Piping Class Ratings - Classes and Pressure Numbers (PN)
Piping Class Ratings based on ASME B16.5 and corresponding PN (Pression Nominal/Pressure Nominal):
|Flange Pressure Nominal, PN||20||50||68||100||150||250||420|
Pressure Nominal is the rating designator followed by a designation number indicating the approximate pressure rating in bars.
1 bar = 1x105 Pa (N/m2) = 0.1 N/mm2 = 10,197 kp/m2 = 10.20 m H2O = 0.98692 atm = 14.5038 psi (lbf/in2)
PN ratings do not provide a proportional relationship between different PN numbers, whereas class numbers do. Class numbers are therefore recommended before PN ratings.
Size Conversion Table - NPS to DN to OD
The following table can be used to convert NPS (nominal pipe size) to DN (diameter nominal) and to OD (outside diameter in mm). Engineers typically use NPS; however the three are interchangeable in terms of valve applications.
Contact - The Valve Pipeline
Forged valves usually cost more but you don't need to worry about bad castings i.e. porous castings.