Proven performance in gravity filtration

Enviroquip® Folded Plate Filter Underdrain

Underdrains are the heart of every granular media filter. The Enviroquip Folded Plate Filter Underdrain provides a durable, corrosion‐resistant system for collecting filtered effluent and accurately metering uniform air and water backwash flows.

The fine-opening design of the Enviroquip Folded Plate Filter Underdrain incorporates the same principles and premium materials that have proven performance in gravity filtration for over three decades.

The low-profile (152 to 203 mm (6 to 8 in) vertical height) and media-retaining design of the Enviroquip Folded Plate Filter Underdrain allows for deeper media stacks than is available in other underdrains.

Our 0.25 mm openings place filter media directly on the underdrains and air laterals. The uniform introduction of air and water through separate conduits provides superior simultaneous air/water cleaning of the entire filter bed. This cleaning is done over a short time period, with low water wash/air rates resulting in reduced volume of wash water.

Separate uniform distribution of air and water provides the vigorous agitation required for effective media cleaning. Most other systems introduce air and water through the same orifices creating a surging action and non-uniform distribution of air and water resulting in irregular cleaning of the filter media.

The gauge stainless steel design is strong and permanent. The 16-gauge stainless steel folded plate underdrain and air scour laterals meet the most stringent structural requirements. All stainless steel construction is corrosion resistant and maintenance free.

The system can be installed new or retrofitted into existing filters. It is easy to install and has no critical construction tolerances. The folded plate underdrain air scour lateral system is also simple to install and requires fewer installation hours than other similar systems.

Other features and benefits include:

  • Enhanced air scour prolongs media bed life and reduces wash water volume.
  • Lower air scour rate equals lower capital costs and lower energy use.

Separate air and water laterals provide superior simultaneous air and water backwash. Uniform distribution of air, and then water, is virtually instantaneous during simultaneous air and water backwash. Using a simultaneous air and water backwash, instead of a water only backwash, reduces the total volume of water required to clean a filter by up to 50 percent, which is a potential benefit to all municipal utilities.

The filter underdrains are stainless steel folded plate type manufac­tured by Ovivo. The underdrain plates have punched openings that have been placed by Ovivo to provide optimum headloss characteris­tics for flow distribution during the filter and backwash cycles.


The filter underdrain plates are cold formed into a folded cross section from AISI Type 304 stainless steel sheets. The resulting cross section will provide the required stiffness for support and a low headloss lateral flow channel.


The folded plates are clamped and sealed to the concrete structure by means of clamping tubes overlapping the edge flanges of adjacent plates. The clamp tubes are secured to the floor with a series of Type 304 stainless steel anchors and epoxy capsules located at approx­imately 30 in centres. The tubes are fabricated from AISI Type 304 stainless steel. Ovivo can also provide AISI Type 316 stainless steel, if required.