1. Standard pressure rating range
The nominal pressure (PN) rating of ductile iron valves usually covers PN10 to PN40, including PN10 (1.0MPa), PN16 (1.6MPa), PN25 (2.5MPa), PN40 (4.0MPa), etc.17. Its maximum allowable working pressure depends on the combination of material grade and working temperature (such as QT400-15, QT450-10, etc.).
2. The influence of temperature on pressure rating
Normal temperature conditions (-30℃~200℃):
PN10/P16 valves can maintain nominal pressure under QT400-15 material, and PN40 (4.0MPa) is the maximum nominal pressure limit of ductile iron valves;
When the temperature rises to 150℃, the allowable pressure of PN16 valves made of QT450-10 material drops to 1.55MPa (about 3% reduction).
High temperature limit (200℃~350℃):
When the temperature reaches 300℃, the maximum allowable working pressure of the PN16 valve made of QT600-3 material drops to 0.7MPa (a drop of 56%);
When the temperature exceeds 350℃, it is recommended to use cast steel or stainless steel valves.
3. Material and pressure adaptability
QT400 series (QT400-15/18):
Adapt to PN10-PN25 levels, suitable for low-pressure scenarios such as normal temperature water supply and fire protection;
QT500/600 series (QT500-7, QT600-3):
Support PN40 high pressure level, but the temperature needs to be controlled ≤200℃ to maintain strength.
4. Typical application scenarios
Municipal engineering:
PN10-PN16 valves are widely used in urban water supply and drainage networks (DN50-DN1200), adapting to normal temperature and pressure requirements;
Industrial system:
PN25-PN40 valves are used for sewage treatment or low-pressure steam pipelines containing sediment media, and need to be matched with a galvanized layer to enhance corrosion resistance.
5. Selection recommendations
For medium containing particles, PN16 or above valves are preferred to avoid pressure leakage caused by wear of the sealing surface;
For high temperature conditions (＞200℃), the allowable pressure attenuation value of the material needs to be calculated, and if necessary, it should be upgraded to cast steel valves.