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A tailgate at work.

Backflow flap

The backwater flap is used in systems Sewerage and drainage systems as a final device. It is used to prevent the backflow of water or sewage back into the system. Backwater flaps can be installed at the outlets of sewerage systems and embankment culverts (for drainage ditches and natural watercourses) to sewage channels with a variable water table. The backwater flap is designed for installation at the end of gravity (not pressure) pipelines. It is not suitable for pumping loads, especially high capacity pumping loads. Szagru check valves are manufactured according to individual customer orders.


  • Straight check valve, wall mounting (KP)
  • Slanted check valve, wall mounting (KS)
  • Slanted check valve, mounting to flange pressure flange (drilled according to customer requirements) (KSK)
  • Slanted check valve, mounting to pipe (bare end) (KNR)
  • Slanted check valve, mounting to pipe (KDR)


The backwater flap operates automatically under the influence of the pressure difference, which acts on the surfaces inside the device disc. The flap, closed in the rest position, opens when there is more water pressure on the sewer side, and closes when there is more water pressure on the receiving side. By proper balancing, it does not impede the outflow of sewage from the sewer system


Backflow preventers are supplied as devices for mounting on the face of the concrete wall of the outlet of a sewer or drainage collector. They can also be adapted for flanged or socket connection to the existing sewer system. On individual order, dampers can be supplied adapted to existing installation conditions.


Check valves are made of high-density PEHD polyethylene. Polyethylene is non-corrosive and resistant to the effects of aggressive substances found in sanitary or rainwater wastewater. Rubber or silicone gaskets are used to seal the flap. The catalog contains typical and standard design solutions of products, the drawings included in the catalog are only a part of the available solutions.

In dampers above DN600 we use stainless steel axes encased in plastic from the outside.

Each time we individually agree on the details of assembly and the type of design solution most beneficial for the given conditions of assembly, place of installation. As a result of the arrangements, we are able to design and manufacture structures of different shape, strength or specific purpose of the product depending on customer needs.

Proper loading of check valves is a prerequisite for their proper operation.

Backflow dampers, gates and gate valves manufactured by us have a National Technical Assessment No. ITP-KOT-2017/0005 issue 1