Wafer vs Lug Butterfly Valve
Butterfly valves are available in two body configurations for installation between flanges: wafer type and lug type. The choice between them depends on whether the valve must support dead-end (one-sided) service, how often the downstream piping will be disconnected, and the project’s cost constraints.
Both types comply with API 609 (Butterfly Valves: Double Flanged, Lug-Type, and Wafer-Type) and ASME B16.10 face-to-face dimensions.
Side-by-Side Comparison
| Feature | Wafer Type | Lug Type |
|---|---|---|
| Body design | Flat body sandwiched between two flanges; no bolt holes in the body | Threaded inserts (lugs) around the body circumference for bolting |
| Bolting | Long through-bolts pass through both flanges and around the valve body | Each flange bolts independently to the valve body lugs with separate bolts |
| Dead-end service | Not suitable (cannot hold pressure from one side if the other flange is removed) | Suitable (downstream flange can be removed; valve holds pressure with upstream bolts) |
| End-of-line installation | Not suitable | Suitable (acts as a blind when downstream piping is disconnected) |
| Downstream piping removal | Requires disassembly of the entire joint (both flanges must be unbolted) | Downstream flange can be unbolted independently without disturbing upstream connection |
| Weight | Lighter (no lugs) | Heavier (lugged body with threaded inserts) |
| Cost | Lower (simpler body) | 20-40% more than wafer equivalent |
| Face-to-face | Per ASME B16.10 / API 609 | Per ASME B16.10 / API 609 (same as wafer) |
| Size range | 2” to 48”+ | 2” to 48”+ |
| Pressure rating | Class 150-300 (typically) | Class 150-300 (typically) |
When to Use Each Type
| Application | Recommended Type | Reason |
|---|---|---|
| Inline isolation (permanent) | Wafer | Lowest cost; adequate when both flanges stay bolted |
| Dead-end service | Lug | Holds pressure from one side when downstream piping is removed |
| Pump discharge | Lug | Allows pump removal without draining the upstream header |
| Temporary piping connections | Lug | Downstream line can be disconnected for tie-ins |
| Between pipe spools in a permanent run | Wafer | Cost-effective; no need for one-sided removal |
| Cooling water systems | Wafer (most common) | Low pressure, permanent installation |
| Fire protection | Wafer or lug | Depends on system isolation requirements |
Installation Notes
Wafer valves require precise alignment during installation because the body must be centered between the flanges before the through-bolts are tightened. Misalignment can pinch the disc or damage the seat. Lug valves are somewhat more forgiving because each flange bolts independently.
Both types require flat-face or raised-face flanges with smooth gasket seating surfaces. The valve body itself acts as the gasket between flanges, so no separate flange gasket is used between the valve and the flange (the valve has integral sealing faces).
Offset Compatibility
Both wafer and lug body styles are available in concentric, double offset, and triple offset disc configurations. The offset type determines the pressure-temperature capability and seat material; the body type (wafer vs. lug) determines the installation and piping disconnection capability.
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