Manhole flange Large closed containers (tanks, towers, pipes) for maintenance or other needs, there will be a hole for people or materials in and out, the passage made of flanged connection form.  When normal, with a blind flange closed, open during maintenance.  

Manhole flange is installed on top of the tank safety emergency ventilation device, usually with flame damper, using mechanical breather valve, can avoid the accident caused sharp overpressure or vacuum in tank and tank damage and accident, security fire effect, is to protect the safety of tank device, especially suitable for the storage of materials with nitrogen gas cap vault atmospheric tank.  

It has the advantages of constant pressure discharge, constant pressure suction, flexible opening and closing, safe fire resistance, compact structure, good sealing performance, safe and reliable, etc.