A brief introduction to elliptical pressure manholes for you.

When the atmospheric pressure in the upper gas space of the tank causes the negative‑pressure valve disc of the carbon‑steel vent manhole to lift, external air enters the tank, preventing further pressure drop. This is a device for maintaining the integrity of the carbon‑steel vent manhole on the storage tank. When the pressure within the tank remains within the operating range controlled by the vent manhole, the vent valve remains closed, ensuring the tank’s seal; however, when the pressure in the tank’s internal space rises and reaches the vent valve’s positive‑pressure set point, the valve opens.

The relief cover of the pressure-relief manhole is automatically lifted to provide rapid pressure relief, maintaining normal internal tank pressure. When the tank experiences a sudden pressure drop or falls into a vacuum, the valve opens to allow swift venting to atmospheric pressure, thereby safeguarding the tank’s internal pressure. Should sparks or flames be present in the atmosphere, the flame-arresting layer generates a “wall‑effect” that inhibits flame propagation, protecting the storage tank. Manholes are classified into types such as emergency pressure‑relief manholes, explosion‑proof flame‑arresting breather manholes, roof manholes, wall manholes, and core‑type manholes. Manufacturers of emergency pressure‑relief manholes produce these devices, which serve as emergency venting systems installed on the tops of storage tanks.

When the pressure inside the tank reaches the rated positive relief pressure, the pressure valve disc opens and the standard‑type breathing manhole vent valve lifts, allowing air to enter. 1. Removing the packaging—this step in the product instructions for the standard‑type breathing manhole is critical. 2. Lifting the breathing valve and the standard‑type breathing manhole using appropriate lifting equipment to prevent damage to the valve disc and its protective cap. 3. Verifying that the tank or the standard‑type breathing manhole’s pressure–vacuum relief valve (breathing valve) is functioning properly is essential. 4. Ensuring that the tank or the standard‑type breathing manhole is clean and free of debris.

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 ports, elliptical manholes, boiler manholes, atmospheric‑pressure manholes, manhole doors, and more. In addition, we provide cutting‑edge ancillary facilities and technologically advanced 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 the petroleum, refining, chemical, metallurgical, power, shipbuilding, gas‑transport, and pipeline‑conveyance industries both domestically and internationally.

A manhole is an opening structure used for maintenance and inspection, featuring a carbon‑steel core. It typically consists of a short cylindrical section (or stub pipe), a flange, and a manhole cover 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. Depending on the operating pressure, manholes are classified as atmospheric‑pressure types with carbon‑steel cores; selection or design should follow applicable handbooks. A breather valve is a device that, while maintaining atmospheric isolation under normal conditions, allows communication with the atmosphere when the pressure exceeds or falls below a specified range—thus “breathing.” A standard breather‑manhole assembly comprises a valve disc, guide rod, spring, spring seat, and sealing ring, among other components. When the internal tank pressure reaches the rated positive venting pressure, the pressure‑activated valve disc opens, permitting air to enter.

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Non-standard rotary‑cover manholes offer excellent sealing performance and reliability. Manholes are classified into emergency non‑standard rotary‑cover manholes, flame‑arresting breather manholes, tank‑top manholes, tank‑wall manholes, and core‑type manholes, among others. Typically, manholes are fabricated from stainless steel plates or carbon steel. The non‑standard rotary‑cover manhole features a fully enclosed opening structure, consisting primarily of a short cylindrical section (or short pipe), a flange, and a manhole cover with a handle. For inspection purposes, the required number and minimum dimensions of manholes for pressure vessels are specified in the relevant standards.

Manholes are categorized into emergency pressure-relief manholes, explosion-proof flame-arresting breathing manholes, tank‑top manholes, tank-wall manholes, and core‑type manholes. Our company’s main manhole series includes: rectangular insulated manholes, circular insulated manholes, steel manholes, atmospheric‑pressure manholes, swivel‑cover plate‑type flat‑weld flange manholes, swivel‑cover manholes with butt‑weld (socket‑weld) flanges, vertical‑lift cover plate‑type flat‑weld flange manholes, horizontal‑lift manholes with butt‑weld (socket‑weld) flanges, horizontal‑lift plate‑type flat‑weld flange manholes, horizontal‑lift manholes with butt‑weld flanges (socket‑weld), atmospheric‑pressure quick‑opening manholes with rotary handles, elliptical swivel‑cover quick‑opening manholes, coal‑dust purging ports, flat‑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 arranged gravity‑type explosion‑proof doors, among other products.

Most high‑tech equipment is derived from foreign designs; accordingly, such devices typically adhere to the American standard series, namely the HG20615 series. Our company primarily manufactures internal‑opening manholes, circular manholes, pressure‑rated manholes, valves, fittings, flanges, and heads. In response to market demand and industry trends, we continuously refine our business philosophy and place great emphasis on brand building, having now established ourselves as a reputable domestic manufacturer of specialized light‑industrial machinery. Our products are widely used across industries including dairy, brewing, food processing, pharmaceuticals, beverages, and chemicals.

Because manholes are located at the bottom of oil tanks, they are subjected to substantial liquid pressure. To prevent leakage, strict quality control is essential during installation. Sealing grooves are machined on both the flanges and the cover plates; care must be taken during construction to protect these grooves and avoid oil seepage during service. Each time a manhole is removed, it should be clearly marked to ensure proper alignment upon reinstallation, thereby maintaining tightness. When tightening the nuts on the manhole cover, apply even torque in opposite diagonal pairs to prevent deformation of the cover or uneven stress that could lead to oil leakage. At locations where pipelines cross railways or roads, manholes must be provided at both ends of the pipeline. Manholes should also be installed at pipe branches, bends, and entry points, as well as at sites equipped with cathodic protection stations.

The manhole of a non-metallic carbon steel pressure vessel shall be positioned no more than 90° apart from the oil inlet and outlet pipelines. When only one manhole is provided, it shall be located opposite the light‑transmitting opening at the top of the tank. For carbon steel pressure vessels, the manhole should be spaced at least 90° from any other manhole. The emergency venting device mounted on the top of the storage tank, typically used in conjunction with a flame arrester and a mechanical breathing valve, prevents damage to the tank caused by sudden overpressure or vacuum conditions, while also serving as a fire‑prevention measure. It is an essential safety device for protecting storage tanks, particularly suitable for storing materials that require regulated pressure relief, stable pressure control, flexible opening and closing, flame‑retardant performance, compact construction, and reliable sealing.

A pressure-relief manhole is an emergency venting device installed on equipment and storage tanks in the petrochemical industry and other sectors. It is typically used in conjunction with a breather valve mounted on the tank roof to maintain normal internal pressure, thereby preventing damage to the tank caused by sudden overpressure or vacuum conditions resulting from unforeseen circumstances. It offers advantages such as fixed-pressure discharge, reliable operation, flexible sealing, a compact structure, and excellent sealing performance.

Quick-opening manholes are typically installed at the bottom or top of storage tanks and are often used in conjunction with flame arrestors. This arrangement not only prevents tank damage and potential personnel hazards during sudden pressure surges or vacuum conditions caused by accidents, but also enables the manhole itself to serve as an effective flame barrier, thereby providing maximum protection for the tank. Design considerations are applied to hygienic quick-opening manholes and handholes commonly used in pharmaceutical and food-processing equipment.

Stainless steel manholes are categorized into emergency pressure-relief manholes, explosion-proof flame-arresting breather manholes, tank‑top manholes, tank‑wall manholes, and core‑type manholes, among others. YAB stainless steel manhole covers are manufactured from SUS304 or 316L grades, meeting the stringent requirements of various media in the food and biopharmaceutical industries. Their smooth, seamless design and automatic drainage channels for process fluids make them particularly suitable for steam‑based CIP (clean-in-place) applications. Throughout the manufacturing process, rigorous quality control is implemented in accordance with specified standards, and computer‑aided 3D design is employed to ensure compliance with GMP regulations. Since manholes are located at the bottom of the tank, they must withstand substantial liquid pressure. To prevent leakage, strict adherence to installation quality is essential. Flanges and cover plates are sealed with gaskets; care must be taken during installation to protect these seals and avoid oil leaks during operation.

For more than two decades, we have remained dedicated to the production and R&D of components for tank‑type storage and transportation equipment. Our product range includes manhole cover sealing rings, woven manhole sealing rings, flange gaskets, PTFE valve gaskets, O‑rings, thermometers, pressure gauges, dust caps, manhole bolts, document tubes, and more.

An enterprise experienced an accident involving the overpressure‑induced explosion of a cryogenic liquid nitrogen storage tank. The incident resulted in damage and collapse of the tank, creating a scene reminiscent of a blockbuster film. Surveillance footage reveals that, following the pressure surge, both the inlet line of the inner vessel’s vent valve and the pressure‑control loop line—along with what appears to be the inner vessel’s manhole cover—burst open simultaneously (see Figure 3). Preliminary analysis suggests that the direct cause was a failure of the pressure‑control system for the inner vessel, leading to a rapid increase in tank pressure. With the vent valve unable to function, the inner vessel underwent an overpressure‑induced explosion, while liquid nitrogen entered the intermediate jacket space; the ensuing rapid vaporization of the cryogenic liquid caused the outer shell to explode under excessive pressure.