What causes water pipes to shake violently with no known catalyst?

Question

I woke up this morning to the sound of my water pipes shaking violently. So violently that I could feel the walls moving. The house was built around 10 years ago, and has water hammers.

Normally I would assume this is a water hammer problem, but it didn't happen when water was turned off, or anything else. No water in the house was running, and the shaking went on for at least an hour. The only way I could stop it, was by turning on the cold water to the room where the shaking occurred. I've now turned the water off to the house.

Things I've tried

1. I tried turning off the water to the house, draining all the pipes, and after turning the water back on, slowly turning the ports closed starting from the end of the line to the front (slowly)

2. Screaming at my wall.

Things I thought could be the problem

1. Maybe the water hammer, but I thought that only happened if you turned off water quickly or didn't have water hammers in the house. I have those water hammer valves in several places in the house.

2. Just a loose pipe. This is a real possibility since my builder of my house was terrible and I can hear that pipe shaking around like crazy. But can just a loose pipe cause this? I would think that it shouldn't try to shake that violently whether it was loose or not, and why now?

3. I've googled the water pressure could be too high, but that's definitely not it. Our water pressure in our neighborhood is always low.

Once again, this isn't a knocking that happens for a few seconds after I turn off the water. This is a violent vibrating that happens all the time unless the cold water is turned on in the room where the vibrating is the loudest.

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UPDATE

After leaving the water off for a long time, and re-draining all the pipes, it looks like now it's acting more like a water hammer issue and only shakes right after I cut water off.

More Update

Now it appears to have stopped and I can't reproduce it. Maybe air in the line or something crazy? Ghosts?

Answer 1

Water hammer happens when you abruptly close a valve. Water has mass. Once you get it moving toward the valve, if you slam the valve shut, the water is still moving. It slams into the closed valve and bounces -- water cannot compress. Where can that ultimately go in a house where all the pipes are 100% full of water and all valves closed? Back out to the street. The energy is dissipated into the piping system and adjacent houses.

These last two words might just answer your question.

However, if you have anything that draws water automatically (and right on cue, as I typed this, my refrigerator dumped and refilled the ice tray), then that could be a source of internal water hammer. Machine valves are particularly notorious for closing very hard.

So your ultimate pressure damper is the rest of the city. But check valves are starting to appear that permit flow only one way, and these may even be part of water meters now. Needless to say, fitting a check valve makes water hammer much worse.

The conventional way to arrest water hammer (besides making sure all pipes are firmly anchored) is creating an air space intentionally in the piping. Water is not compressible. Air is very easily compressed. Now, the water expands by compressing the air slightly, and that dissipates the energy. It's a very simple fix, easily done by extending a pipe in a (at least slightly) upward direction and capping it off, creating an air space within.

Also, they actually make fat pipes or tanks designed to do this same thing. In the tanks, the air isn't "free" but is inside a "balloon" or diaphragm, so the water contacts the balloon instead of the air.

I suspect your problem arose because these intentional air spaces somehow became 100% full of water. It is certainly possible for air to effervesce into water. (exactly the problem the tank balloons are designed to avoid.) By fully draining the system, you removed the water and allowed those spaces to refill with air.

Answer 2

Some times a small leak can cause water hammer. It is rare but I have a leak that was not much more than a slow drip cause a loud water hammer it was like a resonant frequency it was very loud and the pipes were not moving much but they were vibrating and making a loud squeal. Once I found the leak and stopped it the problem was solved.

Answer 3

This same thing happened in my house last night. I turned off the main and went back to bed. This morning I reset the pressure by opening a faucet upstairs and flushing the toilet downstairs. It all went back to normal.

Turns out a water main had busted up the street and that’s probably what caused the situation.