About Waterhammer

Waterhammer can be dangerous and expensive.  Good steam trapping should seek to eliminate it rather than provide steam traps to withstand it.  You'll see in the diagram below a steam main with a low point in which condensate can and does collect.  Steam passing at, say, 120 feet per second - or about 75 m.p.h. and raising ripples on the condensate.  Eventually, as more water collects, the steam gale picks up a slug of condensate and carries it along the main until it reaches some obstruction, such as a bend, reducing valve or temperature regulator.  The effect of suddenly stopping a few pounds of water at 75 m.p.h. or even more can be imagined.  So prevent waterhammer by avoiding water pockets if possible and, if not, drain them efficiently and avoid opening stop valves too quickly.  Remember that waterhammer is caused by steam velocity, not by pressure.  It can be just as bad at 5 psi as at 260 psi.

Contributed by Bruce Gorelick, Enercheck Systems, Inc.