Abstract:
A debris-filtering downspout and other water runoff conduits and receptacles are disclosed, and include a Coanda screen mounted within a conduit, a culvert, a storm water conveyance or secured to a water collection basin. The Coanda screen provides high water throughput and is self-cleaning while effectively filtering debris contained in an incoming water stream.

Description:
The rain and storm water filtration systems discussed herein relate to filtration systems that employ screens to filter debris and other unwanted material from water streams and, more specifically, to filtration systems having a Coanda screen for filtering water streams. 
     BACKGROUND OF THE INVENTION 
     Rainwater downspouts, curbside storm water runoff collectors, and similar water conduits share a common purpose: removal of water from where it is undesired, be it the roof of a building, a city street, a storm basin, or the like. All such conduits allow a volume of water to pass therethrough. Leaf litter, sand, dirt, grit, and other debris can accumulate within such conduits and clog them, rendering them ineffective. Equally bad, the poor design of many water conduits allows debris to pass through to downstream channels and, ultimately, the ocean, with a consequent negative environmental impact. 
     Not surprisingly, much effort and money has been spent devising ways to avoid clogged water conduits and contaminated water streams. Patents have been granted for inventions designed to filter water at curbside storm drains (U.S. Pat. No. 6,231,758 to Morris et al.), to treat water in a horizontal passageway (U.S. Pat. No. 6,190,545 to Williamson), to create temporary stream filtration systems (U.S. Pat. No. 4,297,219 to Kirk et al.), to remove downspout debris (U.S. Pat. No. 5,985,158 to Tiderington), and to shield rain gutters on the eaves of a building (U.S. Pat. No. 4,435,925 to Jefferys). 
     However, with respect to downspouts and storm water systems, the prior art has several shortcomings. Among other things, it is difficult to devise a system that both operates under high flow and effectively filters out small particulate matter and other debris. This is because a filter element that accommodates large flow must also be designed with large spacing to suit the large flow. However, large spacing allows medium to small particulates and waste to pass through unfiltered. Conversely, a filter element designed to trap small particulate matter typically obstructs flow. An ideal water runoff filter would be both capable of passing high flow therethrough and removing small waste and debris. 
     Accordingly, there remains a need for a filter system for removing debris from a water stream using a filter element that is amenable to high volume flow, capable of removing or trapping waste the size of or even smaller than the size of the gap used for the filter and, preferably, self-cleaning. 
     SUMMARY OF THE INVENTION 
     The present invention integrates a Coanda screen (sometimes called “Coanda-effect” screen) into water collection systems such as downspouts, storm runoff collectors, sewer drains, and similar conduits and receptacles. An exemplary embodiment includes retrofitting an existing downspout section (or customizing a new downspout section) with a Coanda screen to provide a downspout with a highly efficient filter for removing debris from a stream of water. Depending on the water flow rate and the size of the debris encountered, different screen sizes and different screen mounting angles maybe selected to accommodate the same. Filtered water can pass through the screen, while debris is retained by the Coanda screen and then collected in an optional retaining basket. 
     In another embodiment, a curbside inlet to a storm drain is fitted with a Coanda screen. The screen is mounted between a raw inlet basin and an outlet basin. Filtered water is allowed to pass over the screen and then fall through the screen into the outlet basin, which then flows onward via an outlet pipe. Captured debris and waste are allowed to fall into a retention basin. To remove waste and debris more effectively, a retaining basket is used. When full, the basket can be lifted out of the curbside inlet and emptied. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the invention will be better understood when considered in conjunction with the accompanying drawings, wherein like part numbers denote like or similar elements and features, and wherein: 
     FIG. 1 is a side elevation view of a downspout with a Coanda screen in accordance with practice of the present invention; 
     FIG. 2 is a front elevation view of the downspout of FIG. 1; 
     FIG. 2A is a partial cross-sectional view of a deflector plate; 
     FIG. 3 is a cross-sectional view of the downspout of FIG. 2, taken at line  3 — 3 ; 
     FIG. 4 is an enlarged view of the Coanda screen attached at its downstream end to the downspout; 
     FIG. 5 is another enlarged view of the same Coanda screen attached at its upstream end to the downspout; 
     FIG. 6 is an enlarged view of a section of the Coanda screen of FIGS. 4 and 5; 
     FIG. 6A is a depiction of a concave screen surface; 
     FIG. 7 is a side elevation view of a storm drain system in accordance with practice of the present invention; 
     FIG. 8 is a top plan view of the storm drain system of FIG. 7; 
     FIG. 9 is a partial cross-sectional view of the storm drain system of FIG. 7 taken at line A—A; 
     FIG. 10 is a front elevation view of an alternative downspout with a Coanda screen; 
     FIG. 11 is a side elevation view of the embodiment of FIG. 10; 
     FIG. 12 is a front elevation view of another alternative downspout embodiment with a Coanda screen; and 
     FIG. 13 is a side elevation view of the embodiment of FIG.  12 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with the present invention, a highly effective filter system for a rain water downspout, sewer inlet, curbside storm water drain, or similar water runoff conduit or receptacle is provided. A preferred embodiment of an improved downspout  10  is shown in FIG.  1 . The downspout is mounted to an exterior wall  12  of a building by conventional mounting means (not shown), such as welds, adhesives (e.g., glue, cement, mortar, etc.), mechanical fasteners (e.g., rivets, bolts, screws, clamps, bands, straps, etc.), and other means known in the art. The downspout  10  includes a Coanda screen  20  mounted within a portion  40  of the downspout, referred to herein as the “upgraded downspout portion” or “upgraded downspout section”. The screen is accessible via a downspout opening  60  in the upgraded downspout portion. Water that flows into the downspout from a gutter (not shown) is filtered as it passes through the Coanda screen. Debris caught by the screen can slide out of the downspout opening into an optional retaining basket  80  mounted outside of and below the downspout opening. Effluent from the downspout empties into a splash guard or basin  100  which, preferably, is seated on a concrete slab  102 . Alternatively, the downstream end of the downspout is coupled to an underground header or a drain line (not shown) running to a main sewer or storm drain. The Coanda screen, upgraded downspout portion, retaining basket, and other features are described below in more detail. 
     An existing downspout can be upgraded or retrofitted by cutting out or otherwise removing a portion thereof, and installing an upgraded downspout portion or section  40  therein, using a slip joint, welds, adhesives, mechanical fasteners, or other conventional attachment means. Alternatively, an entire downspout can be fabricated as such and installed as part of a rain water removal system that includes one or more gutters and mounting hardware. In either case, the improved downspout provides a path for funneling water from a roof (or a deck, mezzanine, or other surface) to grade (e.g., street level) or to a storm water runoff drain or a main sewer line. Effluent from the downspout eventually flows to a storm drain or sewer system and then to the ocean, in some cases via a water treatment facility. 
     The downspout  10  is preferably constructed of stainless steel, galvanized steel, aluminum, plastic, or some other durable and water-resistant material, and has an interior and an exterior, and a cross-sectional shape that is generally rectangular. Alternatively, the downspout can have a generally circular cross-section or other desired geometry. In an exemplary embodiment, the downspout  10  is physically attached to an exterior wall  12  of a house or a building by any conventional means, such as downspout bands (not shown) anchored to the exterior wall. Water falling into the downspout passes into the upgraded downspout section  40  to the Coanda screen  20 . The Coanda screen  20  allows water to pass through, but traps waste and debris behind. 
     A Coanda screen acts by a shearing action referred to as the “Coanda effect,” which is discussed below in greater detail. In FIG. 1, the Coanda screen  20  has an upper surface  22 , a lower or underside surface  24 , a first (upstream) end  26 , a second (downstream) end  28 , and left and right sides, and is made of a plurality of wedge-shaped wires  30 . Additional details of the wires&#39; shape and relative orientation is provided below. 
     The Coanda screen  20  is mounted at an angle within the upgraded downspout portion  40 , with the upstream end  26  of the screen elevated relative to the downstream end  28  of the screen. As shown in FIG. 1, the upgraded downspout portion  40  has four walls—front  46 , back  47 , left  48 , and right  49 —and has substantially the same shape and dimensions as the remainder of the downspout. The Coanda screen is affixed within the upgraded downspout portion by, e.g., securing the upstream end  26  of the screen to the back wall  47  of the upgraded downspout portion, and the downstream end  28  of the screen to the front wall  46  of the upgraded downspout portion. So installed, the screen is seen to form an angle θ (theta) with the back wall. In practice, it has been found that best results are achieved when θ has a value of about 15 to 50 degrees, more preferably, about 20 to 45 degrees. 
     To ensure that a substantial portion of the water entering the downspout is filtered, it is preferred that the screen have a large enough area to make contact with all four walls  46 - 49  of the interior of the downspout housing. Alternatively (or, in addition), one or more baffles are mounted within the downspout to divert the flow of water toward the screen. In FIG. 1, two baffles  52  and  54  are shown secured to the front wall  46  and side wall  48 , respectively, of the upgraded downspout portion at a position above the downspout opening  60 , and oriented such that the baffle projects toward the Coanda screen  20 . The side baffle  54  comprises a front plate  58  and a rear plate  59 . The rear plate  59  is attached to the side wall  48  by known methods, including welding, adhesive, mechanical fasteners and the like while the front plate  58  protrudes from the side wall  48 . The front plate  58  protrusion acts as a diverter to divert water that clings to the side wall towards the screen  20 . Similar attachment and configuration is discussed below for a deflector plate (FIG.  2 A). 
     In FIG. 3, two side baffles  54  and  56  are shown, secured to the left  48  and right  49  side walls of the downspout. Fewer or greater numbers of baffles can be mounted within the downspout to provide optimal diversion of water toward the Coanda screen. For example, the back wall  47  can also be configured to include a baffle. This may be desirable where the upstream end  26  of the screen is not recessed within the surface of the back wall  47 . The presence of such a baffle ensures that water cannot bypass the screen. The baffles can be attached to the inside walls of the downspout using any conventional means, including, without limitation, welding, adhesives, and mechanical fasteners. 
     The downspout opening  60  provides access to the Coanda screen for maintenance and cleaning. Although the screen is self-cleaning, occasionally debris may become trapped within the downspout or (rarely) wedged between the wires  30  that form the screen. Access to the screen is facilitated by providing the downspout opening  60  with appropriate dimensions relative to the screen  20 . A preferred downspout opening  60  has a width approximately 50-100% of the interior width of the downspout, and a height approximately 33-75% of the vertical profile of the screen  20 , the latter being measured at the wall opposite the downspout opening (the back wall  47  in FIG.  1 ). The downspout opening  60  is located intermediate the upstream and downstream ends of the downspout  10 , but not necessarily equidistant from both ends. 
     A retaining basket  80  to catch debris caught by the Coanda screen is mounted to the downspout just below a debris deflector plate (further discussed below), using conventional means, such as welding, adhesives, mechanical fasteners, and the like. In an exemplary embodiment, the retaining basket  80  comprises a tightly woven screen made of steel, aluminum, or other weather-resistant material. Debris that does not freely fall into the retaining basket  80  (i.e., debris that clings to the filter due to friction) is eventually pushed out the downspout opening  60  by additional water flowing from the gutter. Water clinging to debris caught in the retaining basket  80  can drip onto the splash guard  100  by passing through the holes of the retaining basket  80 . Alternatively, if an underground header is used to connect with the downspout, water that passes through the retaining basket can be caught by a collector (not shown) mounted beneath the retaining basket, and channeled to the header. 
     In an exemplary embodiment, the downspout is also equipped with an external debris deflector plate  110 . The debris deflector plate is mounted just below the downspout opening  60  along the external surface of the front wall  46 , just above the retaining basket  80 . The debris deflector plate covers any space between the downspout  10  and the retaining basket  80 , and ensures that debris exiting the downspout opening does not fall between the downspout and the retaining basket. 
     In an exemplary embodiment shown in FIG. 2A, the deflector plate  110  includes a front plate section  112  configured to deflect debris into the retaining basket, and a rear plate section  114  configured to be attached to the downspout. In an exemplary embodiment, the deflector plate  110 , like the downspout itself, is made of a durable, weather-resistant material, such as aluminum, plastic (e.g., polyvinyl chloride and unplasticized vinyl), galvanized steel, and the like. The deflector plate can be mounted to the downspout by known methods, including welding, adhesives, mechanical fasteners, and so forth. 
     Reference is now made to FIG. 4, which is an enlarged view of Detail A indicated in FIG.  1 . The downstream end  28  of the Coanda screen is shown secured to the downspout front wall  46  by an upper bracket  70  and a lower bracket  72 , without obstructing the flow of debris from the upper surface of the Coanda screen into the retaining basket. The two brackets are attached to the downspout by conventional means, such as welding, adhesives, mechanical fasteners, and so forth. Preferably, the upper bracket is substantially flush with the outer wall of the downspout housing at the bottom of the downspout opening. 
     Similarly, FIG. 5 provides an enlarged view of Detail B indicated in FIG.  1 . The upstream end  26  of the Coanda screen  20  is shown secured to the downspout back wall  47  by upper  74  and lower  76  brackets. However, in addition to securing the upstream end of the screen  20 , the upper bracket  74  also serves to divert water flow along the back wall  47  of the downspout to the screen. Although not shown, similar upper brackets may also be mounted around the entire perimeter of the screen so that any water flow along any of the four downspout walls is diverted toward the screen. The two brackets  74 ,  76  are attached to the downspout by conventional means, such as welding, adhesives, mechanical fasteners, and so forth. 
     FIG. 6 shows an exemplary cross-sectional view of the Coanda-effect screen  20 . The screen comprises a plurality of individual wedge wires  30 , which are parallel to one another and separated from each other by a gap or a spacing  32 . The individual wedge wires  30  are held together in the indicated arrangement by welding two or more backer rods (not shown) to the base portions  34  of each individual wedge wire  30 . Coanda screens are commercially available in several standard sizes. Generally, the difference in screen selection relates the width, height, and tilt angle  36  of the wedge wires, and the gap spacing  32  between the wedge wires. In addition, the Coanda screen may be ordered with an overall concave shape. As shown in FIG. 6A, the term “concave” implies a curved contour when viewed with respect to the upper surface  22  of the screen  20 . When a concave screen is specified, the concave shape has the effect of increasing the tilt angle of the individual wedge wires. This in turn allows the leading (upstream) edge  38  of the wedge wire to shear a greater amount of the water, provided that all other parameters are unchanged. In an exemplary embodiment, the Coanda screen has a gap spacing of about 0.1 to 1.0 mm and a tilt angle of about 3 to 15 degrees, with a radius (“R”) of concavity of from about 6 inches to infinity (when R=infinity, the screen is flat). Alternatively, other screen parameters may be used, taking into account the size of the debris likely to be encountered, the anticipated water flow rate and volume, and so forth. 
     Coanda screens are available from a number of manufacturers and retailers, including on-line retailers such as www.hydroscreen.com, www.johnsonscreens.com, and www.eni.com/norris/default.html. The screen is described in an article entitled “Hydraulic Performance of Coanda-Effect Screens” by Tony Wahl for publication in the Journal of Hydraulic Engineering, Vol. 127, No. 6, June 2001, the entire contents of which are expressly incorporated herein by reference as if set forth in full. 
     As explained by Wahl, the Coanda effect is a tendency of a fluid jet to remain attached to a solid flow boundary. As shown in FIG. 6, when water  130  flows across the screen  20  from the upstream direction, it tends to remain attached to the upper surface of the screen as it travels in the direction of the downgrade  79 . At a given point along the screen, the water has a thickness “X”. As water  130  flows down the screen, its thickness X is sheared by the leading edge  38  of each individual wedge wire  30 . The sheared water is then redirected approximately tangentially 120 to the direction of the original flow due to the contour of the wedge wire  30 . Thus, different wedge wire contour will cause water to be redirected differently. This shearing action is repeated as water traverses down the screen along the direction of the downgrade  79 . Water is sheared as it travels over other wedge wires  30 . After each layer of water is sheared, it is caused to flow along one of several filtered water paths  120   a ,  120   b ,  120   c ,  120   d , etc. The thickness of the water stream gets progressively smaller as the downstream end of the screen is approached, and the flow of water appears to slow to a mere trickle, or even drop off altogether. 
     This phenomenon is used to great effect in the present invention. Debris-laden water is effectively filtered at the Coanda screen. Any debris that does not fall into the retaining basket  80  during rainfall eventually dries on the screen, and either falls into the basket later, or can be manually removed via the downspout opening  60 . 
     In an alternate embodiment of the invention shown in FIGS. 7-9, an effective filter system for removing debris from a storm water runoff collector is provided. The runoff collector  200  comprises a Coanda screen  20  installed between a raw inlet basin  210  and an outlet basin  220 . As before, the screen  20  filters incoming water while trapping debris, but the source of water is a raw stream  212 , from an inlet  214 , and the effluent is a discharge stream  222  for an outlet line  224 . 
     In an exemplary embodiment, the Coanda screen  20  is mounted between a first weir  230  and a second weir  240 . The screen has a concave surface, with a radius of from about 6 inches to infinity, and is outfitted with an acceleration plate  250 . The acceleration plate  250  is a metal plate of hardened steel, such as stainless steel and the like, mounted to the upstream end  26  of the screen. 
     The acceleration plate has a width of approximately 2 inches or higher depending on the size of the storm drain system. When water flows from the raw inlet basin  210  over the weir  230 , it has a relatively low flow velocity. If water is allowed to flow over the screen  20  without first having the necessary flow velocity, the screen&#39;s ability to filter out debris will greatly decrease. The acceleration plate provides a vertical drop of about 2 inches or higher, allowing in-coming water to build up velocity before it contacts the first wedge wire on the screen. 
     Debris caught by the Coanda screen can slide into a retention basket  260  located within a retention basin  262 . In an exemplary embodiment, the retention basket  260  is equipped with a handle  264 , which allows the retaining basket to be lifted out of the basin, whereupon the debris can be discarded. The basket  260  may be a conventional basket and may be constructed out of medium to large steel wire mesh. Due to its size, it may be necessary to lift the basket with a crane or a flit truck having a lift. 
     In an alternate embodiment of the upgraded downspout  10  shown in FIGS. 10 and 11, a tapered front wall  46  and a modified back wall  47  having a tapered back wall section  270  is provided. The tapered front wall  46  and tapered back wall section  270  allow the screen  20  to be moved forward in the direction of the retaining basket  80 , and provide clearance for the installation of an acceleration plate  250 . In an exemplary embodiment, additional wall mounted baffles for diverting water toward the screen  20  are not necessary, as the screen is positioned directly below the incoming flow path and even extends past the incoming path. This screen configuration allows all or substantially all of the incoming flow to flow through the screen. 
     In another alternate embodiment of the upgraded downspout  10 , shown in FIGS. 12 and 13, an optional hinged cover  272  is provided over the downspout opening  60  of an enlarged upgraded downspout  10 . The enlarged upgraded downspout  10  is slightly larger than a conventional or existing downspout section, but has a much larger depth (the distance between the front wall  46  and the back wall  47 ), e.g., on the order of about 1.3 to 3 times deeper. This allows the enlarged upgraded downspout to accommodate a much larger screen  20  than a standard size upgraded downspout. This in turn, allows the much larger screen  20  to filter substantially all of the incoming flow without the need for wall mounted baffles. However, in the embodiment of FIGS. 10-13, wall mounted baffles, such as baffles  52  and  54 , can be used. 
     Although the invention has been described with reference to preferred and exemplary embodiments, various modifications can be made without departing from the scope of the invention, and all such changes and modifications are intended to be encompassed by the appended claims. For example, an upgraded downspout section can be manufactured as a separate unit and installed as a new downspout. Other materials than those described herein can be used to make the various components of the apparatus described. Changes to the way the baffles are installed, the way they are shaped, the way the deflector plates are installed, and the way the screens are installed within the housing can be made. Other alterations and modifications may be made by those having ordinary skill in the art, without deviating from the true scope of the invention.