The Trilateral Underdrain system is a traditional HDPE combination air/water underdrain utilizing passive air-scour to improve the efficiency of conventional filter backwash cycles. It is designed to provide efficient distribution of air and water for concurrent air/water backwashes as well as separate air and water backwash sequences.

The orifices incorporated into the design of the Trilateral underdrain are sized and arranged to accommodate the optimal air and water flow rates required to optimize your backwash sequence. Typical air flow rates range from 3-5 scfm/sf (54.54-90.9 m³/hr/m²) with backwash water rates from 15 – 22 1/2 gpm/sf (36.5-54.8 m³/hr/m²). When provided with thick porous plate, the Trilateral underdrain supports filter media directly without the need for traditional support gravel. Additionally, the Trilateral underdrain offers several unique design features to improve reliability and extend the underdrain’s life cycle.

Trilateral underdrain
The Trilateral underdrain includes a specifiable third row of screws to further improve the attachment of the porous plate to the underdrain surface, and only Roberts’ Trilateral underdrain offers multiple sets of mounting locations for porous plate replacement. Replacing media retention plates on competitor’s HDPE underdrain can severely compromise the integrity of the underdrain installation.

The rigid top surface of the Trilateral Underdrain is designed to transfer surface loads directly into the side walls of each individual block. This load transfer forces the outer walls of each block into the grout, thereby strengthening the interlock between the underdrain and grout and increasing the hold down capacity of the underdrain.

NOTES: Only Roberts Trilateral Underdrain offers multiple sets of mounting locations for porous plate replacement. The rigid top surface increases the hold down capacity of the under. Specifiable third row of screws for improved porous plate mounting.

Technical Details:

Material: Virgin High Density Polyethylene (HDPE)
Weight: Approximately 4.6 pounds / square foot (22.4 kg/m²)
Standard Block Dimensions: 48″ long x 10 5/8″ wide x 12″ high (121cm long x 26.9cm wide x 30.48cm high)
Distribution Orifices: Approximately 1/4″ (.635cm) diameter with approximately 22/square foot (2 m²)
Connections: Bell & spigot with integrally molded clips and o-ring seal