Vetus Type ASDV Anti Siphon Device with Valve, for 1/2", 3/4", 1" and 1-1/4" hose. Airvent is interchangeable with type AIRVENT and has the same fixing hole centers. It has the advantage that the air bleed connection rotates through 360?. In addition, this is the only valve that requires virtually no maintenance. It can easily be dismantled by hand for cleaning.