| Nominal valve size | Specify the line size using the applicable nominal designation, such as DN or NPS. Butterfly valves are commonly available across a wide range of sizes, but availability varies by design and manufacturer. | Start with the connected pipe size and required flow. Confirm the valve’s flow capacity and pressure drop at the expected operating conditions rather than selecting by pipe size alone. | Check the valve’s face-to-face dimensions, flange drilling, pipe schedule or inside diameter, and connection standard. Do not assume that valves with the same nominal size have identical dimensions. |
| Flow and operating conditions | Relevant conditions include flow rate, fluid density, operating pressure, temperature, and whether flow is continuous or intermittent. | Use the supplier’s flow coefficient data and sizing method to check that the valve can control or isolate the required flow without excessive pressure loss or unsuitable operating torque. | Consider minimum and maximum flow, pressure fluctuations, throttling duty, and the actuator’s available torque. A butterfly valve may not be suitable for every throttling application. |
| Body material | Gray cast iron and ductile iron are distinct materials. Gray iron is commonly used for general-purpose water-service valve bodies; ductile iron provides greater strength and ductility. | Choose a body material appropriate to the system pressure, service, piping standard, and installation environment. | Verify the material grade, applicable product standard, corrosion protection, and pressure-temperature rating. “Cast iron” alone does not identify a specific grade or rating. |
| Pressure rating | Common designations include ASME Class 125 or Class 150 for certain valve and piping applications; the actual rating depends on the valve design, material, size, and governing standard. | Select a valve rated for the system’s maximum working pressure, including foreseeable surges and temperature effects. | Confirm the manufacturer’s pressure-temperature limits and the applicable standard. A class designation should not be treated as a universal pressure value for every size or material. |
| Disc design | Concentric (centered), double-offset, and triple-offset designs are common butterfly-valve configurations. | Concentric designs are widely used for general-purpose, resilient-seated isolation. Offset designs can reduce seat contact during rotation and may be selected for particular pressure, temperature, or service requirements. | Check the valve’s shutoff direction, allowable leakage class, seat arrangement, operating torque, and whether the design is intended for isolation, throttling, or both. |
| Disc material and coating | Disc materials and protective coatings vary by valve construction; options may include iron-based materials, stainless steel, or coated surfaces. | Match the disc’s wetted material and coating to the fluid, corrosion conditions, and required service life. | Confirm compatibility with the process fluid and any cleaning chemicals. Check whether the disc edge contacts the seat and whether the coating is suitable for the application. |
| EPDM seat | EPDM is commonly used in water and some aqueous services. It is generally not suitable for petroleum oils and many hydrocarbon fluids. | Consider EPDM for compatible water-service applications when its pressure and temperature limits meet the system requirements. | Check the exact compound’s temperature range and chemical compatibility, including additives, disinfectants, and cleaning agents. Limits vary by product. |
| NBR (Buna-N) seat | NBR is often considered for oils and certain hydrocarbon services, but compatibility depends on the particular fluid and compound. | Consider NBR where oil resistance is needed and the operating temperature and fluid composition are within the seat manufacturer’s limits. | NBR may have limitations with weathering, ozone, some chemicals, and hot-water service. Verify compatibility for the actual fluid, not just its general category. |
| PTFE seat or liner | PTFE offers broad chemical resistance and low friction, but butterfly-valve designs using PTFE have construction-specific pressure, temperature, and sealing limits. | Consider PTFE when chemical compatibility is a key requirement and the valve design meets the system’s shutoff and operating conditions. | Confirm the full valve assembly’s limits, including backing materials, seals, and seat support. Broad chemical resistance does not mean universal compatibility. |
| End connection | Common configurations include wafer, lug, and flanged bodies, subject to the valve’s design and size range. | Choose a connection that matches the piping layout, required maintenance access, and the applicable flange standard. | Check flange dimensions and bolting. A lug-style body may permit certain end-of-line arrangements only when specifically rated by its manufacturer. |
| Actuation and installation | Valves may be operated by a lever, gear operator, or powered actuator, depending on size and application. | Choose the operator based on valve torque, operating frequency, required control, and available power or manual access. | Verify actuator torque against the valve’s required torque under the worst operating conditions. Check mounting interfaces, position indication, and installation clearance. |
| Final specification | Record nominal size, body and disc materials, seat material, pressure-temperature rating, end connection, operating method, and required leakage performance. | Compare complete valve specifications against the project requirements before ordering. | Have the final selection reviewed against the applicable piping code, product standard, fluid compatibility data, and manufacturer documentation. |
