A Quick Guide to End Connections
Here is a quick reference guide to typical end connections.
The following is a list of the most common end connections for valves:
ANSI Flanges — are connections that do not have threads, but rather a rim at the end of a pipe or valve for a bolted connection to a corresponding rim at another pipe or valve. They are useful for quick and easy removal from the line. There are various rating classes such as 125#, 150#, 300#, 600#, 900#, 1500# that cover a wide range of operating pressures and temperatures. One note: an ANSI 300# rating can accept pressures above 300 psi at certain temperatures, so the rating does not necessarily indicate the absolute maximum pressure limit.
FNPT — Female National Pipe Tapered is a typical connection in sizes 2” and smaller for most applications in the USA and US-influenced areas. Compared to other thread types, NPT is particularly useful in steam applications where they provide excellent leak resistance for a threaded connection.
BSPT — British Standard Pipe – Tapered is similar to NPT. This tapered thread has a slight concentricity to it allowing the pipe to seal ever tighter the more it is threaded into the valve. It is common in the UK and Europe in smaller line sizes (2” or smaller).
BSPP – British Standard Pipe – Parallel – a parallel thread that allows for the pipe to be threaded completely into the valve until coming to a mechanical stop. Unlike the tapered thread, it does not seal as it is threaded deeper into the valve, relying instead on seals and ring nuts to produce a pressure tight joint.
Union Ends — are connections that allow for quick removal of the valve from the pipe via a coupling which does not require rotating the pipe or the valve for installation or removal.
DIN Flanges — in various ratings such as DN10/16/25/40/100, the DIN standard is very popular in Europe, and is the standard in Germany. The Deutche Institut fuer Normen (DIN) rates these according to the bar unit of measure. Slightly different than the ANSI in dimensions, the DIN rating is the maximum rating. DN100 corresponds to a 100 bar maximum pressure rating.
Tri-Clamp® —The most common form of mechanical joining for pipes, valves, and fittings in the Food, Dairy, Beverage, and Life Sciences industries. These connections allow for a quick disconnection of the valve from the line via a clamp. Incorporating a gasket seal, they also provide good leak prevention. Ideally, a Tri-Clamp connection will have identical ID dimensions with the clamp connection of the
pipe to ensure a sanitary or sterile area.
Buttweld — Chamfers are machined on the ends of the valve to “butt” against matching chamfers on the pipe in the system. The chamfered ends of both pipe and valve form a “V” groove to accommodate welding. Often used in large valves or high-pressure applications, the buttweld connection does not allow for easy removal of the valve from the line.
Socketweld — A valve or fitting which slips over the end of pipe and is made pressure-tight by welding. This connection is often used on smaller valves, up to 2”.
RTJ Flanges — Ring Type Joint – These flanges have a groove in the raised face that uses a special soft metal ring which serves as a gasket for sealing. Often applied to higher pressure applications.