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A plumber recently installed a new pressure reduction valve and expansion tank in my house (which previously had neither) because the water pressure was unusually high. About a week after the install, I started hearing a low, loud foghorn noise whenever I turned on any faucet in the house or flushed the toilet. The noise comes a few seconds after the water comes on, and it typically only happens after periods of no water usage, such as in the morning or when I get home from work. I spoke to the plumber who is coming back next week, and he doesn't think the problem is the PVR unit itself, but everything I'm seeing online indicates that usually is the problem. What could be causing this noise?

Update: the plumber came out and agreed it sounds like the PRV. He replaced it, and two days later I haven't heard the noise once.

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    Stand next to the valve and have your wife open a faucet elsewhere in the house. Rule of thumb in any system is if a problem starts happening what was the last thing that was changed? – Ted Mittelstaedt Feb 26 at 3:41
  • All foghorn sounds are LOW. "I say boy, i say listen to me when im talkin to you boy!". Foghorn Leghorn. - foghornleghornquotes.com/foghorn-leghorn-sayings – Alaska Man Mar 4 at 20:35
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To me it sounds like the Pressure Reducing valve or Regulator is not properly sized but it could be a less expensive model also.

The noise you are hearing is the regulator a spring tensioned device getting close to its pressure setting and chattering this often sounds like a fog horn on water pipes in some cases it can be a high pitched also. I have found that high end valves or water regulators have fewer problems but these are expensive.

The pressure tank will usually dampen the noise is your air charge close to your operating pressure? If the air charge is set up like a well down at 30-40 psi the bladder will be flattened with a 60 psi tank pressure.

If your PRV is set at 60 your pressure tank should be charged to 56-58 and that will help dampen the noise as the air dampens the vibrations.

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Instead of flowing air which is used in instruments like flutes or trompets, oscillations can be produced by flowing water as well. The complete system consisting of the spring in the reduction valve, the tube dimensions and the expansion tank could be in resonance depending on a certain pressure and water flow.

It should be influenced by the pressure that can be adjusted turning the black part of the reduction valve.

If there is a water heater downstream of the pressure reduction valve, a safety pressure relief valve must be installed, since the expansion tank could fail and the reduction valve would close if the water is heated up thus preventing the pressure to be relieved into the upstream net.

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