Automatic air vent valve is installed in heating and air conditioning systems, in order to remove the air, without the need of manual intervention. The accumulation of air in the valve body causes the drop of the inside foating so that it is possible to discharge the air. The valve has to be installed in the vertical position. During operation the upper cap must be loosened. The maximum discharge pressure is 6 bar. The regular operation of the automatic air vent valve can be compromised if the system water carries suspended impurities. In these cases (if there is no possibility of installing flters) it is opportune to carry out periodical washing of the system.