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　　Which industries will use it? Hygienic manhole ?

　　Because nearly all manholes are made from higher‑grade stainless steel, with 304 and 316—and to a lesser extent 316L—being the most common options, both grades are relatively expensive and require meticulous polishing. Their surface finish is exceptionally bright, which is why they are collectively referred to as sanitary‑grade manholes.

　　So, are all sanitary manholes used exclusively in the food‑processing machinery industry? That’s not necessarily the case. While they are widely employed in other relatively hygienic sectors—such as pharmaceutical equipment and environmental‑protection machinery—the majority of applications are indeed in the food‑processing field, particularly in large‑scale equipment for brewing and beverage production. This seemingly simple, unassuming piece of auxiliary equipment is nonetheless an indispensable component.

　　More specifically, Hygienic manhole There are many different shapes, including circular manholes, elliptical manholes, square manholes, and numerous types of manhole covers. Emergency venting devices installed at the top of storage tanks via atmospheric‑pressure sanitary manholes are typically used in conjunction with fire extinguishers and mechanical vent valves. In the event of a sudden accident that causes overpressure or vacuum, these devices help prevent damage to the tank. They serve as protective equipment for storage tanks, particularly well suited for nitrogen‑filled, arched, atmospheric‑pressure tanks. They offer advantages such as constant‑pressure discharge, constant‑pressure suction, flexible opening and closing, excellent fire resistance, a compact structure, and superior sealing performance. The plastic forming process for sanitary manholes has evolved in response to ongoing demands for higher quality, greater flexibility, reduced part counts, improved working conditions, and the widespread use of computers.

　　1. The high quality of components is reflected in two key aspects: the refinement of billet dimensions and the production of high-performance materials. To achieve finer grain structures in forgings, it is essential to advance precision shearing, precision casting for billet fabrication, and low-oxidation heating technologies, while also enhancing press rigidity and optimizing die design. For parts requiring tight dimensional tolerances, warm forging and cold forming processes can be employed. Meanwhile, to enhance forging performance, clearly defining forging requirements and developing new materials—particularly those with poor ductility—represent important directions for future research.

　　2. The goal of flexible manufacturing is to meet the demands of product variety. This requires extremely short changeover times; hygienic‑grade manholes should support as many motion modes as possible—multi‑slide and multi‑directional sliding—and their operating systems should be controlled, whenever feasible, by CNC systems and PNC (teach‑and‑reproduce) technology. At the same time, efforts should be made to adopt “flexible” production processes, favoring small‑batch, low‑volume, and dieless forming techniques, such as automatic tool‑change systems, free forging presses, multi‑directional forging presses, and ring‑rolling processes.

　　 Hygienic manhole They are categorized into emergency pressure-relief manholes, explosion‑ and fire‑proof vent manholes, tank‑top manholes, tank‑wall manholes, and core‑sampling manholes. Manholes are typically fabricated from 304 or 316L stainless steel plates or carbon steel.

　　Manholes shall be provided on the right side of the inlet and outlet pipelines, and should, whenever possible, be positioned adjacent to the tank door to facilitate worker access. The maintenance tank must be kept naturally ventilated. Since sanitary‑grade manholes are installed in the lower section of the tank, leakage can appear quite severe. It is stipulated that the mating surfaces of the two flanges must be perpendicular and free from deformation. Lifting plates and flanges should, wherever feasible, be laser‑cut from a single thick steel plate rather than assembled by splicing. Flanges and rear cover plates shall be manufactured and machined with sealing rings and maintained at the construction site. Sealing shall be achieved using 2 mm‑thick asbestos‑rubber gaskets; wedging is not permitted. After installation, if anchor bolts are fastened to the cover plate, the top corners must be symmetrically aligned to prevent deformation of the cover plate.