Valves are indispensable control elements in fluid piping systems, and they can be connected to pipelines in various ways to suit different application scenarios and fluid properties. Below are some common valve connection methods along with their brief descriptions:
Valves are connected to piping systems through flange connections, which are suitable for high-temperature, high-pressure, and large-diameter piping systems. Flange connections use paired flanges and bolt fasteners to secure the valve to the pipeline, providing a strong connection and excellent sealing performance. This method is particularly suitable for extreme conditions such as high pressure, high temperature, and corrosive media. Flange connections are easy to disassemble and repair, making maintenance and valve replacement convenient. However, installing flange connections requires a significant number of bolts and nuts, leading to higher installation and maintenance costs.
Additionally, flange connections are relatively heavy and occupy more space. The standards for flange connections mainly include the following aspects: According to the shape of the connection surface and the sealing structure, flanges can be divided into flat welding flanges, butt welding flanges, and loose set flanges. The size of the flange is usually expressed in terms of the nominal diameter (DN) of the pipeline, and flange sizes may vary across different standards. The pressure rating of a flange connection is typically indicated by PN (European standard) or Class (American standard), with different ratings corresponding to different working pressures and temperature ranges. The sealing surface of flanges can take various forms such as flat face, raised face, concave-convex face, and tongue-and-groove face, and the appropriate sealing surface form should be chosen based on the nature of the fluid and sealing requirements.
Thread connections use internal and external threads to tightly screw the valve into the pipeline, mainly applicable to small-diameter and low-pressure piping systems. Thread connections are simple to execute and easy to operate, without requiring special tools or equipment. They are suitable for connecting small-diameter valves to low-pressure pipelines, offering a cost-effective solution. However, thread connections have relatively poor sealing performance and are prone to leakage. They are only suitable for low-pressure and low-temperature conditions, and may not meet the requirements for high-pressure or high-temperature environments. Thread connections are primarily used for small-diameter valves and low-pressure piping systems, with standards including the following aspects: Commonly used thread types include pipe thread, taper pipe thread, and NPT thread. The appropriate thread type should be chosen based on the pipe material and connection requirements. The thread size is usually expressed in terms of the nominal diameter (DN) or pipe diameter (inches), with sizes varying across different standards. To ensure a tight seal, threads are usually treated with sealants or wrapped with sealing tapes.
Welded connections involve directly welding the valve to the pipeline through a welding process, which is suitable for scenarios that require high sealing and a permanent connection. Welded connections provide high connection strength and excellent sealing performance, and are corrosion-resistant, making them suitable for permanent and high-sealing scenarios such as in the petroleum and chemical industries. However, welded connections require specialized welding equipment and skilled operators, resulting in higher installation and maintenance costs. Once welding is completed, the valve and pipeline form a single unit, making disassembly and repair difficult. Welded connections are suitable for scenarios requiring high sealing and a permanent connection, with standards mainly including the following aspects: Common weld types include butt weld and fillet weld, and the appropriate weld type should be chosen based on pipe material, wall thickness, and connection requirements. The choice of welding process should be based on factors such as the parent material, thickness, and welding position to ensure welding quality and connection strength. After welding is completed, necessary inspections and tests, such as appearance inspections and non-destructive testing, should be conducted to ensure welding quality and sealing integrity.
Socket connections involve one end of the valve having a socket into which the pipe is inserted and sealed, commonly used in plastic piping systems. Socket connections provide a secure way to connect plastic pipes and are easy to install and disassemble. However, this type of connection is only suitable for specific types of plastic pipes and low-pressure applications.
Clamp connections, also known as groove connections, use a clamping device on both sides of the valve to secure it to the pipeline, suitable for quick installation and dismantling occasions. Clamp connections are quick and easy to install and dismantle, suitable for low-pressure applications that require frequent maintenance. They require minimal tools and are ideal for low-pressure systems. However, clamp connections are less robust than other methods and not suitable for high-pressure environments.
Ferrule connections are typically used in plastic piping systems, utilizing special ferrule tools and tube fittings to connect the pipeline and valve. Ferrule connections are easy to install and remove, suitable for plastic pipes and low-pressure applications. They are cost-effective and adaptable to various types of piping systems, but are limited to plastic materials and low-pressure systems.
Bonding connections are mainly used in some non-metallic piping systems, such as PVC or PE pipes. Pipes and valves are bonded together using special adhesives to form a permanent connection. Bonding connections provide a strong and durable connection for plastic pipes, making them ideal for non-metallic piping systems. They are cost-effective but, being permanent, are not easily removable and are only suitable for specific types of pipes and adhesives.
In summary, choosing the appropriate valve connection method is crucial for ensuring the safe and reliable operation of the valve and piping system. When selecting a connection method, factors such as pipeline material, working pressure, temperature range, installation environment, and maintenance requirements should be considered. During installation, it is essential to follow relevant standards and guidelines to ensure the correctness of the connection and sealing, thereby ensuring the normal operation of the fluid piping system.
