Valves, pipe and fittings connect every piece of equipment in a treatment plant. They are often bought in large quantities from mixed suppliers, which is exactly where mismatched standards and incompatible materials cause trouble.
The core of good specification is simple: the right pressure rating at the right temperature, materials that suit the fluid, and connection standards that match what is already installed.
What falls under this category
- Isolation valves
- Butterfly, ball and gate valves for shutting off flow.
- Control and throttling valves
- Globe and diaphragm valves, with diaphragm valves common for chemical and hygienic service.
- Check valves
- Swing, dual-plate and ball check valves to prevent backflow.
- Automated valves
- Valves with pneumatic or electric actuators, positioners and limit switches.
- Pipe systems
- PVC-U and CPVC, HDPE, polypropylene, ABS, stainless steel, duplex steels, GRP and ductile iron.
Specifications to compare
- Pressure rating at temperature
- Nominal pressure (for example PN10 or PN16, or ASME class 150) and, for pipe, SDR or schedule. Plastic pipe and valve ratings fall as temperature rises, so check the rating at your operating temperature.
- Body material
- Matched to the fluid, concentration and temperature. Standard 304 and 316 stainless steels can suffer pitting in seawater and high-chloride brines.
- Seal and seat material
- EPDM, FKM (Viton), NBR or PTFE. EPDM suits water and many acids and alkalis but not oils; FKM handles oils and many acids. Check the specific chemical.
- End connections
- Flange standard (for example EN 1092 or ASME B16.5), solvent-weld, threaded, butt-fusion or electrofusion for HDPE, or tri-clamp for hygienic systems. BSP and NPT threads are not interchangeable.
- Actuation
- Air supply pressure or voltage, fail-safe position (spring-return open or closed), and feedback signals.
- Certification
- Material test certificates (for example EN 10204 3.1 for metallic parts), potable-water approvals and hygienic surface finish where relevant.
Information to send suppliers with your enquiry
- Piping and instrumentation diagram or line list, if available.
- Fluid, concentration, temperature and maximum pressure for each line.
- Sizes, quantities and the connection standard already used on site.
- Actuation requirements and control signals.
- Documentation and certificates you need.
Common sourcing mistakes
- Mixing BSP and NPT threads, or PN and ASME flanges, which have different bolt patterns.
- Rating plastic pipework at room temperature for a warm process line.
- Choosing the right body material with the wrong elastomer.
- Using standard stainless steel in seawater or brine service.