Check valve slam and water hammer at pumping stations: causes and fixes
A loud bang in the pipework when a pump stops shows that the check valve is closing too late. Repeated slams damage valves, supports and pipes.
TAZ Engineering Team · · 6 min
What happens
After a pump trip, flow in the rising main slows, stops and reverses. If the disc is still open, the reverse flow slams it shut, and the sudden stop of the water column sends a pressure wave along the line.
What it depends on
The longer and higher the rising main and the lower the pump inertia, the faster the flow reverses. The heavier the disc and the longer its travel, the slower the valve closes. That is why a classic heavy swing check on a long main often slams.
Valve-level fixes
Fast-closing valves such as spring-assisted, dual-plate, tilting-disc and short-stroke designs close before reversal. Alternatively, controlled-closure valves with counterweights and hydraulic dampers close in two stages.
System-level fixes
Soft pump stop with a variable-speed drive, an actuated valve that closes before the pump stops, surge anticipators and air vessels. Large stations need a transient analysis.
What to send
Station layout, rising main length and profile, DN, pump flow and head, and start-stop regime. TAZ will propose the check valve type and isolation valves.
Checklist
- rising main length and profile
- flow and head
- pump stop method
- check valve type
- damper or spring
- surge protection
- transient analysis