Quick answer: a butterfly valve isolates or regulates flow with a disc that rotates inside the pipe bore. It is compact, light and cheaper than a gate valve at large diameters, which is why it dominates water, HVAC and utility service. The trade-off is a disc that stays in the flow path, so pressure drop is higher than a gate valve even when open.
Body types
| Type | Installation | Notes |
|---|---|---|
| Wafer | Held between two flanges by through bolts | Lightest and cheapest; cannot be used as a line end |
| Lug | Bolted to one flange, threaded inserts | Can be used for dead-end service and maintenance isolation |
| Double flange | Flanged both sides | Strongest connection, usual for large diameters and higher classes |
Seat and disc options
- Soft seats: EPDM, NBR, PTFE for tight shut-off in water and utility service
- Metal seats for higher temperatures and abrasive media
- Concentric and double-offset (high performance) designs
- Stainless steel, aluminium bronze and nickel-plated discs
Selection points that decide the outcome
- Seat material must suit the medium and temperature, not just the pipe size
- Check whether the valve must isolate one side of a line (lug or double flange)
- Confirm whether the valve will be used for regulation — a standard butterfly valve is not a control valve
- Allow for actuator clearance in tight plant layouts
Testing and documentation
- Shell and seat tests before shipment
- Seat tightness confirmed against the agreed acceptance class
- Actuator and position indicator function check when supplied assembled
待补内容位：待补：可生产口径与压力上限、软密封与金属密封座材料清单、阀门结构长度执行标准、交期。