water hammer

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A banging noise heard in a water pipe following an abrupt alteration of the flow with resultant pressure surges.
• noun A banging noise in steam pipes, caused by steam bubbles entering a cold pipe partially filled with water.

from The Century Dictionary.

• noun The concussion of a moving volume of water in a pipe or passage, caused by sudden stoppage of flow, as by the abrupt closing of a faucet.
• noun The noise, resembling a blow of a hammer, caused by the presence of water in a steam-pipe when live steam is passed through it.
• noun A philosophical toy consisting of a hermetically sealed tube from which the air has been exhausted and which contains some water. It is so called because the water strikes against the tube with a noise similar to that of a hammer, there being no air to impede its motion.
• noun A metal hammer heated in a flame or in boiling water.

from the GNU version of the Collaborative International Dictionary of English.

• (Physics) A vessel partly filled with water, exhausted of air, and hermetically sealed. When reversed or shaken, the water being unimpeded by air, strikes the sides in solid mass with a sound like that of a hammer.
• A concussion, or blow, made by water in striking, as against the sides of a pipe or vessel containing it.
• A metal hammer used when heated, as by dipping in hot water, to blister the skin, as for counterritation.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A surge of pressure in a pipe carrying a fluid; especially the banging sound in a steam or hot water pipe caused by bubbles of air, or by an abrupt alteration of the flow.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the banging sound of steam in pipes