Valve Nominal Pressure: PN, ASME Class and Pressure–Temperature Ratings
PN and ASME Class are standardized rating designations, not universal maximum working pressures printed in different units. The allowable pressure for a valve depends on the applicable rating or product standard, material group, design temperature, valve construction and any special service limitation. Transients, minimum temperature, corrosion allowance, seats, packing, ends and piping-system rules also matter. Selection should compare every operating and upset case with the controlled pressure–temperature basis for the complete valve.
Inputs required before choosing a valve rating
Use the project design case, not only normal operating pressure, and include credible static head or blocked-in conditions.
Check high and low design temperatures, startup/shutdown and thermal transients because material capacity changes.
Different body materials can carry different allowable pressures under the same class or PN designation.
Valve type, end style, body joint and product-standard scope can alter the governing rating route.
Pressure-boundary rating does not prove allowable differential pressure, shutoff or seal performance at temperature.
Mating flanges, pipe, fittings, gaskets, bolting and connected equipment need compatible design ratings.
Keep the pressure terms in a datasheet separate
| Term | What it describes | What it does not prove | Where to verify |
|---|---|---|---|
| Operating pressure | Expected process pressure during a stated normal or operating case. | Design margin, upset cases or valve allowable pressure. | Process datasheet and operating-case list. |
| Design pressure | Pressure used with design temperature and governing rules for component selection. | A fixed valve class without material/rating review. | Project mechanical design basis and valve datasheet. |
| PN designation | A nominal pressure designation used within the applicable EN/ISO or other system. | That allowable pressure equals the PN number at every temperature. | Controlled product/rating standard and material data. |
| ASME Class | A rating class such as 150 or 300 used with applicable ASME/product rules. | That the number is psi or identical across materials and temperatures. | Applicable pressure–temperature tables in the licensed standard. |
| Cold working pressure marking | A rating reference under defined material/temperature conditions where applicable. | Suitability at elevated/low temperature or for every seat/trim. | Product standard, nameplate convention and manufacturer data. |
| Test pressure | Pressure used for a defined shell/seat test under an approved procedure. | Continuous allowable operating pressure or service qualification. | Applicable test/product standard and approved test procedure. |
Rating checks beyond the body pressure boundary
Flange or weld-end rating and geometry must suit the piping system.
Seat, disc/ball and stem/shaft loads can limit shutoff or operation.
Required torque/thrust must cover worst differential and temperature cases.
Blocked-in liquid, thermal expansion or double-isolation arrangements need relief review.
Material toughness, bolting and seals may govern cold service.
Corrosion, erosion and cyclic/fatigue considerations belong in project design.
Claims and shortcuts this page does not support
Class 150 does not simply mean 150 psi
The allowable pressure depends on material and temperature under the applicable rating rules.
PN16 does not state every service limit
Seat differential, material, temperature and construction limitations still apply.
Passing a hydrotest does not increase the design rating
Test pressure verifies defined integrity and is not a new operating allowance.
From requirement to auditable evidence
Information and records to define
How this resource should be used
Foundational engineering guidance for buyers comparing PN and ASME pressure classes and needing the correct pressure–temperature selection workflow.
Raymon Valve technical content team. Final project decisions require the controlled documents and responsible engineer or quality reviewer.
Use the licensed applicable product and rating standards, project design basis and approved manufacturer data. This page intentionally reproduces no rating tables; values must be checked for the exact material, temperature, class/PN and standard edition.
Technical scope reviewed 27 July 2026. Editions, procedures, acceptance criteria and product evidence must be reconfirmed before order.
Valve Nominal Pressure PN and ASME Class Guide FAQ
Is PN16 equal to Class 150?
No direct universal equivalence should be assumed. Rating systems, allowable pressure–temperature values, dimensions and flange interfaces differ. Compare the full requirements for the actual material and temperature.
Does Class 300 mean 300 psi?
No. Class is a designation, not a direct pressure value. Use the applicable pressure–temperature rating for the material group and design temperature.
Should valve class be selected from operating pressure or design pressure?
Use the approved design pressure-temperature cases and governing rules, then check all valve functional and material limits. Normal operating pressure alone is insufficient.
Why is hydrostatic test pressure higher than design pressure?
A controlled test uses a defined pressure to verify specified integrity under test conditions. It does not authorize continuous service at the test pressure.
Send the requirement and the evidence you need to verify
We will identify the applicable scope, missing records and approval path without inventing compliance claims.
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