Content and Precautions for Flange and Manhole Accessories

Manhole Factory is a manufacturer specializing in the production and processing of manhole products. It is a professional manhole supplier that integrates the manufacturing and sales of manholes, elbows, flanges, tees, and other pipe fittings. The company offers custom fabrication based on customer specifications, can process materials supplied by the customer, and provides tailor-made solutions from drawings. It is one of the most reputable manufacturers in the region.

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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 easily 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.

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 include: 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 flanges, vertical‑lift cover plate‑type flat‑weld flange manholes, horizontal‑lift manholes with butt‑weld flanges, horizontal‑lift plate‑type flat‑weld flange manholes, horizontal‑lift manholes with butt‑weld flanges, 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 mounted gravity‑type explosion‑proof doors, among other products.

This is for personnel access, tank maintenance, and ventilation pipe connections. Given that carbon‑steel square manholes are prone to leakage, proper installation is especially critical. 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. Special care must be taken to protect the flanges of carbon‑steel square manholes. A 3 mm‑thick asbestos‑rubber gasket shall be used for sealing, and it must be free of cracks or splits. When tightening the bolts on the manhole cover, ensure that the carbon‑steel square manhole cover does not deform.

This week, we’ve covered the fundamental principles and methods for selecting pipeline fittings, including waterproof sleeves, limited‑travel flexible joints, flanged flexible joints, and several other series. By now, you should have a solid understanding of which fittings are appropriate for different operating conditions. Flanged flexible joints are primarily used to connect centrifugal pumps to pipelines. During operation, they provide a degree of multidirectional misalignment compensation, reducing the thrust loads on pipeline flanges and offering reliable protection for the piping system—while also greatly simplifying installation, maintenance, and repair.

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.

The rubber duct compensator consists of a rubber composite material, steel flanges, a sleeve, and thermal insulation. It is primarily used for flexible connections between various fans and ductwork, providing vibration isolation, noise reduction, and media‑resistant sealing, while facilitating movement and installation. It is an excellent accessory in the field of environmental protection, offering superior performance in vibration damping, noise suppression, and smoke‑and‑dust elimination.

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

If a flange develops a leak, it must be promptly repaired based on the specific circumstances of the leak and the actual operating conditions of the equipment. In addition to the four causes mentioned above, factors such as corrosion and thermal expansion–contraction can also lead to flange leaks. Therefore, regular and routine inspections of the equipment are essential. Different types of devices are used in various applications; one such type is the drain outlet, which serves as an exit point for wastewater flowing into underground channels.

The manhole shall be located near the right side of the oil inlet and outlet pipes, with its position aligned as closely as possible with the tank compartment’s airtight door, to facilitate personnel access, tank maintenance, and ventilation‑pipe connection. Since the manhole is mounted on the tank’s base ring, leak prevention is of paramount importance. The mating surfaces of the two flanges must be kept perfectly flat, with no warping or twisting. Reinforcing plates and flanges should be cut from a single sheet of steel whenever possible, rather than assembled from multiple pieces. Sealing rings are machined into both the flange and the cover plate; special care must be taken during installation to preserve them. A 3‑mm‑thick asbestos‑rubber gasket is used for sealing, and it must remain intact without any cracks or splits. When tightening the bolts that secure the manhole cover, apply force evenly in a diagonal pattern to prevent deformation of the cover.

How to connect a water‑passing rubber seismic joint: The pipe‑connecting rubber joint consists of a rubber expansion joint, with a sealed ring and a short‑tube flange, along with nuts and bolts. Its function is to accommodate pressure surges and compensate for installation deviations in pipelines, absorbing radial misalignment. It is particularly suited for connecting pump lines and other fittings. The advantages of rubber expansion joints include easy installation, convenient pipeline assembly, and the ability to withstand radial tensile forces. Their design also helps to concentrate and dissipate installation stresses.

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 access 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 light‑industrial machinery. Our products are widely employed across sectors including dairy, brewing, food processing, pharmaceuticals, beverages, and chemicals.

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.

Installation method for ductwork: Prior to installation, the main and branch ducts can be pre‑assembled in sections on the ground. Depending on lifting conditions and duct‑to‑duct connections, each straight section should be approximately 10 meters long. Gaskets must be placed between flanges, and the bolts and nuts securing the flanges should all be on the same side. Before installation, verify that supports and hangers are secure and properly aligned. During overhead work, the ropes used to lift the ductwork must be securely fastened; they may only be released once the duct has been firmly connected to its fittings and leveled and fixed with the supports.

Flange sealing faces come in two types: flat and raised. They are commonly used under relatively mild service conditions, such as low‑pressure non‑purified compressed air or low‑pressure circulating water, and their main advantage is their cost‑effectiveness. Dezhou Flange Fitting Processing Plant specializes in manufacturing flanges, ductwork, elbows, and related fittings of various specifications, backed by years of production experience—offering superior quality at competitive prices. Your choice!

Since 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, thereby avoiding oil seepage during operation. Each time a manhole is removed, it should be clearly marked to ensure proper alignment upon reinstallation and maintain tightness. When tightening the nuts on the manhole cover, apply even torque in diagonally opposite 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 installed at both ends of the pipeline. Manholes should also be provided at pipeline branches, bends, and entry points, as well as at sites equipped with cathodic protection stations.

Application areas: Zhangzhou PN10 Japanese‑standard flexible pipe‑fitting components, including flanged telescopic butterfly valves (with a structural length that can be adjusted within a certain range). These valves facilitate disassembly and assembly, relieve pipeline stresses, and protect the valve itself, while also consolidating the installation method of a butterfly valve paired with an expansion joint, resulting in a more compact footprint. Under normal operating conditions, such valves require no special maintenance; routine checks are sufficient to ensure that the telescopic section shows no signs of leakage or detachment. Although the initial investment for a flanged telescopic butterfly valve is lower than that of a conventional flanged butterfly valve combined with an expansion joint, when factoring in long‑term maintenance costs, this approach ultimately proves less economical. Return to homepage for more details.

Manhole is a polysemous term. In the context of equipment, it refers to an opening designed to allow personnel to enter and exit for installation, maintenance, and inspection. It typically consists of a short cylindrical section, a flange, and a manhole cover with a handle. Standardized manholes are available, usually with a diameter of 600 mm, and the center-to-floor height is generally 750 mm, facilitating access for personnel during installation, cleaning, and maintenance, as well as ensuring adequate ventilation.