タイトルまたは説明

Manhole (boiler, sewer for human access to and repair) manhole, manhole (A hole, usually with a cover, through which a person may enter a sewer, boiler, drain, or similar structure.) Sewer entry and exit hole: a hole often with a cover, 
People can get in and out of drains, boilers, sewers, weak wells including telecommunications and cable television, internal passageways for maintenance of large bridges, and so on. 
Manhole is a safety emergency ventilation device installed on the top of a storage tank. it is usually used in conjunction with a fireproof device and a mechanical breathing valve, which can avoid accidents caused by sudden overpressure or vacuum in the tank and damage to the storage tank. 
It also plays the role of safety fire resistance, is a safety device to protect the storage tank, especially suitable for storage materials with nitrogen capped arch roof atmospheric pressure tank. 
The utility model has the advantages of constant pressure discharge, constant pressure suction, flexible opening and closing, safe fire resistance, compact structure, good sealing performance, safety and reliability, etc. 
Manholes are divided into emergency pressure relief manholes, explosion-proof and fire-proof breathing manholes, tank top manholes, tank wall manholes and core manholes, and so on. 
Manholes are generally made of 304316L stainless steel plate or carbon steel.