PN25 Pressure Rating Explained: Bar, PSI, Valve Selection, and Flange Matching

PN25 is a metric pressure-class designation used for valves, flanges, pipes, and other piping components. In practical ambient-temperature water applications, a PN25 pressure rating is commonly associated with 25 bar, equal to 2.5 MPa, 2,500 kPa, or approximately 362.6 psi.

That conversion is useful, but it is not the whole selection rule. PN25 does not independently guarantee that every valve marked PN25 can operate at exactly 25 bar under every temperature, material, fluid, or transient condition. The governing product standard, pressure-temperature rating, body material, seat design, flange standard, and maximum credible system pressure must all be checked.

This guide explains what PN25 means, how to convert PN25 to psi, when a PN25 valve is appropriate, and how to avoid flange and pressure-class mismatches during procurement.

Quick Answer: What Does PN25 Mean?

PN25 identifies a nominal pressure class in the European and metric piping system. The letters “PN” are followed by a dimensionless number that relates to the component’s mechanical and dimensional characteristics.

For common water-service purchasing at or near room temperature:

The direct conversion is:

25 bar × 14.5038 = 362.595 psi

For quick site calculations, PN25 ≈ 363 psi. For engineering documents, retain the original PN designation and state the applicable component and flange standards instead of replacing PN25 with a rounded psi value.

Important: EN 1333 treats PN as a reference designation, not as a standalone measured pressure. The allowable working pressure must be confirmed from the relevant valve or flange standard and the manufacturer’s pressure-temperature data.

Is PN25 Always Exactly 25 Bar?

No. “PN25 = 25 bar” is a useful nominal interpretation, especially for ambient-temperature water systems, but it should not be used as a universal maximum allowable working pressure.

The actual allowable pressure of a PN25 component can depend on:

• Body and flange material
• Operating and design temperature
• Valve product standard
• Body, bonnet, stem, disc, wedge, and closure design
• Seat and seal material
• Flange type and facing
• Corrosion or erosion allowance
• Cyclic loading and expected service life
• Manufacturer’s published pressure-temperature limits

This distinction becomes more important in hot water, steam, oil, gas, chemical, or high-cycle service. Metal strength and seal performance change with temperature. A valve body may remain structurally suitable while an elastomeric seat, gasket, coating, or actuator becomes the limiting component.

For a broader comparison of metric and ASME ratings, see Norite’s guide to PN10, PN16, PN25, and Class 150 valve pressure ratings.

PN25 in Bar, PSI, MPa, and kPa

Buyers frequently receive one datasheet in bar, another in MPa, and a project specification in psi. The following comparison prevents unit-conversion errors.

These are unit conversions of the PN numbers, not universal pressure-temperature guarantees.

PN25 Is Not the Same as 250 PSI

A 250 psi marking equals only about 17.24 bar. It is therefore not another way to write PN25. Similarly, 300 psi equals approximately 20.68 bar. A catalog that lists “PN25,” “250 PSI,” and “300 PSI” may be describing separate available configurations rather than equivalent markings on the same valve.

Ask the supplier to identify the exact rating, standard, material, and flange drilling for the offered unit.

Pressure Terms to Check Before Selecting a PN25 Valve

Normal operating pressure is only one value in the system pressure envelope. A reliable selection should distinguish at least the following conditions:

For water networks, project documents may also use PFA, PMA, and PEA terminology for allowable operating, occasional maximum, and allowable site test pressures. Confirm the definitions used by the governing project specification rather than assuming that every pressure value means the same thing.

A Simple PN25 Selection Example

Consider a transmission pipeline with these preliminary conditions:

• Normal operating pressure: 14 bar
• Maximum static pressure: 18.5 bar
• Calculated positive surge: 4 bar
• Maximum credible pressure: 22.5 bar
• Water temperature: 30°C

A PN16 valve is not adequate because the credible pressure exceeds 16 bar. A PN25 valve becomes a logical candidate, but final approval still requires confirmation of the valve’s pressure-temperature rating, product standard, seat differential-pressure capability, flange standard, and project safety requirements.

This example also shows why “the pipeline normally runs at 14 bar” is not a complete purchasing specification.

PN16 vs PN25 vs PN40: Which Pressure Class Should You Choose?

Do not automatically choose the highest class. A higher-pressure valve may have thicker flanges, larger bolts, greater weight, different face-to-face dimensions, higher actuator torque, and a higher purchase price. The correct class is the one that satisfies the full pressure-temperature envelope and applicable design standard with the required margin.

Is PN25 Equivalent to ASME Class 150 or Class 300?

PN25 has no exact ASME Class equivalent. It falls between common Class 150 and Class 300 pressure capabilities for many carbon-steel components near ambient temperature, but that observation does not make the classes interchangeable.

The two systems work differently:

• PN is a metric reference designation used with standards such as EN 1333 and EN 1092.
• ASME Class designations such as Class 150 and Class 300 refer to pressure-temperature tables that vary by material group.
• Class 150 does not mean 150 psi, and Class 300 does not mean 300 psi.
• EN and ASME flanges can have different outside diameters, pitch circle diameters, bolt-hole patterns, facings, and thicknesses.

Therefore:

• Do not replace a PN25 flange with a Class 150 flange because the pressure values appear close.
• Do not call PN25 “Class 150” or “Class 300” on an RFQ.
• If an existing pipeline uses ASME B16.5, order the required ASME Class configuration.
• If a catalog lists both PN25 and Class 150, verify whether they are separate drillings and separate pressure-rated versions.

A transition spool or purpose-designed adapter may be required when an EN PN system must connect to an ASME system.

How to Select the Right PN25 Valve

The PN25 marking confirms only one part of the selection. Use the following process to specify the complete valve.

1. Define the Fluid

Identify whether the medium is drinking water, raw water, wastewater, seawater, oil, gas, steam, or a chemical fluid. Fluid composition affects body material, coating, seat, gasket, stem, and trim selection.

For drinking-water service, request the potable-water approvals required by the destination market and confirm that all wetted elastomers, lubricants, and coatings are approved—not only the valve body.

2. Define the Full Pressure Envelope

Provide normal, maximum static, design, surge, differential, and test pressures. State whether each value is gauge or absolute pressure when there is any possibility of confusion.

For pump stations and long transmission mains, include a surge analysis. A check valve that closes too slowly can permit reverse flow, while one that closes too aggressively can create a damaging pressure spike.

3. Confirm Maximum and Minimum Temperature

The selected body, seat, O-rings, gasket, coating, and actuator must all remain suitable over the full temperature range. For example, EPDM is common in water service, while NBR may be chosen for certain oil-containing media. Neither should be selected from a pressure marking alone.

4. Choose the Valve Type by Function

Norite offers PN25 configurations for applications including the Z45X resilient seated gate valve, D342X double-eccentric butterfly valve, H44X swing check valve, and F8020 pressure reducing valve. Availability should always be confirmed for the required DN, material, standard, and operating condition.

5. Check Body, Trim, Seat, and Coating

For municipal water systems, ductile iron is widely used because it combines strength, castability, and cost efficiency. Carbon steel or stainless steel may be more appropriate for higher temperature, aggressive fluids, or project-specific process requirements.

A complete material specification should identify:

• Body and bonnet material
• Disc, wedge, or ball material
• Stem or shaft material
• Seat and O-ring material
• Fastener material
• Internal and external coating system
• Required dry-film thickness
• Potable-water or chemical-service approvals

6. Confirm Shutoff Direction and Differential Pressure

A valve marked PN25 may have a lower recommended differential-pressure limit across the closure element. This is especially important for butterfly valves, check valves, control valves, and large-diameter resilient seated valves.

State whether the valve must seal in one direction or both directions, the maximum shutoff differential pressure, and the required leakage rate or tightness class.

7. Size the Valve Hydraulically Where Required

Isolation valves are often line-sized, but control valves and pressure reducing valves must be sized using flow, inlet pressure, outlet pressure, and cavitation criteria. Selecting a DN200 PRV simply because the pipe is DN200 can produce unstable control, noise, excessive velocity, or cavitation.

Use a proper pressure reducing valve sizing calculation when specifying a PN25 PRV.

PN25 Flange Matching: What Must Be the Same?

A PN25 valve does not automatically connect to every flange described as PN25. The mating connection should be checked as a complete dimensional specification.

At minimum, confirm:

1. Nominal size: DN50, DN100, DN200, and so on
2. Pressure designation: PN25
3. Flange standard and part: for example, EN 1092-2 for cast or ductile iron flanges, or EN 1092-1 for steel flanges
4. Flange type: integral, weld-neck, plate, blind, threaded, or another specified type
5. Facing: flat face, raised face, or the specified EN facing type
6. Outside diameter: flange OD
7. Pitch circle diameter: PCD or bolt-circle diameter
8. Bolt pattern: number and diameter of holes
9. Bolting: bolt or stud size, grade, length, washers, and coating
10. Gasket: type, dimensions, material, pressure, temperature, and fluid compatibility
11. Face-to-face length: particularly when replacing an installed valve

The exact EN 1092 part matters. EN 1092-1 covers steel flanges, while EN 1092-2 covers cast-iron and ductile-iron flanges. Specifying only “EN 1092 PN25” can be incomplete, particularly when a steel pipe flange must mate with a ductile-iron valve flange.

Selected EN 1092-2 PN25 Flange Drilling Reference

The following values are a practical reference for common cast- and ductile-iron PN25 connections. They are not a fabrication drawing; always verify the latest project-adopted standard and the manufacturer’s approved dimensional sheet.

Can a PN25 Valve Be Installed Between PN16 Flanges?

Do not assume so. Some smaller PN classes and sizes may share certain drilling dimensions, but physical bolt alignment does not upgrade the connected PN16 flange, pipe, fitting, gasket, or equipment to PN25. The complete assembly is limited by its lowest-rated component.

At larger sizes, bolt number, hole diameter, PCD, flange OD, and thickness may differ. A forced fit, slotted hole, or site modification is not an acceptable substitute for verified compatibility.

Flange Facing and Gasket Risks

Matching the bolt holes is not enough. If a flat-faced ductile-iron valve is connected to a raised-face steel flange, the concentrated gasket load can impose unintended bending stress on the iron flange. Use a compatible facing and gasket arrangement or obtain written approval from the valve and piping engineer.

For wafer and lug butterfly valves, also check:

• Flange inside diameter and disc clearance
• Whether the liner serves as the gasket
• Bolt length and body-lug engagement
• Suitability for dead-end service
• Maximum bidirectional differential pressure
• Installation between the exact specified flange standard

For removable valves, a correctly rated dismantling joint can provide axial adjustment and simplify future maintenance, but its DN, PN rating, drilling, tie rods, and coating must also match the system.

PN25 Valve Pressure Testing and Inspection

Pressure testing should verify both the pressure boundary and the closure system. A purchase order should not state only “hydrotest required.” It should identify the test standard, test medium, test pressure, holding time, leakage acceptance, and documentation.

Commonly referenced standards include ISO 5208, EN 12266-1, and the applicable EN 1074 valve product standard for water-supply valves.

Where the selected standard calls for a shell test at 1.5 times the rated pressure and a high-pressure closure test at 1.1 times the rated pressure, the calculated PN25 test values would be:

• Shell test: 25 × 1.5 = 37.5 bar
• High-pressure closure test: 25 × 1.1 = 27.5 bar

These figures are examples of test-pressure calculations, not permission to operate the valve continuously at those pressures. The governing product standard and approved inspection and test plan control the actual test values and acceptance criteria.

Norite’s valve hydrostatic testing guide explains the difference between shell testing, seat testing, ISO 5208, and other project requirements.

Documents to Request for a PN25 Valve

• Approved datasheet and dimensional drawing
• Material certificates as specified by the purchase order
• Pressure and seat test report
• Leakage-rate or tightness result
• Flange dimensional inspection record
• Coating thickness and holiday-test record where required
• Rubber or coating approval for potable-water service
• Valve marking and serial-number photographs
• Installation, operation, and maintenance manual
• Certificate of conformity
• Third-party inspection release note when required

The test report should identify the actual valve size, model, serial or batch number, test pressures, holding times, medium, leakage result, test date, and inspector—not merely state “passed.”

Common Applications for PN25 Valves

PN25 valves are commonly considered for:

• High-rise building booster systems
• Pump discharge headers
• Long-distance water transmission mains
• High-elevation or high-static-head pipelines
• Irrigation pumping stations
• Industrial process-water systems
• Fire-water networks where the approved design requires PN25
• Pressure reducing stations with high upstream pressure
• Hydropower and dam auxiliary-water systems
• Sections exposed to significant transient pressure

PN25 is not automatically required in every application on this list. The system pressure analysis and governing specification determine the required valve pressure class.

Eight Common PN25 Procurement Mistakes

1. Selecting from Normal Pressure Only

Ignoring static head and water hammer can leave the valve under-rated during pump trips or rapid closure.

2. Treating PN25 as a Universal 25-Bar MAWP

The allowable pressure depends on the component standard, material, design, and temperature.

3. Converting PN25 Directly to an ASME Class

PN25 is neither Class 150 nor Class 300. Pressure-temperature ratings and flange geometry must be checked separately.

4. Writing “PN25 Flange” Without the Standard

Always include the full flange standard, material-related part, DN, and facing requirement.

5. Assuming Any PN25 Valve Can Seal Against 25 Bar Differential

Confirm the closure differential-pressure rating, direction, seat design, and actuator torque.

6. Ignoring the Seat and Seal Temperature Limit

The body can remain strong while the elastomer, gasket, or coating exceeds its service range.

7. Accepting a Generic Test Certificate

Require traceable results tied to the supplied valve or production batch.

8. Forgetting Connected Components

The pipeline is only as strong as its lowest-rated flange, pipe, joint, strainer, air valve, check valve, gasket, fastener, or instrument connection.

PN25 Valve RFQ Example

The following format gives a supplier enough information to prepare a technically comparable offer:

Service: Treated water
Valve type: Resilient seated gate valve
Quantity: 12 units
Nominal size: DN200
Pressure class: PN25
Normal pressure: 15 bar(g)
Maximum static pressure: 19 bar(g)
Maximum pressure including surge: 23 bar(g)
Fluid temperature: 5–45°C
Valve standard: EN 1074-1 and EN 1074-2, latest project-adopted edition
Flange connection: EN 1092-2 PN25, facing as approved drawing
Face-to-face: EN 558, required basic series to be confirmed
Body: EN-GJS-500-7 ductile iron
Wedge/seat: Potable-water-approved EPDM
Stem: Stainless steel, grade to be stated
Coating: Potable-water-approved fusion-bonded epoxy, minimum DFT specified
Operation: Gearbox with handwheel
Shutoff: Bidirectional, maximum differential pressure stated
Testing: Applicable EN/ISO standard, pressures and duration stated in ITP
Documents: Drawing, datasheet, material certificates, pressure test report,
coating report, certificate of conformity, O&M manual
Inspection: Buyer or third-party witness point before shipment

For replacement valves, attach clear photographs and measurements of the existing flange OD, PCD, bolt-hole quantity and diameter, facing, and installed face-to-face length.

Frequently Asked Questions About PN25 Pressure Rating

How many bar is PN25?

PN25 is commonly associated with a nominal pressure of 25 bar in ambient-temperature water-service discussions. Technically, PN is a dimensionless class designation, and the allowable pressure must be confirmed from the relevant component standard and pressure-temperature data.

What is PN25 in psi?

PN25 converts nominally to approximately 362.6 psi, usually rounded to 363 psi.

What is PN25 in MPa?

PN25 corresponds nominally to 2.5 MPa or 2,500 kPa.

Is PN25 suitable for 25 bar continuous pressure?

Not automatically. Check the valve standard, body and trim materials, design temperature, seal limits, differential pressure, surge pressure, and manufacturer’s pressure-temperature rating. A design operating continuously at the nominal limit deserves a full engineering review.

Is PN25 the same as Class 150?

No. The rating method and flange geometry differ. Do not substitute PN25 and Class 150 without verifying pressure-temperature capability and providing a properly designed transition connection.

Is PN25 the same as Class 300?

No. Class 300 generally has a significantly higher pressure capability for common materials near ambient temperature, and its ASME flange dimensions differ from EN PN25 dimensions.

Can PN25 and PN16 flanges connect?

Some sizes may appear dimensionally similar, but compatibility is not universal and the PN16 component remains the pressure-limiting part. Check the exact DN, standard, PCD, bolt holes, facing, gasket, and approved drawings.

What is the test pressure for a PN25 valve?

It depends on the governing valve and test standard. If a specified test basis uses 1.5 times rating for the shell and 1.1 times for the closure, the example values are 37.5 bar and 27.5 bar. Confirm the actual requirements on the approved inspection and test plan.

Does PN25 describe flange dimensions?

PN25 helps define a dimensional series only when combined with DN and the relevant flange standard. A complete description may be “DN200, PN25, EN 1092-2, facing Type A,” followed by any project-specific requirements.

Should I choose PN25 if operating pressure is below 16 bar?

Possibly. Maximum static pressure, surge, elevation, temperature, testing, and project design margin may justify PN25 even when normal pressure is below 16 bar. Base the decision on the complete pressure envelope.

Final PN25 Valve Selection Checklist

Before approving a PN25 valve order, confirm:

• [ ] Fluid and concentration
• [ ] Normal, maximum static, design, surge, and test pressures
• [ ] Maximum differential pressure across the valve
• [ ] Minimum and maximum temperature
• [ ] Valve type and operating function
• [ ] DN and required flow capacity
• [ ] Body, trim, seat, gasket, and coating materials
• [ ] PN25 pressure-temperature capability
• [ ] Full flange standard, part, type, and facing
• [ ] PCD, bolt-hole pattern, flange OD, and gasket compatibility
• [ ] Face-to-face dimension
• [ ] Actuator or gearbox torque
• [ ] Shutoff direction and leakage requirement
• [ ] Pressure-test standard and acceptance criteria
• [ ] Certification, inspection, documentation, and packing requirements

Conclusion

The short answer is simple: PN25 is commonly treated as 25 bar, 2.5 MPa, or approximately 363 psi. The correct engineering answer is more precise: PN25 is a valve pressure class that must be used together with the component standard, material, design temperature, full system pressure envelope, and exact flange specification.

For reliable valve selection, do not stop at the PN25 marking. Verify surge pressure, shutoff differential pressure, seat and coating limits, EN or ASME connection standard, flange drilling, facing, gasket, bolting, test criteria, and traceable inspection documents.

If you need a PN25 gate valve, butterfly valve, check valve, pressure reducing valve, or matching pipeline component, contact Norite with your DN, medium, pressure-temperature conditions, flange standard, and project documents for a technical review and quotation.

Standards Commonly Referenced in PN25 Projects

Use the latest edition adopted by the contract or project specification:

• EN 1333 — Definition and selection of PN
• EN 1092-1 — PN-designated steel flanges
• EN 1092-2 — PN-designated cast-iron and ductile-iron flanges
• EN 1074 series — Valves for water supply
• EN 558 — Face-to-face and center-to-face dimensions of metal valves
• EN 12266-1 — Pressure tests, test procedures, and acceptance criteria for metallic valves
• ISO 5208 — Pressure testing of metallic valves
• ASME B16.34 — Pressure-temperature ratings and requirements for applicable valves
• ASME B16.5 — Pipe flanges and flanged fittings for applicable ASME systems