VALVE CONNECTION TYPES
Valves should be tightly connected to pipes to ensure a tight sealing. The most used types of pipe / valve connections are:
A flanged connection requires the use of two flanges with the related bolts, nuts and washers. Flanged connections are widely used in pipeline systems regardless the pressure and the bore of the valves and the connected pipes. Flanged connections are generally a cheap solution to join pipes with valves
In case of welded connections, the valve is welded directly onto the pipe. This type of connection is generally more expensive but ensures a good protection against leakages. Weld connections are used in high pressure pipelines and can be of two types, butt weld and socket weld (the valve has a socket and the pipe is welded therein, generally in case of pipelines below 2 inches of diameter).
In this case the valve is connected to the pipe by a thread (tapered thread). This type of connection is generally used for low pressure pipelines with bore size lower than 2 inches. It is also a very cheap connection, because no other material, then the pipe and the valve are necessary, and no flanges, no bolts and no weld operation are needed. In case of leakage, however, the repair chances are limited in case of threaded connections.