Welded valve

For large nominal diameter and high temperature, groove of body usually adopts welding. For strict requirements of welded seam, welding must be carried out by skillful welders.

 

Welded valve whose nominal diameter bellows 50mm usually uses welded socket to connect with flat pipes. Welded socket may cause cracks which may be corroded by medium between socket and pipes. Otherwise, vibration of pipes may cause fatigue of pipes. For that, the utilization of socket weld has limitation. 

 

Welded vale is applicable for different pressure and temperature. Welded valve is more reliable than flanged valve under harsh conditions. However, disassembly and reinstallation of welded valve are quite difficult. For that, welded valve is usually utilized under high pressure and temperature, such as thermal power, nuclear and ethylene. 

 

Screw valve

The nominal diameter of screw valve bellows to 50mm. If nominal diameter is too large, installation of connecting part is quite difficult. The ends of screw valve are processed into taper pipe or straight pipe thread so that can be connected to taper thread joint or pipes directly.

 

Screw valve may have large leakage channel. Sealant, sealing adhesive tape or packing are used to block channel. If materials of body can be welded, having great differences of coefficient of expansion or working temperature, connecting screws must be seal welded.

 

For installation and disassembly of screw valve, couplings are utilized in pipes. Valve whose nominal diameter bellows 50mm can use fitting union as coupling. The screws of fitting union connect two parts. 

 

Flanged valve

Flanged valve is convenient for installing and dismantling. However, flanged valve is heavier than screw valve and the price is high too. It is applicable for different pressure and temperature. When temperature is higher than 350℃, loosen of bolt, gasket and flange decrease load on bolt. Leakage may be caused if flange is stressed heavily.