In This Article
- 1.Wafer Butterfly Valve
- 2.Lug Butterfly Valve (Tapped Lug / Lug Type)
- 3.Comparison Table
- 4.Double-Flanged Butterfly Valve
- 5.How to Specify
Critical rule: wafer butterfly valves CANNOT be used at the end of a pipeline (dead-end or blank-flanged service). You MUST use a lug butterfly valve for any dead-end, pump inlet, or vessel nozzle application where one side of the pipe must be disconnected.
Wafer Butterfly Valve
A wafer butterfly valve has no flanged face of its own — it fits between two pipe flanges, with the pipe bolts passing through the flange bolt holes on either side of the valve body. The pipe bolts clamp the valve sandwich-style between the two flanges. This makes the wafer design very compact, light, and cheap. However, the pipe bolts must pass through BOTH flanges — if you remove one flange, the valve immediately becomes unsupported and can fall. You cannot disconnect either side of the pipe without removing the entire valve.
Lug Butterfly Valve (Tapped Lug / Lug Type)
A lug butterfly valve has threaded inserts (lugs) moulded into the valve body flange. Separate bolts go into each lug from each side of the pipe flanges — the downstream and upstream flanges each bolt independently to the valve. This means you can remove the downstream flange bolts, disconnect and remove the downstream pipeline, and the valve remains fully supported and seated by the upstream flange bolts — allowing dead-end service.
Comparison Table
| Parameter | Wafer | Lug |
|---|---|---|
| End-of-line (dead end) service | NOT suitable | Suitable |
| One-side disconnection | NOT possible | Possible |
| Cost (same size) | Lower (simpler body) | 10–20% higher |
| Weight | Lighter | Heavier (more material) |
| Installation time | Faster | Slightly longer (2× bolt sets) |
| API 609 Category | Both covered by API 609 Category A and B | Both covered by API 609 Category A and B |
| Typical applications | Mid-line isolation in water, HVAC, process | End-of-line, pump isolation, vessel nozzles |
Double-Flanged Butterfly Valve
A third style — double-flanged — has its own integral raised-face flanges on both sides, bolted directly to the pipe flanges like a gate or globe valve. This is the most robust and rigid design, used for large bore (DN600–DN2000) and higher pressure class (Class 300–600) butterfly valves where the body must be self-supporting. More expensive than wafer or lug but required for heavy industrial and pipeline applications.
How to Specify
- For all mid-line service (both sides of pipeline connected at all times): specify wafer type to save cost and weight.
- For any end-of-line, pump suction, vessel nozzle, or location where one side must be disconnectable: specify lug type.
- For large bore (DN600+), Class 300+, or pipeline service: specify double-flanged type.
- Always state the face-to-face dimension standard — for wafer and lug types: ISO 5752 (Series 20) is common for EN flanges; ASME B16.10 for ANSI flanges.
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