Gate Valves for Water & Wastewater

AWWA C509 covers resilient-seated (rubber-seated) gate valves with ductile iron or cast iron bodies, rated to 250 psi (PN 17 approx.), for potable water service up to DN600 (24"). The rubber seat completely encloses the gate and provides zero-leakage shut-off. AWWA C515 covers the same resilient-seated design but extends it to larger sizes (up to DN900 / 36") and adds requirements for ductile iron bodies specifically (no cast iron). C515 also tightens dimensional standards for interchangeability. For water utilities: specify C509 for DN80–DN600 standard distribution mains; C515 for DN600–DN900 transmission mains. Both require NSF 61-compliant internal coatings.

No. Standard industrial API 600 carbon steel gate valves are not approved for potable (drinking) water service. The reasons are: (1) body and internal materials must meet NSF/ANSI 61 or WRAS approval — this certifies that materials do not leach harmful substances into drinking water; (2) carbon steel without protective lining will corrode and impart taste, odour, and turbidity to the water; (3) industrial gate valves use mineral-oil-based thread compounds and packing greases that are not approved for drinking water contact. Always use AWWA C509/C515 resilient-seated gate valves with NSF 61 approval for potable water systems.

Use knife gate valves (not standard gate valves) when: (1) the fluid contains fibrous materials — rags, screenings, organic solids that can jam a standard wedge gate — the knife-edge gate cuts through these cleanly; (2) slurry service — primary sludge, digested sludge, grit slurry — where settled solids can lock a standard gate in the closed position; (3) large sizes (DN200+) where the low-pressure (PN 6–10) wastewater circuit doesn't need the higher pressure rating of an API 600 gate valve — knife gate valves are significantly lighter and cheaper at large bores; (4) screenings return, sludge thickener, and dewatered cake transfer where fibrous solids content exceeds 1% by weight.