What are the characteristics of a pressure-relief manhole?

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.

Both pressure‑relief manholes and vent manholes must be used in conjunction with breather valves. Under normal conditions, gas venting and intake are managed by the breather valve; only in the event of a fire or breather‑valve failure would the pressure‑relief or vent manhole be activated. This approach naturally reduces the frequency of operation of these manholes and extends their service life. Since pressure‑relief and vent manholes have very high discharge capacities, omitting a breather valve would result in substantial daily venting of gases from the tank roof—leading to increased costs if nitrogen is involved, or severe environmental contamination if toxic gases are present. 3. When the tank contents are particularly dirty, the pressure‑relief or vent manhole should be maintained promptly. Inspection personnel should regularly visit the tank roof to inspect the pressure‑relief manhole, using a clean cloth to wipe both the upper and lower sealing surfaces and ensure they remain free of contaminants.

The relief cover of the pressure‑relief manhole is automatically lifted to provide rapid pressure release, maintaining normal internal tank pressure. When the tank experiences a sudden pressure drop or falls into a vacuum, the valve opens to admit air quickly, thereby restoring normal internal pressure. If atmospheric air contains sparks or flames, the flame‑arresting layer creates a “wall‑effect” that prevents flame propagation, thus 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.

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.

The pressure-relief manhole is connected to the flange pre‑installed at the top of the storage tank. It is typically mounted within the first ring of the tank and used in conjunction with the vent valve, positioned adjacent to the vent valve.

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 manhole product line primarily includes: 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 purge 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.

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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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 pressure‑regulated discharge, reliable operation, flexible sealing, a compact structure, and excellent sealing performance.

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 drain‑off fluid channels make them particularly suitable for steam‑based CIP cleaning. Throughout the manufacturing process, rigorous quality control is implemented in accordance with specified standards, and computer‑aided 3D design is employed—ensuring compliance with GMP regulations. Since manholes are located at the bottom of fuel tanks, they must withstand substantial liquid pressure. To prevent leakage, strict adherence to installation quality is essential. Flanges and cover plates are sealed using water‑tight gaskets; during installation, care must be taken to protect these seals and avoid oil leaks during operation.