JRVAL
Jul 31 2025Decoding Valve Specifications
A practical guide to understanding and converting butterfly valve pressure ratings (PN, Class, bar, MPa) and nominal sizes (DN, Inch). Select the right valve with confidence.
Pressure Ratings: PN vs. Class
Understanding pressure ratings is critical for safety and performance. While PN and Class both define a valve's pressure capacity, they are based on fundamentally different systems.
What is PN (Pression Nominale)?
PN is the European standard designation, derived from the French "Pression Nominale" (Nominal Pressure). It is a straightforward rating system where the number indicates the maximum allowable pressure in bar a valve can withstand at a nominal room temperature (e.g., 20°C). A PN16 valve is designed to handle 16 bar of pressure under these standard conditions. As the operating temperature increases, the pressure-handling capability of the valve decreases.
What is Class?
Class is the American standard designation, defined by ASME (American Society of Mechanical Engineers). Unlike PN, a Class rating (e.g., Class 150, Class 300) does not directly equal a specific maximum pressure. Instead, it represents a pressure-temperature curve. A Class 150 valve, for example, can handle approximately 19.6 bar at ambient temperature but only around 6.8 bar at 400°C. Therefore, Class is a more comprehensive rating that defines a valve's performance across a range of temperatures. The conversion between Class and PN is an approximation, as PN is a single point reference while Class is a curve.
Pressure Conversion Table
| ASME Class | Approx. European PN | Pressure (bar) | Pressure (MPa) |
|---|---|---|---|
| Class 150 | PN 20 | 20 bar | 2.0 MPa |
| Class 300 | PN 50 | 50 bar | 5.0 MPa |
| Class 400 | PN 68 | 68 bar | 6.8 MPa |
| Class 600 | PN 100 | 100 bar | 10.0 MPa |
| Class 900 | PN 150 | 150 bar | 15.0 MPa |
| Class 1500 | PN 250 | 250 bar | 25.0 MPa |
| Class 2500 | PN 420 | 420 bar | 42.0 MPa |
Note: 1 MPa (Megapascal) = 10 bar. These conversions are standard approximations for carbon steel valves at ambient temperature and should be used for general reference. Always consult the specific pressure-temperature chart for a given valve material and standard for critical applications.
Nominal Size: DN vs. Inch
Valve size defines its connection to the pipeline. The two primary systems, DN and Inch (NPS), are used globally and can be easily converted.
What is DN (Diamètre Nominal)?
DN is the metric standard, from the French "Diamètre Nominal" (Nominal Diameter). It represents the approximate inner diameter of the pipe connection in millimeters. It is a dimensionless number that standardizes pipe and valve sizes across the European system.
What is Inch (NPS)?
NPS, or Nominal Pipe Size, is the North American standard unit in inches. Similar to DN, it is a dimensionless number that refers to the nominal diameter. For NPS 12 and under, the NPS number is slightly larger than the actual inner diameter of the pipe. For NPS 14 and above, the NPS number is equal to the pipe's outside diameter in inches.
Size Conversion Table
| DN (mm) | Inch (NPS) | DN (mm) | Inch (NPS) |
|---|---|---|---|
| 15 | 1/2" | 900 | 36" |
| 20 | 3/4" | 1000 | 40" |
| 25 | 1" | 1050 | 42" |
| 32 | 1 1/4" | 1100 | 44" |
| 40 | 1 1/2" | 1200 | 48" |
| 50 | 2" | 1300 | 52" |
| 65 | 2 1/2" | 1400 | 56" |
| 80 | 3" | 1500 | 60" |
| 100 | 4" | 1600 | 64" |
| 125 | 5" | 1700 | 68" |
| 150 | 6" | 1800 | 72" |
| 200 | 8" | 1900 | 76" |
| 250 | 10" | 2000 | 80" |
| 300 | 12" | 2200 | 88" |
| 350 | 14" | 2400 | 96" |
| 400 | 16" | 2600 | 104" |
| 450 | 18" | 2800 | 112" |
| 500 | 20" | 3000 | 120" |
| 600 | 24" | 3200 | 128" |
| 700 | 28" | 3400 | 134" |
| 800 | 32" | 3600 | 142" |
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