Flexscour® Underdrain

The innovative FlexScour® underdrain design eliminates the two problems that have plagued other air + water cleaning systems, namely the improper sizing of variable diameter orifices and media displacement with surges or irregular flows. Reduced backwash and storage requirements make the system compact and economical, and enhances its ability to operate on a low influent head.


Built-in flexibility makes Ovivo’s FlexScour® underdrains an ideal choice for retrofits. The FlexScour underdrain was originally developed as a retrofit system that would be sufficiently flexible to accommodate any existing pipework and tank arrangements without compromising efficient flow management. FlexScour underdrains do not require false floors – they are an anchored system, not a grouted system. This ensures rapid, straightforward installation, ideal for rehabilitating older filters.

The low, five inch high laterals also allow for extra filter media depth (meeting today’s most stringent effluent quality standards) and clearance for air-scour bed expansion without raising the launder elevation.

  • Uniform cleaning achieves peak filter performance.
  • Rapid, straightforward installation (ideal for retrofits) reduces installation cost.
  • Allows greater depth of filter media, to meet stringent effluent quality requirement.

Flexscour® underdrain systems are available in prefabricated steel tank filters. Underdrain components are shipped for rapid installation onto the concrete floor prior to installation of the tank. Filter tanks are shop assembled and trucked to the site where they are field welded to preset anchor channels. Because of their rectangular configuration, Flexscour filters of up to 540 square feet (equal in area to a 26’ diameter round tank) can be shipped fully assembled.

Most header and lateral underdrains attempt to regulate backwash flow with variably sized orifices, but traditional hydraulic models have proven inadequate for accurate sizing in areas of higher header flow velocity. The Flexscour underdrain designers conducted exhaustive tests to gain a better understanding of the relation between crossflow velocity and turning resistance. These tests yielded a superior set of orifice sizing guidelines and an unequaled level of backwash uniformity.

Uniform flow distribution is key to successful air + water backwashing. FlexScour underdrains feature lateral ducts manufactured in 18 ga. stainless steel, partitioned into upper and lower channels for air and water respectively. Typically, air is supplied by a stainless steel pipe, with filtrate and backwash water flowing through a concrete floor channel and primary orifices in lateral baseplates. A variety of different feed and drainage systems are possible, depending on the existing layout and pipework.

Q: What are the air-water rates for simultaneous air-water backwash?

A: Air rate is 3.0 scfm/sf. Water rate is 8 gpm/sf.

Q: Does Ovivo offer a media retaining design backwash trough?

A: Yes, it is the ScourGuard backwash trough.

Q: What is the opening in the D90 media retaining panels?

A: Openings are 0.36 mm.

Q: Are the D90 panels removable?

A: Yes. They are secured and sealed to the underdrain sloped sides with stainless steel machine screws and a neoprene gasket.

contact us