Structural characteristics: 1. It can drain successively with stable performance ,large displacement and low air leakage. 2. It can saturate water successively so as to have little condensate water of equipment,rapid heating up and stable heating temperature. 3. Automatic cold air exhaust mechanism with reliable operation ,but without air lock or noise. Working principle: The ball float inside the valve body lifts up and down as water level changes so as to close or open the valve viz. both drainage and air resistant.