Which type of check valve,piston, ball, or swing, is best for preventing water hammer in my pump discharge lines?

Piston check valves respond the fastest to reverse flow and are best for preventing water hammer in high-pressure or high-cycle applications. Swing check valves such as Bonney Forge's have a lower pressure drop and work well in horizontal lines with steady, consistent flow, but their slower closing disc can allow reverse flow surges. Ball check valves are a good middle ground for low-pressure, vertical installations. For pump discharge on high-pressure systems, a piston or nozzle-style check valve is generally the safest choice to minimize surge.