Published by: Valve Test Bench
 

Valve Nominal pressure PN and subsequently followed by the letters of the integer numbers. Piping system components with the mechanical properties and size-related features.
    In our country, involving nominal pressure, in order to clarity, it is usually given in units of measurement, in order to "MPa" said.
In the United States, Britain and some European countries, despite the current in the standard has been included in the concept of nominal pressure PN, but the actual applications still use the U.S. customary (English) units of the pressure-tier system (CL), said. Nominal pressure and stress levels due to the temperature of the base is different from the order that there is no strict correlation.
Valve end connections
Valves are available in various forms of end connected with the pipeline. The most important methods are threaded flange connections and welding connections.
(1) The screw connection threaded connection is usually fair share two kinds of thread and external thread connection. Internal thread connection is usually processed into the valve on the tube or straight tube cone Yam threads, the tube processed into cone-tube or straight tube male to make it into the valve on the rotation. Because of this connection may be greater the leakage channel, it can be brought about filling the channel seal. If the valve body material is weldable, and can also be carried out in the thread after the close air and naval welded connection. If the connection is to allow welding material components, but very different expansion coefficients, or the operating temperature range are larger, then the screw connection must be Tightlock Department of welding. External screw connection is designed to facilitate installation and removal of thread end of the valve, in the body of the pipe end with external thread connection with the pipe joints, pipe connectors and then connect with the pipeline welding.
(2) The flange valve flange connection, installation and removal are more convenient. However, appear more cumbersome than the threaded connection. As the flange connection is tied to by a number of screw fastening, while tied to a single screw fastening torque required to thread than the corresponding connection is small, it is applicable to the nominal size and nominal pressure wide. But when the temperature exceeds 350 ℃ (660F), due to bolts, gaskets and flange creep relaxation at any time will be significantly lower bolt load, when high temperature bolt material should be selected.
    National standards can provide a variety of flange flange design of the structure of design structure, and gives corresponding flange sealing surface in the form and surface roughness values, according to the level of work pressure can choose the form of flange sealing surface. Fine dentate flange sealing face of the soft gasket effective. Metal gaskets need to lower surface roughness value of the flange sealing surface to get better results. Metal ring connections for the higher working pressure.
    (3) welded end connections welded connections for a variety of pressures and temperatures. At higher temperatures and more stringent conditions used, more reliable than the flange. But the welded connection of the valve replacement of the demolition and re-installation is more difficult, so its use is limited to typically long-term reliable operation, or use under harsh conditions and higher temperatures occasions.
Nominal size DN in 50mm (2in) below the welded connection of valves usually have welded socket to take over with a flat side of the pipe. As in the socket and the pipe socket weld formed between the cracks, and thus has the potential to crevice corrosion by certain media. While the vibration of pipeline will connect the Department of fatigue. Therefore, the use of socket welded connections subject to specification limits.