Waste water outlet sanitary plant comprising a siphon

A hydraulic device for the drainage of waste water from a spilling unit into a sewer comprising a container adapted for receiving a water seal therein, an inlet pipe extending from the spilling unit into said container having a lower end adapted to extend into the water seal contained in said container, an outlet pipe extending from said container and adapted to be connected to a sewer, automatic air valve means connected to said container for permitting the inlet of air into said container and blocking the outflow of air from said container, said automatic air valve means comprising an upper part of said container defining a frusto-conical neck diminishing in diameter upwardly of said container, a cover extending over said container and defining with said frusto-conical neck of said container a peripheral air inlet, and an annular valve resting over said peripheral air inlet, said annular valve adapted to be lifted by air entering said chamber when a negative pressure occurs in said outlet pipe so as to permit the introduction of sufficient quantity of fresh air and for resting over said peripheral air inlet to block the passage of air out of said container when air pressure in said outlet pipe is balanced with respect to pressure exterior to said container and when there is an overpressure in said outlet pipe whereby waste water can flow through an entire cross-sectional area of said outlet pipe into the sewer, whereas the air flow takes place after the waste water stops streaming from the spilling unit.