Let’s learn about atmospheric-pressure manholes.

Atmospheric storage tanks have numerous attachments, and among them, atmospheric manholes and pressure-relief manholes are often confused. Here, we would like to clarify that a pressure-relief manhole is by no means an atmospheric manhole.

Manholes are categorized into emergency pressure-relief manholes, explosion-proof flame-arresting breather manholes, tank‑top manholes, tank‑wall manholes, and core‑type manholes. Our company’s main manhole series include: rectangular insulated manholes, circular insulated manholes, steel manholes, atmospheric‑pressure manholes, rotary‑cover flat‑weld flange manholes, rotary‑cover manholes with butt‑weld flanges, vertical‑lift cover flat‑weld flange manholes, horizontal‑lift manholes with butt‑weld flanges, horizontal‑lift flat‑weld flange manholes, horizontal‑lift manholes with butt‑weld flanges, atmospheric‑pressure quick‑opening manholes with rotary handles, elliptical rotary‑cover quick‑opening manholes, coal‑dust purging ports, plain‑wall coal‑passage ports, round‑wall coal‑passage ports, round welded manholes, flue‑gas ash‑removal ports, square dampers (single‑axis, double‑axis, triple‑axis, quadriaxial, quinti‑axial), round dampers (electric, manual), explosion‑proof doors, gravity‑type explosion‑proof doors, fan inlet plenums, inclined‑plane explosion‑proof doors, and horizontally mounted gravity‑type explosion‑proof doors, among other products.

It is typically used in conjunction with a mechanical breathing valve, serving to prevent damage to the tank caused by sudden overpressure or vacuum conditions while also providing flame‑arresting protection. As a safeguard for storage tanks, it is especially suited for dome‑top atmospheric tanks that use nitrogen blanketing. It offers advantages such as pressure‑regulated venting, consistent pressure control, flexible opening and closing, flame arrestment, excellent sealing performance, and high reliability. An atmospheric manhole is also a type of manhole fitting; however, customers are often unfamiliar with manholes.

Special care must be taken to protect the flush‑type cleaning opening in accordance with national standards. A 3 mm thick asbestos‑rubber gasket shall be used for sealing, and no cracks or splits are permitted. When installing the manhole cover over a flush‑type cleaning opening, apply sufficient force to prevent deformation of the cover. Custom‑made boiler handholes are manufactured with an open‑type structure designed for inspection and maintenance. They typically consist of a short pipe, a flange, and a handhole cover equipped with a handle. Commonly used handholes have nominal diameters; custom boiler handholes may include open‑type designs. Quick‑opening handholes are intended for frequent access and are available in atmospheric‑pressure versions, featuring a rotary handle and a hinged cover. For non‑metallic oil tanks, custom boiler handholes or manholes are employed. The installation of manholes should ensure that the angle between the manhole and the inlet/outlet oil pipelines does not exceed 90°. When only one manhole is provided, it should be positioned opposite the tank’s light‑viewing port; when two manholes are installed, one should face the light‑viewing port, while the other must be spaced at least 90° from the first.

Based on their load‑bearing capacity, national‑standard oil‑ventilation ports are classified into two grades: Class 20 and Class 10. Carbon steel GTQ‑type vent ports, manufactured by Juchao, prevent damage to storage tanks under conditions of excessive positive pressure or vacuum; they serve as protective devices and are particularly suitable for dome‑top atmospheric tanks that use nitrogen blanketing. These ports feature constant‑pressure venting, reliable sealing, and flexible opening and closing. Types of manholes include carbon steel GTQ‑type vent ports with fire‑breathing functionality, tank‑top manholes, tank‑wall manholes, and core‑equipped manholes.

Although they are similar in appearance, they differ in many respects. We have long been dedicated to the design and manufacture of pressure-relief manholes. Below, we present a comparative analysis across several key aspects, with the aim of helping you distinguish between atmospheric‑pressure manholes and pressure‑relief manholes.

Atmospheric‑pressure manholes, as common opening fittings on the top of atmospheric storage tanks, are installed by welding to the tank’s top. Their function is to facilitate inspection and cleaning of the tank contents.

Pressure-relief manholes are increasingly being widely used on the top of atmospheric storage tanks and represent a cost-effective accessory. Their function is to rapidly vent tank pressure in the event of breather valve failure or during a fire, thereby preventing the tank from rupturing or being lifted off its supports.

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Storage tanks are commonly used in industries such as chemical processing, where they come into contact with a variety of materials. During loading and unloading, the lids of atmospheric‑pressure manholes are frequently opened, allowing acidic substances to spill out and corrode the flanges. Even after repair, these flanges remain susceptible to re‑corrosion. Consequently, when repairing damaged flanges, it is necessary to install a plastic under‑flange; it is important to ensure that the plastic under‑flange matches the dimensions of the original flange.

Manhole structures and dimensions are generally standardized, allowing for selection or design based on relevant handbooks. Manhole doors open and close smoothly and conveniently, offering thermal insulation, easy and flexible operation, and resistance to deformation, making them well suited for use in boilers, hot-air ducts, and similar applications. With the continuous advancement of modern production systems and the development of China’s machinery industry, power plants, chemical plants, and construction sites alike are increasingly seeking high‑quality, premium‑grade products such as atmospheric‑pressure quick‑opening handholes, atmospheric‑pressure manholes, and support‑and‑hanger components.

Stainless steel manhole product features: The stainless steel manhole is an emergency venting device installed on the top of storage tanks. It is typically used in conjunction with flame arrestors and mechanical breathing valves, serving to prevent tank damage caused by sudden overpressure or vacuum conditions while also providing flame‑retardant protection. This makes it an essential safeguard for storage tanks, particularly suitable for dome‑top atmospheric tanks that use nitrogen blanketing. It offers advantages such as pressure‑regulated venting, consistent pressure control, flexible opening and closing, flame‑arresting capability, a compact structure, excellent sealing performance, and high reliability. Classification of manhole types.

We boast state-of-the-art manufacturing processes, advanced production equipment, and comprehensive testing and inspection systems, offering a wide range of standard‑type manholes, drain ports, quick‑opening manholes, tank manholes, light‑transmitting openings, vent holes, air‑ventilation openings, elliptical manholes, boiler manholes, atmospheric‑pressure manholes, manhole doors, and more. In addition, we provide cutting‑edge ancillary facilities and technological products that are distributed nationwide. We also undertake custom fabrication to meet specific customer requirements. Hebei Chenrun Pipeline is a specialized manufacturer dedicated to supplying high‑end products and services to domestic and international industries, including petroleum, refining, chemical processing, metallurgy, power generation, shipbuilding, gas transmission, and pipeline transportation.

Manhole structures and dimensions are generally standardized and can be selected or designed by referring to relevant handbooks. A manhole is an opening provided to allow a person’s hand or tools to reach into the equipment for installation, maintenance, or inspection. It typically consists of a short nozzle, a flange, and a manhole cover with a handle. Common nominal diameters for manholes range from 150 to 250 mm, and they are fabricated from carbon steel or stainless steel. Manholes are classified according to their pressure conditions as either atmospheric‑pressure or pressurized types, and according to their opening speed as either standard‑type or quick‑opening types.

A manhole is an emergency venting device installed on storage tanks, typically used in conjunction with flame arrestors and mechanical breathing valves. It prevents damage to the tank caused by sudden overpressure or vacuum resulting from unforeseen circumstances, while also serving as a flame‑arresting barrier. As such, it is an essential safety device for protecting storage tanks, particularly those with fixed roofs operating at atmospheric pressure and sealed with nitrogen.

A manhole is an opening structure used for maintenance and inspection, typically constructed with a carbon steel shell. It mainly consists of a short cylindrical section (or short pipe), a flange, and a manhole cover equipped with a handle. From an inspection standpoint, the required number and minimum dimensions of manholes for pressure vessels are specified in relevant standards. Manhole materials include carbon steel and stainless steel. Based on operating pressure conditions, manholes are classified as atmospheric‑pressure carbon steel manholes with a core; selection or design should follow applicable handbooks. A breather valve is a device that, while maintaining atmospheric isolation in accordance with national standards, also allows communication with the atmosphere when the internal pressure exceeds or falls below a specified range—thus “breathing.” A standard‑compliant breather valve assembly comprises a valve disc, guide rod, spring, spring seat, and sealing ring, among other components. When the tank’s internal pressure reaches the rated positive venting pressure, the pressure‑activated valve disc opens, permitting air to enter.

Stainless steel manholes are emergency venting devices installed on the tops of storage tanks, widely used in large tanks and vessels across industries such as dairy, brewing, food, beverage, pharmaceuticals, and bioengineering. They are typically employed in conjunction with flame arrestors and mechanical breathing valves, effectively preventing tank damage caused by sudden overpressure or vacuum conditions while also providing flame‑retardant protection. These devices are essential for safeguarding storage tanks, particularly those with nitrogen‑blanketed dome roofs operating at atmospheric pressure. They offer advantages including pressure‑regulated venting, reliable pressure control, flexible opening and closing, flame‑arresting capability, a compact design, excellent sealing performance, and high reliability.

Application areas: Flexible 10k acid- and alkali-resistant flexible connectors—numerous successful applications. For vertical atmospheric‑pressure coal‑fired hot water boilers, all the heating‑surface tubes are straight, and ample manholes are provided to facilitate manual and mechanical cleaning of scale and internal inspections. For horizontal atmospheric‑pressure coal‑fired hot water boilers, a sufficiently large manhole is installed at the top, allowing personnel to enter the boiler interior. The boiler design is compact, occupies a small footprint, and is easy to transport; it is delivered as a quick‑assembly unit, significantly shortening the installation period. Return to Sohu for more.