How to Read Valve Markings: WOG, WSP, PN, Class Explained
Valve markings look like a confusing code at first — WOG, WSP, PN16, Class150, CF8M… But once you understand what they mean, you’ll know exactly what a valve is rated for and whether it fits your application. As a valve manufacturer with 20+ years of experience, we’ll break down every common valve marking in simple terms.
1. WOG: Water, Oil, Gas
WOG stands for Water, Oil, Gas — it tells you the maximum pressure the valve can handle at room temperature (typically 70°F / 21°C). The number after WOG is the pressure in PSI.
| Valve Marking | Meaning | Common Applications |
|---|---|---|
| 150 WOG | 150 PSI at room temp | Low-pressure water, HVAC |
| 1000 WOG | 1000 PSI at room temp | General industrial, compressed air |
| 2000 WOG | 2000 PSI at room temp | Hydraulic, high-pressure process |
| 3000 WOG | 3000 PSI at room temp | Oil & gas, high-pressure systems |
Important: WOG is only for room temperature. If you’re using hot water or steam, you need to look at the WSP rating instead.
2. WSP: Working Steam Pressure
WSP stands for Working Steam Pressure — it tells you the maximum pressure the valve can handle with steam at high temperatures. This is always much lower than the WOG rating, because steam weakens the valve material.
| Valve Marking | Steam Pressure Rating | Temperature Range |
|---|---|---|
| 150 WSP | 150 PSI steam | Up to +200°C / 392°F |
| 200 WSP | 200 PSI steam | Up to +250°C / 482°F |
| 300 WSP | 300 PSI steam | Up to +300°C / 572°F |
Rule of thumb: For every 50°C (122°F) increase in temperature, the pressure rating of a steel valve drops by about 20-30%.
3. PN: European Pressure Rating
PN stands for Pression Nominale (Nominal Pressure) — it’s the European (DIN/EN) standard for pressure ratings, measured in bar.
| PN Rating | Equivalent PSI | Common Use |
|---|---|---|
| PN10 | 145 PSI (10 bar) | Water treatment, HVAC |
| PN16 | 232 PSI (16 bar) | General industry, most common |
| PN25 | 362 PSI (25 bar) | Process industry, chemical |
| PN40 | 580 PSI (40 bar) | High-pressure process, oil & gas |
4. Class: American Pressure Rating
Class (also called “Lb” or “Rating”) is the American (ANSI/ASME) standard for pressure ratings. Unlike PN, Class is not a direct bar/PSI conversion — it’s a pressure-temperature class.
| Class Rating | Equivalent PN | PSIG at Room Temp |
|---|---|---|
| Class 150 | PN20 (approx PN16) | 285 PSI |
| Class 300 | PN50 (approx PN40) | 740 PSI |
| Class 600 | PN100 | 1480 PSI |
| Class 1500 | PN250 | 3705 PSI |
Quick reference: For most general industrial use, Class 150 ≈ PN16, and Class 300 ≈ PN40. This is close enough for most applications.
5. Other Common Valve Markings
Besides pressure ratings, you’ll also see these markings on valve bodies:
| Marking | Meaning | What It Tells You |
|---|---|---|
| WCB | Carbon Steel Body | General purpose, oil & gas, water |
| CF8 / CF8M | Stainless Steel (304 / 316) | Corrosion resistant, food/pharma |
| API 608 | Ball Valve Standard | Oil & gas industry certified |
| EN 593 | Butterfly Valve Standard | European standard for butterfly valves |
| CE | European Conformity | Meets EU safety standards |
How to Read a Valve Nameplate
A typical valve nameplate will have all the information you need to identify the valve:
Example: 2″ CF8M Ball Valve, PN16, RF Flanged, API 608, CE
This means: 2 inch size, 316 stainless steel body, 16 bar pressure rating, flanged ends, meets API 608 standard, CE certified.
Not sure which valve rating you need? Tell us your application — we’ll help you choose the right valve within 24 hours.