Squealing Pipes

[mhase]

I have consulted two plumbers on this one, and both are stumped.

Whenever I use the hot water in the house, about 5 minutes after I turn it off, it starts making short, loud squealing noises (about 5 times, only squealing, no air hammer or rumbling sounds). This does not happen with the cold water. The noise will happen with any of the hot water sources in the house. Here is what the plumbers have done so far: Bled the lines, replaced the entire water heater, replaced the pressure regulator twice. I've had the City check the main line, and they say the pressure increase is not coming from the main line, which is constant at 120. So the pressure must be coming from the house? It has been measured in the new water heater and on the faucet that is connected to the pressure regulator. Pressure goes up to about 100 at the regulator. It seems that the squeal itself is coming from a pressure relief valve outside the house, next to the regulator, but what is causing the pressure?

[jadnashua]

Do you have an expansion tank? If so, it is shot. If not, add one.

[Cass]

Without an expansion tank the water system will build pressure as the water in the heater heats, expands, and has no where to go until the pressure relief valve operates.

[mhase]

What is an expansion tank? Where does it get installed and what is its function? How big is it?

[Dunbar Plumbing]

Looks like a small propane tank that "should" be installed between the top of the source of thermal expansion (water heater) and the cold water inlet valve.

Any device that creates hot water can in turn create thermal expansion. In a closed system where a PRV or Double Check Valve is present, there must be an allowance for the expansion of water molecules when heating of water takes place. Otherwise your potable water system will be subjected to premature wear due to elevated pressure caused by thermal expansion.

Expansion Tank (http://www.msnusers.com/DUNBARPICTUREALBUM/waterheateralbum.msnw?action=ShowPhoto&PhotoID=665)

[mhase]

I hope that's it. I've been dealing with this for 6 months now. Thanks a lot!

[jadnashua]

A good plumber would have come up with this on their first visit.

heating water causes it to expand. Piping systems are pretty rigid, so the pressure goes up. The expansion tank gives the water someplace to go. It is required if you have a check valve in the system. Your prv has one in it. It is making noise as the excess pressure squeezes water back out through the valve like the reed of a clarinet.

[Gary Swart]

The expansion tank is air-charged to the same pressure as the pressure regulator valve setting. The tank has a air valve just like a tire and is charged with a small pump such as a bicycle air pump. I installed a pressure gauge in the water supply line between the pressure regulator and the expansion tank so I can easily check the balance. The basic installation of the tank is quite simple. You just cut the supply line and solder in the tee and threaded adapter that the tank screws on to. The line and tank does have to be well supported because of the added weight, but there are illustrations on the packing box on various ways to do this. The tank costs about $50.