Definition - What does Manway mean?
A Manway is an entry used by workers to provide easy access to vessels or storage tanks for the cleaning and maintenance purposes. It is always present on the intake air-side in gassy mines. These openings provide a passage for the workers into the tanks or other kinds of vessels. They have plates or covers which fit inside the opening of the vessel or tank and are pulled back against the gasket or the external flange. The round covers do not fit inside the opening as it must be larger in diameter than the opening so as to serve its operation. The gaskets for these flanges are generally ob-round or oval in shape so that covers can be fitted through the openings.
Petropedia explains Manway
Manways are used in tanks to move from drift mouth or shaft bottom to the working section. They are secured by a transverse beam that is attached to the center of the plate or the cover. The transverse beam assures the even distribution of the arresting force to develop a fitting that is gas-tight. The Manways are present inside the vessels or the tanks and the pressure inside the tank acts in a different way on the assembly than on the typical bolted flange connections. Later the internal pressures act in a way to unload the gasket after separating the flanges. The internal pressure of the vessel or the tank pushes the flanges into the place, loads the gasket and generates more compressive force than the bolts.