Valve Pressure & Temperature Ratings Reference Chart | Apex Flow

A valve's nameplate pressure is not a single number that applies everywhere — it is the rating at one reference temperature, and it drops as the system gets hotter. Misreading a valve's pressure-temperature rating is one of the most dangerous errors in piping, because a valve rated 1,000 PSI at room temperature may be good for only a fraction of that in hot service. This reference explains WOG and WSP ratings, ASME pressure class, and how to derate by temperature and material so you specify with a safe margin.

Apex Flow Solutions supplies valves across brass, stainless, and PVC with published pressure-temperature ratings. Use this chart to read those ratings correctly.

Operating at elevated temperature?

Pressure ratings derate with heat, and steam ratings are far lower than WOG. Contact our team with your pressure and temperature and we will confirm the right pressure class.

WOG vs WSP Ratings Explained

WOG stands for Water, Oil, Gas, and is the non-shock pressure rating at ambient temperature (typically 100°F / 38°C). A valve stamped "600 WOG" handles 600 PSI of cold, non-shock water, oil, or gas. WSP (also seen as SWP) stands for Working Steam Pressure — the rating in saturated steam service. Because steam combines high temperature with pressure, the WSP rating is always much lower than the WOG rating on the same valve; a common brass ball valve might be 600 WOG but only 150 WSP. Never use the WOG number to justify a valve for steam.

Close-up of a valve body stamped with WOG and WSP pressure ratings

A valve carries two ratings: WOG (cold water/oil/gas) and WSP (working steam pressure). The steam rating is always the lower of the two.

ASME Pressure Class

Industrial valves are often specified by ASME pressure class (Class 150, 300, 600, 900, etc.) rather than a single PSI number. The class is a reference rating, and the actual allowable pressure depends on the material group and temperature per the ASME B16.34 pressure-temperature tables. A Class 150 carbon steel valve, for example, is rated about 285 PSI at 100°F but only about 170 PSI at 500°F. The class number is a shorthand — the controlling number is always the value read from the P-T table at your operating temperature.

Typical WOG Ratings by Material

Representative ambient-temperature WOG ratings for common threaded valve types and materials. Verify against the specific valve's data sheet.

Valve / Material	Typical WOG (cold)	Typical WSP (steam)	Max Temp
Brass ball valve	600 PSI	150 PSI	~366°F
316 SS ball valve	1000 PSI	150–250 PSI	~450°F+
PVC ball valve	150–235 PSI	Not for steam	~140°F
Brass gate valve	200–300 PSI	125–150 PSI	~406°F
SS needle valve	up to 6000 PSI	varies	~450°F+

Temperature Derating Reference

Allowable pressure falls as temperature rises. The table shows approximate derating factors to apply to the ambient WOG rating — multiply the cold rating by the factor for your temperature. PVC derates fastest and is unusable above its thermal limit.

Temperature	Brass Factor	316 SS Factor	PVC Factor
73°F (23°C)	1.00	1.00	1.00
100°F (38°C)	1.00	1.00	0.62
140°F (60°C)	0.90	0.95	0.22
250°F (121°C)	0.70	0.85	Not rated
400°F (204°C)	0.50	0.75	Not rated

Example: a 600 WOG brass ball valve at 400°F derates to roughly 600 × 0.50 = 300 PSI allowable. Factors are approximate; always use the manufacturer's published P-T curve for the specific valve.

Line graph of allowable pressure decreasing as temperature rises for brass, stainless, and PVC

Pressure-temperature curves slope down with heat. PVC drops off a cliff near 140°F; brass and stainless decline more gradually.

Applying a Safety Margin

Never select a valve rated at exactly your operating pressure. Standard practice is to choose a valve rated for at least 25% above the maximum operating pressure at the operating temperature, to absorb pressure spikes, water hammer, and thermal expansion. For a system running 600 PSI at 250°F in brass, first derate (600 WOG × 0.70 = 420 PSI allowable at 250°F), confirm that exceeds 600 PSI × 1.25 = 750 PSI required — it does not, so a brass valve is unsuitable and a higher-class stainless valve is required. Working the derating and the margin together is what prevents field failures.

Standards & References

Industrial valve pressure-temperature ratings are governed by ASME B16.34 (valves — flanged, threaded, and welding end), which publishes the P-T tables by material group and class. Threaded ball valves also reference MSS SP-110. Bronze and brass gate, globe, and check valves follow MSS SP-80. Thermoplastic (PVC/CPVC) valve ratings derive from the pipe standards ASTM D1784 and the manufacturer's published derating curves. For potable water, confirm NSF/ANSI 61 certification. The applicable piping code (e.g., ASME B31.1 power piping or B31.3 process piping) governs the required design margin.

Frequently Asked Questions

What does WOG mean on a valve?

WOG stands for Water, Oil, Gas — the valve's non-shock pressure rating at ambient temperature (about 100°F). A "600 WOG" valve handles 600 PSI of cold water, oil, or gas. It does not apply to steam or hot service.

Why is the steam rating lower than the WOG rating?

Steam combines high temperature and pressure, which stresses valve components far more than cold fluid. The Working Steam Pressure (WSP/SWP) rating accounts for this and is always lower than the WOG rating on the same valve.

How much does a valve's pressure rating drop with temperature?

It varies by material. Brass loses roughly half its rating by 400°F; 316 stainless retains about 75% at 400°F; PVC is unusable above about 140°F. Apply the manufacturer's derating factor at your operating temperature.

How much safety margin should I use when sizing a valve?

Select a valve rated at least 25% above your maximum operating pressure at the operating temperature, to cover spikes, water hammer, and thermal expansion. Critical service may require more per the applicable piping code.

What is ASME Class 150 in PSI?

Class 150 is a reference pressure class, not a fixed PSI. For carbon steel it is about 285 PSI at 100°F, derating to roughly 170 PSI at 500°F per ASME B16.34. Always read the value from the P-T table at your temperature.