The Roberts PWI® rehabilitation system for Precast and Monolithic Wheeler Bottom Underdrains quickly convert existing Wheeler Bottoms from a conventional system into a gravel-less underdrain. This rehabilitation system utilizes a porous plate insert assembly anchored in each hopper by a stainless steel toggle bolt. The toggle bolt passes through the porcelain thimble and locks the PWI® insert securely to the underdrain. By incorporating the PWI® inserts, filter freeboard can typically be increased by 9″ – 12″ (22.8cm – 30.4cm) without any structural modifications to your existing filter basins.

The PWI® inserts are available in appropriate sizes to fit snugly into the Precast or Monolithic Wheeler underdrain hoppers.

The use of the toggle mounting system eliminates the need for bolt on systems which are difficult to seal and may structurally compromise the underdrain.

When installed, the PWI® unit is flush to the top of the existing concrete underdrain. This maximizes the available freeboard within the filter basin. By maximizing freeboard, the filters can be retrofit with the maximum media depth profile possible.

The PWI® assembly includes integrated backwash water distribution orifices which eliminate the need for porcelain spheres. By eliminating the porcelain, there is no possibility additional concrete will wear within each underdrain depression.

NOTES: Flush mounted gravel-less design maximizes available filter freeboard. Filter downtime is minimized, filters are typically converted in under 1 week. Toggle mounting simplifies installation and does not affect the structural integrity of the underdrain.

Technical Details

Material: Vacuum formed polystyrene insert with high density polyethylene porous plate and stainless steel toggle.
Roberts’ Retroliners® should be installed during all Monolithic Wheeler bottoms rehabilitation. The Retroliner® provides a smooth and consistent hopper lining to assure that each of the 12 porcelain spheres seat properly in your newly rehabilitated underdrain. Available with multiple orifice configurations, the Roberts Retroliner® system is the only wheeler bottoms liner system which can be utilized to improve underdrain distribution and system performance.

Retroliner installation 01w

Rehabilitation and New Construction

Roberts maintains the experienced construction superintendents and original Manganese forms to furnish and install new Precast and Monolithic Wheeler Bottoms Underdrain. In addition, Roberts will rehabilitate your existing Wheeler Bottom Underdrains to “like new” condition and will guarantee your rehabilitated underdrain with the same product warranty we provide for all of our new products.