PN25 vs Class 150 Valves: Pressure Rating, Flange Standard, and Interchangeability

Direct answer: PN25 and Class 150 are not equivalent valve ratings, and their flanges are not generally interchangeable. PN25 is a nominal pressure designation commonly used with EN and ISO systems. Class 150 is a dimensionless ASME rating whose allowable pressure changes with material and temperature. A PN25 valve should not be installed between ASME Class 150 flanges unless the manufacturer has designed, rated, drilled, tested, and documented that exact valve configuration for the ASME connection.

The numbers invite a quick PN25 vs Class 150 valve comparison. PN25 is commonly associated with 25 bar, or about 362.6 psi, while a Class 150 carbon steel valve may be rated around 285 psi near ambient temperature. This can make PN25 look like the stronger option.

That conclusion is incomplete. Pressure capability is only one part of the connection. The flange outside diameter, bolt circle, hole count, hole diameter, facing, gasket, valve face-to-face length, material group, and pressure-temperature table must all agree with the project specification.

PN25 vs Class 150 at a glance

For a focused explanation of the metric designation, see PN25 pressure rating explained. If the project documents mix bar and psi, use the PN16 and PN25 pressure conversion guide for the arithmetic, then return to the governing standard for the selection decision.

What PN25 means

PN is a reference designation, not a promise that every valve marked PN25 can operate continuously at exactly 25 bar under every condition.

For basic unit comparison:

25 bar x 14.5038 = 362.595 psi

The rounded figure is 362.6 psi. It remains a conversion of 25 bar, not an ASME pressure class.

The allowable pressure of the assembled valve can be limited by the body material, bonnet joint, shaft design, seat, elastomers, coating, flange material, gasket, bolts, operating temperature, differential pressure, or applicable product standard. A soft-seated ductile iron water valve and a carbon steel process valve can both carry a PN25 description while having very different temperature ranges and service limits.

PN25 also does not define one universal flange. Steel pipe flanges commonly follow EN 1092-1, while ductile iron waterworks valve flanges commonly follow EN 1092-2. Corresponding DN and PN connections may be designed to mate, but the facing and complete joint still need verification. The EN 1092 PN25 flange guide explains the steel-to-cast-iron interface, gaskets, bolting, and flange markings in more detail.

What Class 150 means

Class 150 does not mean 150 psi, 150 bar, or a fixed maximum working pressure. The number is a class designation.

For example, an ASME B16.34 valve made from ASTM A216 WCB carbon steel is commonly rated at 285 psi, or about 19.6 bar, at temperatures up to 100 degrees F (38 degrees C), subject to the adopted standard edition and exact construction. The allowable pressure falls as temperature rises. Stainless steel and alloy material groups follow different tables.

The same distinction applies to flanges. ASME B16.5 sets pressure-temperature ratings and dimensional requirements for flanges from NPS 1/2 through NPS 24. Larger flanges may fall under ASME B16.47, depending on size and series. The valve itself may also have to comply with ASME B16.34 and a valve-specific standard.

Do not treat the following terms as synonyms:

• ASME Class 150
• 150 psi working pressure
• 150 lb or 150# used informally in trade
• AWWA pressure classes such as Class 150B
• JIS 10K or other national designations

They may appear close in a catalog or enquiry, but they do not establish the same pressure-temperature capability or flange interface.

Is PN25 higher than Class 150?

There is no universal yes-or-no answer.

PN25 has a higher nominal pressure number than the near-ambient rating of many Class 150 carbon steel valves. That makes it reasonable to say PN25 has the higher nominal ambient pressure reference in that narrow example: 25 bar versus about 19.6 bar.

It is still wrong to rank every PN25 valve above every Class 150 valve. The comparison changes with:

• valve body and flange material
• operating temperature
• governing valve standard
• seat and seal temperature limits
• corrosion allowance and fluid compatibility
• permitted occasional and test pressures
• the manufacturer’s documented rating for the exact model

The correct PN25 vs Class 150 valve decision asks whether the offered valve satisfies the project’s complete pressure-temperature envelope and connection standard. A pressure number by itself cannot answer that.

A safer pressure comparison

The Class 150 figure in this table is an example, not a universal conversion factor. The purchaser must identify the material group, temperature, standard edition, and valve construction before using an ASME pressure-temperature value.

ASME vs EN flange standards

Pressure rating and flange geometry come from related but separate standard requirements. A useful standards map prevents a common purchasing error: asking for a PN25 body with an unspecified “ANSI flange.”

One standard does not automatically cover the whole valve. ASME B16.5 primarily addresses the flange joint, while ASME B16.34 addresses valves. In the EN system, the flange part depends on material, and the valve performance standard depends on valve type and service.

PN25 and Class 150 flange dimension comparison

The table below compares selected common EN 1092 PN25 drilling dimensions with ASME B16.5 Class 150 dimensions. It is intended for preliminary identification only. ASME inch dimensions have been converted to millimetres and rounded.

DN100 is a good warning example. Its 190 mm PN25 bolt circle looks very close to the 190.5 mm Class 150 bolt circle. That does not make the flanges interchangeable. The flange outside diameters and hole diameters differ, and the facing, thickness, bolts, gasket dimensions, and allowable joint loads still require approval.

For a wider DN50 to DN600 EN drilling reference, use the PN25 valve size chart. Fabricate pipe spools only from the approved valve and mating-flange drawings for the order.

Can a PN25 valve connect to a Class 150 flange?

An ordinary EN PN25 flanged valve should be treated as incompatible with an ASME B16.5 Class 150 piping flange. There are three acceptable project routes.

1. Order the valve with the required ASME ends

Some valve bodies are manufactured in separate EN PN and ASME Class versions. If the pipeline uses ASME B16.5 Class 150, order the valve with Class 150 flanges and obtain the matching dimensional drawing, pressure-temperature rating, marking, and test documentation.

A catalog statement such as “PN25 / Class 150 available” usually means the supplier offers different configurations. It does not mean one randomly selected valve fits both systems.

Norite’s Z45X resilient seated gate valve and D342X double eccentric butterfly valve can be discussed against the connection standard required by the project. The quotation and drawing should identify the chosen version explicitly.

2. Use an engineered transition spool or adapter

A transition spool can place an EN PN25 flange on one end and an ASME Class 150 flange on the other. The spool must be designed for the piping code, pressure, temperature, material, corrosion allowance, flange facing, gasket, bolting, loads, and test requirements.

This is usually clearer than forcing two incompatible flanges together. It also gives the project team a defined boundary between standard systems.

3. Replace the mating flange under an approved design change

For a fabricated line that has not entered service, the engineer may approve replacing the pipe flange with the correct standard. The revised spool drawing, welding procedure, material records, inspection, and pressure test must follow the project requirements.

Do not slot, enlarge, weld-fill, or redrill flange holes on site as an improvised conversion. This changes the flange geometry and may reduce ligament strength, bearing area, alignment control, and traceability. A few bolts passing through does not make the joint acceptable.

PN16 vs PN25 is a separate comparison

PN16 vs PN25 stays within the PN designation system, but that does not guarantee universal dimensional compatibility.

Some smaller EN flange sizes share basic drilling between PN16 and PN25. Other sizes use different outside diameters, pitch circles, hole diameters, or bolt sizes. Even where the holes align, the connected assembly remains limited by its lowest-rated component.

A PN25 valve installed in a PN16 system does not make the pipeline PN25. Pipe, fittings, expansion joints, instruments, gaskets, bolts, and test limits still control the system rating. The PN10 vs PN16 vs PN25 valve guide covers this selection in more depth.

Interchangeability requires more than matching bolt holes

Two valves are interchangeable only when the new valve can perform the required duty and fit the complete installed interface. Check each item below.

Pressure and temperature

Collect normal operating pressure, maximum static pressure, pump shut-off pressure, surge pressure, maximum differential pressure, field test pressure, minimum temperature, and maximum temperature. Compare each condition with the correct limit in the applicable standard and manufacturer data.

Avoid applying a blanket 1.2 or 1.5 multiplier to every project. Design margins come from the piping code, project specification, operating uncertainty, surge analysis, and service risk. A percentage chosen without those inputs can still miss water hammer or temperature derating.

Flange drilling and facing

Compare flange standard, size, class, outside diameter, bolt circle, hole count, hole diameter, facing type, surface finish, and bore. Select the gasket and bolts as parts of the same joint.

Face-to-face length

An EN valve commonly uses an EN 558 face-to-face series. An ASME valve may use ASME B16.10. Equal nominal size and similar pressure capacity do not guarantee equal installed length. A short replacement can leave a gap; a longer one can overload the pipe when installers force it into place.

A correctly selected dismantling joint can provide controlled axial adjustment and simplify valve removal, but it is not a PN-to-Class flange converter unless its two ends were designed and documented for that purpose.

Bore and moving-part clearance

Butterfly and wafer check valves need special attention. The disc or plates may swing into the mating pipe, flange bore, liner, or gasket. Confirm internal diameter and movement clearance from the manufacturer’s drawing.

For a wafer or lug butterfly valve, a multi-standard claim is valid only when the compatibility chart lists the exact DN or NPS and flange classes. Lug thread, bolt length, liner design, and dead-end rating also need confirmation. A double-flanged design such as the D341X flanged butterfly valve avoids some wafer-specific fit questions, but the end flanges must still match the pipeline standard.

Check valves also need their own face-to-face length, flow direction, disc clearance, minimum velocity, and closing behavior reviewed. The H44X swing check valve illustrates why valve type matters beyond its pressure designation.

Materials, seats, and service

Confirm body, bonnet, disc or wedge, stem, seat, coating, and fastener materials. A body may have enough structural pressure capacity while an EPDM, NBR, PTFE, or elastomer-lined component sets a lower temperature or chemical limit.

Testing, marking, and documents

Request the standard edition, valve nameplate details, dimensional drawing, material certificates, pressure test report, coating report where applicable, and certificate of conformity. If the valve is described with both PN and Class values, ask whether it has a genuine dual rating or whether the catalog combines separately manufactured options.

Three practical selection examples

DN100 PN25 valve in an EN water transmission line

The line specification calls for DN100 PN25 flanges. A supplier offers a 4-inch Class 150 valve because its bolt circle is almost the same.

Reject the substitution until a formal engineering review proves the complete interface. The common EN PN25 reference uses a 235 mm flange OD, 190 mm PCD, and eight 22 mm holes. The Class 150 reference uses a 228.6 mm OD, 190.5 mm BCD, and eight 19.1 mm holes. Close numbers are still different standards.

The clean purchasing choice is a DN100 PN25 valve with the required EN flange configuration.

NPS 4 Class 150 valve in an ASME process-water line

The line operates at 12 bar and ambient temperature. A PN25 valve appears to have more pressure capacity, so the buyer proposes it as an upgrade.

The pipeline connection still calls for ASME B16.5 Class 150. Order a valve rated and flanged for Class 150. Verify the body material, maximum temperature, applicable ASME rating, face-to-face length, and test standard. The higher PN number does not make an EN-flanged valve a drop-in replacement.

PN16 pump discharge with a predicted 22 bar surge

The normal pressure is 11 bar, but a transient study predicts 22 bar after a pump trip. A PN16 valve selected only from normal pressure is not enough. PN25 may cover the calculated surge if the product’s occasional maximum pressure, temperature, and full system design are suitable.

The project should also address the surge cause. Valve closing time, pump inertia, air management, non-return valve behavior, surge vessel sizing, and pipeline profile may matter. Raising one valve’s PN rating does not protect the remaining PN16 components.

How to specify the correct PN25 or Class 150 valve

Use this sequence before asking for a price:

1. State the governing piping and valve standards.
2. Give DN or NPS without treating the two labels as measured dimensions.
3. State PN or Class exactly as required by the line specification.
4. Provide fluid composition and solids content.
5. List minimum, normal, and maximum operating temperatures.
6. List working, static, shut-off, surge, differential, and test pressures.
7. Specify body, trim, seat, coating, and fastener materials.
8. State flange standard, facing, and gasket requirement.
9. State face-to-face standard or supply the available installed length.
10. Identify the operator, actuator supply, fail position, and maximum differential pressure for operation.
11. Request a general arrangement drawing and flange detail before production.
12. List required certificates, inspections, tests, and document language.

RFQ wording example

Please quote DN200 double-flanged butterfly valves for treated-water service. Design pressure 18 bar, maximum surge pressure 23 bar, field test pressure 25 bar, operating temperature 5 to 45 degrees C. Required connection: EN 1092-2 PN25 with the project-specified facing. Face-to-face dimension to EN 558 series as stated in the attached data sheet. Please confirm body, disc, shaft, seat, coating, allowable pressure-temperature rating, operating torque, gearbox selection, flange drilling, weight, pressure test standard, and certificate package. Submit the general arrangement drawing for approval before production.

For an ASME project, replace the EN connection statement with the required ASME B16.5 or B16.47 class and facing, then identify the applicable valve standard and material rating.

Frequently asked questions

Is PN25 the same as Class 150?

No. PN25 and Class 150 belong to different designation and standards systems. Their allowable pressures are determined differently, and their flange dimensions are generally different.

Which has the higher pressure rating, PN25 or Class 150?

PN25 has a 25 bar nominal reference. A Class 150 A216 WCB valve is commonly rated around 285 psi, or 19.6 bar, near ambient temperature. This limited comparison makes PN25 numerically higher, but it does not rank every material, temperature, valve type, or standard configuration.

Does Class 150 mean 150 psi?

No. Class 150 is a dimensionless ASME class designation. The allowable pressure comes from the applicable pressure-temperature table for the material and temperature.

Does PN25 always mean a 25 bar working pressure?

No. Twenty-five bar is the nominal reference commonly associated with PN25. The valve’s permissible working pressure depends on its material, design, temperature, product standard, and manufacturer’s documented rating.

Can an EN 1092 PN25 flange mate with an ASME B16.5 Class 150 flange?

Do not assume it can. Flange OD, bolt circle, hole count, hole diameter, facing, gasket, thickness, and joint rating can differ. Use the correctly flanged valve or an engineered transition.

Can a PN16 flange connect to a PN25 valve?

Some DN sizes may share basic drilling, while others do not. If the joint dimensions are compatible and the project approves the connection, the assembly is still limited by the PN16 component and other lower-rated parts.

Can a flange be redrilled to change PN25 into Class 150?

Site redrilling is not an acceptable default solution. It changes the flange and may compromise strength, alignment, sealing, and traceability. Use an approved transition spool, replace the mating flange, or order the correct valve ends.

Are DN100 and NPS 4 interchangeable size labels?

They refer to corresponding nominal size families, but they do not prove identical bores, flanges, or installed dimensions. The flange standard and valve drawing remain necessary.

Can one valve carry both PN25 and Class 150 ratings?

Only if the manufacturer has designed, tested, marked, and documented the exact configuration for both ratings. A catalog that lists both may be describing separate flange versions rather than one dual-rated valve.

What should be checked before approving a substitute valve?

Check the governing standard, pressure-temperature rating, material, service limits, flange geometry, facing, gasket, bolting, face-to-face length, bore clearance, operating torque, actuator, testing, marking, and documentation. Approval should be based on the submitted drawing and data sheet, not on a short catalog label.

Send the flange standard, not only the pressure number

The most reliable enquiry states the complete connection: DN100 EN 1092-2 PN25, or NPS 4 ASME B16.5 Class 150 RF, for example. Add the operating envelope, materials, valve type, face-to-face requirement, and test documentation.

If an existing line mixes EN and ASME references, contact Norite with the valve schedule, mating-flange drawing, fluid, temperature, working pressure, surge pressure, and available installation length. Norite can review whether the project needs a PN25 valve, a Class 150 valve, a separately drilled version, or an engineered transition arrangement.