filtration medium which defines a hollow space, for a gas stream to flow from the space through the wall to be filtered, the filtration medium including a filtration layer, and a drainage layer located outside the filtration layer in which liquid separated from the gas stream can collect, and first and second end caps at opposite ends of the wall, one of the end caps including a port for a gas stream which communicates with the space within the wall; and   b. a drainage promoter connected to the filter element so that it extends along the filter element substantially an entire distance between the first and second end caps, the fin compressing the drainage layer along its length to promote drainage of liquid which has collected in the drainage layer.       

     The filter element and the drainage promoter may be configured to be manipulated by a user as a unitary component for positioning in a housing of a filter. 
     The filter element and/or the drainage promoter may have any of the further features defined elsewhere in this document, particularly in or with reference to the first aspect. 
     In a further aspect of the present disclosure, there is provided a filter element for location in a housing of a filter, the filter element comprising:
         a. a wall of a filtration medium which defines a hollow space, for a gas stream to flow from the space through the wall to be filtered, the filtration medium including a filtration layer, and a drainage layer located outside the filtration layer in which liquid separated from the gas stream can collect;   b. first and second end caps at opposite ends of the wall, one of the end caps including a port for a gas stream which communicates with the space within the wall; and   c. at least one connection feature configured to cooperate with a connection feature on a drainage promotor fin, for connecting the filter element to the drainage promotor fin.       

     The at least one connection feature may be provided on one of the first and second end caps. A connection feature may be provided on both of the end caps. The first end cap may comprise a first connection feature and the second end cap may comprise a second connection feature. The first and second end cap connection features may each be configured to cooperate with respective first and second connection features of the drainage promoter fin, to connect the fin to the element. 
     The filter element may have any of the further features defined elsewhere in this document, particularly in or with reference to the first aspect. In particular, the at least one connection feature of the filter element may have any of the further features defined in, or in relation to, the first aspect. 
     Filter element assemblies, drainage promoters, filter elements and a method of improving drainage of liquid from a drainage layer of an existing filter element are defined in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG.  1    is a front view of a filter element assembly in accordance with an embodiment of the present disclosure; 
         FIG.  1 A  is a longitudinal cross-sectional view of a filter comprising the filter element assembly of  FIG.  1   , drawn to a smaller scale; 
         FIG.  2    is an end view of the filter element assembly shown in  FIG.  1   , taken in the direction of the arrow A in  FIG.  1   ; 
         FIG.  3    is an end view of the filter element assembly shown in  FIG.  1   , taken in the direction of the arrow B in  FIG.  1   ; 
         FIG.  4    is a longitudinal cross-sectional view of the filter element assembly shown in  FIG.  1   ; 
         FIG.  5    is a front view of a drainage promoter forming part of the filter element assembly shown in  FIG.  1   ; 
         FIG.  6    is an end view of a drainage promoter forming part of the filter element assembly shown in  FIG.  1   ; 
         FIG.  7    is a perspective view of a drainage promoter forming part of the filter element assembly shown in  FIG.  1     
         FIG.  8    is a perspective view of the filter element assembly shown in  FIG.  1   , drawn to a smaller scale; 
         FIG.  9    is an end view of the filter element assembly, drawn to the smaller scale of  FIG.  8   , and showing fitting of the drainage promoter to a filter element of the assembly; 
         FIG.  10    is a perspective view of the filter element assembly, drawn to the smaller scale of  FIG.  8   , and showing fitting of the drainage promoter to a filter element of the assembly; 
         FIG.  11    is a front view of a filter element assembly in accordance with another embodiment of the present disclosure; 
         FIG.  12    is an end view of the filter element assembly shown in  FIG.  11   , taken in the direction of the arrow A in  FIG.  11   ; 
         FIG.  13    is an end view of the filter element assembly shown in  FIG.  11   , taken in the direction of the arrow B in  FIG.  11   ; 
         FIG.  14    is a perspective view of the filter element assembly shown in  FIG.  11   , drawn to a smaller scale; 
         FIG.  15    is a longitudinal cross-sectional view of the filter element assembly shown in  FIG.  11   , drawn to a smaller scale; 
         FIG.  16    is an end view of the filter element assembly, drawn to the smaller scale of  FIG.  14   , and showing fitting of a drainage promoter to a filter element of the assembly; 
         FIG.  17    is a front view of the drainage promoter forming part of the filter element assembly shown in  FIG.  11   ; 
         FIG.  18    is an end view of the drainage promoter forming part of the filter element assembly shown in  FIG.  11   ; 
         FIG.  19    is a perspective view of the drainage promoter forming part of the filter element assembly shown in  FIG.  11   ; 
         FIG.  20    is an enlarged detail view showing connection features of the filter element and the drainage promoter following connection of the drainage promoter to the filter element; 
         FIG.  21    is a further enlarged detail view showing connection features of the filter element and the drainage promoter following connection of the drainage promoter to the filter element; 
         FIG.  22    is a front view of a filter element assembly in accordance with a further embodiment of the present disclosure; 
         FIG.  23    is an end view of the filter element assembly shown in  FIG.  22   , taken in the direction of the arrow A in  FIG.  22   ; 
         FIG.  24    is an end view of the filter element assembly shown in  FIG.  22   , taken in the direction of the arrow B in  FIG.  22   ; 
         FIG.  25    is a longitudinal cross-sectional view of the filter element assembly shown in  FIG.  22   ; 
         FIG.  26    is a perspective view of the filter element assembly shown in  FIG.  22   , illustrating a drainage promoter being fitted to a filter element of the assembly; 
         FIG.  26 A  is a side view of the filter element assembly shown in  FIG.  22   , showing a first step fitting of a drainage promoter to a filter element of the assembly; 
         FIG.  26 B  is a side view of the filter element assembly shown in  FIG.  22   , showing a second step fitting of a drainage promoter to a filter element of the assembly; 
         FIG.  26 C  is a side view of the filter element assembly shown in  FIG.  22   , showing a third step fitting of a drainage promoter to a filter element of the assembly; 
         FIG.  27    is a side view of the drainage promoter forming part of the assembly of  FIG.  22   ; 
         FIG.  28    is an end view of the drainage promoter forming part of the assembly of  FIG.  22   ; 
         FIG.  29    is a perspective view of the drainage promoter forming part of the assembly of  FIG.  22   ; 
         FIG.  30    is a front view of a filter element assembly in accordance with a further embodiment of the present disclosure; 
         FIG.  31    is a front view of a drainage promoter forming part of the filter element assembly shown in  FIG.  30   ; 
         FIG.  32    is an end view of a drainage promoter forming part of the filter element assembly shown in  FIG.  30   ; 
         FIG.  33    is a perspective view of a drainage promoter forming part of the filter element assembly shown in  FIG.  30   ; 
         FIG.  34    is a front view of a filter element assembly in accordance with a further embodiment of the present disclosure; 
         FIG.  35    is an end view of the filter element assembly shown in  FIG.  34   , taken in the direction of the arrow A in  FIG.  34   ; 
         FIG.  36    is an end view of the filter element assembly shown in  FIG.  34   , taken in the direction of the arrow B in  FIG.  34   ; 
         FIG.  37    is a perspective view of the filter element assembly shown in  FIG.  34   , drawn to a smaller scale; 
         FIG.  38    is a longitudinal cross-sectional view of the filter element assembly shown in  FIG.  34   , drawn to a smaller scale; 
         FIG.  39    is a front view of a drainage promoter forming part of the filter element assembly shown in  FIG.  34   , drawn to a smaller scale; 
         FIG.  40    is an end view of a drainage promoter forming part of the filter element assembly shown in  FIG.  34   , drawn to a smaller scale; 
         FIG.  41    is a perspective view of a drainage promoter forming part of the filter element assembly shown in  FIG.  34   , drawn to a smaller scale; 
         FIG.  42 A  is an end view of the filter element assembly of  FIG.  34   , shown during fitting of the drainage promoter to the filter element; 
         FIG.  42 B  is an end view of the drainage promoter forming part of the filter element assembly of  FIG.  34   , showing assembly of the drainage promoter; 
         FIG.  43    is a front view of a filter element assembly in accordance with a further embodiment of the present disclosure; 
         FIG.  44    is an end view of the filter element assembly shown in  FIG.  43   , taken in the direction of the arrow A in  FIG.  43   ; 
         FIG.  45    is an end view of the filter element assembly shown in  FIG.  43   , taken in the direction of the arrow B in  FIG.  43   ; 
         FIG.  46    is a front view of a drainage promoter forming part of the filter element assembly shown in  FIG.  43   , drawn to a smaller scale; 
         FIG.  47    is an end view of a drainage promoter forming part of the filter element assembly shown in  FIG.  43   , drawn to a smaller scale; 
         FIG.  48    is a perspective view of a drainage promoter forming part of the filter element assembly shown in  FIG.  43   , drawn to a smaller scale; 
         FIG.  49    is a front view of the filter element assembly shown in  FIG.  43   , shown during fitting of the drainage promoter to a filter element of the assembly, drawn to a smaller scale; 
         FIG.  50    is an end view of the filter element assembly shown in  FIG.  43   , shown during fitting of the drainage promoter to a filter element of the assembly, drawn to a smaller scale; 
         FIG.  51    is a longitudinal cross-sectional view of the filter element assembly shown in  FIG.  43   , drawn to the smaller scale of  FIG.  49    and shown following fitting of the drainage promoter to the filter element; and 
         FIG.  52    is a perspective view of the filter element assembly shown in  FIG.  43   , drawn to the smaller scale of  FIG.  49    and shown following fitting of the drainage promoter to the filter element. 
     
    
    
     DETAILED DESCRIPTION 
     Turning firstly to  FIG.  1   , there is shown a front view of a filter element assembly in accordance with an embodiment of the present disclosure, the filter element assembly indicated generally by reference numeral  10 . The filter element assembly  10  is also shown in the end views of  FIGS.  2  and  3   , taken in the direction of the arrows A and B respectively in  FIG.  1   , and the longitudinal cross-sectional view of  FIG.  4   , which is drawn to a larger scale. 
     In use, and as is well known in the field of fluid filters, the filter element assembly  10  is located in a filter  2 , as shown in the cross-sectional view of  FIG.  1 A , drawn to a smaller scale. The filter element assembly  10  is located within a chamber defined by a housing  4  of the filter  2 . The housing  4  includes an opening  5  through which the filter element assembly  10  can be inserted into the housing for location in the chamber  3 . A cover  6  is then coupled to the housing  4 , to secure the filter element assembly  10  in the chamber  3  so that fluid to be filtered can be directed through the filter element assembly  10 , from a filter head  7 . A tie-rod  8  secures the filter element assembly  10  within the housing  4 . Gas to be filtered enters the filter head  7  through a port  9  and flows into the filter element assembly  10  to be filtered. 
     The filter element assembly  10  comprises a filter element  12 , and a drainage promoter, which is indicated by reference numeral  14 . As best shown in  FIG.  4   , the filter element  12  comprises a wall  16  of a filtration medium defining a hollow space  18 , for a gas stream to flow from the space through the wall to be filtered. The filtration medium includes a filtration layer  20 , and a drainage layer  22  located outside the filtration layer, in which liquid separated from the gas stream can collect. Filter elements having such filtration and drainage layers are well known in the field of fluid filters, and persons skilled in the art will appreciate their general construction and operation during use. Accordingly, the filtration and drainage layers  20  and  22 , including their materials and methods of manufacture, will not be described in detail in this document. In general terms however, the filtration and drainage layers  20  and  22  may have the following features. 
     The material for the filtration medium in the filtration layer  20  of the filter element  12  will be selected according to the nature of the gas that is to be filtered, the nature of the contaminants (liquid droplets, aerosols, solid particles etc.) to be filtered from the gas, the pressure differential across the filter and so on. Such materials are known, including those used by Parker Domnick Hunter in products which are available under the trademark OIL-X. Suitable materials include, but are not restricted to, borosilicate and other glass fibres, activated carbon minerals, activated silica materials and so on. 
     The filtration layer  20  can be made from woven fibres. However, as will be appreciated, the filtration layer can be made from sheets of non-woven fibres. For example, a microfibre filtration layer made from fine organic or inorganic fibres may be employed. A coarser fibre layer may be fitted on the inside of a microfibre filtration layer, which may protect a microfibre filtration layer from gross pollution. The filtration layer  20  may comprise a layer of a material which has been folded so that it is fluted (or pleated). This can increase the surface area of the filtration layer  20  through which gas flowing through the filter element  12  will pass. This can also help to increase the rigidity of the filtration layer  20 . 
     The drainage layer  22  comprises a material that is capable of retaining liquid that has been coalesced by the filtration layer  20  and is carried to the drainage layer by the gas stream that flows through the drainage layer. The drainage layer  22  will generally be porous and made from a material which encourages flow of coalesced liquid towards the base of the filter element  12 . Factors affecting the drainage characteristics may include pore size and structure, and the material of the drainage layer  22 , including for example the surface energy of liquid which is in contact with the material. Materials suitable for use in the drainage layer are used in similar products sold by Parker Domnick Hunter under the trade mark OIL-X. Suitable materials include open-celled foam plastics, felted fabric material, expanded foam materials, woven and non-woven materials. 
     The filter element  12  also comprises first and second end caps  24  and  26  at opposite ends of the wall  16 , the first end cap including a port  28  for the gas stream to flow into the filter element from the filter head port  9 , the filter port  28  communicating with the space  18  within the wall. In normal use of the filter, the filter element  12  will be substantially horizontally oriented as shown in  FIG.  1 A , so that the first end cap  24  defines a first lateral end of the filter element, and the second end cap  26  defines a second lateral end of the filter element. 
     Perforated tubular supports  30  and  32 , typically of a metal or metal alloy material, are secured to the end caps  24  and  26 , and serve for securing both the filtration layer  20  and the drainage layer  22  to the end caps and separating the different layers. As is well known in the field of the invention, this is suitably achieved by ‘potting’ the supports  30  and  32 , and the filtration and drainage layers  20  and  22 , within annular channels  34  and  36  defined by the end caps  24  and  26 , using an adhesive such as an epoxy-based adhesive. 
     The filter head comprises a flow conduit  33  which defines the inlet port  9  and serves to direct a gas stream entering the filter head into the filter element  12  through its inlet port  28 , so that contaminants in the gas stream can be removed. The filter may have a wide range of uses but may have a particular use in removing contaminants from a gas stream such as a compressed or vacuum gas stream which is to be used in an industrial application, to remove residual oil from a compressor used to pressurise the gas. 
     The first end cap  22  of the filter element  11  comprises a seal in the form of an O-ring  37  ( FIG.  1 A ), which is mounted in a groove  38  defined in a tubular wall  40  of the end cap defining the port  28 . The O-ring seal  37  serves for sealing the filter element  12  relative to the filter head conduit  33 , so that gas entering the head is directed into the filter element. The gas stream entering the filter element  12  flows through its port  28  generally in a direction along an axis  42  of the filter element, and into the space  18 . The gas stream containing the contaminants flows from the central space  18  radially outwardly, through the wall  16  of the filter element  12 , passing through the filtration layer  20  and the drainage layer  22 . The filtration layer  20  serves for filtering out contaminants, which as described above may be residual oil entrained in the gas stream. Oil droplets coalesce and enter the drainage layer  22 , building up to form a ‘wet band’ towards a lower part of the drainage layer. The liquid oil in this wet band progressively drains from the lower part of the drainage layer  22  into a sump  43  of the filter housing  4  and can flow out of the sump via a drain  45 . 
     The ‘clean’ gas stream exiting the drainage layer  22  flows out through an external surface  44  of the filter element  12  (defined by the drainage layer  22 ) and into the chamber  3 , before passing to an outlet conduit  47  of the filter housing  4 . The gas stream exiting the filter  2  flows on to a downstream location. 
     The filter element assembly  10  of the present disclosure also comprises the drainage promoter  14 . The drainage promoter  14  is shown separately in the front and end views of  FIGS.  5  and  6   , and the perspective view of  FIG.  7   . The drainage promoter  14  comprises a fin  46  which can be fitted to the filter element  12  so that it extends along the filter element substantially an entire distance between its first and second end caps  24  and  26 , as can be seen for example in  FIGS.  1  and  4   . The fin  46  acts to compress the drainage layer  22  of the filter element  12  along its length, to promote drainage of liquid which has collected in the drainage layer. In the exemplary use discussed above, this is oil which has coalesced from the gas flowing through the filter element  12 , in the drainage layer  22 . The drainage promoter fin  46  compresses the drainage layer  22  of the filter element  12 , breaking the surface tension of the drainage layer material and promoting quicker and more deficient drainage of liquid from it. The filter element  12  and the drainage promoter  14  are capable of being connected to one another so that the filter element and the drainage promoter can be manipulated by a user as a unitary component for positioning in the housing  4  of the filter  2 . 
     The fin  46  is elongate, having first and second axial ends  48  and  50 . The fin  46  also comprises a base  52  which extends along a length of the fin between its axial ends  48  and  50 , and a tip  54  which defines a free edge of the fin. The tip  54  is disposed opposite the base  52 , and similarly extends along the length of the fin  46 . A length dimension of the fin  46  measured between its two ends  48  and  50  is greater than a height dimension, measured from the base  52  to the tip  54 . In the illustrated embodiment, the height dimension is substantially constant along the length of the fin  46 . However, the height may vary along a length of the fin  46 , for example the fin (in particular its base  52 ) may be curved and may be generally convex. 
     As discussed above, during use, the fin  46  presses into the drainage layer  22 . This is best shown in the cross-sectional view of  FIG.  4   , the fin base  52  pressing into the drainage layer  22  to break the surface tension and promote drainage of liquid. Liquid flowing from the drainage layer  22  on to the fin  46  flows in a direction from the base  52  towards the tip  54 , the tip defining a discharge location from which the liquid can be discharged from the fin into the housing sump  43 , as discussed above. The fin  46  has a tapered shape in cross-section, taken in a direction which is perpendicular to a longitudinal axis  56  of the fin. This tapered shape can be best seen in the end and perspective views of  FIGS.  6  and  7   . Providing the fin  46  with such a tapered shape helps to promote the flow of liquid along the fin to its tip  54 , and subsequent discharge. As can be seen, a cross-sectional width of the fin decreases in a direction away from its base  52  towards its tip  54 . The base  52  has a generally rounded profile so as to reduce a likelihood of damaging the material of the drainage layer  22 . 
     The fin  46  is releasably connectable to the filter element at its first and second end caps  24  and  26 . Releasably connecting the fin  46  to the filter element  12  allows the drainage promoter to be fitted to the filter element following assembly of the element. It may also allow the drainage promoter  14  to be used with a further filter element, for example if the existing filter element in the filter  2  becomes clogged and requires replacement. 
     In the illustrated embodiment, the fin  46  comprises first and second connection features  58  and  60  at its first and second axial ends  48  and  50 , which serve for connecting the fin to the filter element  12 . The first and second connection features  58  and  60  each take the form of a male feature, in particular a protrusion or projection defining a pivot pin, as best shown in  FIG.  7   . The pivot pins  58  and  60  are generally cylindrically shaped and have respective rounded heads  59  and  61 . The filter element  12  comprises corresponding first and second connection features  62  and  64 , which cooperate respectively with the first and second connection features  58  and  60  of the fin  46 . In the illustrated embodiment, the first and second connection features  62  and  64  of the filter element  12  are provided respectively on the first and second end caps  24  and  26  and are female connection features in the form of a pivot mount or socket which is shaped to receive the pins  58  and  60  of the fin  46 . To this end, the sockets are typically circular in shape, defining a cylindrical space which can receive the cylindrical pins  58  and  60 . 
     The pins  58  and  60 , and the sockets  62  and  64 , together provide a pivoting connection between the fin  46  and the filter element  12 . The pins  58  and  60  can rotate within the sockets  62  and  64 , so that the fin  46  can be pivoted between a folded or installation position, and a deployed or used position. Reference is made here to  FIGS.  8 ,  9  and  10    which are a perspective view of the filter element  12 , an end view taken in the direction of the arrow B in  FIG.  1   , and a front view similar to  FIG.  1   , respectively, all drawn to a smaller scale. The fin  46  is shown in its deployed position in  FIG.  8    (as well as  FIGS.  1  to  4   ).  FIG.  9    also shows the fin  46  in its deployed position, as well as the folded position of the fin, which is indicated in the drawing with a broken line  66 . The fin  46  can pivot between its folded position  66  and its deployed position in the direction of the arrow C in  FIG.  9   . When the fin  46  is in its folded position  66 , the tip  54  of the fin is disclosed closer to the external surface  44  of the drainage layer  22  than when the fin is in its deployed position. A flank  68  of the fin is disposed proximate the external surface  44  when the fin is in its folded position. The ability of the fin  46  to fold or pivot in this way can facilitate fitting of the filter element assembly  10  in its filter housing, for example if access to the housing is restricted, such as in a tight or confined space, or if the housing opening  5  is small compared to the filter element assembly  10  with the fin deployed. 
     As can best be appreciated from  FIGS.  5  to  7   , the pivot pins  58  and  60  are aligned along the longitudinal axis  56  of the pin  46 , so that the fin pivots about its longitudinal axis when it is moved between its folded and deployed positions. The portion of the fin  46  defining the base  52  extends a certain distance away from the longitudinal axis  56 , so that the base  52  presses into the external surface  44  of the drainage layer  22  to compress it, when the fin is pivoted to its deployed position. Shaping the base  58  so that it is rounded as discussed above helps to prevent damage to the drainage layer  22  as the fin  46  pivots between its different positions. 
     Fitting of the fin  46  to the filter element  12  is shown in  FIG.  10   . The fin  46  is typically of a polymeric material and may be resiliently deformable for fitting to the filter element  12 . The fin  46  may be fitted by locating one of the pivot pins  58  and  60  in its respective mounting socket  62  or  64  on the filter element  12 . This requires that the fin  46  be disposed at an angle relative to the filter element  12 , so that its longitudinal axis  56  is transverse to the filter element axis  42 . The fin  46  can then be moved to a position in which the other one of the pivot pins  58  and  60  is proximate its mounting socket  62  or  64 , and the fin resiliently deformed to a certain extent in order to snap the pivot pin into its socket. This may be achieved by deforming the fin  46  along its length, for example by causing it to adopt a curved shape, and/or the pin itself may be resiliently deformable so that it can pass into the socket. To facilitate fitting of the fin  46 , the sockets  62  and  64  on the end caps  24  and  26  may comprise radially outer lips  70  and  72  forming outer wall portions of the sockets, over which the pivot pins  58  and  60  can pass in order to be received in the sockets. 
     Although the fin  46  can be fitted to the filter element  12  by locating the fin at a transverse angle relative to the filter element, the sockets  62  and  64  on the end caps  24  and  26 , and in particular their lips  70  and  72 , may be dimensioned so that the fin  46  can be press-fitted to both sockets at the same time. This is shown in  FIG.  10    and can be achieved by bringing the fin  46  adjacent to the filter element  12  with the fin axis  56  substantially parallel to the filter element axis  42 . The pivot pins  58  and  60  can then be press fitted into the sockets, passing over the lips  70  and  72 , this involving a small deformation of the fin  46  to adopt a curved shape, and/or deformation of the pivot pins  58  and  60 , as discussed above. 
     The fin  46  will typically be located in its folded position during installation of the filter element assembly  10  in a filter housing. Following location of the filter element assembly  10  in the housing with the fin disposed at the bottom of the element (considered in a circumferential sense and viewing along the assembly), the fin  46  can be manually rotated towards its deployed position, in which a transverse axis  74  of the fin ( FIG.  6   ) is disposed substantially on a radius of the filter element  12 , which radius intersects with its longitudinal axis  42 . 
     As discussed above, the drainage promoter fin  46  may be of a polymeric material, and may be moulded, for example injection moulded. Suitable materials may include Nylon, ABS (Acrylonitrile Butadiene Styrene), Polypropylene and Acetal (POM, PolyOxyMethylene). Constructing the fin  46  from such materials may provide it with sufficient resilience/elastic deformability for it to be fitted to the filter element  12 . Other materials and manufacturing techniques may however be suitable, including die casting using an aluminium or zinc alloy, for example. 
     In the illustrated embodiment, the fin  46  includes pivot pins  58  and  60 , and pivot mounts  62  and  64  are provided on the filter element  12 . It will be understood however that this arrangement may be reversed so that the fin  46  is provided with mounts, and the filter element with pivot pins. Equally, the fin  46  may be provided with one pivot pin and one pivot mount, for engaging a corresponding mount and pin on the filter element  12 . 
     As discussed above, the drainage promoter  14  can readily be fitted to the filter element  12  and facilitates drainage of liquid contaminants from the gas stream flowing through the filter. The drainage promoter fin  46  is fitted to the end caps  24  and  26  of the filter element  12 , which must carry appropriate fittings such as the pivot sockets  62  and  64 . Dedicated end caps will therefore need to be manufactured, although it is conceivable that existing filter elements could be modified by mounting additional structure on its end caps, providing mountings for the connection features on the fin  46 . 
     Turning now to  FIG.  11   , there is shown a front view of a filter element assembly in accordance with another embodiment of the present disclosure, the filter element assembly indicated generally by reference numeral  10   a . The filter element assembly  10   a  comprises a filter element  12   a  and a drainage promoter  14   a . Like components of the filter element assembly  10   a  with the filter element  10  shown in  FIGS.  1  to  10    share the same reference numerals, with the addition of the suffix “a”. 
     The filter element  12   a  is of substantially the same construction as the filter element  12  shown in  FIGS.  1  to  11    and described above. Accordingly, details of the construction and operation of the filter element  10   a  will not be described again in detail, reference instead being made to the discussion of the filter element  12  forming part of the filter element assembly  10  described above. Only substantial differences between the filter element assembly  10   a  and the assembly  10  will be described herein. In addition, the filter element assembly  10   a  can be located in a housing  4  of a filter  2  in a horizontal orientation in the same way as the filter element assembly  10 . Reference will therefore be made to the discussion above concerning the way in which the filter element assembly  10   a  is located in a filter housing, and the way in which it operates during use. 
     The filter element assembly  10   a  is also shown in the end views of  FIGS.  12  and  13   , taken in the direction of the arrows A and B respectively in  FIG.  11   .  FIG.  14    is a perspective view, and  FIG.  15    a longitudinal cross-sectional view of the filter element assembly  10   a , both drawn to a smaller scale. 
     In this embodiment, the drainage promoter  14   a  again comprises a fin  46   a  which is releasably connectable to the filter element  12   a . The fin  46   a  is pivotable relative to the filter element  12   a  for connecting it to the element, the fin being shown in a connected position in  FIGS.  11  to  15   , and in a disconnected position in the side view of  FIG.  16   , during fitting of the fin to the filter element. The fin  46   a  is also shown separately in the front, end and perspective views of  FIGS.  17 ,  18  and  19   , the end view being taken in the direction of the arrow D in  FIG.  17   . The fin  46   a  is drawn to the same scale in  FIGS.  17  and  19    as it is in  FIG.  11    but is shown in a different orientation. 
     The filter element assembly  10   a  of  FIGS.  11  to  19    differs from the filter element assembly  10  largely in relation to the way in which the fin  46   a  is connected to the filter element  12   a . To this end, both the filter element  12   a , and the fin  46   a , include connection features which are different to those of the respective filter element  12 , and fin  46 . 
     In this embodiment, a pivoting connection is provided between the fin  46   a  and the filter element  12   a  which facilitates fitting of the fin to the filter element. The fin  46   a  has a first axial end  48   a  and a second axial end  50   a . A first connection feature  58   a  is provided at the first axial end  48   a , which is a male connection feature in the form of a pivot pin. The male connection feature  58   a  in fact comprises first and second pivot pin portions  76  and  78 , which are generally cylindrical and have rounded heads. The pivot pin portions  76  and  78  are aligned along a transverse axis  80 , which is disposed substantially perpendicular to a longitudinal axis  56   a  of the fin  46   a . The first pivot pin portion  76  extends in a first lateral direction away from the longitudinal axis  56   a , and the second pivot pin portion  78  in a second lateral direction. 
     The filter element end cap  24   a  comprises a first connection feature  62   a  in the form of a pivot socket or mount, which is a female feature that is shaped to receive the male connection feature defined by the pivot pin portions  76  and  78  on the fin  46   a . The female pivot mount  62   a  on the first end cap  24   a  is best shown in the enlarged perspective detail view of  FIG.  20   , as well as the end views of  FIGS.  12  and  13   . The connection socket  62   a  includes a channel  82  which is shaped to receive the pivot pin portions  76  and  78 , the channel being defined by a pair of curved arms  84  which extend from an outer perimeter  86  of the first end cap  24   a . A slot  88  is defined between ends of the two arms  84 , which is shaped to receive the fin  46  and communicates with the channel  82 . The channel  82  has a closed end  90  ( FIG.  20   ), which defines a detent for the pivot pin portions  76  and  78 . 
     The fin  46   a  is connected to the filter element  12   a  by aligning the pivot pin portions  76  and  78  with the channel  82 , as shown in  FIG.  13   . The pivot pin portions  76  and  78  can then be translated along the channel  82  until they come to rest at the closed end  90 . The fin  46   a  is then in the position shown in  FIG.  16    and can be pivoted about the transverse axis  80  of the pivot pin portions  76  and  78 , by moving the second axial end  50   a  of the fin  46   a  in the direction of the arrow F in  FIG.  16   . The fin  46   a  can then be secured to the second end cap  26   a  at its second axial end  50   a , to secure the fin to the filter element  12   a.    
     Referring to  FIG.  21   , which is an enlarged detail view of the connection between the fin  46   a  and the second end cap  26   a , the fin comprises a second connection feature  60   a , which in this embodiment is a latch feature that provides a latching engagement with the second end cap  26   a . The second end cap  26   a  comprises a second connection feature  64   a , and the latch feature  60   a  on the fin  46   a  engages the latch feature  64   a  on the end cap  26   a  to secure the fin  46   a  to the filter element. 
     In the illustrated embodiment, the latch feature  60   a  on the fin  46   a  comprises a resiliently deformable latch arm  92  having a latch tooth  94 . The latch feature  64   a  on the end cap  26   a  comprises a recess  96  which the latch tooth  94  of the latch arm  92  can engage in order to secure the fin  46   a  to the end cap  26   a . A plurality of such recesses  96  may be provided in the end cap  26   a , as shown in the end view of  FIG.  13   . This may facilitate orientation of the end caps  24   a  and  26   a  during manufacture of the filter element  12   a , so that the connection features  62   a  and  64   a  can be aligned for receiving the fin connection features  58   a  and  60   a.    
     When the fin  46   a  is pivoted from its disconnected position of  FIG.  16    to its connected position of  FIG.  21   , the latch arm  92  comes in to contact with a chamfered surface  98  on the end cap  26   a . The latch tooth  94  is similarly chamfered such that application of force to the fin  46   a  in the direction F causes the latch arm  92  to deform, so that the latch tooth  94  can pass along the chamfered surface and over an end surface of the end cap  26   a , before latching into the recess  96  as shown in  FIG.  21   . The fin  46   a  is then connected to the filter element  12   a.    
     The fin  46   a  also includes a recess  100  at its second axial end  50   a , the recess being shaped to receive an outer peripheral portion  102  of the end cap  26   a . When the peripheral portion  102  is located in the recess  100 , the fin  46   a  is securely connected to the end cap  26   a , constrained between end faces of the recess. A further resilient latch tooth  104  on the fin  46   a  snaps over an inner peripheral surface  106  of the end cap  26   a , to provide an additional restraint against separation of the fin  46   a  from the filter element  12   a . Engagement of the second axial end  50   a  of the fin  46   a  to the end cap  26   a  also acts to maintain engagement between the first axial end  48   a  of the fin and the first end cap  24   a , because it prevents movement of the pivot pin portions  76  and  78  out of the channel  82  defined between the arms  84 . When fitted to the filter element  12   a , the fin  46   a  extends over the second end cap  46   a , and partly over the first end cap  24   a . A portion of the fin  46   a  including its base  52   a  is disposed between the end caps  24   a  and  26   a  and spans the distance between the end caps. 
     It will be understood that the orientation of the fin  46   a  relative to the filter element  12   a  may be reversed, with the pivoting connection provided at the second end cap  26   a , and the latching connection at the first end cap  24   a.    
     Turning now to  FIG.  22   , there is shown a front view of a filter element assembly in accordance with another embodiment of the present disclosure, the filter element assembly indicated generally by reference numeral  10   b . The filter element assembly  10   b  comprises a filter element  12   b  and a drainage promoter  14   b . Like components of the filter element assembly  10   b  with the filter element  10  shown in  FIGS.  1  to  10    share the same reference numerals, with the addition of the suffix “b”. 
     The filter element  12   b  is of substantially the same construction as the filter element  12  shown in  FIGS.  1  to  11    and described above. Accordingly, details of the construction and operation of the filter element  10   b  will not be described again in detail, reference instead being made to the discussion of the filter element  12  forming part of the filter element assembly  10  described above. Only substantial differences between the filter element assembly  10   b  and the assembly  10  will be described herein. In addition, the filter element assembly  10   b  can be located in a housing  4  of a filter  2  in a horizontal orientation in the same way as the filter element assembly  10 . Reference will therefore be made to the discussion above concerning the way in which the filter element assembly  10   b  is located in a filter housing  4 , and the way in which it operates during use. 
     The filter element assembly  10   b  is also shown in the end views of  FIGS.  23  and  24   , taken in the direction of the arrows A and B respectively in  FIG.  22   .  FIG.  25    is a longitudinal cross-sectional view of the filter element assembly  10   b , and  FIG.  26    is a perspective view of the assembly, showing a fin  46   b  of its drainage promoter  14   b  prior to connection to the filter element  12   b . The fin  46   b  is shown in its connected state in  FIGS.  22  and  25   , and in its disconnected state in  FIG.  26   , as mentioned above.  FIGS.  26 A , B and C are front views of the filter element assembly  10   b  showing successive steps in connection of the fin  46   b  to the filter element  12   b.    
     In this embodiment, a sliding connection is provided between the fin  46   b  and the filter element  12   b , the sliding connection being defined by connection features of the fin and the filter element. The connection features on the fin are shown in more detail in the enlarged front and end views of  FIGS.  27  and  28   , and the perspective view of  FIG.  29   , the end view taken in the direction of the arrow D in  FIG.  27   . The fin  46   b  is translatable relative to the filter element  12   b  between its disconnected position and its connected position. The fin  46   b  has a first axial end  48   b  and a second axial end  50   b . A first connection feature  58   b  is provided at the first axial end  48   b , and a second connection feature  60   b  at the second axial end  50   b . The filter element  12   b , in particular first and second end caps  24   b  and  26   b  of the filter element, define corresponding connection features  62   b  and  64   b , which cooperate with the respective first and second connection features  58   b  and  60   b  on the fin  46   b , so that the fin can be connected to the filter element end caps. 
     The second connection feature  60   b  on the fin  46   b  takes the form of a protrusion or projection which defines a key, and which takes the form of an elongate finger. The second connection feature  64   b  defined by the second end cap  26   b  defines a keyway in the form of a channel which is shaped to receive the key  60   b  of the fin  46   b  in a sliding fit. The key  60   b  has to be aligned with the keyway  64   b  in order for the features to be connected. This is best shown in the end view of  FIG.  24   . 
     The first connection feature  58   b  on the fin  46   b  similarly takes the form of a protrusion or projection defining a key. The first connection feature  62   b  defined by the first end cap  24   b  defines a keyway which similarly receives the key  58   b  in a sliding fit. Once again, the key  58   b  and the keyway  62   b  must be aligned for connection of the features. A restraint in the form of a shoulder  108  on the fin  46   b  proximate the key  60   b  acts to resist further translation of the fin relative to the filter element  12   b , once the fin has been translated a sufficient distance relative to the filter element and adopted its connected position. 
     The key  58   b  defined by the fin  46   b  comprises key portions  110  and  112  which are aligned along a transverse axis  80   b  ( FIG.  28   ) of the fin, the key portion  110  extending in a first lateral direction away from the fin, and the second key portion  112  in a second, opposite lateral direction. The key portions  110  and  112  are shaped to engage within a channel  114  of the keyway  58   b  on the first end cap  24   b , which is defined by a pair of arms  116  and  118 . The channel  114  tapers in a direction radially outwardly of the filter element  12   b  and the key portions  110  and  112  have a corresponding taper. This provides secure engagement of the key portions  110  and  112  within the channel  114  and acts to resist radial separation of the fin  46   b  from the first end cap  24   b  when connected. Latch teeth  120 ,  122  on the respective arms  116  and  118  engage on radially outer ledges  124 ,  126  of the respective key portions  110 ,  112  to restrain them in the channel  114 . 
     The keyway  64   b  defined by the second end cap  26   b  is similarly tapered, as is the key  60   b  defined by the fin  46   b . This acts to restrain the key  60   b  within the keyway  64   b  once the fin  46   b  has been connected to the filter element  12   b . The key  60   b  also has a tapered leading end  128  which assists alignment with the keyway  64   b  during connection of the fin  46   b . The leading end  128  defines a latch tooth  130  which can engage in a circumferential recess  132  ( FIG.  25   ) defined on a lower end of the second end cap  26   b . This acts to resist sliding movement of the fin  46   b  away from its connected position. 
     The keyways  62   b  and  64   b  on the end caps  24   b  and  26   b , and the keys  58   b  and  60   b  defined by the fin  46   b , must be aligned along an axis which is parallel to a longitudinal access  42   b  of the filter element  12   b  in order for connection of the fin to the element. The alignment axis is shown in the perspective view of  FIG.  26    and given the reference numeral  134 . In use, and once the fin  46   b  has been connected to the filter element  12   b , a longitudinal axis  56   b  of the fin  46   b  resides on the alignment axis  134 . 
     Fitting of the fin  46   b  to the filter element  12   b  is shown in the views of  FIGS.  26 A  to C. As can be seen from  FIG.  26 A , a base  52   b  of the fin  46   b  has an axial length which is slightly smaller than an axial length L 1  of the drainage layer  22   b  disposed between the filter end caps  24   b  and  26   b . This allows the base  52   b  to be inserted between the end caps  24   b  and  26   b , in contact with the drainage layer  22   b . This is shown in  FIG.  26 B . The key  60   b  is aligned with the keyway  64   b , and the key  58   b  with the keyway  62   b , along the axis  134 . The base  52   b  of the fin  46   b  has facing end surfaces, one of which is defined by the shoulder  108 , and the other by a shoulder  136  ( FIG.  29   ). The key portions  110  and  112  of the key  58   b  are spaced along a length of the fin  46   b  from the shoulder  136 , defining an area  138  which can receive the arms  116  and  118  of the keyway  62   b , so that the fin  46   b  can be located between the end caps  24   b  and  26   b  as shown in  FIG.  26 B . In this position, the key  60   b  is axially spaced from the keyway  64   b  on the second end cap  26   b , and the key  58   b  is axially spaced from the keyway  62   b  on the first end cap  24   b.    
     With the keys and keyways aligned as discussed above, the fin  46   b  can then be translated in the direction of the arrow G in  FIG.  26 C . This advances the key  60   b  into the keyway  64   b , and the key  58   b  into the keyway  62   b , so that they are located in their respective positions shown in  FIG.  24    and  FIG.  23    and described above. The latch tooth  130  engages in the circumferential recess  132  on the second end cap  26   b , and a lip  140  adjacent the shoulder  108  on the fin  46   b  engages over an inner peripheral surface  106   b  ( FIG.  25   ) of the second end cap  26   b . When the fin  46   b  is connected to the filter element  12   b , there is a small gap  142  between the shoulder  136  on the fin and the first end cap  24   b . This gap enables fitting of the fin  46   b  between the end caps  24   b  and  26   b , and the translational movement of the fin between its positions of  FIG.  28    and  FIG.  29   . 
     As can best be seen from  FIGS.  24  and  26   , the second end cap  26   b  in fact comprises a plurality of keyways  64   b , which are spaced around a circumference of the end cap. The provision of such a plurality of keyways  64   b  can aid manufacture of the filter element  12   b . In particular and as discussed above, the filtration and drainage layers  20  and  22  of the filter element  12   b , as well as other components such as the perforated support tubes  30   b  and  32   b , are potted in the end caps  24   b  and  26   b  using a suitable adhesive. In order for the fin  46   b  to be fitted to the filter element  12   b , the keyway  62   b  on the first end cap  24   b  must be aligned with a keyway  64   b  on the second end cap  26   b . Providing the large number of keyways  64   b  spaced around the circumference of the second end cap  26   b  can simplify alignment with the keyway  62   b  during assembly. 
     When fitted to the filter element  12   b , the fin  46   b  extends along the second end cap  26   b , and partly over the first end cap  24   b . A portion of the fin  46   a  including its base  52   a  is disposed between the end caps  24   a  and  26   a  and spans a majority of the distance between the end caps. 
     Turning now to  FIG.  30   , there is shown a front view of a filter element assembly in accordance with another embodiment of the present disclosure, the filter element assembly indicated generally by reference numeral  10   c . The filter element assembly  10   c  comprises a filter element  12   c  and a drainage promoter  14   c . Like components of the filter element assembly  10   c  with the filter element assembly  10  shown in  FIGS.  1  to  10    share the same reference numerals, with the addition of the suffix “c”. 
     The filter element  12   c  and the drainage promoter  14   c  are in fact of very similar construction to the filter element  12   b  and the drainage promoter  14   b  of the filter element assembly  10   b  shown in  FIGS.  22  to  29    and described above. In particular, the drainage promoter  14   c  comprises a fin  46   c  which is connected to the filter element  12   c  in a sliding connection, in the same way as the fin  46   b  is fitted to the filter element  12   b . Reference is therefore made to the discussion of  FIGS.  22  to  29    concerning the way in which the fin  46   c  is fitted to the filter element  12   c.    
     The drainage promoter  14   c  is shown separately, disconnected from the filter element  12   c , in the front, end and perspective views of  FIGS.  31 ,  32  and  33   . The drainage promoter fin  46   c  differs from the fin  46   b  in that it comprises a plurality of drainage elements  144  to  162 , each of which is coupled to the fin  46   c  and extends in a direction away from the fin. The drainage elements  144  to  162  each take the form of a finger, rib, arm or the like, and are typically moulded integrally with the fin  46   c . It will be understood however that the drainage elements  144  to  162  may be manufactured separately and subsequently connected to the fin  46   c . The drainage elements  144  to  162  each extend in a direction around an outer surface of a drainage layer  22   c  of the filter element  12   c , as shown in  FIG.  30   , and act to compress the drainage layer along their lengths, to further promote the drainage of liquid from the drainage layer and on to the fin  46   c.    
     A first row or array of drainage elements  164  comprises drainage elements  144 ,  148 ,  152 ,  156  and  160 , which each extend from the fin  46   c  in a first lateral direction, from a first flank  165  of the fin. A second row or array  166  comprises the drainage elements  146 ,  150 ,  154 ,  158  and  162  which each extend from the fin  46   c  in a second lateral direction, from a second flank  167  of the fin. The drainage elements in the arrays  164  and  166  each extend partway around a circumference of an external surface  44   c  of the drainage layer  22   c  when the drainage promoter  14   c  is fitted to the filter element  12   c . The drainage elements  144  to  162  in the two rows  164  and  166  together act to promote drainage of liquid from a wet band or zone  170 , which can form during use of the filter element  12   c . Accordingly, the drainage element need only extend around part of the circumference of the drainage layer  22   c  in order to provide the enhanced drainage effect. 
     The drainage elements  144  to  162  are each disposed transverse to a longitudinal axis  56   c  of the fin and are suitably disposed substantially perpendicular to the fin axis, as can be seen in  FIG.  31   . It will be understood however that the drainage elements  144  to  162  may be oriented so that they are transverse to the fin axis  56   c  but at non-perpendicular angles. The drainage elements  144  to  162  are each curved, having inner surfaces which have a curvature that substantially matches a curvature of the external surface  44   c  of the drainage layer  22   c , an inner surface of drainage element  144  being shown in  FIG.  33    and given the reference numeral  172 . 
     The drainage elements  144  to  162  each have a base at which they are coupled to the fin, a base  174  of the drainage element  146  being shown in  FIG.  33   . The drainage elements  144  to  162  each taper in a direction from their base towards a respective tip, the tip  176  of drainage element  146  being shown in  FIG.  33   . As can best be seen from  FIG.  31   , a width of each drainage element W 1  at its base (shown for the drainage element  146  in  FIG.  31   ) reduces in a direction towards its tip, to a width W 2 . An effective depth D 1  of the drainage element  144  to  162  also reduces in a direction from its base  174  towards its tip  176 , as again shown in  FIG.  31   . The reduced depth at the tip  176  can be appreciated from the perspective view of  FIG.  33   . Providing drainage elements  144  to  162  which taper in width and/or depth may help to promote the flow of liquid along the drainage elements and on to the fins  46   c  for subsequent discharge, during use of the drainage promoter  14   c.    
     The drainage elements in the first row  164  are axially staggered along a length of the fin  46   c  relative to the drainage elements in the second row  166 . This can best be seen from  FIG.  31   . Staggering the drainage elements in the first row  164  relative to the second row  166  can help to improve drainage of liquid from the drainage layer  22   c  in the wet band  170 . It will be understood however that the drainage elements in the first and second rows  164  and  166  may be axially aligned, for example by arranging the elements in pairs at common axial positions. For example, and viewing  FIG.  31   , the drainage elements  144  and  146  may be arranged at a common axial position, and so aligned along a transverse axis of the fin  46   c.    
     Whilst the drainage elements  144  to  162  have been shown on a fin  46   c  which is a sliding connection to its filter element  12   c  in the fashion of the fin  46   b  to the element  12   b , it will be understood that similar such drainage elements may be provided on any of the other drainage promoters/fins disclosed in this document. By way of non-limiting example therefore, similar such drainage elements may be provided on the fin  46  of  FIG.  1   , and on the fin  46   a  of  FIG.  11   . 
     Turning now to  FIG.  34   , there is shown a front view of a filter element assembly in accordance with another embodiment of the present disclosure, the filter element assembly indicated generally by reference numeral  10   d . The filter element assembly  10   d  comprises a filter element  12   d  and a drainage promoter  14   d . Like components of the filter element assembly  10   d  with the filter element  10  shown in  FIGS.  1  to  10    share the reference numerals, with the addition of the suffix “d”. 
     The filter element  10   d  is of substantially the same construction as the filter element  12  shown in  FIGS.  1  to  11    and described above. Accordingly, details of the construction and operation of the filter element  10   d  will not be described again in detail, reference instead being made to the discussion of the filter element  12  forming part of the filter element assembly  10  described above. Any substantial differences between the filter element assembly  10   d  and the assembly  10  will be described herein. In addition, the filter element assembly  10   d  can be located in the housing  4  of a filter  2  in a horizontal orientation in the same way as the filter element assembly  10 . Reference will therefore be made to the discussion above concerning the way in which the filter element assembly  10   d  is located in a filter housing  4 , and the way in which it operates during use. 
     The filter element assembly  10   d  is also shown in the end views of  FIGS.  35  and  36   , taken in the direction of the arrows A and B respectively in  FIG.  34   .  FIG.  37    is a perspective view and  FIG.  38    a longitudinal cross-sectional view of the filter element assembly  10   d , both drawn to a smaller scale. 
     In this embodiment, the drainage promoter  14   d  can be connected to a drainage layer  22   d  of the filter element  12   d , rather than to first and second end caps  24   d  and  26   d  of the filter element  12   d , in the way that the previously described drainage promoters are connected to their respective filter elements. The drainage promoter  14   d  is connected to the filter element  12   d  at a location between first and second end caps  24   d  and  26   d  of the filter element. A fin  46   d  of the drainage promoter  14   d  comprises connection features which serve for connecting the fin directly to the drainage layer  22   d . In this case, the connection features take the form of resilient elements which are similar to the drainage elements  144  to  162  forming part of the drainage promoter  14   c  discussed above. 
     The drainage promoter  14   d  is shown separately in the front, end and perspective views of  FIGS.  39 ,  40  and  41   . A first array  164   d  of connection elements is provided, comprising connection elements  144   d ,  148   d ,  152   d ,  156   d  and  160   d . A second row or array  166   d  comprises connection elements  146   d ,  150   d ,  154   d ,  158   d  and  162   d . The connection elements  144   d  to  162   d  are of similar construction to the drainage elements  146  to  162  described above, and can also provide a drainage function, serving to enhance the flow of liquid from the drainage layer  22  to the fin  46   d . However, a primary function of the connection elements  144   d  to  162   d  in this embodiment is to connect the fin  46   d  to the drainage layer  22   d , and so to the filter element  12   d.    
     The connection elements  144   d  to  162   d  each have a shape which is substantially similar to the drainage elements  144  to  162 , tapering from a base  174   d  towards a tip  176   d , which is shown for the connection element  144   d  in the end view of  FIG.  40   . In this embodiment however, the drainage elements  144   d  to  162   d  are arranged to impart a clamping force on the drainage layer  22   d , for connecting the drainage promoter  14   d  to the filter element  12   d . Specifically, the connection elements are arranged in pairs, axially adjacent connection elements (taken in a direction along a length of the fin  46   d ) acting together to provide the clamping force. A clamping force is therefore exerted between the connection elements  144   d  and  146   d , as well as between successive pairs of connection elements along the length of the fin  46   d . Thus, a clamping force is along exerted between the connection elements  146   d  and  148   d , the connection elements  148   d  and  150   d  and so on. This is achieved by providing the connection elements as resilient arms, fingers or the like in a similar fashion to the drainage elements  144  to  162  described above. 
     In order to provide the clamping force, the connection elements  144   d  to  162   d  each extend from the fin  46   d  around a circumference of the filter element  12   d  to an over-centre position, relative to a central longitudinal axis  56   d  of the filter element  12   d . A location of the central axis  56   d , and the over-centre positioning of the connection elements  144   d  to  162   d , is shown in the end view of  FIG.  40   . As can be seen, the pair of connection features  144   d  and  146   d  together encompass more than half of a circumference of the circular section drainage layer  22   d , and so the filter element  12   d . Effectively, the connection elements  144   d  to  162   d  together describe a generally cylindrical passage or opening  178  which is shaped to receive the filter element  12   d . A space is defined between the ends  176  of the connection elements  144   d  to  162   d , the space indicated generally by reference numeral  180  in  FIG.  20   . A dimension W 2  of the space  180  is smaller than a diameter of the filter element  12   d  at its drainage layer  22   d . This serves to provide the clamping force. 
     The drainage promoter  14   c  described above is typically moulded as a unitary or one-piece component, comprising its fin  46   c  and drainage features  144  to  162 . The drainage promoter  14   d  can similarly be constructed as a unitary or one-piece structure, which would then require a push-fit of the drainage promoter to the drainage layer  22   d . This would require that the space  180  defined between the tips  176  of the connection features  144   d  to  162   d  be opened up to pass around the drainage layer  22   d , over its diameter to the over-centre position shown in  FIG.  40   . 
     It may therefore be preferable to construct the drainage promoter  14   d  as a two-piece structure, to facilitate fitting of the drainage promoter to the filter element  12   d . This is best shown in the end view of the drainage promoter  14   d  in  FIG.  42 B , and the end view of the assembly in  FIG.  42 A , showing fitting of the drainage promoter to the filter element  14   d . Referring to  FIG.  42 B , first piece  182  of the drainage promoter  14   d  comprises a first part  184  of its fin  46   d  and the first row  164   d  of connection features. A second piece  186  comprises a second part  188  of the fin  46   d  and the second row  166   d  of connection features. The first part  184  of the fin  46   d  defines a first flank  165   d  of the fin and a planar inner mating surface  190 . The second part  188  of the fin  46   d  comprises a second flank  167   d  of the fin and a planar inner mating surface  192 . The planar mating surface  190  is shown in the cross-sectional view of  FIG.  38    and carries a number of mating protrusions  194  and mating apertures  196 , the protrusions engaging in corresponding apertures (not shown) on the mating surface  192  and the apertures receiving corresponding mating protrusions  198  (one shown) on the mating surface  192 . Engagement between the respective mating protrusions and apertures on the planar surfaces  190  and  192  serves for connecting the first and second pieces  182  and  186  of the fin together as shown in  FIG.  40   . The first fin piece  182  is typically fitted to the drainage layer  22   d  of the filter element  12   d  as shown in  FIG.  42 A , and then the other fin piece  186  is connected to the first fin piece, so that the connection features  144   d  to  162   d  clamp the drainage layer  22   d.    
     When fitted to the filter element  12   d , the fin  46   d  is disposed between the end caps  24   d  and  26   d  and spans a majority of the distance between the end caps. 
     Turning now to  FIG.  43   , there is shown a front view of a filter element assembly in accordance with another embodiment of the present disclosure, the filter element assembly indicated generally by reference numeral  10   e . The filter element assembly  10   e  comprises a filter element  12   e  and a drainage promoter  14   e . Like components of the filter element assembly  10   e  with the filter element assembly  10  shown in  FIGS.  1  to  10    share the same reference numerals, with the addition of the suffix “e”. 
     The filter element  12   e  is of substantially the same construction as the filter element  12  shown in  FIGS.  1  to  11    and described above. Accordingly, details of the construction and operation of the filter element  10   e  will not be described again in detail, reference instead being made to the discussion of the filter element  12  forming part of the filter element assembly  10  described above. Any substantial differences between the filter element assembly  10   e  and the assembly  10  will be described herein. In addition, the filter element assembly  10   e  can be located in a housing  4  of a filter  2  in a horizontal orientation in the same way as the filter element assembly  10 . Reference will therefore be made to the discussion above concerning the way in which the filter element assembly  10   e  is located in a filter housing  4 , and the way in which it operates during use. 
     The filter element assembly  10   e  is also shown in the end views of  FIGS.  44  and  45   , taken in the direction of the arrows A and B respectively in  FIG.  43   . In this embodiment, the drainage promoter  14   e  can be connected to the filter element  12   e  at a location between first and second end caps  24   e  and  26   e  of the filter element. The drainage promoter  14   e  can be connected to a drainage layer  22   e , in a similar fashion to the drainage promoter  14   d  discussed above. 
     The drainage promoter  14   e  comprises a fin  46   e  and first and second connection elements  200  and  202  which can engage the drainage layer  22   e , to connect the fin to the filter element. In the illustrated embodiment, the connection components  200  and  202  are spaced spart along a length of the fin  46   e  and are suitably provided at respective first and second axial ends  48   e  and  50   e  of the fin  46   e . It will be understood however that the connection components  200  and  202  may be provided at alternative locations on the fin  46   e , and/or that more than two connection components, or conceivably only a single connection component, may be provided. 
     The connection components  200  and  202  each take the form of a strap or tie which extends from the fin  46   e  and around a circumference of the drainage layer  22   e . The drainage promoter  14   e  is shown separately in the front, end and perspective views of  FIGS.  46 ,  47  and  48   , which are drawn to a smaller scale,  FIG.  47    viewing in the direction of the arrow D in  FIG.  46   . 
     The first strap  200  comprises a first strap portion  204  which extends in a first direction away from the fin  46   e  and around part of a perimeter of the drainage layer  22   e , and a second strap portion  206  which extends in a second opposite direction away from the fin and around a further part of the perimeter of the drainage layer. The first and second strap portions  204  and  206  can be coupled together to connect the fin  46   e  to the filter element  12   e . To this end, the strap portions  204  and  206  comprise respective connection features  205  and  207  which serve for coupling the portions together. 
     The first strap portion  204  comprises a female connection feature in the form of an aperture  205  formed in a stepped end section  209 . The second strap portion  206  comprises a male connection feature in the form of a protrusion such as a button  207 , which can be located within the aperture  205  in a press-fit, to secure the strap portions  204  and  206  together. The button  207  may include an enlarged head and may be resiliently deformable for passing through the aperture  205  and securing the strap portions  204  and  206  together. It will be understood that this represents just one option for the way in which the strap portions  204  and  206  can be coupled together. Alternatives can be envisaged, including a zip-tie type structure, a separate mechanical connection, or the use of an adhesive. The second strap  202  comprises similar such first and second strap portions  208  and  210  which also comprise connection features in the form of an aperture  212  and a button  214 . 
     The straps  200  and  202  extend from the fin  46   e  to encompass the entire circumference of the drainage layer  22   e , when their respective strap portions  204 / 206  and  208 / 210  are coupled together. In a variation however, a strap may be provided comprising a single portion which substantially encircles the drainage layer  22   e , the strap being coupled at one end to the fin  46   e  and having a free end which can be connected to the fin after encircling the drainage layer. In a further variation, one or more straps may be provided separately, and may be connectable to the fin  46   e  to secure it to the filter element  12   e , for example by passing through a locating aperture in the fin and around the drainage layer (or in an alternative, around an end cap). 
       FIGS.  49  and  50    are front and end views of the filter element assembly  10   e  shown during fitting of the drainage promoter  14   e  to the filter element  12   b , drawn to a smaller scale. As shown in these drawings, the drainage promoter is introduced to the filter element  12   e  so that the fin  46   e  is positioned adjacent to the drainage layer  22   e  and located between the end caps  24   e  and  26   e . The first strap portions  204  and  208  pass away from the fin  46   e  on one side of the fin, and the second strap portions  206  and  210  pass away from the other side of the fin. The strap portions  204  and  206  can then be brought together to encircle the drainage layer  22   e , by bringing ends of the strap portions together in the direction of the arrows E and F shown in  FIG.  50   . The stepped end portion  209  on the first strap portion  204  can be located so that it passes over the button  207  on the second strap portion  206 , and the button press-fitted through the aperture  205  to connect the two strap portions together. A similar procedure can then be followed for the strap portions  208  and  210  of the second strap  202 . 
     Engagement of the strap portions  204 ,  206  and  208 ,  210  exerts a clamping force on the drainage layer  22   e , causing the fin  46   e  to press into its external surface  44   e , as shown in the longitudinal cross-sectional view of  FIG.  51   . The fitted drainage promoter  14   e  therefore adopts the position shown in the perspective view of  FIG.  52   . The connection straps  200  and  202  can also act to compress the drainage layer  22   e , to provide improved drainage, in a similar fashion to the drainage elements discussed above. 
     When fitted to the filter element  12   e , the fin  46   e  is disposed between the end caps  24   e  and  26   e  and spans the distance between the end caps. 
     Drainage promoters of the type disclosed in this document which can be connected to a drainage layer of a filter element (in particular the drainage promoters  14   e  and  14   d ) may provide the advantage that they can be connected to filter elements of a standard type, without necessarily requiring any modification to be made to the structure of the filter element, in particular its end caps. These and other drainage promoters disclosed in this document can provide the advantage that they can be removed from the filter element and connected to a further element, say in the situation where the filter element becomes clogged during use and requires replacement. This may provide material and cost benefits. 
     Various modifications may be made to the foregoing without departing from the spirit or scope of the present invention. 
     Numerous different embodiments of drainage promoters and filter elements to which the disclosed drainage promoters can be fitted are disclosed in this document. In further variations, the features of one or more of the disclosed embodiments may be provided in combination. Thus, for example, combinations of sliding and pivoting connection features, and connection features involving connection to a drainage layer rather than end caps of a filter element, may be provided in combination in further embodiments. 
     In each embodiment of filter element assembly disclosed in this document, either of the first and second end caps may comprise a port for the entry of gas into the filter element. In relevant embodiments, the fin may be connected differently to end caps of the filter element, for example in the embodiment of  FIG.  11   , the fin  46   a  may be pivotally connected to the second end cap  26   a  and may latch-fit to the first end cap  24   a.    
     Reference is generally made in this document to a filter element comprising a wall of a filtration medium which defines a hollow space for a gas stream to flow from the space through the wall to be filtered, and a drainage layer located outside the filtration layer in which liquid separated from the gas stream can collect, as well as to a drainage promoter which compresses the drainage layer to promote drainage of liquid which has collected in the drainage layer. Reference may however be made generally to a fluid stream (which may not specifically be a gas), and to the drainage of fluid (which may not specifically be a liquid) which has collected in the drainage layer. The fluid which is collected in the drainage layer may have been filtered from the fluid stream flowing through the wall of the filter element. The fluid stream may therefore comprise a first fluid and at least one further fluid, which further fluid may collect in the drainage layer.