Water Hammer vs. Thermal Expansion

Brad White_9

Thermal expansion shows up most often as incremental creeping, sort of "dunk-dunk-dunk" sound during a warm-up cycle. Sometimes it happens on a cool-down cycle longer than the normal steam pressure off-cycle.

What I describe is the sound of a pipe against wooden structure, a joist or wooden floor penetration. This is not to say that this is acceptable, just that it occurs. Your conditions may well be different. The pipe should not contact any carbonaceous material for it can char over time even at low temperatures. An inch of air space is recommended.

Thermal expansion is more muffled than water hammer. The only time it would be louder is when the forces of expansion build up then suddenly release. This may be what happens when the flange or thread boss of a fitting is held back against a joist then releases. Sort of like tectonic plate movement in earthquake zones, only different. A build-up then a bang.

If the pipe is already warmed and banging occurs, I would suspect water hammer.

Water hammer is appropriately named. More metallic for it is a force applied to metal rather than metal applied to wood. Can be a "tink" sound when mild but more often sounds like a hammer tapping or banging the pipe. The two heard adjacent to one another are entirely distinguishable.

Granted the sounds are subjective and hard to describe in words, but I did my best.

Can you imagine the challenge of writing a review of Mahler's 4th? Me neither.

Adam Buchsbaum

Water Hammer vs. Thermal Expansion

How does one distinguish between noises caused by water hammer and those caused by thermal expansion? I have a one-pipe steam system. Some radiators make clanging/knocking sounds as they begin to heat up but also after the boiler shuts off and they cool down. Were it not for the cool-down noises, I'd more likely assume water hammer. What can I do to diagnose this? Thanks.

Adam Buchsbaum

thanks!

That's an excellent response. From the description, I'd say it's water hammer, but then I'm still left wondering about the cool-down sounds, which are very similar.