News and Information
31
2022
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05
Where are atmospheric‑pressure manholes installed? What kind of product is an atmospheric‑pressure manhole? An atmospheric‑pressure manhole is a standard, non‑pressurized type of manhole typically mounted on the top of a tank. It serves as an access point for construction workers or maintenance personnel during tank erection, cleaning, and draining operations. The strength and sealing of the manhole are critical technical considerations; however, compared with pressurized manholes, the requirements for strength and tightness are secondary.
A atmospheric‑pressure manhole is a safety and emergency venting device installed on the top of storage tanks. It is typically used in conjunction with a mechanical breathing valve, serving to prevent tank damage and potential accidents caused by sudden overpressure or vacuum conditions. It also provides a safety flame‑arresting function, making it an essential safety device for protecting storage tanks—particularly dome‑top atmospheric tanks that use nitrogen blanketing. It offers advantages such as pressure‑regulated discharge and intake, flexible opening and closing, reliable flame arrestment, excellent sealing performance, and overall safety and dependability. The atmospheric‑pressure manhole is also the most common type of manhole.
Since manholes are installed on the lower shell ring of oil tanks, leak prevention is of particular importance. The mating surfaces of the two flanges must be perfectly flat, with no warping or twisting. Reinforcing plates and flanges should be cut from a single sheet of steel whenever possible, rather than being assembled from multiple pieces. Sealing rings are machined into both the flanges and the cover plate; special care must be taken during installation to protect them. A 3-mm-thick asbestos‑rubber gasket is used for sealing, and it must be free of cracks or splits. When tightening the bolts on the manhole cover, apply torque in alternating diagonal pairs to prevent deformation of the cover.
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