The problem recently was solved by retrofitting the traveling bridge filters with Gravisand technology from USFilter-Davco Products. This technology incorporates proprietary tubular non-segmented underdrain components which eliminate media loss and are not subject to irreversible biological fouling. Another significant advantage unique to the Gravisand approach is a "No-Wear" backwash shoe.
In addition, this technology uses a unique method to clean the filter media. Rather than using a continuously moving bridge - which is known to displace the filtration media - the Gravisand approach employs an indexing system that isolates each filter cell to ensure maximum media cleaning without the troublesome media migration problems that have haunted old-style, two-pump TBFs. The indexing system also eliminates the frequent filter-bed maintenance common with old-style TBFs.
Older TBF design employed a strip liner-contact seal which caused a side load on the bridge and, in addition to seal wear, resulted in bridge alignment problems. The Gravisand approach, however, does not use a strip liner-contact seal but utilizes a non-load "expansion shoe" that seals directly to the basin wall automatically upon pump energization at the backwash point.
"We retrofitted with Gravisand components and I will tell you I am well pleased. The backwash is beautiful and there's no way they can leak media now. It's simple, we don't have to shovel sand anymore," explains Mr. Witkowski.
Gravisand components use a simple "bolt-in" design and are particularly beneficial to installations that have older, existing, two-pump filter systems in need of an upgrade.
