Valve end connections: flanged RF/RTJ, butt-weld, socket-weld and threaded
Why the end is a selection decision, not a detail
The end connection decides how the valve joins the piping, and with it the leak path, the ability to maintain or replace the valve, and the flange/welding work the installer must budget. A valve with the right spec but the wrong end is unusable on the line — and since ASME and EN flange drilling differ, "flanged" alone is not a complete specification.
The connection families
Published model pages in this catalogue list provenance-backed end-connection fields in these groups. Counts are identifier pages whose spec table lists the group.
| Connection group | How it joins | Published model pages listing the group |
|---|---|---|
| Flanged (RF / RTJ / MF) | Bolted flange face with gasket; RF seals on a raised face, RTJ on a metal ring | 48 |
| Butt-weld (BW) | Welded flush into the pipe — permanent, leak-tight join | 30 |
| Socket-weld (SW) | Pipe inserted into a recessed socket and welded — small-bore duty | 15 |
| Threaded (NPT) | Screwed into the line — quick install, thread seal is the leak path | 15 |
| Wafer (clamped between flanges) | Body sandwiched between the line flanges by through-bolts | 7 |
| Lug (independent lug bolts) | Threaded lugs let upstream/downstream be disconnected independently | 4 |
Flange facets: RF, RTJ and the drilling standards behind them
A raised face (RF) flange seals on a raised, serrated face with a ring or full-face gasket and is the general-purpose flanged end. A ring-type joint (RTJ) uses a machined groove and solid metal ring and appears on higher-class steel-valve ends where metal-to-metal sealing is required. The sealing face finish and gasket type are part of the same decision — the face is part of what the end-connection field publishes.
Drilling standard and pressure class complete the flange specification. ASME B16.5 covers imperial flanges in Class 150–2500 style ratings; DIN 2543/2545 and EN 1092-1 cover the metric PN families. An ASME-drilled flange does not bolt to an EN/DIN-drilled flange — the bolt circle and hole counts differ — so the drilling standard must match the mating pipework, not just the class number. The standards center’s pressure-class cross-reference covers the Class↔PN pairing; the drilling standard is the additional half of the answer.
Welded, threaded and clamped ends
Butt-weld (BW) ends weld flush into the pipe — the strongest, most leak-tight join, used on high-pressure/temperature steel valves where permanence is wanted and future removal is not. Socket-weld (SW) ends take the pipe into a recessed socket, a small-bore convenience for Class 3000/6000 forged valves. Threaded ends (NPT in the published pages) screw in — fastest to install, common on instrumentation, gauge and small utility valves, with the thread seal as the leak path.
Wafer and lug are not welds or threads but clamping styles for butterfly and some check valves: a wafer body is sandwiched between the line flanges, while a lug body has its own threaded lugs so the upstream side can be detached while the downstream stays piped — the difference that matters for dead-end service and maintenance sequencing.
What to state in an inquiry
Specify the end in one line: connection type + standard + class + size — for example "RF flange, ASME B16.5 Class 300, NPS 4" or "flanged, EN 1092-1 PN16, DN100". If the line is welded, add the pipe schedule so wall thickness matches. Where a published model page lists several end options (the common "NPT, RF, RTJ" pattern on safety-valve pages), the inquiry selects among them; combinations not shown are a customisation question to raise at quotation.