Views: 0 Author: J-VALVES Publish Time: 2026-11-12 Origin: Site
A valve's face-to-face dimension is not a property of the casting. It is an entry in a table: for a given valve type, size and pressure class, the distance between the two flange faces has been fixed so that valves from different makers can replace each other in a line. That is the entire purpose of the dimension. It is also why the table is worth opening before the replacement is ordered, rather than after the old valve is lying on the floor and the line is open.
ASME B16.10 gives the dimension for the valve types it covers, one value per size and class. Europe does it differently. EN 558 does not give one length per size; it gives a set of series, and the same nominal size appears in several of them, series 1, series 3, series 13, series 14 among others. A DN 100 gate valve built to one series and a DN 100 gate valve built to another are both standard, both correct, and not the same length. That is the trap. Two valves can carry the same size, the same class and the same standard number and still not replace each other, because the series was never written on the enquiry.
Butterfly valves have no B16.10 entry at all. Their width comes from API 609, and in Europe from the EN 558 series that cover wafer, lug and double flanged bodies. A wafer body is the narrowest. A lug body is usually the same width, because a lug is a wafer body with threaded inserts so that it can hold a dead end on its own: what changes is the bolting, not the gap. A double flanged body is a different animal, with a flange at each end and a much greater length, and fitting one where a wafer came out means cutting the pipe. Gate valves carry the same split between short and long pattern, and strainers change length with body type, so the body style belongs on the enquiry next to the size.
The clear gap is the measurement everybody takes and the least informative one. Before ordering, note the flange outside diameter, the bolt circle, the number and size of the holes, the raised face diameter and height, and whether the pipe can be moved at all. Then look at what surrounds the valve, because a body that fits between the flanges can leave no clearance once the handwheel or the gearbox is fitted, or be too tall for the platform above, and insulation only has thickness if someone remembers it. All of it is measurable in twenty minutes with the line cold and the old valve out.
| Valve type | Where the dimension comes from | What changes it | What to write on the order |
|---|---|---|---|
| Gate | ASME B16.10, or an EN 558 series | Short or long pattern, pressure class | Standard and series, not just size |
| Globe | ASME B16.10, or an EN 558 series | Straight, angle or Y pattern | Pattern plus series |
| Check | ASME B16.10, or an EN 558 series | Swing, lift or wafer body | Body type and series |
| Butterfly | API 609, or an EN 558 series | Wafer, lug or double flanged | Body style and the gap to be met |
| Strainer | Maker pattern, checked against the line | Y, basket or T body | The measured gap, in writing |
If the new valve is longer than the gap, the studs become a press. The pipe is sprung, the flanges are drawn together until the holes line up, and the joint that results is preloaded in the wrong direction: the gasket is loaded at the inside and unloaded at the outside diameter, the flanges rotate, and the valve body carries a bending moment it was never designed for. A cast body under that moment distorts its seat, and a distorted seat leaks at the disc long before it leaks at the flange. The usual ending is a valve that passed its shop test, was condemned on site, and turns out to have been dimensionally correct all along.
Order by series, not by size, and put the measured gap on the enquiry so the maker has something to check against. Where the gap cannot change, a spool piece, a short length of pipe with a flange at each end, made to the exact gap, is the engineering answer: it moves the problem to two welds and a support, which is a problem with a procedure and an inspection. Where the gap is too long, the answer is a longer body pattern, not a stack of gaskets, because every extra gasket is another place for the medium to escape. And if the mating flanges are themselves from a different standard, the spool has to solve both problems at once, which is where Class against PN drilling comes in.
J-VALVES builds gate, globe, check, plug and strainer patterns from 1/2 to 56 inch and butterfly valves from 2 to 112 inch to Class 900, in Class 150 to 2500 and in WCB, CF8 and CF8M bodies, rated from -29 to +425 C, shell tested at 1.5 times rating and seat tested at 1.1 times, with an EN 10204 3.1 certificate for each order. Face-to-face is quoted against the dimension standard and the series on the enquiry, so a replacement can be checked before it is made rather than after it arrives, and where a line has an unusual gap the drawing is confirmed first. The wedge gate valve and the bolted bonnet globe valve are the two patterns most often ordered as drop-in replacements.
Is size and class enough to order a replacement? No. Size fixes the bore and class fixes the rating; neither fixes the length. Ask for the dimension standard and the series as well, and compare the answer with the gap you measured. The same nominal size can be supplied in more than one standard length.
The new valve is slightly longer. Can the pipe be sprung? A small misalignment can be taken up by the bolts within the tolerance of the joint. A body that is visibly longer cannot: once the studs are pulling the flanges together they are loading the valve body in bending, and the seat distorts before the joint leaks. Use a spool piece instead.
Does gasket thickness change the fit? It changes the gap by its compressed thickness, which is why the same valve can fit with one gasket and not another. It does not change whether the flange faces are parallel, and that is the condition the joint depends on.
