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Speaker 1: Welcome to brain Stuff from how stuffworks dot com where

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Speaker 1: smart Happens. Hi. I'm Marshall Brain with today's question, what

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Speaker 1: causes the loud banging noise in my homes pipes? The

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Speaker 1: problem of pipes banging in the wall is often called

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Speaker 1: water hammer. It can happen on a normal faucet, but

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Speaker 1: it's more common on pipes attached to a washing machine

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Speaker 1: or a dishwasher. In both of these machines, the valve

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Speaker 1: is electrically operated. It's called a solenoid valve. Solenoid valves

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Speaker 1: close very quickly, so imagine the following scene. The washing

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Speaker 1: machine is filling, so the valve is open. Water is

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Speaker 1: rushing through the pipe towards the washing machine. When the

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Speaker 1: washing machine is full, the valve slam shut very abruptly.

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Speaker 1: In the pipe, there may be five or ten pounds

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Speaker 1: of water that had been moving at a significant speed,

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Speaker 1: and now it suddenly comes to a complete halt. The

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Speaker 1: water's momentum carries the entire phipe system forward, and it's

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Speaker 1: the shifting of the pipes that makes the noise. If

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Speaker 1: it's a long, straight pipe carrying the water, the amount

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Speaker 1: of motion and therefore the noise can be especially significant. Obviously,

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Speaker 1: this is not good for the pipes. Each time you

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Speaker 1: hear the noise that means your pipes have been stressed

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Speaker 1: and flexed. The normal solution is to put a shock

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Speaker 1: absorber in the pipe near the valve. A simple shock

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Speaker 1: absorber would be a foot long piece of vertical pipe

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Speaker 1: attached near the valve. This pipe is filled with air.

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Speaker 1: Now when the valve closes, the moving water rushes up

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Speaker 1: into the vertical pipe and compresses the air so it

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Speaker 1: slows down gradually. The problem with a simple vertical pipe

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Speaker 1: is that the bubble can get dissolved into the water,

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Speaker 1: so a sealed system using a rubber bladder can be purchased.

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Speaker 1: This solution also allows you to orient it other than vertically.

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Speaker 1: Another approach is to use a spiral of copper pipe.

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Speaker 1: When the water hits the spiral, the coil absorbs the

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Speaker 1: shock like a spring. Do you have any ideas or

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Speaker 1: suggestions for this podcast? If so, please send me an

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Speaker 1: email at podcast at how stuff works dot com. For

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Speaker 1: more on this and thousands of other topics, go to

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Speaker 1: how stuff works dot com.