It is the responsibility of the valve manufacturer to establish the pressure ratings for their products. The design professional should consult the manufacturer's published information and not assume it is the same as the flange or fitting being bolted to it.However, the pressure ratings of many ANSI/ASME B16.x flanged valves used in waterworks service are defined in AWWA standards applicable to that type of valve. The pressure rating (or Pressure Class) listed in the AWWA valve standard may or may not conform to the ANSI/ASME B16.x or the AWWA C110 pressure rating, leading to even more confusion.The AWWA "valve" standards which define a Pressure Class or pressure rating are too numerous to detail in this commentary but include C500 gate valves, C504 butterfly valves, C507 ball valves, C508 check valves and C517 eccentric plug valves. The design professional should become familiar with the applicable AWWA valve standard and select the pressure class that is adequate for the working pressure and be aware that the valve's pressure class and connection flange class may not correspond.One should remember that "a chain is only as strong as its weakest link" so every component of a piping system should be able to withstand the highest pressure that could be realized at the location where it is installed.It's hoped the above sheds some light on the pressure ratings for flanges and flanged valves. GA Industries LLC factory engineers will be happy to provide assistance on any specific application involving our valves.
Curtis has indeed provided some generally good historical information. Actually, it is also kind of hard to divorce the chosen gasket style (and maybe even bolts) also from the Pneumatic and electric  diaphragm pump discussion of flanges, ratings and pressure etc. In this regard, I think in 2003 AWWA added a forward and footnote to many tables with regard to AWWA ductile iron flanges only (I think which are generally flat-faced) to the effect, "The scope of the standard was amended and Tables 12 and 15 through 19 were footnoted to recognize that 24-in. (610-mm) and smaller flanged fittings may be rated for 350 psi with the use of specially designed gaskets, either ring or full-face, using annular rings molded into the gasket to improve performance as recommended by the manufacturer." This rating, with the use of such special gaskets only, of course matches the maximum standard 350 psi pressure rating of AWWA ductile iron pipes (though manufacturers can be/and have been consulted for higher pressure requirements).      
 

2011-08-24

Back