Ships can be set up ballast tank, through the ballast water to adjust the floating state of the ship. Because these ballast tanks belong to a closed space, when the ship uses the bilge pump to produce pressure to inject or discharge ballast water, it is easy to cause the ballast tank overpressure or negative pressure, affected by the strength of the hull structure, the ballast tank can withstand limited pressure, especially in the negative pressure, generally can only withstand one atmosphere of negative pressure (0.1MPa). In order to protect the ballast tank structure, ships generally set up air pipes at the top of the ballast tank to provide air flow and maintain the balance of pressure inside and outside the tank. In the ballast tank, all kinds of oil tanks and fresh water tanks on the ship that need to fill and pump liquids will also be set up with air pipes. Therefore, the ballast tank air vent head becomes an essential device in the ballast tank.