A new underdrain system is designed to exceed the maldistribution standard and can improve performance in retrofit applications, allowing for deeper media and greater flow rates in older, shallow beds, according to the manufacturer.
The new LP Block? underdrain from Tetra Process Technologies, a Severn Trent Services Company, exceeds the maldistribution standard of < ? 5 percent as well as the previous market best of ? 31/2 percent. In addition, the underdrain holds its maldistribution performance over a 30 foot lateral, while allowing for substantial reduction in material and installation costs.
The LP Block is lightweight and easy to handle. It features a snap-fit, single-gasket, bell-and-spigot joint assembly to ensure a tight fit with no leaking. It has no moving or wearing parts, and does not require the use of corrosive materials. Suitable applications include new and old filter designs, for either hydraulic-only or air/water backwash installations.
Piezometer testing for the new underdrain has shown maldistribution results of ? 21/2 percent or less over a 30 foot lateral at 20 gpm per square foot. The new unit is scheduled for its initial municipal waterworks installation during the first quarter of this year.
Gary T. Hunkele, Tetra?s manager of field service, said the new underdrain offers better performance than previously was available and is suitable for use in larger filters.
?We?re not only showing dramatically advanced maldistribution results with this product, but we?re also using less underdrain material and less installation time to accomplish the same function,? he said.
?That?s because we?re providing a design for installation on 18 inch centers instead of 12 inch centers, which means they need 1/3 less block.?
The underdrain system allows for washing of media evenly across the entire bed without mounding media to the front or back. The net effect allows for deeper media beds and the higher filtration rates needed to accommodate higher flow rates. The system can be used in retrofit applications as a means for increasing flow rates without adding more filters.
Tetra designed its LP Block to provide superior distribution for both water and air, separately or concurrently. Air distributes evenly across the entire filter bottom area to scour the media, and to provide an air lift, which, with the water, removes the released solids from the filter.
The lower profile of the low-headloss, non-clogging underdrain allows for the retrofit of existing shallow filters with air/water backwash and greater media depth. Its wider profile means fewer filter blocks can cover the filter floor, which means fewer joints and less grouting. In addition, a unit cut in half lengthwise can reduce the amount of grout-filled space that would not accommodate a full width block.
Installing the underdrain with Tetra?s Media Retention Plate (introduced previously as the patent-pending Savage Plate?) eliminates the need for a gravel filter media support layer. Any shallow filter can accept installation of a deeper media load. The Media Retention Plate comes in three application-specific, micron-opening sizes.
