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　　 Pressure-resistant manhole A safety emergency venting device is installed at the top of the tank, typically equipped with a flame arrester and featuring a mechanical breathing valve. This device prevents damage to the tank and potential accidents caused by rapid overpressure or vacuum conditions inside, thereby providing fire‑safety protection. It serves as a critical safeguard for tank integrity and is especially suitable for atmospheric tanks with nitrogen‑filled roofs. The device offers advantages such as pressure‑regulated discharge and intake, flexible opening and closing, enhanced fire safety, a compact design, excellent sealing performance, and reliable operation.

　　They are used by tank-cleaning or maintenance personnel to enter and exit the tank and are also referred to as manholes. During tank maintenance and cleaning, manholes provide natural lighting and ventilation. The installation of manholes shall maintain a minimum 90° separation from all inlet and outlet pipelines. When only one manhole is provided, it shall be positioned opposite the tank’s roof light opening; when two manholes are installed, one shall be located opposite the sight glass, and the other shall be spaced at least 90° away from the first.

　　A manhole shall be provided on the right side of the oil inlet and outlet pipelines, positioned as close as possible to the tank compartment to facilitate personnel access for maintenance of the tank and its ventilation system. Since pressure‑rated manholes are mounted on the tank shell ring, leak prevention is of paramount importance. The mating surfaces of the two flanges must be perfectly flat, with no wobble or torsional distortion. Reinforcing ribs and flanges should be cut from a single sheet of steel whenever possible; they must not be joined by welding. Both the flange and the cover plate are equipped with sealing rings, which require careful protection during installation. A 3 mm‑thick asbestos‑rubber gasket shall be used for sealing, and cracking is strictly prohibited. When tightening the bolts on the manhole cover, tighten them diagonally opposite each other to prevent deformation of the cover.

　　 Pressure-resistant manhole As a safety device mounted on the top of a tank, it is typically used in conjunction with a breather valve and a flame arrester. Its presence not only safeguards the tank from external hazards but also provides fire‑safety protection, helping to prevent accidents. Naturally, its advantages are readily apparent: both venting and intake operate at constant pressure, the design is compact, the operation is more responsive, and its safety performance is superior.

　　indicate Pressure-resistant manhole With its multifunctionality and advantages, we must highlight the critical flange. Typically, to ensure the pressure and sealing performance of the atmospheric-pressure chamber, we install a pipe section on the manhole cover and two flanges—one at the top and one at the bottom—on the welded joint. Since this component is the core of the normal-pressure chamber, it requires careful handling during use, particularly to prevent corrosion.

　　Therefore, when repairing damaged flanges, we need to install an additional plastic flange. It’s important to note that the dimensions of the plastic lower flange must match those of the manhole flange, and the inner diameter of the flange is typically determined based on our specific application requirements. Additionally, we usually fit a sealed plastic cover over the flange, which further prevents material flow and mitigates flange corrosion. This effectively provides the flange with double protection—both guarding against corrosion and enhancing the tank’s overall safety to a certain extent.