PN vs ASME Class: Valve Pressure Ratings for Buyers

PN and ASME Class are pressure-rating designations used with their respective component standards. Neither designation is a complete operating limit: the applicable material, temperature, construction and end connection still need to be checked.

EN 1333 addresses the definition and selection of PN. KSB's PN explanation describes the number after PN as a reference designation, rather than a value to insert directly into a calculation. ASME B16.34 covers pressure-temperature ratings and other requirements for the valve constructions within its scope; ASME B16.5 addresses covered pipe flanges and flanged fittings.

This comparison is a purchasing checklist, not a PN-to-Class conversion table. Use the project-specified standard and edition for the final selection.

No. PN16 and Class 150 identify different rating systems; the labels alone do not establish equal working pressure or interchangeable flange dimensions. A replacement needs both a pressure-temperature review and a dimensional review.

Keep the rating on the existing line specification unchanged in the enquiry. If an alternative is proposed, ask for a written deviation covering the offered valve, the operating and design conditions, and its mating connections. Check these items before accepting the substitution:

• Body and bonnet material specification, construction and applicable pressure-temperature rating.
• Seat, packing and gasket limits for the fluid and temperature.
• Flange standard, nominal size, facing, drilling, bolts and gasket arrangement.
• Face-to-face or end-to-end dimensions and installation clearance.
• Required test records, approved drawing and acceptance of the deviation by the project reviewer.

ASME B16.5 covers both ratings and dimensions for the flanges within its scope. For the broader installation comparison, use the flanged, butt-weld, socket-weld and threaded connection guide.

Confirm the allowable pressure for the exact offered valve at the specified design temperature, then check every limiting part of the assembly. A body rating by itself does not confirm the seat, packing, gasket or end-connection capability.

HISAKA's ball-valve rating guidance distinguishes the body's pressure-temperature envelope from the seat limit and the temperature limits of packing and gaskets. That is a general selection principle; its product charts are not KEHUA ratings.

For a ball-valve enquiry, compare the soft-seated floating ball valve and metal-seated floating ball valve as separate constructions. Request the model-specific limits rather than applying one seat's curve to the other. The valve body-material guide can help identify the material information to send with the enquiry.

State normal operating pressure separately from design pressure, and include minimum and maximum temperatures and the maximum differential pressure during operation or shutoff. If any value is unknown, mark it pending for technical review instead of selecting a rating from the product name.

No. A series-level size range and a pressure range do not prove that every size is available at every rating. Confirm the size-rating combination for the exact construction shown on the offered datasheet and drawing.

When a catalogue lists separate rows by rating, retain those row relationships in the enquiry. Do not combine the largest diameter from one row with the highest pressure from another. The same review applies when changing body material, seat construction, operation or end connection.

Use the existing KEHUA series information as the starting point. Where a public page does not provide a temperature curve, a specific size-rating pair or a detailed interface dimension, request that information before purchase approval. This guide adds no new KEHUA product ratings.

Choose the valve family from its required duty, then review its exact series and pressure-temperature limits. A PN or Class designation alone does not select a ball, butterfly, gate, globe or check valve.

• Ball valves: identify the floating or trunnion construction, seat type, bore and differential pressure. Start with the soft-seated trunnion-mounted series when that construction is specified.
• Butterfly valves: identify the connection arrangement, seat and permitted shutoff duty. The wafer butterfly series still needs confirmation of mating-flange and size-rating compatibility.
• Gate valves: identify the construction, material and installation clearance. Review the cast steel wedge gate series with the line specification.
• Globe valves: state the required flow duty and differential pressure as well as the rating. Review the forged steel globe series against the requested configuration.
• Check valves: state flow direction, installation orientation and service conditions alongside the pressure specification. Review the swing check series as a specific candidate, not an automatic substitute for another construction.

Send one consistent line-item specification containing the required rating system, standard, material, size and service conditions. Ask the supplier to return an offered datasheet and a deviation list so competing quotations can be reviewed on the same basis.

• Valve tag, required function, family, construction and quantity.
• Nominal size and bore requirement; required PN or ASME Class; applicable standard and contract edition.
• Fluid and phase; normal operating pressure; design pressure and temperature; minimum temperature; maximum operating or shutoff differential pressure, with units.
• Body and trim materials; seat, packing and gasket requirements; unresolved selections marked pending.
• End-connection standard, flange facing or weld/thread details, mating dimensions and installation limits.
• Required pressure-temperature evidence, drawing, inspection records and any project-specific approvals.

Use the complete industrial valve RFQ checklist for the remaining commercial and document fields. A successful shell or seat test is a separate inspection result; it does not replace confirmation of the operating rating.

Send the valve specification for a KEHUA quotation review. Include the existing piping class and any proposed substitution; leave unconfirmed fields open for review.