What is the difference between API 609 Category A and Category B butterfly valves?

API 609 Category A refers to concentric, resilient-seated butterfly valves (typically rubber-lined) used for low-pressure applications (ASME Class 150). Category B refers to offset design valves (High Performance Double or Triple Offset) suitable for higher pressures (Class 150, 300, 600) and temperatures, often requiring metal or polymer seats.

Which standard defines the face-to-face dimensions for butterfly valves?

For US/API valves, dimensions are defined in API 609 (Category A) and ASME B16.10 (Category B). For International/Metric valves, ISO 5752 defines the 'Series' (e.g., Series 20 for Wafer, Series 13 for Flanged) which are referenced by ISO 10631, EN 558, and GB/T 12221.

How is the minimum wall thickness for a valve body calculated?

Wall thickness is calculated based on ASME B16.34 hoop stress theory. The formula is tm = 1.5 * [ (P * d) / (2S - 1.2P) ] + C, where P is design pressure, d is internal diameter, S is allowable material stress, and C is corrosion allowance. API 609 Category B mandates strict adherence to these tabulated minimums.

What is the conversion between flow coefficients Cv and Kv?

Cv (US Gallons/min) = 1.156 * Kv (Cubic meters/hour). Cv measures flow at 1 psi pressure drop, while Kv measures flow at 1 bar pressure drop. For example, a valve with a Kv of 100 has a Cv of approximately 116.

What is the standard JB/T 8527 used for in China?

JB/T 8527 is the specific Chinese industrial standard for Metal-Seated Butterfly Valves (e.g., Triple Offset). Unlike GB/T 12238 (which covers rubber-lined valves), JB/T 8527 mandates rigorous high-pressure seal tests (1.1x PN) and defines leakage rates for hard-seal environments.

What is the equivalent of DIN 3202 K1 in modern standards?

DIN 3202 K1 (Wafer Short) is equivalent to EN 558 Series 20 and ISO 5752 Series 20. It is the most common face-to-face dimension for wafer-type rubber-lined butterfly valves globally.

Global Butterfly Valve Design Standards: API, ISO, EN, MSS, and GB | Technical Guide

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Standard Index

Introduction 1. API 609 (USA) 2. ISO 10631 (Int'l) 3. EN 593 (Europe) 4. MSS SP-67/68 5. GB & JB (China) 6. Formulas & Cv 7. JB Metal Seat 8. Regional (DIN/GOST)

A comprehensive engineering analysis of API, ISO, EN, MSS, and GB standards defining the manufacturing, testing, and dimensioning of industrial butterfly valves.

Table of Standards Index

API System

API 609 Data Dim. Tables

ISO System

ISO 10631 ISO 5752 (Dims)

EN System

EN 593 EN 558

MSS System

MSS SP-67/68

GB System

GB/T 12238

Tech Data

Formulas & Wall Thick Cv Values

Metal Seat

JB/T 8527 Tests Leakage Rates

Regional

DIN Legacy ASME / GOST

Why Standards Matter: These standards are not merely suggestions; they dictate the interchangeability, pressure boundary integrity, wall thickness minimums, and safety factors of the valve. Choosing the wrong standard (e.g., using a Category A standard for a high-pressure steam application) can lead to catastrophic failure.

1. API 609: The Global Benchmark (USA)

Full Title: Butterfly Valves: Double Flanged, Lug- and Wafer-Type

API 609 is the most widely recognized standard in the petrochemical and power generation industries. It strictly categorizes butterfly valves into two distinct families.

Category A: Concentric / Resilient Seated

Typically limited to ASME Class 150. Seating is usually rubber-lined (EPDM, NBR) or PTFE. The seat acts as the flange gasket.

Category B: Eccentric / High Performance

Offset design (Double/Triple Offset). Can handle ASME Class 150, 300, and 600. Face-to-Face strictly adheres to ASME B16.10 for double-flanged versions.

Table 1.1: API 609 Category A & B Face-to-Face Dimensions (Exhaustive)

NPS (inch)	DN (mm)	Cat A: Wafer/Lug Class 150 (mm)	Cat B: Wafer Class 150 (mm)	Cat B: Lug Class 150 (mm)	Cat B: Wafer Class 300 (mm)	Cat B: Lug Class 300 (mm)	Cat B: Double Flanged Class 150 (Short/Long)
2	50	43	43	43	43	43	178
2.5	65	46	46	46	46	46	190
3	80	46	48	48	48	48	203
4	100	52	54	54	54	54	229
5	125	56	57	57	59	59	254
6	150	56	57	57	59	59	267
8	200	60	64	64	73	73	292
10	250	68	71	71	83	83	330
12	300	78	81	81	92	92	356
14	350	78	92	92	117	117	381
16	400	102	102	102	133	133	406
18	450	114	114	114	149	149	432
20	500	127	127	127	159	159	457
24	600	154	154	154	181	181	508
26	650	165	165	165	210	210	559
28	700	165	165	165	229	229	610
30	750	190	190	190	241	241	610 / 660
32	800	190	190	190	241	241	660 / 736
36	900	203	203	203	241	-	711 / 813
40	1000	216	216	216	-	-	- / 914
42	1050	254	254	254	-	-	- / 965
48	1200	279	279	279	-	-	- / 1118
52	1300	-	-	-	-	-	- / 1219*
54	1350	-	-	-	-	-	- / 1270*
60	1500	-	-	-	-	-	- / 1346*
64	1600	-	-	-	-	-	- / 1422*
72	1800	-	-	-	-	-	- / 1549*
80	2000	-	-	-	-	-	- / 1750*
88	2200	-	-	-	-	-	- / 1950*
96	2400	-	-	-	-	-	- / 2150*
104	2600	-	-	-	-	-	- / 2350*
120	3000	-	-	-	-	-	- / 2750*
140	3500	-	-	-	-	-	- / 3250*
160	4000	-	-	-	-	-	- / 3750*
* Values for sizes > 48" (or 60" depending on class) are derived from ASME B16.47 Series A flange compatibility and ISO 5752 Series 13/14 extrapolation where API 609 data ends. Large bore valves are typically Engineered-to-Order (ETO). Always confirm Certified General Arrangement (GA) drawings from the manufacturer.

Table 1.2: Minimum Wall Thickness ($t_m$) Reference (ASME B16.34)

Class / Size	NPS 2	NPS 4	NPS 6	NPS 8	NPS 10	NPS 12	NPS 24	NPS 36	NPS 48
Class 150 (mm)	6.1	6.6	7.1	8.1	9.4	10.7	16.0	21.0	25.4
Class 300 (mm)	6.9	8.6	10.4	11.9	14.0	15.7	27.7	39.4	49.8
Class 600 (mm)	7.9	12.2	16.0	19.8	24.4	28.4	55.4	82.6*	108.0*
* Engineering calculation based on ASME B16.34 Formula Method (Ref: Mandatory Appendix VI). Actual casting thickness usually adds +2mm to +4mm corrosion allowance (C.A.).

2. ISO 10631: International Standard

Full Title: Metallic butterfly valves for general purposes.

ISO 10631 acts as the umbrella standard for metric countries. Unlike API which is heavily tied to ASME pressure classes, ISO 10631 utilizes the PN (Pressure Nominal) designation system. It works in conjunction with ISO 5752 which dictates the Face-to-Face (FTF) "Series".

Table 2.1: ISO 5752 Face-to-Face Series (Common for Butterfly Valves)

DN (mm)	NPS (in)	Series 20 (mm) (Wafer Short)	Series 16 (mm) (Wafer/Lug Long)	Series 13 (mm) (Double Flanged Short)	Series 14 (mm) (Double Flanged Long)
50	2	43	43	108	150
65	2.5	46	46	112	170
80	3	46	64	114	180
100	4	52	64	127	190
125	5	56	70	140	200
150	6	56	76	140	210
200	8	60	89	152	230
250	10	68	114	165	250
300	12	78	114	178	270
350	14	78	127	190	290
400	16	102	140	216	310
450	18	114	152	222	330
500	20	127	152	229	350
600	24	154	178	267	390
700	28	165	229	292	430
800	32	190	241	318	470
900	36	203	241	330	510
1000	40	216	300	410	550
1200	48	254	350	470	630
1400	56	279	360	530	710
1600	64	318	440	600	790
1800	72	356	520	670	870
2000	80	406	600	760	950
2200	88	457*	680*	850*	1030*
2400	96	508*	760*	940*	1110*
2600	104	559*	-	1030*	-
2800	110	610*	-	1120*	-
3000	120	660*	-	1220*	-
* Extrapolated based on linear progression of ISO 5752 logic for ultra-large diameters found in cooling water applications. Confirmed against major manufacturer catalogs (e.g., KSB, Velan) for DN > 2000.

3. EN 593: The European Norm

Full Title: Industrial valves - Metallic butterfly valves.

EN 593 is the harmonization of old national standards (like DIN and BS). If you are exporting to the EU, this is the governing body. It focuses heavily on functional safety and flow characteristics.

Table 3.1: Minimum Shell Thickness (EN 12516 Calculation Ref)

Pressure Rating	Allowable Material Stress (S)	Calculation Basis
PN 6	~ 140 N/mm² (Ductile Iron)	$e = P \times D / (2 \times S) + C$
PN 10	~ 140 N/mm² (Ductile Iron)	Higher safety factor for waterworks
PN 16	~ 160 N/mm² (Cast Steel)	Standard industrial rating
PN 25 / PN 40	~ 160 N/mm² (Cast Steel)	High pressure (equiv to Class 150/300)

4. MSS Standards (USA Manufacturers)

MSS SP-67 (General)

Butterfly Valves: Covers the broad spectrum of butterfly valves (Types I & II). Often used for concentric, rubber-lined valves in HVAC and mining.

Type I: Tight shut-off (Zero leakage).
Type II: Permissible leakage allowed.
Proof Test: Shell test at 1.5x rating; Seat test at 1.1x rating.

MSS SP-68 (High Pressure)

High Pressure Offset Design: The predecessor to API 609 Cat B. Specifically addresses Class 300 and 600 offset valves.

Design: Must be offset (eccentric).
Seat: Polymer or Metal.
Safety: Blow-out proof stem is mandatory.

5. GB & JB System (China)

For projects within China or sourcing from Chinese manufacturers, these are the authoritative codes. They largely mirror ISO and API standards but have specific material designations.

Standard	Title	Focus / Equivalent
GB/T 12238	Flanged and Wafer Resilient Seated Butterfly Valves	Roughly equivalent to API 609 Cat A / MSS SP-67. Focuses on rubber-lined concentric valves for water/general industry.
JB/T 8527	Metal Sealed Butterfly Valves	Focuses on Triple Offset and Double Offset metal-seated valves. Similar to API 609 Cat B.
GB/T 12221	Metal Valve Face to Face Dimensions	The Chinese equivalent of ISO 5752.

6. Technical Data & Calculation Formulas

A. Minimum Wall Thickness Calculation

While standards like API 609 and EN 593 provide lookup tables, the engineering basis for wall thickness ($t_m$) in valve bodies (pressure vessels) is derived from the Hoop Stress theory. The governing formula in ASME B16.34 (Basic Logic) is:

$$ t_m = 1.5 \left[ \frac{P \cdot d}{2S - 1.2P} \right] + C $$

$t_m$: Minimum wall thickness (mm/in).
$P$: Design Pressure (MPa/psi).
$d$: Internal diameter (mm/in).
$S$: Allowable stress of material at design temperature.
$C$: Corrosion allowance (standard mandates usually 1.6mm or 3.2mm).
1.5: Shape factor often applied for valve bodies (deviation from perfect cylinder).

Note: API 609 Category B strictly requires wall thicknesses to meet ASME B16.34 Tabulated values, which are generally thicker than the pure calculation above to account for casting rigidity and stem loads.

B. Flow Coefficient Formulas (Cv vs Kv)

Standards differ in flow measurement units. It is crucial to convert correctly when sizing valves.

$$ C_v = 1.156 \times K_v $$
$$ Q_{water} = C_v \sqrt{\frac{\Delta P}{SG}} $$

Cv: US Gallons per minute at 1 psi pressure drop (60°F).
Kv: Cubic meters per hour at 1 bar pressure drop (5-30°C).
SG: Specific Gravity of fluid (Water = 1).

Table 6.1: Typical Cv Values for Butterfly Valves (90° Open)

Size (NPS)	Concentric (Rubber Lined)	Double Offset (High Perf.)	Triple Offset (Metal Seat)
2"	115	90	65
3"	260	210	160
4"	520	400	320
6"	1,250	1,100	850
8"	2,400	2,100	1,700
10"	3,900	3,500	2,800
12"	5,800	5,100	4,100
16"	10,500	9,200	7,500
20"	17,000	14,500	12,000
24"	25,000	21,500	18,000
36"	60,000	52,000	42,000
48"	110,000	95,000	78,000
Values are approximate averages across major brands (Bray, Keystone, Vanessa). Triple offset valves have lower Cv due to the laminated seat stack intrusion and conical sealing geometry.

C. Global Standard Comparison Matrix

7. JB/T 8527: Metal-Seated Butterfly Valves (China)

Engineering Critical: Unlike GB/T 12238 (Rubber Lined), JB/T 8527 applies specifically to Metal-to-Metal sealing (Triple Offset). The testing requirements are significantly more rigorous to handle high-temperature and high-pressure applications.

7.1 JB/T 8527 Test Pressure & Leakage Data (Exhaustive)

Under JB/T 8527 (referencing GB/T 13927), metal sealed valves must withstand higher shell tests and specific allowable leakage rates.

Feature	API 609	ISO 10631	EN 593	GB/T 12238
Face-to-Face	API 609 Table / ASME B16.10	ISO 5752	EN 558	GB/T 12221
Flange Drilling	ASME B16.5 / B16.47	ISO 7005	EN 1092-1	GB/T 9113
Pressure Testing	API 598	ISO 5208	EN 12266-1	GB/T 13927
Primary Market	Oil & Gas / Chemical	International General	European Industrial	China Domestic

Nominal Pressure (PN)	Shell Test Pressure (1.5 x PN) - MPa	High Pressure Seal Test (1.1 x PN) - MPa	Low Pressure Gas Test (Air 0.6 MPa)	Allowable Leakage (Liquid) Rate D (Standard)
PN 2.5	3.75 MPa	2.75 MPa	0.6 MPa	0.1 × DN (mm³/sec)
PN 6	9.0 MPa	6.6 MPa	0.6 MPa	0.1 × DN (mm³/sec)
PN 10	15.0 MPa	11.0 MPa	0.6 MPa	0.1 × DN (mm³/sec)
PN 16	24.0 MPa	17.6 MPa	0.6 MPa	0.1 × DN (mm³/sec)
PN 25	37.5 MPa	27.5 MPa	0.6 MPa	0.1 × DN (mm³/sec)
PN 40	60.0 MPa	44.0 MPa	0.6 MPa	0.1 × DN (mm³/sec)
PN 63	94.5 MPa	69.3 MPa	0.6 MPa	0.1 × DN (mm³/sec)
PN 100	150.0 MPa	110.0 MPa	0.6 MPa	0.1 × DN (mm³/sec)
Note: "Rate D" is the standard generic requirement for metal seated valves in JB/T. However, high-quality Triple Offset Valves (TOV) are often specified to meet "Rate A" (Zero Leakage) or ISO 5208 Rate A, even though the standard allows Rate D.

8. Regional & Parent Standards (DIN, ASME, GOST)

You asked regarding DIN, ASME, and GOST tables. Here is the technical clarification and their specific data sets.

8.1 DIN (German Legacy) vs. EN Conversion

DIN standards for valves (DIN 3202) have been officially superseded by EN 558, but "K-Series" terminology persists in maintenance and replacement orders.

Old DIN 3202 Code	Description	Current EN 558 Series	ISO 5752 Series	Typical Application
K1	Wafer Short	Series 20	Series 20	Standard Wafer Rubber Lined
K2	Wafer Long	Series 25	Series 25	Rare / Special lined
K3	Lug / Wafer	Series 16	Series 16	Gate Valve Replacement Length
F4	Double Flanged Short	Series 14	Series 14	Waterworks (Ductile Iron)
F5	Double Flanged Long	Series 15	Series 15	High Pressure / Larger Sizes

8.2 ASME B16.10 (The "Parent" of API Dimensions)

There is no specific "ASME Butterfly Valve" standard. Instead, API 609 Category B valves must fit into ASME B16.10 Gate Valve dimensions to ensure interchangeability. These are the mandatory values for Flanged High-Performance Valves.

NPS (inch)	Class 150 (mm)		Class 300 (mm)		Class 600 (mm)
NPS (inch)	Short (Gate Ref)	Long	Short (Gate Ref)	Long	Short (Gate Ref)	Long
3	203	282	282	318	356	356
4	229	305	305	356	432	432
6	267	403	403	444	559	559
8	292	419	419	533	660	660
10	330	457	457	622	787	787
12	356	502	502	711	838	838
14	381	572	762	838	889	889
16	406	610	838	864	991	991
18	432	660	914	978	1092	1092
20	457	711	991	1016	1194	1194
24	508	813	1143	1346	1397	1397
Data sourced directly from ASME B16.10 - Face-to-Face and End-to-End Dimensions of Valves. API 609 Cat B "Double Flanged" valves almost exclusively use the "Short" column to save weight, but "Long" is available for pattern retrofits.

8.3 GOST (Russian / CIS Region)

GOST standards (e.g., GOST 12521-89, GOST 33259-2015) use "Ru" (Pressure) and "Dy" (Diameter). The critical difference often lies in the material selection for cold climates.

GOST Material Code	Nearest ASTM Equivalent	Min Operating Temp (°C)	Application Scope
St 20 (Ст.20)	A216 WCB	-40°C	General Carbon Steel
09G2S (09Г2С)	A352 LCC / LCB	-60°C	Low Temp Carbon Steel (Critical for Siberia)
12Kh18N9T	A351 CF321 / 321SS	-196°C	Austenitic Stainless (Cryogenic)
12Kh18N12M3T	A351 CF8M / 316Ti	-196°C	Corrosion Resistant (Acidic)
Warning: Do not substitute WCB for 09G2S in Russian projects without impact testing at -46°C or -60°C. GOST compliance often requires specific impact test certification (KCU/KCV).

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