thanks nabilia

well i need the details of that plate.
i have checked in our warehouse about the breather valve. recently 12" Breather valve with flame arrester is present in our warehouse. 2nd step will surely be to install that breather dia 12" on that manhole plate dia 24"...
can u send the details of how thick the plate must be, so that it can support the breather...
and calculations for that plate thickness..

also
if i use the manhole, how will i acheive the purpose of manhole?
can some one share the detail how to fabricate that plate?