The present invention relates to filters, and particularly to underdrains in gravity filters. More particularly, the present invention relates to underdrains in gravity filters having a cap or plate supporting a filter media.
Gravity filters frequently employ underdrain blocks to channel fluid away from the filter bed and to direct backwash fluids evenly into the filter bed during a backwash cycle. Underdrain blocks are assembled end to end forming rows, also known as laterals. Several laterals are placed next to one another to define the filter bottom. A filter media (e.g., granular activated carbon, anthracite, coal, magnesium oxide, ilmenite, sand including garnet, silica or quartz, etc.) placed on top of the laterals completes the filter bed and performs a majority of the filtration.
In operation, the filter bed receives a flow of fluid to be filtered and passes it through the filter media to the underdrain blocks. The size and arrangement of the filter media allows it to filter out the undesired contaminates, with finer filter media being able to filter out smaller contaminates. The flow, or filtrate, enters the underdrain blocks through openings generally provided in the tops of the underdrain blocks. The underdrain block laterals provide a convenient channel or flow path, allowing removal of the filtrate from the filter bed.
Periodically, a backwash cycle is initiated to clean the filter media. During a backwash cycle, fluid flow reverses, thus flowing into the underdrain blocks and upwardly through the filter media to loosen and remove contaminates.
It is desirable to have large openings in the filter blocks to allow free filtrate flow into the blocks. However, large openings are incapable of supporting the filter media and instead allow the media to pass into the underdrain blocks, which is undesirable. Small openings on the other hand, are capable of supporting the filter media, but are easily plugged by the filter media disposed above and upstream of the underdrain blocks. Also, small openings provide greater restriction to flow than large openings even when unclogged. Therefore, it is desirable to provide an underdrain block capable of supporting the filter media above, while simultaneously reducing the likelihood of media entering the underdrain block, and minimizing plugging of the openings. It is also desirable to provide an underdrain block having a high percentage of open surface area, thereby allowing a free fluid flow therethrough.
Thus, according to the present invention, a filtration system provides a block including a first wall and a second wall substantially parallel to the first wall. A top surface that is substantially perpendicular to the first wall is disposed between, and coupled to, the first and second walls to at least partially define an inner chamber. The top surface further includes an orifice defining a passageway between a block exterior and the inner chamber. A plate including a plurality of slots, each slot having a width of less than about 0.065 inches, and a slot outlet, is coupled to the top surface of the block. The slot outlets in the plate are substantially coplanar and the plate, when coupled to the block, substantially covers the orifice.
The invention further provides a method of manufacturing the filtration system. The filtration system includes an underdrain block, a retaining plate, and a filter media. The underdrain block includes an outer wall having a first side and a second side substantially parallel to the first side. The outer wall also includes a top surface substantially perpendicular to the first and second sides. A plurality of orifices are defined within the top surface. The retaining plate has an upper surface and a lower surface. The method includes the steps of forming the retaining plate such that the upper surface and the lower surface are substantially parallel to one another. The method further includes laser etching the plurality of slots into the retaining plate such that the area of the slots is at least equal to the area of the orifices, and such that the slot outlets are coplanar. The method further comprises aligning the retaining plate with the underdrain block, and coupling the retaining plate to the underdrain block such that the retaining plate at least partially covers the plurality of orifices of the underdrain block.
In preferred embodiments, the retaining plate is manufactured from a stainless steel plate that is less than one-eight of an inch thick. The plurality of slots are preferably laser-etched through the plate and have a width between 0.002 inches and 0.025 inches. A series of longitudinal and cross members defined by the block provide support to the plate when attached to the block. In preferred embodiments, a plurality of screws attach the retaining plate to the block.
Additional features and advantages will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.