When selecting an Industrial Butterfly Valve, one of the first questions buyers often face is whether to choose aEuropean-standard butterfly valve or an American-standard butterfly valve.

At first glance, the difference may appear to be simply PN versus Class pressure designations. In engineering practice, however, the differences involve a much broader range of requirements, including valve design standards, pressure-temperature ratings, face-to-face dimensions, flange connections, testing procedures, materials, and actuator interfaces.

This distinction becomes particularly important for international projects and valve replacement applications. Two butterfly valves with the same nominal size and similar pressure ratings may not be directly interchangeable if their face-to-face dimensions, flange compatibility, or other installation dimensions are different.

As an experienced butterfly valve manufacturer, KEFA VALVE supplies butterfly valves for both European- and American-standard applications, with configurations selected according to the customer's piping system, project specifications, and service conditions.

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1. What Is the Difference Between European and American Butterfly Valves?

The fundamental difference is not simply:

Europe = PN
America = Class

Instead, the difference lies in the combination of standards applied to the valve and the surrounding piping system.

A typical European-oriented butterfly valve specification may reference:

• EN 593 — Metallic butterfly valves for general purposes

• EN 558 — Face-to-face and centre-to-face dimensions

• EN 1092-1 / EN 1092-2 — Flanges and their joints

• EN 12266-1 — Pressure testing of valves

• ISO 5211 — Mounting interface for actuators

A typical American-oriented specification may reference:

• API 609 — Butterfly valves

• API 609 CAT. A/C — Face-to-face and end-to-end dimensions

• ASME B16.5 — Pipe flanges and flanged fittings

• ASME B16.34 — Valves and pressure-temperature ratings

• API 598 — Valve inspection and testing

The exact standards required depend on the valve design, pressure class, connection type, piping system, service conditions, and project specification.

Therefore, the correct approach is to evaluate the complete technical specification rather than selecting a valve based only on its PN or Class designation.

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2. European-Standard Butterfly Valves — EN 593

European-standard butterfly valves are commonly specified for piping systems designed around EN, DIN, PN and ISO standards.

EN 593 — Metallic Butterfly Valves

EN 593 establishes general requirements for metallic butterfly valves used for isolating, throttling, and controlling flow in piping systems.

The standard covers different valve configurations, including:

• Wafer Butterfly Valves

• Lug-type Butterfly Valves

• Flanged butterfly valves

• Butt-weld end butterfly valves

EN 593 accommodates both PN and Class pressure designations, so the distinction between European and American valve specifications should not be reduced to PN versus Class alone.

Typical applications include:

• Water treatment

• Water supply and distribution

• Wastewater

• HVAC systems

• Chemical processing

• Power generation

• Marine applications

• General industrial services

For European projects, EN 593 is often considered together with EN 558 for dimensions, EN 1092 for flanges, and EN 12266-1 for pressure testing.

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3. EN 558 and Butterfly Valve Face-to-Face Dimensions

The face-to-face dimension is one of the most critical parameters when selecting or replacing a butterfly valve.

EN 558 specifies face-to-face and centre-to-face dimensions for metallic valves installed in flanged piping systems. It contains a number of dimensional series, including commonly used butterfly valve series.

For butterfly valves, the following series are particularly relevant:

• Series 13 — associated with short-pattern double-flanged butterfly valve dimensions

• Series 14 — associated with DIN dimensional practice

• Series 20 — commonly used for wafer and lug-type butterfly valves

The applicable series should always be confirmed against the valve type, nominal size, pressure designation, and applicable standard.

Why does this matter?

Suppose a customer specifies:

DN200, PN16, face-to-face 250 mm

It would be incorrect to assume that every DN200 PN16 butterfly valve has a 250 mm face-to-face dimension.

The manufacturer should verify:

1. Valve type

2. Nominal size

3. Pressure designation

4. Dimensional series

5. Required face-to-face dimension

6. Flange standard

7. Actual manufacturer's dimensional drawing

For replacement projects, the actual face-to-face dimension can be a critical installation parameter.

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4. American-Standard Butterfly Valves — API 609

American-standard butterfly valves are widely used in projects based on API, ASME, ANSI and MSS standards.

For industrial butterfly valves, API 609 is one of the principal design standards.

API 609 covers several butterfly valve configurations, including:

• Double-flanged butterfly valves

• Lug-type butterfly valves

• Wafer-type butterfly valves

• Butt-welding-end butterfly valves

The standard also addresses requirements related to design, materials, pressure-temperature ratings, dimensions and testing.

Typical applications include:

• Oil and gas

• Refineries

• Petrochemical plants

• Power generation

• Industrial water systems

• Chemical processing

• General process piping

American-oriented specifications commonly use:

• NPS for nominal pipe size

• Class 150 / Class 300 / Class 600, etc., for pressure class

• ASME B16.5 for applicable flanged connections

• ASME B16.10 for applicable face-to-face dimensions

• API 598 for inspection and pressure testing

However, the applicable standard and dimensional requirements should always be confirmed from the project specification.

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5. API 609 Categories and Butterfly Valve Dimensions

One important point when comparing American and European butterfly valves is that API 609 does not define all butterfly valves under a single dimensional configuration.

API 609 uses different categories to address different butterfly valve designs.

The corresponding relationship between European and American butterfly valves in terms of structural length is as follows:

Wafer or lug butterfly valve (concentric/soft seal): Complies with API 609 Category A, and its structural length corresponds to EN 558 series 20.

Double flange butterfly valve (concentric/eccentric/high-performance): Complies with API 609 Category C, and its structural length corresponds to EN 558 series 13.

Therefore, it is not technically correct to assume:

All API 609 butterfly valves = EN 558 Series 20

or:

All double-flanged API 609 butterfly valves = EN 558 Series 13.

The applicable dimensional relationship depends on the API 609 category, valve construction, pressure class, nominal size and specified dimensional standard.

For a specific project, the manufacturer's dimensional drawing should always be used for final verification.

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6. EN 558 vs. API 609 — Why Face-to-Face Dimensions Must Be Verified

EN 558 and API 609 are both important dimensional references, but they should not be treated as automatically interchangeable.

EN 558 establishes standardized face-to-face and centre-to-face dimensions for valves in flanged piping systems.

API 609 establishes face-to-face and end-to-end dimensions for valves and is widely used in ASME-based piping systems.

Valve Size		EN 558-1			API609 CAT.A		API609 CAT.C
		13 Series	14 Series	20 Series
mm	INCH	mm	mm	mm	mm	Inch	mm	Inch
DN40	1.5	106	140	33
DN50	2	108	150	43	43	1.69
DN65	3	112	170	46	46	1.81
DN80	3	114	180	46	46	2.06	114	4.50
DN100	4	127	190	52	52	2.19	127	5.00
DN125	5	140	200	56	56	2.19
DN150	6	140	210	56	56	2.38	140	5.50
DN200	8	152	230	60	60	2.69	152	6.00
DN250	10	165	250	68	68	3.06	165	6.50
DN300	12	178	270	78	78	3.06	178	7.00
DN350	14	190	290	78	78	4.00	190	7.50
DN400	16	216	310	102	102	4.00	216	8.50
DN450	18	222	330	114	114	4.50	222	8.75
DN500	20	229	350	127	127	5.00	229	9.00
DN600	24	267	390	154	154	6.06	267	10.50
DN650	26						292	11.50
DN700	28	292	430	165			292	11.50
DN750	30	—	—	190	165	6.50	318	12.52
DN800	32	318	470	190			318	12.52
DN900	36	330	510	203	200	7.88	330	12.99
DN950	38						410	16.14
DN1000	40	410	550	216			410	16.14
DN1100	42				251	9.88	410	16.14
DN1200	48	470	630	254	276	10.88	470	18.50
DN1400	56	530	710	279
DN1600	64	600	790	318
DN1800	72	670	870	356
DN2000	80	760	950	406

For butterfly valves, dimensional requirements can depend on the valve type, design category, pressure class, nominal size and applicable series.

Consequently:

An EN 558 butterfly valve should not automatically be considered dimensionally interchangeable with an API 609 butterfly valve.

When replacing an existing valve, the most reliable method is to compare the actual required face-to-face dimension with the manufacturer's certified dimensional drawing.

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7. PN Rating vs. Class Rating

European piping systems commonly use pressure designations such as:

• PN10

• PN16

• PN25

• PN40

• PN63

• PN100

American piping systems commonly use:

• Class 150

• Class 300

• Class 600

• Class 900

However:

PN16 is not automatically equivalent to Class 150.

Pressure-temperature ratings depend on factors such as:

• Valve design standard

• Valve body material

• Pressure class

• Operating temperature

• Flange standard

• Seat and sealing materials

• Applicable piping code

Therefore, a professional valve specification should identify the complete pressure-temperature rating rather than relying on a simple PN-to-Class conversion.

For example, when a customer specifies PN16 or Class 150, the manufacturer should verify the applicable pressure-temperature rating for the complete valve configuration.

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8. Flange Standards: EN 1092 vs. ASME B16.5

Flange compatibility is another critical difference between European- and American-oriented piping systems.

European projects commonly use:

EN 1092-1 / EN 1092-2

while American piping systems commonly use:

ASME B16.5

For ASME B16.5, the standard generally covers flanges and flanged fittings for sizes up to NPS 24. Larger sizes may fall under other applicable ASME standards or project specifications.

Differences between flange standards may include:

• Outside diameter

• Bolt circle diameter

• Number of bolt holes

• Bolt-hole diameter

• Flange thickness

• Facing dimensions

• Pressure designation

What about wafer butterfly valves?

A wafer butterfly valve does not have integral flanges, but it must still be compatible with the mating pipeline flanges.

For example:

EN 1092 PN16 piping

and

ASME B16.5 Class 150 piping

should not be assumed to be directly interchangeable without checking the actual dimensions and sealing arrangement.

This is particularly important for large-diameter valves and replacement projects.

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9. Butterfly Valve Materials: Selection by Service Conditions

Material selection should be based primarily on service conditions, rather than on whether the valve is European or American.

Common butterfly valve body materials include:

Cast Iron / Ductile Iron / Carbon Steel / Stainless Steel / Aluminium Bronze

Common disc materials include:

Ductile Iron / Nickel-plated Ductile Iron / Stainless Steel (CF8, CF8M, CF3/CF3M, 904L, 2507, etc) /  Aluminium Bronze

Common stem materials include:

SS410 / SS420 / SS431 /SS304 / SS316 / SS316L / 17-4PH / Monel K500...

Common seat materials include:

EPDM / NBR / FKM / PTFE / RPTFE

The correct material combination depends on:

• Fluid medium

• Operating temperature

• Pressure

• Corrosion

• Abrasion

• Chemical compatibility

• Required service life

For example, EPDM is widely used for many water applications, while NBR is commonly selected for certain oil-containing services. FKM, PTFE or engineered sealing materials may be considered for higher-temperature or chemically aggressive applications, subject to the specific medium and temperature.

Material selection should therefore be based on the actual operating conditions and chemical compatibility rather than a simple European-versus-American classification.

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10. Testing Standards: EN 12266-1 vs. API 598

Testing is another important consideration when specifying butterfly valves.

European projects may specify:

EN 12266-1

while American projects commonly reference:

API 598

EN 12266-1 establishes procedures and acceptance criteria for pressure testing of industrial valves, including shell and seat testing.

API 598 covers valve inspection and pressure testing requirements and is widely referenced for API/ASME-oriented valve applications.

Neither standard should simply be described as universally "stricter" than the other.

Instead, the purchaser should clearly specify:

Shell test, Seat test, Test pressure, Test duration, Test medium, Permissible leakage, Inspection requirements, Additional NDE requirements, where applicable

For critical projects, additional requirements may include:

Material certificates, PMI, NDE, Hydrostatic test reports, Functional testing, Third-party inspection, Traceability documentation

The final testing requirements should always follow the applicable valve standard and project specification.

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11. European vs. American Butterfly Valves — Quick Comparison

Item	European-Oriented Specification	American-Oriented Specification
Principal butterfly valve standard	EN 593	API 609
Common dimensional reference	EN 558	API 609
Common flange standard	EN 1092-1 / EN 1092-2	ASME B16.5
Pressure designation	PN / Class	Class
Nominal size	DN	NPS
Testing reference	EN 12266-1	API 598
Actuator mounting	ISO 5211 commonly used	ISO 5211 / project specification
Typical applications	Water, HVAC, chemical, industrial	Oil & gas, petrochemical, power, industrial
Key dimensional concern	EN 558 series and actual face-to-face dimension	Applicable API/ASME dimensional requirements
Key connection concern	EN 1092 flange compatibility	ASME B16.5 flange compatibility

This table provides a general engineering comparison. The applicable project specification and manufacturer's certified drawings should always take precedence.

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12. Can a European Butterfly Valve Replace an American Butterfly Valve?

In some applications, yes — but not automatically.

A butterfly valve manufactured outside Europe or the United States can be designed and supplied to the required European or American standards.

The critical question is not:

Where was the valve manufactured?

The more important question is:

Does the valve comply with the required design, dimensional, connection, pressure, testing and material requirements?

Before approving a replacement valve, the following should be verified:

Design Standard

• EN 593

• API 609

• Other project-specific standards

Dimensions

• EN 558

• API 609

• Applicable dimensional series

• Actual face-to-face dimension

Flanges

• EN 1092

• ASME B16.5

• Other applicable flange standards

Pressure Rating

• PN10 / PN16 / PN25 / PN40

• Class 150 / 300 / 600

Testing

• EN 12266-1

• API 598

• Project-specific testing requirements

Materials

Body, Disc, Stem, Seat, Bearings, Fasteners

Actuation

Lever, Gearbox, Pneumatic actuator, Electric actuator, Hydraulic actuator

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13. Why Face-to-Face Dimensions Matter in Valve Replacement

For many replacement projects, face-to-face dimension is one of the most important installation parameters.

Consider a customer requirement:

"The required face-to-face length is 250 mm."

The manufacturer should not simply select a valve based on DN200 and PN16.

The proper engineering process is to verify:

1. Valve configuration

2. Nominal size

3. Pressure designation

4. Applicable design standard

5. Applicable dimensional series

6. Required face-to-face dimension

7. Pipeline flange standard

8. Operating conditions

9. Actuator requirements

If the standard product dimension does not match the customer's requirement, the manufacturer should clearly identify the standard dimension and determine whether a special face-to-face configuration is technically feasible.

This approach helps avoid costly modifications during installation.

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14. KEFA VALVE — European and American Standard Butterfly Valve Solutions

KEFA VALVE provides butterfly valve solutions for international projects requiring different design and piping standards.

For European-oriented applications, KEFA VALVE can provide configurations based on applicable requirements such as:

• EN 593

• EN 558

• EN 1092

• EN 12266-1

• ISO 5211

Available configurations may include:

• Wafer butterfly valves

• Lug butterfly valves

• Flanged butterfly valves

• Double-flanged butterfly valves

• Concentric butterfly valves

• Double-eccentric butterfly valves

For American-oriented applications, KEFA VALVE can provide configurations based on applicable requirements such as:

• API 609

• ASME B16.10

• ASME B16.5

• API 598

• ISO 5211 where applicable

Available configurations may include:

• Wafer butterfly valves

• Lug butterfly valves

• Flanged butterfly valves

• High-performance butterfly valves

• Double-eccentric butterfly valves

Valve operation can be configured with:

• Manual lever

• Worm gearbox

• Pneumatic actuator

• Electric actuator

• Positioner

• Solenoid valve

• Limit switch box

• Air filter regulator

• Other valve automation accessories

The final configuration is selected according to the project specification, pipeline standard, service medium, pressure, temperature and operating requirements.

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15. How to Specify a Butterfly Valve Correctly

For an international project, specifying only:

DN200 PN16 Butterfly Valve

is generally not sufficient.

A complete butterfly valve specification should identify the following:

Valve Type

Wafer / Lug / Flanged / Double-Flanged

Size

DN200 / NPS 8

Pressure Rating

PN16 / Class 150

Design Standard

EN 593 / API 609

Dimensional Standard

EN 558 / ASME B16.10 / Specific Face-to-Face Dimension

Flange Standard

EN 1092 / ASME B16.5

Testing Standard

EN 12266-1 / API 598

Materials

Body / Disc / Stem / Seat / Bearings / Fasteners

Operation

Lever / Gearbox / Pneumatic / Electric

Service Conditions

Medium / Temperature / Pressure / Flow conditions

Providing this information at the quotation stage helps the manufacturer select the correct valve configuration and reduces the risk of dimensional, material or installation incompatibility.

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16. European or American Standard — Which Should You Choose?

There is no universal answer that one standard is better than the other.

The correct selection depends primarily on the existing piping system and project specification.

European-oriented specifications are generally appropriate when:

• The project is designed around EN/DIN standards

• The piping uses PN-rated flanges

• EN 558 dimensions are specified

• EN 1092 flange connections are required

• EN 593 is specified for the butterfly valve

• EN-based testing requirements are specified

American-oriented specifications are generally appropriate when:

• The project is designed around ASME/API standards

• The piping uses Class-rated flanges

• API 609 is specified

• ASME dimensional requirements are specified

• ASME B16.5 flanges are required

• API 598 testing is specified

For international projects, the best approach is not to select a valve according to the manufacturer's country of origin.

Instead:

Select the valve according to the requirements of the piping system and project specification.

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17. Final Takeaway

European and American butterfly valves should not be differentiated simply by PN versus Class.

The complete engineering comparison involves:

Design Standard → Valve Configuration → Pressure Rating → Dimensional Series → Face-to-Face Dimension → Flange Standard → Testing → Materials → Actuation

For European-oriented projects, common references include:

EN 593 + EN 558 + EN 1092 + EN 12266-1

For American-oriented projects, common references include:

API 609 + ASME B16.10 + ASME B16.5 + API 598

However, these standards are not automatically interchangeable. The applicable standard depends on the valve design, connection type, pressure class, nominal size and project specification.

Most importantly, never select a replacement butterfly valve based only on DN/NPS and PN/Class.

Always verify:

• Valve type

• Design standard

• Dimensional series

• Face-to-face dimension

• Flange compatibility

• Pressure-temperature rating

• Materials

• Leakage requirements

• Testing standard

• Actuator interface

With experience in international valve manufacturing and export applications, KEFA VALVE provides butterfly valve configurations for both European- and American-standard projects.

For valve selection or replacement, provide the valve type, size, pressure rating, connection standard, required face-to-face dimension, medium and operating conditions. KEFA VALVE can help determine the appropriate butterfly valve configuration for your piping system.