Valve Face-to-Face Dimensions: GB/T 12221 vs EN 558 vs ASME B16.10
What "Face-to-Face" Actually Means
Face-to-face dimension (结构长度, sometimes called structure length or L) is the distance between the two end connection faces of a valve - the two flanges, the two weld ends, or the two threaded faces. It is the single most installation-critical number on a valve. If the face-to-face is wrong, the valve cannot be squeezed between two already-welded or already-bolted pipe flanges, no matter how perfectly the pressure class and bore match.
This dimension is standardised, but not by one global standard. Three families dominate, and they do not always agree:
- ASME B16.10 (and API 6D for pipeline valves) - the US system for Class-rated valves
- EN 558 - the European system, with a basic (long) series and a compact (short) series
- GB/T 12221-2005 - the Chinese system, which covers both PN-rated and Class-rated ends
The GB/T 12221 Short vs Long Trap
GB/T 12221-2005 "Metal Valves - Face-to-Face Dimensions" specifies both a short series and a long series for flanged gate valves. For a DN100 PN16 gate valve the two are:
| GB/T 12221-2005 flanged gate valve, DN100 | Face-to-face |
|---|---|
| Short series | 229 mm |
| Long series (catalog standard) | 300 mm |
That 71 mm gap is the whole game. A Chinese catalogue "Z41H-16C DN100" almost always lists the long series (300 mm), because that is the conventional product. But the standard explicitly permits the short series. If you assume one and receive the other, the valve will not seat between your flanges.
Why "PN16 = Class 150" Is a Dimension Myth
Buyers frequently hears that "PN16 is about the same as Class 150" and extends that to dimensions. At the flange level that approximation is rough and dangerous (see our PN vs ASME Class guide). At the face-to-face level it is simply false in general, even though it looks true at one size:
| Standard / series | DN100 (NPS 4) gate valve face-to-face |
|---|---|
| GB/T 12221-2005 PN16, short series | 229 mm |
| GB/T 12221-2005 PN16, long series | 300 mm |
| ASME B16.10 Class 150 (long pattern) | 229 mm |
| ASME B16.10 Class 300 (long pattern) | 406 mm |
Notice the coincidence: the GB/T 12221 short series at DN100 equals ASME B16.10 Class 150 (both 229 mm). That one overlap is why the myth spreads. But the conventional Chinese long series is 300 mm - it will not fit a Class 150 pipeline that expects 229 mm. And Class 300 jumps to 406 mm, far beyond either Chinese value. The same pattern repeats at every size: never assume dimensional equality from a pressure-equivalence.
Where EN 558 Fits
The European EN 558 system is its own coordinate. It defines a basic (long) series (historically F1-F16) and a compact (short) series (F31-F37). The short series exists so wafer and compact valves can replace longer patterns in tight layouts. Critically, EN 558 values parallel but do not always equal GB/T 12221: a Chinese long-series gate valve and an EN 558 short-series valve of the same DN are not interchangeable. When a project specifies EN 558, confirm the exact series letter (F4, F5, F14, F16, etc.) rather than just "EN 558".
A Practical Replacement Rule
- State the standard and series on every requisition: "GB/T 12221 long series", "ASME B16.10", or "EN 558 F5" - never just "PN16 DN100".
- When replacing an existing valve, measure the actual face-to-face with the valve removed before ordering; do not trust the nameplate class alone.
- Remember that the same DN can have very different lengths across pressure classes: a Class 300 valve is typically much longer than a Class 150 valve of the same bore.
- For butt-weld ends the same logic applies to the end-to-end (weld land) distance, which is tighter in tolerance than flanged layouts.
- Cross-check the quoted face-to-face against a verified specification database before procurement.
Our Chinese-to-international valve standards cross-reference maps the flange and pressure-class side of the same problem, and the PN vs ASME Class pressure rating guide explains why pressure equivalence never implies dimensional equivalence. Face-to-face values across more than ninety manufacturers are catalogued in the ValveSpecs Pro database, which makes it straightforward to confirm the exact length a supplier is quoting.
Frequently Asked Questions
What is the face-to-face dimension of a valve?
It is the distance between the two end connection faces (flange-to-flange, weld-land-to-weld-land, or thread-to-thread). It determines whether the valve fits between existing pipe flanges and is specified by ASME B16.10, EN 558 or GB/T 12221.
What does GB/T 12221 cover?
GB/T 12221-2005 'Metal Valves - Face-to-Face Dimensions' is the Chinese standard for valve structure length. It covers flanged, wafer, butt-weld and threaded ends, and for flanged gate valves it defines both a short series and a long series.
Is a PN16 valve the same length as a Class 150 valve?
Not in general. At DN100 the GB/T 12221 short series (229 mm) equals ASME B16.10 Class 150 (229 mm), but the conventional Chinese long series is 300 mm and will not fit a Class 150 layout. Class 300 at DN100 is 406 mm. Pressure equivalence never implies dimensional equivalence.
What is EN 558?
EN 558 is the European face-to-face standard. It has a basic (long) series and a compact (short) series; the short series lets compact valves replace longer ones in tight spaces. Its values parallel but do not always equal GB/T 12221, so confirm the exact series letter.
What is the difference between short and long series in GB/T 12221?
For a flanged gate valve the short series is the smaller face-to-face (229 mm at DN100 PN16) and the long series is the conventional larger value (300 mm at DN100 PN16). A requisition must name which series is required, because the 71 mm difference decides fit.
How do I measure a valve for replacement?
Remove the valve and measure the centre-to-centre distance between the two end faces. Compare that number to the new valve's stated face-to-face under the correct standard and series before ordering; never rely on the nameplate pressure class alone.