In the industrial field, whether in petroleum, chemical, water supply and drainage, or HVAC systems, fluid control in pipelines cannot do without an important valve, the butterfly valve. With its unique structure and efficient sealing performance, the butterfly valve stands out among various types of valves and is widely applied in a variety of complex working conditions. The core competitiveness of butterfly valves lies in their ingenious sealing principle. This article will explore the sealing principle of butterfly valves in depth, revealing the mystery behind their efficient sealing.
A butterfly valve is a simple-structured control valve, whose main components include the valve body, disc, stem, and sealing device. The disc is mounted along the centerline of the valve body and is rotated by the stem to control the opening and closing of the disc, thereby regulating fluid flow. According to the relative position of the disc to the valve body centerline and the sealing method, butterfly valves are mainly divided into concentric (centerline) butterfly valves, single-offset butterfly valves, double-offset butterfly valves, and triple-offset butterfly valves.
The sealing of a concentric butterfly valve primarily relies on the tight contact between the disc and the seat. Because the contact area between the disc and the seat is large, and the sealing surface is symmetrically distributed around the center, the sealing effect is the same in both directions. When the butterfly valve is closed, the disc is pressed against the seat by the stem to form a seal. Due to its simple structure, the required machining precision of the sealing surface is relatively low, and manufacturing costs are relatively inexpensive. However, the sealing performance of concentric butterfly valves is relatively limited and mainly suitable for low-pressure, ambient-temperature conditions. To improve sealing performance, concentric butterfly valves often adopt rubber-lining, using the elastic deformation of rubber to compensate for minor gaps between sealing surfaces, thereby achieving better sealing.
The sealing principle of a single-offset butterfly valve reduces mechanical wear between the disc and seat through an eccentric design. During opening, the disc sealing surface separates from the seat more quickly than in a concentric butterfly valve. When the disc rotates 8°–12°, the disc sealing surface is completely separated from the seat sealing surface. This design allows the disc to quickly disengage from the seat during opening, reducing friction and extrusion between the sealing surfaces and thereby reducing wear. At the same time, when closing, the disc tightly presses against the seat, forming a good seal. Single-offset butterfly valves have better sealing performance than concentric butterfly valves and are suitable for medium-pressure and medium-temperature conditions.
The sealing principle of double-offset butterfly valves is more advanced. On the basis of a single-offset butterfly valve, it adds an offset angle between the valve seat centerline and the valve body centerline. This design allows the disc to immediately disengage from the seat sealing surface when opening and only contact and press the seat when closing. This instantaneous disengagement and engagement completely eliminate mechanical wear and abrasion between the disc and seat, greatly improving sealing performance and service life. Double-offset butterfly valves have excellent sealing performance, can withstand higher pressures and temperatures, and are widely used in industrial pipeline systems.
The sealing principle of triple-offset butterfly valves is currently the most advanced. Based on double-offset valves, the sealing structure is further optimized. The valve seat sealing ring consists of multiple layers of stainless steel on both sides of a soft T-shaped seal ring. The sealing surface between the disc and seat is a conical structure, with heat- and corrosion-resistant alloy material welded onto the disc's conical surface. This structure allows the butterfly valve to achieve optimal sealing performance during opening and closing. When the butterfly valve is closed, the disc is pressed against the seat by the stem, forming a reliable seal. Triple-offset butterfly valves have outstanding sealing performance, can withstand harsh conditions such as high temperature and high pressure, and are high-end products in the field of industrial fluid control.
The sealing performance of butterfly valves is influenced by multiple factors, including the structure of the sealing pair, the thickness of the sealing surface, the contact pressure of the sealing surface, the physical properties of the medium, and the quality of sealing components.
The structure of the sealing pair is one of the key factors affecting sealing performance. When temperature or sealing force changes, the structure of the sealing pair changes, which affects the interaction between the sealing surfaces. Therefore, when selecting sealing components, it is necessary to choose elastically deformable components to accommodate these changes. In addition, attention must be paid to the thickness of the sealing surface. The contact surfaces of the seal cannot completely match; when the width of the sealing surface increases, the required sealing force also increases. Therefore, when designing the sealing pair, the thickness and contact area of the sealing surface must be fully considered to ensure reliable sealing performance.
Contact pressure refers to the pressure per unit area on the sealing surface. The sealing performance of a butterfly valve is closely related to this contact pressure. Under the same conditions, excessive pressure can damage the valve, while insufficient pressure can cause leakage. Therefore, when designing a butterfly valve, the contact pressure of the sealing surface must be considered to ensure it falls within a reasonable range. Generally, soft-seal butterfly valves have relatively low contact pressure, while hard-seal butterfly valves have relatively high contact pressure. By properly designing the structure and material of the sealing pair, the contact pressure of the sealing surface can be optimized, improving sealing performance.
The physical properties of the medium also significantly affect the sealing performance of butterfly valves. These properties include temperature, viscosity, and surface hydrophilicity. Temperature changes not only affect the relaxation of the sealing pair and the dimensional changes of components but are also closely related to gas viscosity, which increases or decreases with temperature changes. Viscosity is related to fluid permeability; under the same conditions, higher viscosity means lower permeability. Surface hydrophilicity refers to the condition when an oil film exists on metal surfaces; such thin films can destroy hydrophilicity and block flow paths, so they should be removed. Therefore, when selecting sealing components, the physical properties of the medium must be fully considered to ensure stable and reliable sealing performance.
The quality of sealing components is an important factor affecting butterfly valve sealing performance. The quality is reflected in material selection, matching, and manufacturing precision. For example, the fit between the disc and seat directly affects sealing performance. High-quality sealing components provide better sealing and extend valve service life. When selecting sealing components, materials and structures must be chosen according to operational requirements to ensure performance and quality.
Butterfly valve sealing methods are mainly divided into hard-seal and soft-seal types.
Hard-seal refers to both sides of the sealing pair being made of metal or other hard materials. This sealing method is high-temperature resistant, wear-resistant, and has good mechanical properties, suitable for high-temperature and high-pressure conditions. However, the sealing performance of hard-seal valves is relatively poor. Although some manufacturers claim zero leakage, in practice, hard-seal butterfly valves generally do not seal as well as soft-seal valves. Hard-seal butterfly valves are structurally complex, usually using single-offset, double-offset, or triple-offset designs to improve sealing performance. They have a long service life, but improvements in sealing performance are limited.
Soft-seal refers to one side of the sealing pair being metal and the other being elastic non-metallic material. This method provides better sealing, can achieve zero leakage, and is suitable for ambient-temperature, low-pressure conditions. However, soft seals are not high-temperature resistant, wear easily, and have poor mechanical performance. Soft-seal butterfly valves are usually concentric, with seats made of non-metallic materials with certain strength, hardness, and temperature resistance. Soft-seal valves have shorter service life but excellent sealing performance. Soft-seal valves cannot meet process requirements for some corrosive media, while hard-seal valves can. In practice, soft-seal and hard-seal butterfly valves complement each other, and the appropriate sealing type is chosen according to operating conditions.
To improve butterfly valve sealing performance, optimization can be carried out in the following aspects.
Optimize Sealing Pair Structure: By optimizing the structure, sealing performance can be improved. For example, elastic seat designs can adapt to changes in temperature and pressure, reducing mechanical wear between sealing surfaces. Properly designing the sealing surface thickness and contact area reduces sealing force requirements and improves reliability.
Reasonable Selection of Sealing Materials: Choosing sealing materials according to operational requirements can improve sealing performance and service life. For example, high-temperature-resistant materials for high-temperature applications and corrosion-resistant materials for corrosive media. Elasticity and hardness of sealing materials also affect performance and must be reasonably selected.
Improve Manufacturing Precision: The precision of sealing component manufacturing directly affects sealing performance. Higher precision ensures tight contact and reduces leakage. Dimensions and surface roughness should be strictly controlled to maintain stable and reliable sealing.
Adopt Advanced Sealing Technologies: With technological progress, many advanced sealing technologies are applied in butterfly valve design and manufacturing. For example, spring compensation devices can automatically adjust gaps after surface wear to maintain sealing performance. Multi-layer sealing structures can improve reliability and durability. Using these technologies significantly enhances sealing performance.
The sealing performance of butterfly valves is the core factor in their critical role in industrial fluid control. From concentric to triple-offset butterfly valves, sealing structures and designs are continuously optimized to adapt to conditions ranging from low-pressure and ambient temperature to high-pressure and high-temperature operations. Sealing pair structure, contact pressure, medium physical properties, and sealing component quality are all crucial factors affecting sealing. By selecting appropriate sealing methods (hard-seal or soft-seal), optimizing sealing pair structures, choosing suitable materials, improving manufacturing precision, and applying advanced sealing technologies, butterfly valves can achieve reliable, efficient, and long-lasting sealing. Overall, butterfly valves are not only fluid control devices but also vital safeguards for the safe and stable operation of industrial systems. Their sealing principles and technological level directly determine the efficiency and reliability of industrial pipeline systems.
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