PN-10, PN-16, PN-25, PN-40 — what these numbers actually mean, why they're not the same as ANSI Class, and how temperature affects the maximum allowable working pressure.
What Does PN Actually Mean
PN stands for "Pression Nominale" (French) or "Pressure Nominal." It's the European pressure rating standard defined by ISO 7268 and used in EN 1092-1 flange specifications. The number that follows is the maximum working pressure in bar at 20°C with water as the test fluid.
So a PN-16 valve is rated for 16 bar (≈232 psi) at room temperature with water. Simple in concept, but with two important caveats: temperature derating and fluid compatibility.
The most common ratings encountered in UAE projects:
- PN-6: 6 bar — low-pressure water distribution, irrigation
- PN-10: 10 bar — standard for HVAC chilled water and basic plumbing
- PN-16: 16 bar — workhorse rating for HVAC, building services, drinking water mains
- PN-25: 25 bar — high-rise plumbing risers, light industrial
- PN-40: 40 bar — steam, high-pressure water, light process
- PN-63 / PN-100: Heavy industrial, oil & gas (less common)
Temperature Derating
The PN number is the rating at 20°C. As temperature increases, the metallurgy weakens and maximum pressure drops. For brass valves, the derating curve is steep — by 120°C a PN-25 valve can typically only handle around 16 bar safely.
Rough derating multipliers for common materials:
| Material | at 20°C | at 100°C | at 150°C | at 200°C |
|---|---|---|---|---|
| Brass CW602N (DZR) | 1.00 (full PN) | 0.80 | 0.65 | not rated |
| Stainless AISI 316 | 1.00 | 0.92 | 0.85 | 0.78 |
| Carbon steel WCB | 1.00 | 0.95 | 0.88 | 0.80 |
| Ductile iron GGG-40 | 1.00 | 0.85 | 0.70 | not rated |
For UAE applications, the relevant takeaway is for hot water systems: a PN-25 brass valve operating at 90°C in a domestic hot water riser has an effective pressure rating closer to 21 bar, not 25 bar. Always size with the derated value, not the nameplate.
PN vs ANSI Class — Not Interchangeable
One of the most common specification errors in mixed-source projects (where US-spec equipment meets European-spec piping) is treating PN and ANSI Class as equivalent. They're not — they use different reference temperatures, different test methods, and different bolt circle dimensions.
Approximate (NOT exact) equivalence:
| PN (bar) | ≈ ANSI Class | ≈ psi at 20°C |
|---|---|---|
| PN-10 | — | 145 |
| PN-16 | Class 150 (sort of) | 232 |
| PN-25 | Class 150 (closer) | 362 |
| PN-40 | Class 300 | 580 |
| PN-63 | Class 400 | 914 |
| PN-100 | Class 600 | 1450 |
The problem is the bolt circles. A PN-16 DN100 flange (EN 1092-1) has a different bolt circle diameter and bolt count than an ANSI Class 150 4-inch flange. They will not mate. If your project has both standards, you need transition spools or universal flanges.
MT supplies Universal-flanged butterfly valves (the 5114 series) which can bolt to either PN-10/16 or ANSI Class 150 flanges, eliminating this transition headache for most HVAC applications.
Selecting PN for UAE Projects
Quick reference for typical UAE applications:
- Domestic plumbing (cold water): PN-10 sufficient, PN-16 commonly specified
- Domestic plumbing (hot water 60-90°C): PN-16 minimum, PN-25 preferred for high-rise
- HVAC chilled water (5-12°C): PN-10 or PN-16 — derating not relevant at low temp
- HVAC condenser water: PN-16
- HVAC hot water heating (60-95°C): PN-16 minimum
- District cooling primary loops: PN-16, PN-25 for tall towers
- Drinking water mains (DEWA/ADWEA): PN-16 or PN-25
- Steam (saturated up to 6 bar / 165°C): PN-25 minimum, PN-40 recommended
- Compressed air (10 bar): PN-25
Need help with your project? Our engineering team in Dubai can review your spec and propose suitable MT references within 24 hours. Contact sales@mtmiddleeast.com or browse our product configurator.