The steel valve end connections structure and size of the valve end are essential for the normal installation and use of the valve. If improperly selected, it may cause the size or connection structure to be mismatched during the installation process, resulting in the valve not being installed.
Special attention should be paid when selecting the valve. The valve end connection structure should be selected correctly and properly to ensure the smooth installation and use of the valve.
The connection form of the steel valves connection is usually divided into:
- Threaded connection
- Flanged connection
- Welded connection
- Clamped connection
- Card sleeve connection structure
#1 Valve End Connections: Threaded connection
Threaded connections are detachable. Most of them are not suitable for welding or need to be disassembled.
Threaded connections for >DN50 can be used for non-hazardous fluids, but the connection is not easy to control and it is difficult to apply enough without damaging the components. The torque is used to tighten the joints, so the threaded connections are mostly used in pipes with ≤ DN50 without hazardous fluids.
The threaded connection is divided into two types: internal thread connection and external thread connection. The structure is divided into straight pipe thread and taper pipe thread.
The internal thread connection usually processes the end of the valve body into a taper pipe thread or a straight pipe female thread, and the pipe connected thereto is processed into a taper pipe thread or a straight pipe male thread.
The external thread connection is a valve that processes the end of the valve body into a male thread for easy installation and removal of the threaded end. Sealants, sealing tapes or fillers can be used to block these channels due to the large leakage channels that may occur with such connections. If the material of the valve body is weldable, it can be sealed after screwing.
Straight pipe threads are used for some separate sealing, straight pipe threads form a mechanical connection and provide a suitable position for sealing and compression sealing forces
Taper pipe threads are mainly used in process production, and process seals are accomplished by the locking action of tapered threads.
#2 Valve End Connections : Flange connection structure
For pipes > DN50, flanges are the most common connection method. Flanged valves are easy to install and disassemble, and the nominal size and nominal pressure are very wide.
The flange connected to the valve can be divided into flat welding flange, butt welding flange, socket welding flange, integral flange, etc.; according to the sealing surface form, it can be divided into full plane flange, protruding surface flange, bump Face flange and ring connection face flange. The choice of various flange constructions and sealing surface forms depends on the various operating conditions.
Generally, when the customer has no special requirements, the connecting flange of the valve is cast together with the valve, which is called integral flange, and is also the most commonly used in flange connection;
Because of the low structural strength and rigidity, flat welding flanges are often used under mild conditions, such as low-pressure circulating water valves, general low-pressure compressed air valves, etc., which have the advantages of low price and convenient installation;
The use of threaded flanges should not exceed DN150. The applicable working conditions are similar to those of flat welded flanges. However, the sealing and accurate positioning of threaded flanges is difficult to achieve. Therefore, when there is no leakage in the pipeline requirements, the threads and flange are generally not considered
It is common to insert welds in small-sized flanges that are easy to install and weld, but not for toxic fluids because they are difficult to detect by radiographic flaws and cannot be used to cause corrosion or Fluid piping causing corrosion problems, commonly used in pipelines with no hazardous fluids less than or equal to PN100 and less than or equal to DN50
The welded flange has a good strength and rigidity of the transition structure of the neck, can be welded to the pipe and is easy to be detected by radiation, so that it has a very high integrity, so it can be applied to occasions where the working conditions are relatively engraved. Such as oil and gas and chemical media.
Fully flat flanges are typically used in low pressure cast iron, cast steel or non-metallic valves.
The face flange can achieve a good sealing effect under medium and low pressure conditions. Therefore, the medium and low pressure valves mostly use protruding flanges when the customer has no special requirements.
The concave-convex flange is a flat gasket installed in the sealing surface of the concave flange, which is easy to disassemble. The disadvantage is that the gasket is easy to contact with the medium, and is easily washed and deformed by the medium under high pressure, and the sealing effect cannot be achieved. When designing and manufacturing, it can be properly added to the inner and outer rings, and the inner and outer sides according to actual needs to improve the sealing effect.
The ring joint flange is a ring-shaped soft metal ring gasket placed in two flanges with annular grooves. The gasket is slightly deformed to seal. It is widely used for high pressure and toxic fluid pipeline
#3 Valve End Connections : Welded end connection structure
Such as fully welded ball valve for oil, gas applications.
This construction is suitable for a wide range of pressures and temperatures and is more reliable than flanged connections when used under harsh conditions.
However, it is difficult to disassemble and reinstall the valve of the welded joint, so its use is limited to the occasion that it can usually operate reliably for a long time, or when the conditions are high and the temperature is high. Such as thermal power stations, nuclear power engineering, and ethylene engineering pipelines.
For DN50, thin-walled pipe welded valves typically have welded sockets to receive pipes with flat ends. However, since the socket welding forms a gap between the socket and the pipe, it is possible to cause the gap to be corroded by some media, and the vibration of the pipe may cause the joint to be fatigued, so the use of socket welding is also limited.
#4 Valve End Connections : Clamp connection structure
The clamp connection structure has a unique flexibility to make the pipeline resistant to vibration, shrinkage and expansion.
Compared with welded and flanged connections, the stability of the piping system is increased and it is better able to withstand the fatigue caused by vibrations, and is more suitable for temperature changes, thus protecting the pipeline components and reducing the stress on the piping destruction.
The operation is simple, the required operation space is small, and the maintenance is convenient. It is widely used in extreme operating conditions such as district heating, sanitary conditions and rapid disassembly.
#5 Valve End Connections : Card sleeve connection structure
The ferrule connection feature relies on the cutting edge of the ferrule to tightly bite the wall of the steel pipe so that the high pressure fluid in the pipe is completely sealed. The connection structure has the advantages of connection fastening, impact resistance, good vibration resistance, convenient maintenance, high fireproof and explosion proof, high pressure resistance, good sealing performance, etc., and is a kind of advanced connection for power station, oil refining, chemical equipment and instrument measuring pipeline.