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Q. Sometime back you gave an explanation concerning "pipe noise" or "hammerjack?" Something to do with air in the water lines, when a faucet is turned on/off a small "wave" is somehow created and travels back through the system. While my house is only 15 years old there is no "reserve tank" installed near the hot water tank as I have seen in newer homes (not to be confused with the high pressure relief valve on the water heater).
In the past I have shut off the main water input and then opened every faucet in the house. After turning the main back on I then closed the faucets starting with the closest ones in the basement and then upstairs until I get the one farthest away from input. That seems to last for a while. I recently saw an ad for a small "relief tank" that could be installed in the water line at the faucet for the washer-- a screw on type.
What is your opinion of these devices? Second what is the root cause-- changing pressures at the input? How does air get in the closed waterline system ?
A. What you are describing is something called water hammer. Water hammer is a mild to loud bang noise that only happens when a valve closes suddenly. Washing machines and toilets can be prime offenders but any valve in the house including those you can hand close are potential water hammer causing. But it’s not air getting into the pipe system that creates the noise-- it’s the water itself. Water, as you probably know, can’t be compressed and water has a good bit of weight to it-- eight pounds a gallon . So if a column of water is flying through a pipe and the opening through which it’s passing suddenly shuts, it sends an energy wave down the pipe as water stops suddenly, creating the bang. If you gradually shut off the valve the water will slow and bangs wont happen.
There are devices called water hammer arrestors that are or can be placed on problematic pipes that provide a little air cushion and become a water hammer shock absorber that takes care of the sound. Some plumbers fashion arrestors out of a tee fitting, about six inches of pipe placed vertically on a waterline and capped off. Sometimes you’ll see them placed near the washing machines. Manufactured water hammer arrestors look like little torpedoes sticking up off water pipes.
Water hammer arrestors themselves can become water bound and stop working and the water hammer returns. Ironically, the way you free up a water bound water hammer arrestor is exactly the shutting off of water at the main shut off and draining the lines a nd refilling them in the sequence you described.
Water pipes in a can make all sorts of odd noises and each different sound has its cause. Degrading valves can do everything from whistle, chatter or even scream. Pipes that pass through wood framing can make ticking noises as they expand or contract in response to the temperature of the water passing through them. People with hot water baseboard heat often complain of the noise those pipes can make.
And it’s not just supply pipes that can set up a noise. Plastic (PVC) waste lines can tick for quite a while after they’ve been used and I know of a house where the ceiling of the master bedroom was torn out and the plastic waste lines coming from the bath above were replaced with cast iron to quiet them down.
Water hammer is primarily an annoyance but it can get bad enough that over time can shake a joint loose somewhere in the pipe creating a leak. So if you’ve got water hammer, get an arrestor and put in on the line.