Concept reference

Surge and Water Hammer

C.1Plain-language definition

Water hammer is the system’s transient response when flow changes faster than pressure information can travel and reflect through the pipeline. A pump trip, check-valve closure or control action launches waves; high pressure can burst components, while low pressure can collapse pipe, admit contamination or separate the liquid column.

C.2Governing relation or decision logic

The ideal instantaneous velocity-change bound is Δp = ρaΔV or ΔH = aΔV/g, where wave speed a is m/s (ft/s). A characteristic pipeline period is related to 2L/a or 4L/a depending on the event and boundary reflection being judged. Real analysis includes pipe restraint/elasticity, pump inertia, valve law, profile and vapour effects.

C.3The failure to name

Using Joukowsky as the entire analysis can miss column separation and later cavity collapse, which may govern. Assuming a “slow-closing” check valve is always safer can increase reverse velocity before closure and make slam worse.

C.4Field review checklist

• Define credible initiating events, initial operating points and control timelines.
• Establish wave speed from pipe, wall, restraint and fluid assumptions.
• Inspect both maximum and minimum pressure along the full elevation profile.
• Test protection devices and valve/pump dynamics in a documented transient model where consequence warrants.

C.5Where it fits in the course

§8.5 develops the transient mechanisms; §8.4 connects check-valve closure.