TRU-FLAP (Floating Flap)

The TRU-FLAP Floating Flap System is designed to prevent flooding and backflows caused by high downstream water levels and acts as a floating weir whose crest elevation self-adjusts. The TRU-FLAP can and has been installed at combined sewer overflow (CSO) locations, sanitary sewer overflow (SSO) locations, retention tank overflows and basin overflows. Overloading of sewer systems and sewage treatment plants is avoided and energy costs for pumping systems and sewage treatment are reduced.


  • Up to 4 feet (1.2 m) of head
  • Modular construction up to 20 feet (6 m) long
  • Hydraulically ideal shape
  • Flap is open in rest position
  • Rises with minimal increase in downstream water level
  • Low hydraulic resistance
  • Easy to retrofit into existing installations
  • Stainless steel construction

Range of Application

The TRU-FLAP Floating Flap can vary from a model GTF-30-* to GTF-120-*. The GTF-30-* is designed for 12 inches (30 cm) of backflow protection and measures up to a maximum of 20 feet (6 m) in length. The GTF-120-* is designed for 48 inches (120 cm) of backflow protection and measures up to a maximum of 20 feet (6 m) in length. The TRU-FLAP’s model selection is based solely on the concrete weir length and the required backflow prevention height. The units are currently designated with asterix due to the high variety of model options.

System Operation

The TRU-FLAP Floating Flap is a pivoted stainless steel floating flap mounted on a weir. In the rest position the TRU-FLAP hangs down, due to its own weight, thereby allowing the upstream overflow to pass unhindered over its crest, as would any weir. When the downstream water level rises it will cause the floating flap to pivot upwards to prevent backflow into the sewer system, tank or basin while at the same time establishing a new overflow weir height. The TRU-FLAP’s lightweight design makes it highly responsive to minimal water level changes while ensuring structural stability.

The TRU-FLAP Floating Flap can be sealed on all four sides for backflow prevention in the event that the downstream water level rises above the flap height.