installed on the top of oil tanker and used for injecting oil,checking gas recovery,mending the internal inlet.
Also can protect the tanker under the emergency. When inject oil,the outside temperature's change will lead the tanker's inside pressure to change.
Then the manlid's breathing valve can automatically make the tanker pressure to the normal level. If some emergency happen , like the tanker overturn,the breathing valve will automatically close toavoid the tanker's explosion when under the fire condition.