Valve End Connections Explained: Flanged, Welded, Threaded & Wafer
The End Connection Is Part of the Spec
A valve is only as installable as its end connection. Mismatched ends mean adapters, leaks, or a redesign. The end type is driven by pipe size, pressure, temperature, and whether the line is disassembled often.
Connection Types
- Flanged: bolted to matching flanges (ASME B16.5 / B16.47). Easy to remove, dominant above 2 inch.
- Butt-weld (BW): welded into the line. Permanent, smooth bore, best for high pressure and temperature.
- Socket-weld (SW): pipe inserted into a socket and welded. Used up to about 2 inch in high-pressure small-bore lines.
- Threaded (NPT/BSP): screwed in. Cheap, for low-pressure small lines only.
- Wafer / Lug: sandwiched between flanges. Compact, for butterfly and check valves.
Selection Table
| Connection | Max Size (typical) | Pressure | Best For |
|---|---|---|---|
| Flanged | Unlimited | Low-High | Frequent maintenance |
| Butt-weld | Unlimited | High | Permanent, critical lines |
| Socket-weld | 2" | High | Small-bore, high-pressure |
| Threaded | 2" | Low | Non-critical, cheap installs |
| Wafer | 3"-24"+ | Mid-High | Space-limited, lightweight |
Flange Faces and Ratings
Flange fit is defined by face type (RF, FF, RTJ) and class (150-2500). The class must match the pressure-temperature rating of the service, not just the nominal pressure.
Welding Cautions
Butt and socket welds need post-weld heat treatment for some materials and services. Soft-seated valves must be protected from weld heat. Always check the material guide before specifying weld ends on exotic alloys.
Standards Cross-Reference
End-to-end dimensions follow ASME B16.10; flange drilling follows B16.5/B16.47. See the full standards comparison.
End-connection options per product are listed across valve brands in the ValveSpecs Pro database.
Frequently Asked Questions
When should I use flanged instead of welded ends?
Use flanged ends when the valve must be removed for maintenance, or above roughly 2 inch where welding is costly. Use welded ends for permanent high-pressure critical lines.
What size limit applies to threaded valves?
Threaded (NPT/BSP) valves are generally limited to 2 inch and low pressure. Beyond that, flanged or welded ends are required.
What is a wafer end?
A wafer end is a compact body sandwiched between two pipe flanges, used mainly for butterfly and some check valves where space and weight matter.
Do flange classes equal pressure rating?
Not directly. Flange class sets the allowable pressure at a given temperature. You must use the pressure-temperature table, not the class number alone.
Where do I find a product's end connection?
End connection is a standard field per product. The ValveSpecs Pro database records end types across 90-plus brands for easy comparison.