Rattling water pipe inside wall


I had a bathroom added to my house as part of an addition last summer. The copper hot water pipe rattles inside the wall; at least it does when the valve under the sink is not fully open. My wife likes to turn it down halfway or so. When the valve is half closed, running the hot water in the sink cause the pipe to emit a loud "chatter" in the wall. The contractor who did the job, and his plumbing subcontractor, have apparently told my wife that the valve should be open all the way for normal operation. They say of course the pipe will rattle when the hot water valve is turned down. I suspect the pipe somewhere inside the wall was not properly secured. What is the real story here?
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if she likes to turn it down, let's guess: she may be trying to balance the hot and cold to match her preferred lever handle settings or not get splashed. what is her problem exactly, and then what is her reasoning? can it be accomplished by a different sink fixture with a single handle? can it be accomplished quietly instead by adjusting the basement hot riser stop? sometimes the rate of water flow past a loose washer on a stop under the sink might cause this. sometimes "water hammer" solutions are what you seek, in which the supply pipes continue above the sink into a small dead end of air in the water pipe stub which operates as a shock absorber. there are add- on devices for this water hammer problem. sometimes if you are lucky enough to have plenty of water pressure to hose the driveway full blast [or water the entire 80-foot yard from the porch], the high pressure within the indoor fixtures requires some pressure reduction. but first, i would listen carefully to determine where the chatter starts. i would try removing the rubber washer from the under-sink stop. try removing the stop washer from the hot water riser to the noisy fixture at the basement. try removing the aerator at the fixture to change the water flow rate. for fun, i would buy an inexpensive water pressure meter you can screw onto the garden hose sillcock to see what the PSI pounds per square inch pressure is. gallons per minute GPM is the flow rate. new shutoffs may not have rubber washers within. full-flow ball type water valves with lever handles can provide better flow than straight stops.
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Greg Oliva wrote:

The contractor is 100% correct.
Stop valves are intended for "stopping", not modulating. Typically, the washer in them is only loosely attached to the stem. Partly closed, the washer can "flap in the breeze" creating the chatter you have.
If there is some other condition (water pressure, temp) requiring modulation, fix that problem.
Or....install a nice ball valve shut off under the sink for the wife. But don't expect the contractor to pay for it.
Jim
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Speedy Jim wrote:

Opps, I missed that "valve under the sink" part. Please consider my observations in my prior message suspect.

--
Joseph Meehan

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