Industrial valves · Клапаны с сильфонным уплотнением
Bellows-Sealed Shut-Off Valves: Engineering Analysis of Design and Applications for Absolute Leak-Tightness
Engineering and Technical Foundations for the Application of Bellows-Sealed Valves by EV Group China
Absolute leak-tightness of pipeline systems is an indispensable requirement in the chemical, oil refining, and nuclear industries, where leakage of the working medium is unacceptable. Breach of integrity in shut-off valve assemblies, such as flanged connections or gland packings, leads not only to direct economic losses of expensive reagents but also poses a direct threat to industrial and environmental safety. EV Group China's engineering technologists confirm that the integration of advanced design solutions, particularly bellows-sealed valves, allows for achieving zero fugitive emissions and minimizing operational risks.
Loss of seal in a standard gland packing chamber is a primary cause of operational problems. Packing wear, thermal cycling, and the "compression set" effect lead to micro-leaks. For example, at a steam pressure of 10.3 bar (150 psi), a micro-gap in the gland packing with a diameter of only 0.025 mm (0.001 inch) results in a loss of up to 11.3 kg of steam per hour, which is equivalent to significant financial losses on an annual basis. The bellows sealing technology implemented in EV Group China's valves completely eliminates this failure point, creating a static, all-metal barrier between the working medium and the atmosphere.
Engineering Design and Operating Principle of the Bellows Sealing Unit
The bellows assembly is a precision, multi-layered corrugated element made from corrosion-resistant metal. It is hermetically welded on one side to the valve bonnet and on the other to the stem. During valve operation, the bellows convolutions elastically deform (compress or extend), ensuring complete isolation of the movable stem from the external environment. To prevent torsional stresses and increase the cyclic life of the bellows, a non-rotating stem design is used, which performs only translational movement. There are two mounting schemes: with the working medium located inside the bellows or in the annular space between the bellows and the bonnet, which is selected depending on the system parameters.
Manufacturing Technologies and Classification of Bellows
In EV Group China's engineering practice, two fundamental types of bellows are used, differing in manufacturing technology and operational characteristics:
| Bellows Design Type | Manufacturing Method | Key Operational Advantages |
|---|---|---|
| Formed (hydroformed) | Hydrostatic forming from a seamless tube | Monolithic construction without welds, maximum resistance to high pressure and metal fatigue. |
| Welded diaphragm | Precision welding of a stack of stamped metal diaphragms | High flexibility and significant axial displacement in compact dimensions, which allows for reducing the valve's overall height. |
To enhance performance under high pressure, EV Group China engineers use multi-layered (2- or 3-ply) bellows. This design distributes stress across several layers, which increases the nominal pressure rating by 80–100% compared to a single-layer equivalent of the same thickness, while practically maintaining elasticity and a low spring rate.
Materials Science and Industrial Application
The choice of bellows material is a critically important factor determining its durability and reliability. For bellows production, EV Group China uses high-alloy steels and alloys certified for operation in aggressive environments:
- AISI 316Ti (1.4571) — Austenitic stainless steel alloyed with titanium. Prevents intergranular corrosion at temperatures up to 800°C, making it ideal for steam and high-temperature systems.
- Inconel 625 (2.4856) — Nickel-chromium-molybdenum alloy. Provides exceptional resistance to pitting and crevice corrosion, as well as excellent fatigue strength in the range from cryogenic temperatures to +980°C.
- Hastelloy C-276 (2.4819) — Nickel-molybdenum-chromium alloy. Recognized industry standard for working with the most aggressive media: wet chlorine, strong oxidizers, sulfuric and hydrochloric acids.
Bellows-sealed valves manufactured by EV Group China are an indispensable solution for technological processes where media leakage is strictly unacceptable. This includes working with toxic and explosive gases (chlorine, hydrogen, ammonia), operating vacuum systems, nuclear power plant circuits, and pumping high-temperature organic heat transfer fluids. The use of our valves guarantees compliance with strict environmental standards (ISO 15848-1, TA-Luft) and represents a strategic investment in the safety, reliability, and economic efficiency of production.