AU747765B2 - A filter assembly - Google Patents

Description

WO 99/45214 PCT/AU99/00141 1 A FILTER ASSEMBLY" This invention relates to filter assemblies.

This invention has particular application to filter assemblies for stormwater drains and the like for filtering runoff water prior to discharge. However this invention is not limited to such application and may be used as an in-line process filter which is particularly suitable for variable rate liquid flows. However for illustrative purposes only, the present invention will be described hereinafter in relation to its use with stormwater drains.

Stormwater drains typically discharge directly into streams and the like and carry large amounts of debris and other contaminating matter into the streams. In recent years there has been a growing awareness of the need to minimise pollution resulting from groundwater runoff.

One of the difficulties associated with groundwater runoff discharging from the outlets of stormwater drains is that the contaminants discharged therewith can range from relatively large lightweight objects such as aluminium drink cans and plastic bags as well as liquid contaminants such as oils and greases improperly discharged onto the ground and collected in the stormwater drains. In addition stormwater drains gather poisons and other chemicals which have been applied to lawns and plants as well as to buildings and machinery and particles from industrial processes as well as debris from roads and car parks.

Another difficulty associated with stormwater runoff is that the runoff may range from a trickle to a torrent and any apparatus placed in line in the stormwater drain must be capable of handling the full range of flows if it is to be effective.

Some authorities have made attempts to filter stormwater runoff by placing a mesh fence across streams downstream of a stormwater discharge. These are suitable for catching relatively large articles only and require frequent clearing.

WO 99/45214 PCT/AU99/00141 2 In addition such filters represent a hazard in small creeks and the like as during periods of flooding they may snare persons or animals caught in the flow.

Our earlier patent application No. 64385/96 describes filter assemblies which provide guided straight through flow between an inlet and an outlet for substantial storm flows but which divert trickle drainwater water flows through filters with a view to collecting the contaminants which are often concentrated in such flows.

Other types of stormwater filters utilise large inground storage tanks. However these tanks tend to provide a refuge for wild life such as eels and turtles which are difficult to remove and are destroyed when the tanks are emptied.

This invention aims to provide improved filter assemblies for filtering a range of flows which will be efficient in operation.

In another aspect this invention aims to provide filter assemblies which will be easy to service and/or which will operate with minimum head loss.

With the foregoing in view, this invention in one aspect resides broadly in a filter assembly including:a housing; an elevated inlet to the housing; an elevated outlet from the housing through which substantial flows entering through the inlet may be discharged; a filter chamber in the lower portion of the housing having at least two spaced apart in-line filter screens therein; the upper portion of the housing being substantially unobstructed so as to permit full flows through the inlet to pass through the upper portion to the outlet; an elevated open topped flow receiving means for receiving inlet flows; WO 99/45214 PCT/AU99/00141 3 a diversion drain to the filter chamber in the base of the flow receiving means, and the filter chamber providing a trickle-flow path from the diversion drain through the filter chamber to a storage chamber or an outlet drain adjacent the base of the filter chamber and a moderate flow path from the diversion drain to the main outlet bypassing at least one of the filter screens in the filter chamber.

The housing may be of any desired configuration such as of circular or rectangular form. Suitably the housing is provided with an access lid or lids which may be opened to provide direct access from above to the floor zones in which material may be trapped by the filter screens. More suitably the floor of the housing is flat so that the floor zones may be cleaned by vacuum cleaning apparatus.

In a preferred form an access lid provides pumping access to a holding chamber downstream of the final filter so that the housing may be pumped out by pumping from the holding chamber. This water may be discharged through the outlet or onto the ground since it will have passed through the filters of the filter assembly. Thus only the solid residue remaining in the housing upstream of the filters will need to be cleared and transported away to a safe disposal site. Suitably the holding chamber is an relatively small open topped chamber from which wildlife can be manually removed prior to emptying.

The inlet is suitably a round inlet to match the inlet pipe. However if desired it can be formed in other shapes.

The outlet may simply spill onto an apron or it may be connected to a pipe to form an in-line installation.

The axes of both the inlet and the main outlet may be at about the same level so that the fall in height between the inlet and outlet is minimised. This enables underground drains leading to and from the housing to be excavated to about the same depth. Furthermore the main outlet may be WO 99/45214 PCT/AU99/00141 4 larger than the inlet if desired.

The open topped flow receiving means may be an open channel extending from the inlet to the main outlet and having the diversion drain formed in the leading end thereof.

Further in such arrangements the open channel can receive overflows from the filter chamber along the edges thereof and preferably upstream of at least the last of the in-line filters to provide the moderate flow path to the main outlet.

Alternatively the open topped flow receiving means may be a open channel extending from the inlet for discharge of small to moderate flows to a coarse screen adjacent the main outlet and having the diversion drain formed in the leading end thereof but adapted to divert trickle flows only, the open channel providing the bypass flow for moderate flows.

Then again the open topped flow receiving means may be an open receptacle having an open bottom providing the inlet to the filter chamber whereby backflow pressure created in the filter chamber in moderate flow conditions will cause incoming liquid to bypass the filter chamber through the open top of the receptacle through the unobstructed upper portion of the housing to the main outlet.

Preferably the in-line filter screens are graded to provide a relatively fine filter screen remote from the diversion drain and one or more coarser screens between the fine filter screen and the diversion drain.

It is also preferred that the moderate flow path bypasses at least the fine filter screen such that much of the material, which may be silt and sediment in a stormwater drain installation, trapped thereby will be retained in the filter assembly for subsequent collection. It is also preferred that the moderate flow path be so configured as to bypass the more coarse filter screens, or one or more thereof, such that much of the material trapped thereby will be retained in the filter assembly for subsequent collection such as by vacuum cleaning apparatus.

WO 99/45214 PCT/AU99/00141 The open receptacle suitably defines a weir across which the bypass water passes to the outlet and suitably the filter chamber has a top closure wall passing from the upper edge of the weir and downwardly toward the outlet to form a spillway along which bypass water may flow to the outlet. For installations in tidal locations the filter at the inlet of th filter chamber may extend upwardly beyond the weir, such as to the high water level.

In an installation required to catch litter only the filter chamber may include only a coarse final filter.

In another aspect this invention resides broadly in a filter assembly including:a housing; an inlet the housing; a main outlet from the housing through which a substantial flows entering through the inlet may be discharged; an elevated open topped flow receiving means for receiving flows from the inlet, the receiving means extending from the inlet to the main outlet; a filter chamber in the lower portion of the housing; a diversion drain for diverting shallow inlet flows to a filter chamber; filter means for collecting contaminants in the filter chamber and including a primary filter assembly through which diverted flow passes to a secondary filter assembly; a drain outlet from the filter chamber located downstream of the secondary filter, and feedback means for feeding flows in excess of those which can pass through the secondary filter back to the elevated flow receiving means for passage to the main outlet.

For stormwater drainage applications it is also preferred that the upper wall of the filter assembly be provided with a grate to permit flood flows to pass therethrough should the main outlet be incapable of WO 99/45214 PCT/AU99/00 141 6 discharging flood flows.

The diversion drain is suitably formed in the base of the flow receiving means and suitably at any suitable location therealong. Suitably however the diversion drain is located adjacent the inlet and preferably the diversion drain includes blocking means for blocking passage of large objects through the diversion drain. The blocking means is suitably a grille or the like disposed in the base wall of the flow receiving means and suitably configured with elongate openings extending longitudinally of the flow receiving means.

The elevated flow receiving means may be a hollow conduit but preferably it is in the form of an open channel and suitably the conduit or channel is provided with slots along its underside adjacent the inlet which constitute the diversion drain which is blocked to passage of large objects therethrough.

The inlet may be a substantially circular opening so as to facilitate connection to a stormwater drain but if desired the inlet may be rectangular to match up to a box culvert so that flows therethrough may be readily filtered. In either form it is preferred that the fall in height between the inlet and main outlet be minimised so that variation in head pressures in the housing are minimised and so that underground drains leading from the main outlet may be placed with minimum expense in trenches which are relatively shallow.

Preferably the feedback means is upstream of the secondary filter assembly so as to inhibit the excess flows passing to the drain outlet through the secondary filter. It is also preferred that the primary filter assembly is associated with bypass means enabling excess flows to bypass the primary filter assembly without passing back to the elevated flow receiving means.

The feedback means may be associated with the diversion WO 99/45214 PCT/AU99/00141 7 drain so as to partially block the diversion drain during periods of high flow and may be constituted by the configuration of the diversion drain causing high flows to mostly pass across the drain. Alternatively the feedback means may be blocking means for blocking or partially blocking the diversion drain when levels in the filter chamber reach a preset level. The feedback means may be associated with or constituted by the secondary filter.

Preferably the elevated flow receiving means is an open channel or an open sided drain and the feedback means includes an upward extension of an upstanding filter screen forming the secondary filter, the upward extension extending upwardly beyond the open channel or opening in the side of the open sided drain so as to cause liquid build up behind the secondary filter to feed back into the elevated flow receiving means.

It is also preferred that the primary filter is an upstanding filter screen having an upper edge below the open channel or opening in the side of the open sided drain so as to enable excess liquid build up behind the primary filter to bypass thereacross without entering the open channel or opening in the side of the open sided drain.

Suitably the primary and secondary filters are screen type filters and while they could be of the same mesh size it is preferred that the secondary filter be a finer filter than the primary filter. It is also preferred that the drain outlet be screened with a fine filter and suitably finer than the secondary filter. Typically the primary, secondary and drain outlet filters are mesh type filters with decreasing mesh size from the primary filter to the drain outlet.

If desired the filter chamber may incorporate tertiary filter means which may be of the type in which the filtered flows are accumulated for periodical discharge or emptying.

Preferably however the filter chamber is of a simple form so as to facilitate ease of emptying and cleaning.

WO 99/45214 PCT/AU99/00141 8 For cleaning purposes it is preferred that the filter assembly be provided with a folding lid hinged centrally so that the end parts thereof can hinge upwardly to expose substantially all the interior of the filter chamber for maintenance access. Suitably the lid is provided with a grate and with locking means for securing the lid to preclude human access to the filter chamber.

The housing may be cast as an integral concrete unit or it may be formed from FRC sheeting which is bolted together through steel angles and edge glued together for sealing all joints. In a typical size which may be 2400mm long, 1000mm wide and 1500mm deep the FRC sheeting would be in the order of 15mm thick. Alternatively a much thinner sheeting may be used to facilitate manufacture and delivery to site, either constructed or in a kit form to be assembled on site with the fabricated housing being used as an inner liner for an insitu formed concrete housing poured on site.

The elevated flow receiving means is suitably formed as a steel channel with welded in bars in an opening forming a grate across the diversion drain. However slots could be cut into the steel channel for this purpose if desired or a screen could be mechanically fastened or welded to the channel in an aperture therethrough to suit local conditions.

Furthermore the grate may be formed with fixed and movable slats so as to provide adjustment of the grate opening size to suit different applications.

In yet a further aspect, this invention resides broadly in resides broadly in a filter assembly including:a housing having an inlet and an outlet; a filter assembly in the housing through which normal flows through the inlet must pass for passage to the outlet, and feedback means for returning flows unable to pass through the filter assembly into the housing for alternate passage to the outlet. Preferably the alternate passage is WO 99/45214 PCT/AU99/00141 9 an unfiltered passage such as the unobstructed portion of the housing. Coarse filtering of the alternate passage could be provided if desired.

The housing may be rectangular or circular or other shape as required. Suitably the inlet and the outlet are elevated above the base wall of the housing and the inlet discharges normal flows through a primary filter screen which forms an inlet to the filter assembly. This may be a coarse bar or mesh type screen for example. Preferably the outlet has a curved transition to its bore to minimise the resistance to flow into the outlet. Suitably the outlet is larger than the inlet and a rounded collar protrudes into the housing to form the curved transition. The outlet may be configured venturi-like or bellmouthed so as to minimise the resistance to flow into the outlet.

Suitably the axes of both the inlet and the outlet are at about the same level so that the fall in height between the inlet and outlet is minimised. If desired the axis of the outlet could be elevated above the axis of the inlet.

This enables underground drains leading to and from the housing to be excavated to about the same depth.

The filter assembly may be constituted by the lower portion of the housing and the unobstructed part of the housing through which flows bypass to the outlet may be the upper part above the filter assembly. Alternatively the filter assembly may be located medially of the housing and the bypass flows may flow over and/or about the filter assembly to the outlet.

Suitably the filter assembly includes a relatively coarse primary filter and a finer secondary filter. The filter assembly may also include a relatively fine tertiary filter.

Preferably the filters are arranged in a closure which is operatively sealed from the remainder of the housing and communicates with the inlet through a receptacle which opens WO 99/45214 PCT/AU99/00141 to the upper portion of the housing whereby flows which enter the filter assembly must leave therethrough or return to the housing through the open receptacle.

The open receptacle is suitably associated with a surrounding wall and depends therefrom so that buoyant material trapped by the primary filter and which may rise during high flows can be trapped beneath the surrounding wall until the high flow ceases.

Suitably the closure includes a top closure wall which slopes down toward the outlet and the final one of the filter screens to which the closure wall inclines has its upper edge at about the same level or below the lower edge of the outlet so that liquid remaining in the housing during non-flow conditions is at or above the level of the upper edge of the final filter screen.

The primary filter screen is suitably higher than the final filter screen and preferably it extends upwardly to a level across which normal flow from the inlet will not pass and suitably the top closure wall slopes downwardly from the upper edge of the primary filter. This top closure wall may provide a floor for the feedback flows from the inlet to the outlet.

The top closure wall may also have its underside lined with an absorbent filter pad of the type which absorbs oil which will come into contact with the pad when floating on liquids which build up behind the final filter screen.

The housing is suitably provided with a lid which may be removed to enable servicing of the housing to be readily carried out. For floodwater applications the lid may be provided with a grate to permit excess flood flows to pass therethrough should the outlet be incapable of discharging the flood flows. Further it is preferred that the closure wall and the capping wall, if utilised, be removable to facilitate servicing.

In another aspect this invention resides in a filter WO 99/45214 PCT/AU99/00141 11 assembly for a stormwater outflow chamber, the filter assembly including a series of filter screens including a primary filter screen and a final filter screen and an associated upper closure wall extending between the primary filter screen and a final filter screen. Preferably the primary filter screen is higher than the final filter screen and the upper closure wall slopes from the primary filter screen down to the final filter screen. This filter assembly may be placed across a lower portion of a potential flow path so as to filter flows which exist only in the lower portion of the potential flow path. Greater volume flows will pass over the filter which will act as an obstacle to flow and the sloping upper closure wall will provide a flow chamber thereabove which diverges downstream along the filter assembly to facilitate flow past the filter assembly.

In yet another aspect this invention resides in a method of forming a stormwater outflow filter, including:forming a filter chamber having an inlet and an outlet; providing a filter assembly including a series of filter screens including a primary filter screen and a final filter screen and an associated upper closure wall extending between the primary filter screen and a final filter screen; arranging the filter assembly in a lower portion of the filter chamber so that normal flows through the inlet pass through the housing into the filter assembly and abnormal high flows can bypass the filter assembly for flow thereacross to the outlet.

Suitably the primary filter and secondary filters are screen type filters and while they could be of the same mesh size it is preferred that the secondary filter be a finer mesh size than the primary filter mesh.

If desired the filter chamber may incorporate tertiary filter means which may be of the type in which the filtered flows are accumulated in the housing for periodical discharge or emptying.

WO 99/45214 PCT/AU99/00141 12 The housing may be cast as an integral concrete unit or assembled on site. The housing may be formed from FRC sheeting which may be bolted together through steel angles and edge glued together for sealing all joints. In a typical size which may be 2400mm long, 1200mm wide and 2 100mm deep.

FRC sheeting for such embodiment could be in the order of thick. Alternatively a much thinner sheeting may be used to facilitate manufacture and delivery to site, either constructed or in a kit form to be assembled on site with the fabricated housing being used as an inner liner for an insitu formed concrete housing poured on site.

This invention also provides a method of maintaining a stormwater filter assembly of the type variously defined above and having a holding chamber downstream of the filter chamber, including:emptying water trapped in the housing through the holding chamber and discharging the filtered water, and gathering the material retained in the filter chamber for discharge at a safe disposal site.

In order that this invention may be more readily understood and put into practical effect reference will now be made to the accompanying drawing which illustrates a typical stormwater filter assemblies according to various aspects of this invention, wherein:- FIGS. la, lb and lc illustrate one embodiment in plan, side and end elevations; FIG. 2 is a cutaway perspective view of the embodiment of Fig. 1; FIGS. 3a and 3b illustrate a front end and a cutaway side view of the embodiment of Fig. 1; FIG. 4 is a sectional view along the line 4-4 of Fig.

3b; FIG. 5 is a perspective view of another embodiment; FIGS. 6 and 7 illustrate a further typical stormwater application in plan an side elevation respectively; WO 99/45214 PCT/AU99/00141 13 FIG. 8 is an enlarged plan view of the stormwater filter assembly illustrated in Figs. 6 and 7; FIG. 9 is an enlarged side elevation of the stormwater filter assembly illustrated in Figs. 6 and 7, and FIG. 10 is a cut-away perspective view of the stormwater filter assembly illustrated in Figs. 6 and 7.

The filter assembly 10 illustrated in Figs. 1 to 4 includes a concrete housing 11 having an elevated circular inlet aperture 14 in the inlet wall 15 and an open partcircular flow receiving means 16 extending between the inlet wall 15 and the outlet wall 17 for directing full flows to the outlet opening 20. However the flow receiving means 16 is in the form of a solid half pipe conveyor with elongate slots 21 formed in the base thereof adjacent the inlet aperture 14 to form a diversion drain upstream of a primary filter 22 to which liquids diverted through the slots 21 are fed.

In this embodiment the primary filter 22 is in the form of a mesh or bar type wall extending substantially vertically between the side walls 24 and from the bottom wall 26 to the underside of the flow receiving means 16.

The floor 26 of the housing 11 has a central elongate ridge 28 beneath the flow receiving means 16 and removable filter mats 27, suitably formed of aerated nylon fabric material or the like, are positioned at opposite sides of the ridge portion 28. Side outlets 30 are formed in the outlet wall 17 at opposite sides of the main outlet opening 20. The outlets 30 extend to the floor 26.

The flow receiving means 16 terminates short of the outlet wall 17 and is supported adjacent its end by a further mesh type screen wall 31 which extends across the housing 11.

The ridge portion 28 and the filter mats 27 also terminate at the screen wall 31. The inlet end of the flow receiving means 16 is supported by the primary filter 22.

The flow receiving means discharges into a removable WO 99/45214 PCT/AU99/00141 14 filter basket 32 supported in the housing 11 between the screen wall 31 and the outlet wall 17 and a coarse wire basket 34 is provided at the exterior of the housing 11 to receive flow discharged through the outlet opening The housing 11 is provided with a removable top closure panel 36 provided with a lifting lid 37 adjacent the inlet wall 15 and a lifting grate 39 adjacent the outlet wall 17.

The grate 39 provides flood release in case the outlet opening 20 is restricted or blocked. The lid 37 and the grate 39 may also be raised to provide access to the interior of the housing and for accessing the removable basket 32.

In use, regular shallow flows will be diverted through the slots 21 for collection in the chamber 40 formed behind the primary filter wall 22. The filtrate therefrom will flow onto the filter mats 27 for collection of further contaminates such as oils and greases and the like. The further screen wall 31 provides a finer filter than the primary filter wall 22 to trap silt and sediment which will be retained for subsequent removal.

Storm flows which may contain large debris will pass directly along the flow receiving means 16 to the outlet opening 20 without significantly disturbing the material filtered by the secondary filters 22 and the further filter 31 which will be retained in the base of the housing 11 for removal for safe disposal either before or after a storm flow. If desired a storage tank such as a one thousand litre tank may be provided beneath the housing 11 to receive filtrates resulting from shallow flows from the side outlets for subsequent disposal remote from the normal stormwater outlet.

Slight storm flows or the like may discharge into the basket 32 whereas strong storm flows will mostly pass directly to the coarse basket 34 which will trap large objects contained in the storm flow without blocking the outlet opening 20. The basket 34 may be of any desired size WO 99/45214 PCT/AU99/00141 for this purpose.

The filter assembly 60 illustrated in Fig. 5 includes an open topped housing 61 which is fabricated from panels suitably from fibre reinforced concrete or compresses AC or the like, which are connected together at the joints by gluing with a suitable glue such as a two pot epoxy glue for sealing the housing, as well as being mechanically fastened through angle-iron brackets at the corner junctions.

The housing 61 is closed by a lid assembly 62 which is fixed to steel brackets 63 bolted to the opposed side walls of the housing 61. The intermediate brackets 63 support the ends of a hinge bar or pivot while the end brackets 63 support removable bars 65 which are retained by padlocks 64 and which overlie the opposite ends of the lid assembly 62.

In this manner, the bars 65 may be retracted from the brackets 63 to enable both lid parts 66 and 67 to be elevated upwardly to provide substantially unobstructed access to the interior of the housing 61. One lid part 66 is provided with an overflow grate 68 as illustrated.

In this embodiment, the stormwater inlet 70 is a circular inlet which may be cut to suit stormwater drain pipes in the order of 300mm to 450mm diameter. The main flow outlet means 72 is at least as big as or larger than the inlet 70 and an open elevated receiving channel 74 extends from the inlet wall 75 of the housing 61 to the outlet wall 73 thereof just beneath the openings 70 and 72 so as to guide high volume flow thereto through the inlet 70 toward the outlet 72.

The receiving channel 74 has minimal fall so as to minimise head losses through the filter assembly 60 and is suitably formed of galvanised steel. A grill 76 formed of spaced 6mm diameter rods is formed in the receiving channel 74 across the diversion drain 75 adjacent the inlet 70 to prevent passage of large objects through the diversion drain 75. This drain 75 may be lengthened to suit larger inlet WO 99/45214 PCT/AU99/00141 16 diameters.

Small and trickle flows pass into the diversion drain and directly into the filter chamber 80, which is constituted by the lower portion of the housing 61 which is approximately 800mm wide, 2400mm long and 1200mm deep.

Trickle flows into the filter chamber 80 will fall directly to the floor 77 and will build up behind the primary filter screen 81 for flow therethrough. The primary filter screen 81 is a mesh type screen having 1.6mm apertures therethrough. This is sufficiently fine to trap relatively course debris including silt and the like which will build up and provide an absorbent medium for absorbing further contaminants such as oils and greases which may be introduced into the filter chamber.

The upper edge 82 of the primary screen 81 is disposed below the side edges 83 of the open channel 74 so that liquid to be filtered can flow directly over the top of the primary filter screen 81 without passing into the channel 74.

A secondary filter screen 85 is supported in the filter chamber downstream from the primary filter 81 and it is also formed as a fine mesh screen having a smaller mesh opening in the order of 0.6mm which is sufficiently small to restrain oil globules and the like from passing through the secondary fine mesh screen 85 into the discharge chamber 86 from which filtered stormwater is drained by floor level drain apertures 87 and elevated drain apertures 88.

The drain apertures 87, 88 are suitably 100mm diameter apertures so that they may be readily connected to plastic plumbing pipes and fittings and the like so that discharge water can be diverted for collection if required. Further fine mesh screens 91 with mesh openings in the order of 0.4mm are placed across these openings 87, 88 to further limit the contaminants which may pass to the exterior of the housing 61 through the openings 87 and 88.

The secondary filter screen 85 has an upper edge WO 99/45214 PCT/AU99/00141 17 which is disposed above the edges 83 of the channel 74 so that excess buildup therebehind will feed back into the channel 74 for direct discharge through the outlet as opposed to passing into the discharge chamber 86. This will occur during substantial flows into the housing 61.

Typically in use, small flows will precede flood flows and these preceding flows will act to wash exposed surfaces and will thus contain the bulk of contaminants which are on roads and surrounding surfaces. These flows will pass directly through the diversion drain 78 into the filter chamber 80 for staged filtering through the primary and secondary filters prior to discharge through the outlets 87 and 88 covered by fine screens 91.

When flood flows occur, it is not possible to provide the same degree of filtering and generally it is not necessary or practical to do so. Thus these flows pass substantially directly to the outlet 72. In the process, the filter chamber may substantially fill with stormwater, however by the mechanism described above, much of the filtered contaminants will be retained in the base of the filter chamber behind the screens 81 and 85 with excess unfiltered flows passing directly into the channel 74 for discharge through the outlet 72.

When the stormwater flow ceases, the stormwater remaining in the filter chamber will filter through the filter screens for passage through the outlets 87 and 88 as relatively clean water and much of the contaminants which were trapped before the stormwater flows will be retained behind the screens 81, 85 and the fine screens 91 across the outlets 87 and 88.

Periodic removal of that filtered material is facilitated by simply unlocking and removing the bars elevating the lid parts 66 and 67 to an upstanding position where they can be locked together and held to provide easy access to the housing 61.

WO 99/45214 PCT/AU99/00141 18 Conventional industrial vacuum cleaning apparatus may be used to suck out the debris and contaminants from the filter chamber 80 as the base floor 77 is flat as illustrated.

Alternatively it may be accessed for manual removal. Removal is facilitated because of the relatively easy access to the base of the filter chamber 80 beyond the opposite edges 83 of the receiving channel 74.

To further facilitate cleaning and efficient operation of the apparatus, the side wall end portions 89 are returned from the side walls to the front wall 73 so as to create obtuse angles between the walls leading to the outlets 87 and the end wall 73 to assist in the prevention of build up of contaminants which may otherwise be retained in the corners of the housing. After a short dry spell, the well ventilated interior will quickly dry out so that it does not become a breeding place for mosquitoes, bacteria etc.

The filter assembly 110 illustrated in Figs. 6 to includes an open topped housing 111 which may be moulded or fabricated from panels suitably from fibre reinforced concrete or compresses AC or the like. The housing 111 is closed by a lid 112 supported on ledges 113 in the walls of the housing i.

In this embodiment, housing 111 is a rectangular housing 2400mm long, 1200mm wide and 2100mm deep. The stormwater inlet 116 is a circular inlet 450mm diameter and is positioned in one end wall 117, 605mm above the base wall.

The outlet 118 is a circular outlet of 600mm diameter and positioned in the other end wall 119 of the housing 600mm above the base wall.

A filter chamber 120 includes a primary filter panel 121, a secondary filter panel 122 and a tertiary filter panel 123 arranged in series along the base wall 125 and in spaced relationship with the end walls 117 and 119. The primary filter panel 121 has vertical bars at 125mm spacing, the secondary filter 122 is a coarse square mesh having mesh WO 99/45214 PCT/AU99/00141 19 openings of about 110mm square and the tertiary filter 123 is a fine mesh with a mesh size in the order of 0.4mm.

The upper edges 130 of the filter panels 121, 122 and 123 decrease in height progressively toward the outlet 118 whereby the area of the primary filter panel exposed to flow is greater than the area of the secondary panel exposed to flow which is greater than the area of the tertiary panel exposed to flow.

A continuous removable closure wall 126 extends across the upper edges 130 and this wall 126 together with the side walls 128 forms a closure about the filter panels 121, 122 and 123. The wall 126 is formed from two one-half panels 127 hinged to respective opposite sides of the housing 111 and latched at 129 for fixing in position.

In this arrangement the upper closure wall 126 slopes down from the upper extremity 130 of the inlet 116 to a level below the lower extremity of the outlet 118 to act as a guide wall offering minimum resistance to excess flow to the outlet 118 for such flows as are unable to pass through the filter chamber 120.

Further walls 132 and 134 extends at opposite sides of the path of flow from the inlet 116 to the primary filter panel 121. These walls 132 and 134 have dependent flanges 133 bordering the flow path so as to form an inverted chamber beneath the each wall 132 and 134 at opposite sides of the flow opening 135 and into which floating material may pass and be trapped when the liquid level in the housing 111 rises above the upper extremity of the inlet 116. This is illustrated in Fig. 9, such as from tidal influences or flood conditions.

In such instances, such as in a storm flow, flows which cannot pass to the outlet 118 through the filter chamber 120 will feedback through the flow opening 135 and spill over the closure wall 126 to the outlet 118 or the chamber 136 downstream of the tertiary filter 123 for discharge through WO 99/45214 PCT/AU99/00141 the outlet 118.

For in-line installations it is likely that the drains 137 will be closed so as to form the chamber 136 into a storage chamber for filtered water. Lockable access lids 138 are provided for cleaning, including a lid above the chamber 136 from which filtered water may be pumped from the housing, leaving the residue on the base wall 125 in the filter chamber from which it may be removed by suction apparatus from above ground.

When the flows subside, a body of water and contaminates will be retained in the housing 112 at the level of the lower edge of the outlet 116 and the upper edge of the tertiary filter panel 123. An oil absorbing filter pad 140 is supported beneath the closure wall 126 so that oil which floats to the surface will contact the pad 140 as the water level rises and be absorbed thereby. Servicing is carried out by opening the lid 112 and sucking out or otherwise removing the trapped rubbish.

When flood flows occur, it is not possible to provide the same degree of filtering and generally it is not necessary or practical to do so. Thus these flows pass substantially directly to the outlet 118. In the process, the filter chamber may substantially fill with stormwater, however by the mechanism described above, much of the filtered contaminants will be retained in the base of the filter chamber behind the screens with excess unfiltered flows passing directly into the channel or discharge through the outlet.

When the stormwater flow ceases, the stormwater remaining in the filter chamber will filter through the filters for passage through the outlet 118.

It will be realised that the above has been given only by way of illustrative examples of the invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall WO 99/45214 PCT/AU99/00141 within the broad scope and ambit of the invention as is defined in the appended claims.

Claims (24)

1. A filter assembly including: a housing; an elevated inlet to the housing; an elevated outlet from the housing through which substantial flows entering through the inlet may be discharged; an elevated open topped flow receiving means for receiving inlet flows; a diversion drain in the base of the flow receiving means, a filter chamber in the lower portion of the housing and in fluid communication with the diversion drain, said filter chamber has a plurality of upstanding mesh type filter screens, each of said screens extend across the housing and substantially beneath the flow receiving means, one of said screens proximal to the diversion drain has a comparatively larger mesh size than another of said screens remote from the diversion drain; and the upper portion of the housing is substantially unobstructed so as to permit full flows through the inlet to pass through the upper portion to the outlet; wherein a trickle-flow path is provided from the diversion drain through the filter chamber to a storage chamber or an outlet drain adjacent the base of the filter chamber and a moderate flow path is provided from the diversion drain to the elevated outlet bypassing at least one of the filter screens in the filter chamber.

2. A filter assembly as claimed in claim 1, wherein the open topped flow receiving means is an open channel extending from the inlet to the elevated outlet and having the diversion drain formed in the leading end thereof.

3. A filter assembly as claimed in claim 2, wherein the open channel receives overflows from the filter chamber along the edges thereof upstream of at least the last filter screen. If'N PCT/AU99/00141 Received 18 February 2000 23

4. A filter assembly as claimed in claim 1, wherein the open topped flow receiving means is an open channel extending from the inlet for discharge of small to moderate flows to a coarse screen adjacent the elevated outlet and having the diversion drain formed for diverting trickle flows in the leading end thereof.

A filter assembly as claimed in claim 1, wherein the open topped flow receiving means is an open receptacle having an open bottom providing the inlet to the filter chamber whereby backflow pressure created in the filter chamber in moderate flow conditions will cause incoming liquid to pass through the open bottom of the receptacle through the unobstructed upper portion of the housing to the elevated outlet.

6. A filter assembly as claimed in claim 5, wherein the filter screens are graded to provide a relatively fine filter screen remote from the diversion drain and one or more coarser screens between the fine filter screen and the diversion drain.

7. A filter assembly including; a housing; an inlet to the housing; a elevated outlet from the housing through which a substantial flows entering through the inlet may be discharged; San elevated open topped flow receiving means for receiving flows from the inlet, the receiving means extending from the inlet to the elevated outlet; a filter chamber in the lower portion of the housing; a diversion drain for diverting shallow inlet flows to the filter chamber; filter means for collecting contaminants in the filter chamber and including a plurality of upstanding mesh type filter screens, each of said screens extend across the housing and substantially beneath the flow receiving means, one of said screens proximal to the diversion drain has a comparatively larger mesh size than another of said screens remote from the diversion drain; if PCT/AU99/00141 Received 18 February 2000 24 feedback means for feeding flows in excess of those which can pass through one or more of the filter screens to the elevated flow receiving means for passage to the elevated outlet.

8. A filter assembly as claimed in claim 7, wherein the upper wall of the filter assembly is provided with a grate.

9. A filter assembly as claimed in claim 7 or claim 8,wherein the diversion drain is formed in the base of the flow receiving means adjacent the inlet and includes blocking means for blocking passage of large objects through the diversion drain.

A filter assembly as claimed in claim 7, wherein the feedback means is upstream of a last or second filter screen and bypass means are provided for a first filter screen to enable excess flows to bypass the first filter screen without passing back to the elevated flow receiving means.

11. A filter assembly as claimed in claim 10, wherein the last or second filter screen extends upwardly beyond the open channel to provide the feedback means and the first filter screen has its upper edge below the open channel to form the bypass means.

12. A filter assembly as claimed in claim 11, wherein the housing is provided with an access lid or lids which provide access to the floor of the housing and wherein the floor is a flat floor.

13. A filter assembly including: a housing having an inlet and an outlet; filter means in the housing through which normal flows through the inlet must pass for passage to the outlet, said filter means includes a plurality of upstanding mesh type filter screens that extend across the housing wherein one of said screens proximal to the inlet has a comparatively larger mesh size than another of said screens remote -rom the inlet; and S PCT/AU99/00141 Received 18 February 2000 feedback means for returning flows unable to pass through the filter means into the housing for alternate passage to the outlet.

14. A filter assembly as claimed in claim 13, wherein the inlet and the outlet are elevated above a base wall of the housing and the inlet discharges normal flows through the plurality of filter screens.

A filter assembly as claimed in claim 14, wherein the outlet has a curved transition to its bore to minimise the resistance to flow into the outlet.

16. A filter assembly as claimed in claim 14, wherein the outlet is larger than the inlet and a rounded collar protrudes into the housing to form a curved transition.

17. A filter assembly as claimed in claim 16, wherein the filter means includes a relatively coarse first filter screen and a finer second filter screen arranged in a closure which is operatively sealed from the remainder of the housing and which communicates with the inlet through a receptacle which opens to the upper portion of the housing.

18. A filter assembly as claimed in any one of claims 13 to17, wherein the open receptacle has side walls which depend from a surrounding wall.

19. A filter assembly as claimed in any one of claims 13 to 18, wherein the first filter screen extends upwardly to a level across the inlet.

A filter assembly as claimed in any one of claims 13 to 19 and including an absorbent filter pad in the filter means for absorbing oils and greases.

21. A filter assembly as claimed in any one of claims 13 to 20, wherein the alternate passage is an unfiltered passage. 'I, Z o. PCT/AU99/00141 Received 18 February 2000 26

22. A filter assembly as claimed in any one of the preceding claims, wherein the inlet and the outlet are substantially in line with one another.

23. A filter assembly as claimed in any one of the preceding claims, wherein the housing is provided with an access lid or lids which provide access to the floor of the housing.

24. A method of forming a stormwater outflow filter, including: forming a filter chamber having an inlet and an outlet; providing a filter assembly including a plurality of upstanding mesh type filter screens wherein there is an upper closure wall extending between the first filter screen and the second filter screen, each of said screens extends across the filter chamber and the first filter screen proximal to the inlet has a comparatively larger mesh size than the second filter screen remote from the inlet; arranging the filter assembly in a lower portion of the filter chamber so that normal flows through the inlet pass through the housing into the filter assembly and high flows can bypass the filter assembly for flow to the outlet. A method of maintaining a stormwater filter assembly of the type defined in any one of claims 1 to 22 and having a holding chamber downstream of the filter chamber, including: emptying water trapped in the housing through the holding chamber and discharging the filtered water, and gathering the material retained in the filter chamber for discharge at a safe disposal site.