SURE-FLAP (Check Flap)

The SURE-FLAP Check Flap System is designed to prevent flooding and backflows caused by high downstream water levels. The SURE-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. The SURE-FLAP also controls odor, as it is normally in the closed position.


  • Up to 20 feet (6 m) of head
  • Modular construction up to 20 feet (6 m) long
  • Rigid stainless steel flap
  • Hydraulically ideal shape
  • Design ensures airtight seal for odor control
  • Low hydraulic resistance
  • Easy to retrofit into existing installations
  • Stainless steel construction

Range of Application

The SURE-FLAP Check Flap can vary from a model GSF-40-* to GSF-100-*. The GSF-40-* is designed to fit over a concrete opening measuring 16 inches (40 cm) high and up to a maximum width of 20 feet (6 m) and the GSF-100-* is designed to fit over a concrete opening measuring 40 inches (100 cm) high and up to a maximum width of 20 feet (6 m). The SURE-FLAP’s model selection is based solely on the concrete opening size. The units are currently designated with asterix due to the high variety of model options.

System Operation

The SURE-FLAP Check Flap is a pivoted stainless steel flap mounted over a rectangular concrete opening. In the rest position the SURE-FLAP hangs vertically, due to its own weight, thereby closing and sealing the opening. If the water level in the sewer or tank overflow rises, the hydrostatic pressure against the SURE-FLAP Check Flap causes it to open thereby allowing the water to flow over the sill. If the downstream water level rises, the SURE-FLAP is pressed against the concrete opening so that no water can flow back into the sewer system, tank or basin. The SURE-FLAP’s lightweight design makes it highly responsive to minimal water level changes while ensuring structural stability under high downstream water level conditions.

The SURE-FLAP Check Flap can be equipped with a stainless steel frame for embedding in the concrete or anchoring to the structure. This flat and smooth sealing-surface will increase the tightness of the flap and avoid the potential problems caused by irregular concrete openings and surfaces.