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I’m not sure how many of you out there were proximal to the NYC steam pipe explosion, but I from what I hear it was pretty traumatizing. The damage it effected of course drew morbid parallels to other, premeditated explosions, but since I grew up hearing engine room horror stories, I wasn’t surprised to learn the cause attributed directly to a phenomenon I’m sure many of you have heard attacking your household pipes: water hammer. Sprinklers and toilets notoriously suffer from it, but any closed system with a valve is vulnerable, as wisegeek explains:
Water hammer is a very loud banging, knocking or hammering noise in the pipes that occurs when the flow is suddenly turned off. It is caused by a pressure or shock wave that travels faster than the speed of sound through the pipes, brought on by a sudden stop in the velocity of the water, or a change in the direction. It’s also been described as a rumbling, shaking vibration in the pipes.
If you’re concerned about some complicated and/or aged pipes in your vicinity, LMNO Engineering has a calculator that allows you to determine the piezometric pressure (representing the marriage of pressure & weight) in each pipe. I’m not sure what the stats were for the pipe in question, but I don’t envy Con Ed, especially now that the law suits are surfacing.
Comments (5)
Comment
Water hammer problems?????
Install an air tank bladder to cushion the shocks.
So simple–so effective
posted by ernie on 7-27-2007 at 9:56 pm
Ah, the penultimate return of “hammer time”. That rocks!
posted by Scott on 7-30-2007 at 9:52 am
Actually, no. Water hammer is caused AFTER a period of time when there’s been no steam activity and the steam that was left dormant in the lines have condensed to water. Then, when steam is introduced to the lines again it makes a slug of water by pushing the condensed water ahead of it. This slug of water hits every joint at every change of direction at the velocity that the steam is driving it and creates a hammering effect.
posted by Chris on 7-30-2007 at 10:18 am
You’re half-right: the water-hammer described in the post is not the water hammer that happens in steam pipes.
The water-system kind, can happen anytime a valve shuts too quickly - the pipe leading to washing machines is a notorious culprit. Fix it with a bladder tank, like the 1st comment.
Water-hammer in steam pipes is something completely different. Like you said, it’s caused by puddles of condensed steam (i.e., water)in the pipe.
But it doesn’t get pushed anywhere. It gets turned into steam - all at once - by the sudden contact with the next batch of steam from the boiler. Since the steam produced takes up a lot more room than the original puddle… it’s like a mini-explosion in the pipe.
This I know from working with plumbers. If you spend any time in the basement of old, poorly maintained steam-heat buildings, you’ll notice that hammer doesn’t move down the pipe, from one elbow to the next. It repeats in the same spot.
posted by Frank on 8-1-2007 at 2:27 am
so how do you stop it from occurring?cause i sleep uner pipes tat do exactly that but i have no idea how to keep it from happenning
posted by eric j little on 1-5-2008 at 9:43 am