Roof Drains with flow control

Mounted submerged flow regulator for controlling water volumes of 0.1-3.0 l/s.

Roof drain with discharge control, FDE

Roof Drains with flow control, Type FDE  are used to throttle discharge from flat roofs serving as a retention facility.

Type FDE is manufactured with a specific capacity, and typically within the capacity range of 0.1 l/s up to 4.5 l/s.

Mosbaek's roof drain with discharge control is designed to provide a very high flow-control effect to ensure that the discharge is less than what is achieved using simple flow-control techniques with a similar orifice opening. This makes it possible to control the flow of very small water volumes. See the flow regulator’s characteristic illustrated on the curve.


The roof drain with discharge control exerts hydraulic resistance using a vortex chamber. This ideal design gives Mosbaek's roof drain with discharge control unique flow-control properties which is why they have the biggest orifice plates and thus the lowest risk of clogging. When in operation, the flow regulator's orifice opening is unchanged.


Roof drains with flow control are installed in depth points and gutters and the catchment area can be up to 150 m2 per downpipe.

When it rains, the water builds up around the roof drain with discharge control, which means it is partly submerged during operation.

The roof drain with discharge control can be equipped with an integrated overflow.

The roof drain with discharge control, which is surrounded by a grate at a proper distance from the inlets, allows water to flow to the flow regulator from all sides and from above. As the flow regulator is installed on flat roofs, it can be inspected and serviced under ideal hygienic and working-environment conditions.

In many instances, the roof drain with discharge control can be installed on existing or planned flat roofs. The roof is normally dimensioned for a snow load of 100 kg/m2, equivalent to 100 mm of water.


  • Controls flow using centrifugal force in the vortex chamber
  • Large orifice opening that remains unchanged during operation
  • No moving parts
  • No electric components
  • Made of Acid-resistant stainless steel AISI 316L (Werkstoff 1.4404) 

The properties reduce costs for installation, operation and maintenance.