The Short Answer
Face-to-face (F-F) is the dimension between the two sealing faces of a flanged valve — the distance that determines whether the valve fits between two flanges in the line. End-to-end (E-E) is the overall dimension between the extreme ends of the valve (which for flanged valves is the same as face-to-face; for wafer, lug, and welded-end valves it differs). Both are standardized in ASME B16.10 (steel flanged and weld-end valves) and API 6D (pipeline valves), with ISO 5752 as the international equivalent. When you replace a valve, the face-to-face dimension of the replacement must match the existing line — this single number is the most common cause of installation surprises.
The Two Dimensions Defined
Face-to-Face (F-F)
- The distance from the inlet sealing face to the outlet sealing face of a flanged or flangeless valve.
- For flanged valves, it includes both flange faces — this is the dimension the pipe designer leaves for the valve.
- Standardized in ASME B16.10 for steel flanged valves, and in API 6D for pipeline valves (which differ from B16.10 in some sizes).
End-to-End (E-E)
- The overall length between the extremes of the valve’s end connections.
- For flanged valves, E-E = F-F.
- For butt-weld end valves, E-E is measured between the weld-prep ends — often shorter than an equivalent flanged valve.
- For wafer and lug butterfly valves, the dimension between the two face planes that clamp between flanges is the face-to-face; the wafer length is set by the standard for the class.
Which Standard Sets What
| Standard | Scope | What It Gives You |
|---|---|---|
| ASME B16.10 | Face-to-face and end-to-end dimensions for flanged and weld-end steel valves | F-F/E-E tables for gate, globe, check, ball, butterfly by class and size |
| API 6D | Pipeline and piping valves | F-F/E-E for API 6D valves (some sizes differ from B16.10) |
| ISO 5752 | Metal flanged valves (basic series) | International F-F dimensions (series 1–3) |
| EN 558 | Industrial valves — face-to-face | European F-F dimensions (replaces some national standards) |
| ISO 5210/5211 | Actuator mounting dimensions | Flange and drive dimensions for mounting actuators |
Practical rule: flanged steel valves in a North-American-designed plant follow ASME B16.10; pipeline valves often follow API 6D; European-designed plants follow EN 558/ISO 5752. Mixing standards on one line is a fit problem waiting to happen.
Common Dimension Tables (Examples Only — Always Check the Standard)
Typical F-F for flanged gate/globe/check valves (Class 150/300, short pattern, per ASME B16.10):
| NPS | Class 150 F-F (in) | Class 300 F-F (in) |
|---|---|---|
| 2 | 7.00 | 8.50 |
| 4 | 9.00 | 12.00 |
| 6 | 10.50 | 14.00 |
| 8 | 11.50 | 16.50 |
| 12 | 15.00 | 20.50 |
These are illustrative examples, not a replacement for the standard — dimensions vary by valve type, long/short pattern, and standard edition. Always verify against the current ASME B16.10 / API 6D table for the exact valve type and class.
Key Points That Cause Fit Problems
- Long pattern vs. short pattern. Some valve types have both long and short body patterns (e.g., butterfly valves). The data sheet must state the pattern; a “short pattern” valve ordered into a “long pattern” line doesn’t reach the flanges.
- API 6D vs. B16.10 differences. In several sizes, API 6D gate and ball valves have different F-F than ASME B16.10 — a pipeline valve specified to API 6D may not fit a line laid out to B16.10 dimensions. Always check the standard of both the valve and the piping design.
- Wafer vs. lug vs. flanged. A wafer butterfly valve is clamped between flanges (needs long bolts or studs); a lug version bolts directly to each flange. The installed length must match the piping design — switching from lug to wafer on an existing line may require longer bolts.
- Weld-end valves are shorter. If the line was designed for flanged valves, a weld-end replacement changes the effective length and requires pipe adjustments.
- Actuator stack-up height. For actuated valves, the total installed height (valve + mounting bracket + actuator) must fit the available space — check the actuator mounting dimensions (ISO 5211) and the assembly drawing, not just the valve F-F.
- Class changes. A Class 600 valve is longer than a Class 300 valve of the same size in many types. If the line was designed for Class 300 but a Class 600 replacement is fitted, the flanges may not meet.
How to Verify a Valve Will Fit
- Read the data sheet and quote carefully: confirm the F-F/E-E dimension and the standard it references.
- Check the piping design basis: what F-F standard was used when the line was laid out (ASME B16.10? API 6D? EN 558?).
- Compare the numbers: the valve’s F-F must match the design dimension exactly (not “close” — flanges are fixed).
- For replacements: measure the existing valve’s F-F before ordering; the nameplate may not state it, and the standard table is not a substitute for a field measurement of an old valve.
- Check the actuator assembly height and orientation for space-constrained installations.
Data Sheet Wording to Use
On the purchase order or data sheet, write explicitly:
- Flanged gate valve, NPS 6, Class 300, F-F to ASME B16.10 = 14.00 in (356 mm).
- Ball valve to API 6D, E-E per API 6D table for Class 600.
- Wafer butterfly valve, short pattern, installed length per ASME B16.10 (or the manufacturer’s standard if non-standard).
If the exact standard dimension is in doubt, state the dimension and the standard together — then there is no ambiguity at receipt inspection.
Common Mistakes
- Ordering by size and class only. “6” Class 300″ does not define F-F — two different patterns or standards give different lengths.
- Assuming all manufacturers match the standard. Most do, but “short pattern” and specials exist; verify the dimension on the arrangement drawing.
- Ignoring weld-end lengths. E-E for weld-end valves must match the design; a mismatch means cutting and refitting pipe.
- Not checking the actuator height. The valve fits, but the assembly doesn’t clear the structure.
- Trusting an old valve’s nameplate. Nameplates may not show F-F; measure the physical valve for a replacement order.
Conclusion
Face-to-face and end-to-end dimensions are the fit-critical numbers in every valve order. Confirm the standard (ASME B16.10, API 6D, or EN 558), the pattern (long/short), and the actual dimension against the piping design — and verify the actuator assembly height for space-constrained jobs. The valve that “should fit” by size and class is the valve that doesn’t reach the flanges; the one checked against the standard and the field measurement goes in without drama.