Check Valves for Water & Wastewater

Water hammer prevention strategies for pump station check valves: (1) Non-slam (spring-loaded) dual plate check valves close before full reverse flow develops — the spring ensures controlled disc movement rather than slam under reverse flow; (2) Non-return valve with dashpot (hydraulic dashpot check valve) — the dashpot slows the final 10–20 degrees of closure, preventing impact; (3) Surge tanks or air vessels on the pump discharge side absorb the pressure wave from sudden check valve closure; (4) Variable speed drives on pumps allow controlled pump ramp-down, reducing the reverse flow velocity that causes slam; (5) Size check valve correctly — an oversized check valve has a low velocity that doesn't hold the disc open, causing premature chattering and repeated slamming.

For sewage pumping stations: Flap check valves (rubber-seated swing check) are the preferred design — the rubber EPDM flap seals around fibrous rags and soft solids that would prevent a metal disc from seating. Select full-bore design — reduced-bore check valves in sewage service create turbulence that promotes rag accumulation at the constriction. DN100–DN300: EPDM-flap swing check in ductile iron; DN300+: consider a non-return flap valve with counterweight and lever for controlled slow closing, or a powered (actuated) check valve that can be controlled during pump stop sequence to manage water hammer.

A foot valve (spring-loaded check with strainer at the bottom of the suction pipe) is required when: the pump is installed above the water level (positive suction lift) and must maintain prime when idle. Without a foot valve, when the pump stops, water drains from the suction pipe and the pump loses prime — next start requires re-priming (bleeding air from suction). Foot valves retain water in the suction pipe so the pump is always primed and ready to start. For submersible pumps (pump below water level) — no foot valve needed, the pump is always primed. For self-priming centrifugal pumps — no foot valve needed if the self-priming mechanism is reliable. For standard centrifugal pumps with positive suction lift — foot valve is mandatory.