Temperature and pressure ratings define the safe operating limits for industrial valves. Temperature rating specifies minimum and maximum operating temperatures. Pressure rating indicates maximum pressure at a given temperature. These ratings have an inverse relationship: as temperature rises, allowable pressure drops.
What Is the Pressure Rating of a Valve?
A valve pressure rating defines the maximum allowable working pressure (MAWP) the valve can withstand at a given temperature. This rating varies based on operating temperature and valve material. A valve rated for 285 PSI at ambient temperature may only handle 150 PSI at 250°C.
The valve pressure rating is always temperature-dependent because material strength decreases as heat increases. These ratings follow standards like ASME B16.34 for North American valves and EN 1092 for European valves.
Understanding Valve Class 300 Pressure Rating and Other Standards
Here are the different valve class ratings along with their descriptions:
ANSI Class Ratings
ANSI Class ratings are the primary pressure classification system in North America. Common classes include 150, 300, 600, 900, 1500, and 2500. The valve class 300 pressure rating does not mean 300 PSI. It refers to pressure-temperature charts in ASME B16.34. A Class 300 carbon steel valve handles approximately 740 PSI at ambient temperature but only 450 PSI at 400°C.
PN Ratings
PN (Pressure Nominal) ratings are common in European standards. These numbers indicate maximum allowable pressure in bar at 20°C. PN 50 means the valve handles 50 bar at reference temperature.
WOG Ratings
WOG (Water, Oil, Gas) ratings specify maximum pressure at ambient temperatures, typically -29°C to 38°C. A 600 WOG valve handles 600 PSI at room temperature.
| PN Rating | ANSI Class | Approximate PSI at Ambient |
| PN 20 | Class 150 | 285 PSI |
| PN 50 | Class 300 | 740 PSI |
| PN 100 | Class 600 | 1480 PSI |
| PN 150 | Class 900 | 2220 PSI |
| PN 250 | Class 1500 | 3705 PSI |
The Pressure-Temperature Relationship in Valves
The pressure rating of valves follows an inverse relationship with temperature. As operating temperature rises, maximum allowable pressure decreases because materials lose mechanical strength when heated. A Class 150 carbon steel valve rated for 285 PSI at 38°C drops to approximately 75 PSI at 260°C.
This relationship requires consulting pressure-temperature (P-T) charts specific to each valve material and class. You cannot apply the ambient temperature rating at high temperatures. Engineers must reference the exact P-T chart for the valve body material to determine safe operating pressure at maximum system temperature.
CTGV tests all valves under simulated high-pressure and temperature environments to ensure compliance with ANSI, API, and DIN pressure ratings.
How to Select the Right Pressure Rating of Valves
Follow these steps to select the correct valve pressure rating for your system:
- Identify maximum operating conditions: Determine the highest pressure and temperature the valve will experience, including pressure surges from water hammer or thermal expansion.
- Consult P-T charts: Reference the manufacturer’s pressure-temperature rating charts for the specific valve material and class you’re considering.
- Verify material compatibility: Ensure the valve body material is compatible with your process fluid, especially for corrosive or abrasive applications.
- Apply safety margin: Select a valve where your operating pressure stays at 80-90% of the rated capacity at operating temperature.
Conclusion
Valve pressure rating determines safe operating limits and decreases as temperature increases. The valve class 300 pressure rating and other ANSI classes provide standardized specifications.
CTGV tests all valves under simulated high-pressure and temperature environments to ensure compliance with ANSI, API, and DIN pressure ratings. Our valves maintain structural integrity from –196°C to +425°C, which is proven in LNG, chemical, and steam systems.
