Threaded connection : Usually made by machining the inlet and outlet of the valve into a tapered or straight pipe thread to connect to a tapered pipe threaded joint or line. Sealant, sealing tape, or packing can be used to block large leak channels because of the potential for such connections. If the material of the valve body is weldable, but the coefficient of expansion varies greatly, or the operating temperature varies in a wide range, the threaded joint must be sealed.

Threaded valve is mainly nominal pass in 50mm below. If the size is too large, the connection is difficult to install and seal.
To facilitate installation and removal of threaded valves, couplings can be installed in appropriate locations in the piping system. Valves with nominal sizes up to 50mm May use a sleeve joint as a joint to hold the two parts together.

Flanged connection: Flanged Connect valve, its installation and disassembly are more convenient. But heavier than threaded valves, the corresponding price is also high. Therefore, it is suitable for all sizes and pressures of pipe connection. However, when the temperature exceeds 350 degrees, the bolts, gaskets and flanges become relaxed, which also significantly reduces the load of the bolts, and may leak on the flange connections with great stress.

Butt Welded Connect valve. This type connection is suitable for all pressures and temperatures and is more reliable than flanged connect for use under higher load conditions. But welded connect valve disassembly and re - installation are more difficult, so usually can run reliably for a long time, suitable for conditions, high temperature occasions. Such as thermal power stations, nuclear engineering, ethylene engineering on the pipeline.

Welded valves with nominal sizes up to 50mm usually have a welded socket to load the pipe at the flat end. Because the socket welding between the socket and the pipe to form a gap, so it is possible to make the gap by some medium corrosion, at the same time, the vibration of the pipe will make the connection part fatigue, so the use of socket welding is limited to a certain extent.

Nominal diameter is large, the use of conditions, high temperature occasions, the valve body often use groove welding, at the same time, welding joints have original requirements, must choose a good technology welder to complete the work.