Find out how to fix water hammer. Get tips on increasing the number of fasteners that secure the water pipes and the sprinkler pipes and installing water-hammer arrestors.
LESLIE: John in Nebraska is on the line with a sprinkler  question. Tell us what’s going on.
JOHN: Alright. In the spring, when I – after I drain my system and I get ready to recharge it, I go out, close all the valves and the faucet.
JOHN: And when I turn the pressure back on, I was told to turn it back on slowly so the valve on the outside of the house would eventually – the water would moisten it up and then it would finally seal. When it finally does seal, it rattles and knocks so hard, you’d almost think it’s going to come out, come off the floor rafters.
TOM: Right. Yeah.
JOHN: And then it actually forces the pipe itself about an inch away from the exterior of the house.
TOM: Is this because of the racket that it causes?
JOHN: And the pressure, I guess.
TOM: Right. So, what you’re seeing, John, is called water hammer . And it happens because as the water flows through the pipe, that valve then stops the flow of the water. The water has a lot of centrifugal force because it’s actually quite heavy; water weighs about 8 pounds per gallon. So as the valve slams shut, the water stops cold and then all that force just rattles it.
You can address that in a couple of ways: first of all, by increasing the number of fasteners that secure the water pipes and the sprinkler pipes; and secondly, by installing one or more water-hammer arrestors, which are essentially shock absorbers for the plumbing system. They get installed inline and then as that water does slam to a stop, it has sort of a place to expand to and therefore, makes a lot less racket.
JOHN: OK. You said, "Water hammer arrestors"?
TOM: Yes. Water hammer arrestor it’s called, mm-hmm.
JOHN: OK. The size of my – the pipe itself is 1 inch. Would that have something to do with it?
TOM: No, that’s a pretty typical water-pipe  size.
JOHN: OK, OK. OK. Great. Great help, guys. Thanks. Enjoy the show.
TOM: Oh, thanks very much, John. Well, good luck with that project and thanks so much for calling us at 888-MONEY-PIT.