Preventing Valve Slam and Water Hammer in Raw Sewage Pump Stations: Swing vs. Ball Check Valves
Introduction
Raw sewage lift stations and wastewater high-head pumping systems rely heavily on check (non-return) valves to prevent backflow when a pump shuts down. However, when a massive volume of water moving through a large-diameter pipe suddenly reverses direction, the closing check valve can shut with explosive force.
This phenomenon—known as valve slam or water hammer—generates intense hydraulic shock waves. Over time, these shocks break pipe hangers, crack valve bodies, rupture gaskets, and destroy pump casings. In wastewater applications, solving valve slam requires a careful balance between dynamic response time and clogging resistance.
The Pitfall of Standard Swing Check Valves in Wastewater
Traditional swing check valves feature a heavy metallic disc suspended from a top hinge pin. While they provide a clear, unrestricted flow path when fully open, their mechanical closing speed is relatively slow.
When a sewage pump stops, gravity must pull the heavy disc back down through the thick fluid. If the forward fluid column reverses before the disc hits the seat, the reverse flow slams the disc shut violently.
The Wastewater Alternative: Non-Clog Ball Check Valves
For small to medium-diameter wastewater pipelines (DN50 to DN400), Ball Check Valves are proving to be an exceptionally elegant solution to water hammer.
How They Work: Instead of a hinged disc, a heavy, sinking NBR-coated hollow metal ball sits inside the valve body. As the pump starts, the fluid forces the ball completely out of the flow stream into a side pocket, providing a 100%full-bore path that allows rags and solids to pass without snagging.
Anti-Slam Performance: The moment the pump stops, the natural roll of the ball back onto the inclined seat matches the deceleration of the fluid column perfectly, shutting the valve before the fluid has a chance to reverse velocity. This dampens the water hammer effect down to negligible levels.
