タイトルまたは説明

installed on the top of oil tanker and used for loading oil,checking gas recovery,mending the internal inlet. 
alsocan protect the tanker under the emergency.
When loading oil,the outside temperatures change will lead the tankers inside pressure  to change.
Then the manhole covers 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 to avoid the tankers explosion when under the fire condition.