Connecting the valve to the pipeline

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The correct and appropriate selection of the connection method between the valve and the pipelines or equipment directly affects the likelihood of leakage occurring in the pipeline valves. Common connection methods for valves include flange connection, clamp connection, butt welding connection, threaded connection, sleeve connection, band clamping connection, self-sealing connection, and other such connection types. First, flange connection: In this type of connection, the valve body has flanges at both ends, which correspond to the flanges on the pipes; the flanges are then fixed in place within the pipes using bolts. Flange connection is the most commonly used connection type in valves. Flanges come in various types such as raised face (RF), flat face (FF), and male-female face (MF). Based on the shape of the joint surface, they can be further classified as follows: (1) Smooth type: used for valves under low pressure. It is relatively easy to process ； (2) Rippled type: Higher operating pressure; medium-hard gaskets can be used ； (3) Mortise-and-tenon type: It can use washers with significant plastic deformation, is widely used in corrosive media, and provides good sealing performance ； (4) Trapezoidal groove type: An oval metal ring is used as a washer; it is applied to valves with a working pressure of ≥64 kilograms per square centimeter, or to high-temperature valves ； (5) Lens type: The washer is lens-shaped and made of metal. Used for high-pressure valves with a working pressure of ≥100 kg/cm², or high-temperature valves ； (6) O-ring type: This is a relatively new type of flange connection that has developed with the advent of various rubber O-rings; it offers more reliable sealing performance compared to ordinary flat gaskets. Second, the butt-connected type: The valve is installed between two flanges; the valve body usually has positioning holes to facilitate installation and alignment. This connection method involves using bolts to fasten the valve together with the pipes at both ends. Third, Welding Connections: (1) Butt welding connection: The ends of the valve body are prepared with butt welding grooves that correspond to those of the pipeline, and they are fixed to the pipeline through welding. (2) Socket welding connection: The ends of the valve body are processed in accordance with socket welding requirements, and it is connected to the pipeline through socket welding. Fourth, threaded connection: A threaded connection is a simple method of joining, commonly used for small valves. The valve body is manufactured in accordance with various thread standards, and comes in two types: internal threads and external threads. Corresponds to the threads on the pipe. Threaded connections come in two types: (1) Direct sealing: The internal and external threads serve as a seal directly. To ensure that the joints do not leak, lead grease, hemp rope, and PTFE tape are often used for sealing ； Among them, polytetrafluoroethylene gasketing is being used more and more widely ； This material has excellent corrosion resistance and superior sealing properties; it is easy to use and store. When removed, it can be taken off completely, as it is a non-stick film, making it far better than lead paint or hemp rope. (2) Indirect sealing: The force generated by tightening the threads is transmitted to the gasket between the two surfaces, allowing the gasket to perform the sealing function. There are five main categories of common threads: (1) Metric ordinary threads ； (2) Imperial standard thread ； (3) Threaded seal pipe threads ； (4) Non-threaded sealing pipe threads ； (5) American standard pipe threads. The summary is as follows: ① The international standards ISO228/1 and DIN259 specify internal and external parallel threads, denoted as G or PF (BSP.F) ； ②German standards ISO 7/1, DIN 2999, BS 21: external tapered threads and internal parallel threads, designation BSP.P or RP/PS ； ③British standards ISO7/1, BS21: internal and external tapered threads, designated as PT or BSP, Tr or Rc ； ④The American standard ANSI B21 specifies internal and external tapered threads; the codes NPT G(PF), RP(PS), and Rc(PT) are used. The thread angle for these is 55°, while the thread angle for NPT is 60°. BSP.F, BSP.P, and BSP.Tr are collectively referred to as BSP threads. American standard pipe threads include five types: the general-purpose tapered pipe thread NPT, the straight pipe internal thread NPSC for pipe fittings, the tapered pipe thread NPTR for guide rod connections, and the straight pipe threads NPSM (loose-fit mechanical connections) and NPSL (tight-fit mechanical connections with lock nuts) for mechanical connections. It belongs to non-threaded sealing pipe threads (N: American **standard ； P: Pipe ； T: Tapered) Fifth – Collar connection. This type of connection has only become popular in China in recent years. Its principle of connection and sealing is such that when the nut is tightened, pressure is applied to the collar, causing its cutting edges to bite into the outer wall of the pipe; meanwhile, the external tapered surface of the collar fits tightly against the internal tapered surface of the fitting under this pressure, thereby ensuring reliable leakage prevention. Such as instrument valves. The advantages of this type of connection are: (1) small size, light weight, simple structure, and easy assembly and disassembly ； (2) Strong bonding strength, wide range of applications; can withstand high pressure (1000 kilograms/square centimeter), high temperatures (650°C), and shock vibrations ； (3) Various materials can be used, making it suitable for corrosion prevention ； (4) The requirements for processing precision are not high ； (5) Easy to install at high heights. At present, the ferrule connection type has been adopted in some small-diameter valve products in China. Sixth: Clamp connection. This is a quick connection method that requires only two bolts, and it is suitable for low-pressure valves that are frequently disassembled. Such as sanitary valves. 7. Internal self-tightening connections: All of the aforementioned connection types rely on external forces to counteract the pressure of the medium and thus achieve sealing. Next, a connection type that utilizes medium pressure for self-tightening will be introduced. Its sealing ring is located at the inner cone, at an angle to the side facing the medium. The pressure of the medium is transmitted to the inner cone, which in turn passes it on to the sealing ring. On the conical surface at this angle, two forces are generated: one that pushes outward parallel to the center line of the valve body, and another that presses against the inner wall of the valve body. The latter component of force is the self-tightening force. The greater the medium pressure, the greater the self-tightening force. Therefore, this type of connection is suitable for high-pressure valves. It saves a lot of material and labor compared to flange connections, but it also requires a certain degree of pre-tensioning in order to function reliably when the pressure inside the valve is not high. Valves made using the self-sealing principle are generally high-pressure valves. There are many other ways in which valves can be connected; for example, some small valves do not need to be removed and are welded directly to the pipes ； Some non-metallic valves use socket-type connections, among others. Valve users should handle the situation according to specific circumstances. Note: (1) All types of connection methods must comply with the relevant standards; it is necessary to clearly understand the standards required by the user to avoid situations where the selected valves cannot be installed. (2) Generally, large-diameter pipes are connected to valves using flange connections, while small-diameter pipes are connected to valves using threaded connections.