Stopping a liquid column fast converts its momentum into a pressure spike that travels along the pipe at the speed of sound in the fluid; in water, an instant stop raises pressure by roughly 60 psi for every foot per second of velocity lost. Causes include quick-closing valves, slamming check valves and pump trips. In steam lines, slugs of condensate driven by steam cause even more violent hammer.
Every time the quick-closing valve shuts the whole header bangs, that's water hammer, slow the closing time down.
Open steam valves slowly and drain the condensate first; most steam hammer starts with someone in a hurry.
Also heard as
- hydraulic shock
- surge
- steam hammer
Related terms
Slam
A check valve banging shut after flow has already reversed, sending a pressure surge through the line.
Check valve
A self-acting valve that lets fluid pass in one direction and closes on its own when flow tries to reverse.
Crack
To open a valve just slightly, letting a small, controlled flow through.
Chatter
Rapid, violent opening and closing of a relief or check valve that hammers the disc against the seat.