1.  Field of the Invention
The present invention relates to a venting device for sanitary conduits comprising an air inlet and destined to prevent in buildings an escape of gases from a conduit for used water to the ambiance, and comprising a displaceable valve being able to abut sealingly against a seat, said seat being formed by a second and a first edge of an air passage between a conduit for used water and the ambiance. 
2.  Description of the Prior Art
An automatic venting device of this type for sanitary conduits adapted to discharge used water and destined in houses or buildings to cause on the one hand ambient air to flow into conduits at the event of an underpressure; and on the other hand to prevent the escape of contaminated air via the air inlet at the event of an overpressure or a regulated pressure in the conduits, is known from German Offenlegungsschrift No.  28 38 111 and No.  28 38 068. 
Said known automatic venting device exhibits the disadvantage that the seal of the displaceable valve upon the seat is often rather inappropriate so that evil smelling gases may easily escape to the outside from the discharge conduits for used water.  This inconvenience gets the worse in that pollutions such as dust particles, may contaminate the edge of the air inlet, engaging the displaceable valve, thus causing an insufficient seal between said edge and the displaceable valve, in the course of time. 
On the other hand, said valve cannot be removed from the seat in a sufficiently rapid manner at the event of an underpressure in the conduit for the discharge of used water, so that the known disadvantage of noise cannot sufficiently be obviated at the occurence of an underpressure in the discharge conduit.