The valve automatically vents and provides air from and to hydraulic systems such as heating, cooling, air conditioning and sanitary equipment on a continual basis. The combination of an air separator with the aerating and venting greatly increases the efficiency of the venting operation. The ventilation valve is closed by means of a float. If air collects in the cup, the float sinks and releases the ventilation valve. The accumulated air escapes until the (inflowing) water pushes the floater down again and the valve closes. The water once more presses the float against the ventilation valve, and closes the valve.