They are air supply/exhaust devices with the capacity of adjusting air flow. They are commonly used for small premises, low air flows.
They can be installed on the ceiling or on the wall, on the inside or on the outside (VLA, VLB). Internal valves are provided with adjustable central disks that can increase or reduce the free surface, as needed.
Models suited for external mounting are provided with net and sealing gaskets.


Internal valves are most often used in sanitary ensembles, where the flow must be dosed according to the surface, but also in premises with other uses.
External valves are used for facade mounting.