Non Slam Swing Check Valve

Non Slam Swing Check Valve – Dashpot-Dampened Closure Control

Non-slam swing check valves combine the proven reliability and low pressure drop of traditional swing check design with hydraulic dashpot or spring-cushioned closure mechanisms that eliminate water hammer damage. These enhanced swing checks maintain all the advantages of conventional swing designs—minimal pressure drop (0.2-0.5 psi), large size capability (DN 50-1200), and simple robust construction—while addressing the primary weakness: violent slam closure during rapid flow deceleration that destroys piping, valves, and pumps in African water systems experiencing frequent power interruptions.

The dashpot mechanism consists of a hydraulic cylinder attached to the disc lever arm (external to the flow path). As the disc swings closed, a piston moves through the oil-filled cylinder, with closure speed controlled by calibrated orifice bypass flow. The disc accelerates rapidly through the first 60-70% of travel (preventing reverse flow development), then dashpot damping progressively slows the final 30-40% of closure to gentle seat contact—achieving 0.3-0.8 second closure time versus 1-3 seconds for conventional swing checks, while eliminating the destructive impact forces that create pressure spikes, piping fatigue, and equipment damage.

When to Specify Non-Slam Swing vs. Other Check Types

Choose Non-Slam Swing Checks When: (1) Large diameter (DN 300-1200) with water hammer concerns—tilting disc alternative, (2) Horizontal/vertical upflow installation suits swing check orientation, (3) Minimum pressure drop critical but slam prevention also required—best of both worlds, (4) Retrofit of existing swing checks experiencing water hammer—external dashpot kits available for field installation on African water systems without valve replacement.

Choose Alternative Check Types When: (1) Any-orientation installation needed—dual-plate checks, (2) Sizes below DN 300 where dual-plate non-slam checks offer compactness advantage, (3) Lowest first cost priority and water hammer not a concern—conventional swing checks, (4) Ultra-rapid closure (below 0.3s) required—dual-plate or tilting disc faster response.

See parent Check Valve category for general selection guidance. Related non-slam designs: Dual Plate Check Valve and Tilting Disc Check Valve.