Water hammer arrestors stop working after a few days

[dlukas]

I've installed water hammer arrestors on several hot and cold supply lines in my basement (where I have access). The fixtures that cause the water hammer are on the two floors above where the arrestors are installed.

When I installed them, the water hammer stopped for a few days, then restarted. I shut off my water, drained the entire supply system, and the arrestors started working again--but again, the water hammer returned after a few days.

I suspect that the supply lines are not properly secured inside the wall where they're banging, but I would still expect the arrestors to mostly mitigate the issue. Do I need to install the arrestors closer to the fixture? Closer to where the banging is? Do I need to open up the wall...?

Thanks in advance!

 

[CT18]

Did you buy mechanical arrestors. If yes then the pipe is banging and probably needs to be strapped

 

[GReynolds929]

Yes they should be installed at the fixtures causing the issue.

 

[dlukas]

Did you buy mechanical arrestors. If yes then the pipe is banging and probably needs to be strapped

I didn't know there were non-mechanical arrestors. This is the style of arrestor I installed: https://www.acehardware.com/departments/plumbing/pipe-fittings/copper-fittings/44556

So is the pipe banging distinct from water hammer? I thought they were one and the same.

 

[dlukas]

Yes they should be installed at the fixtures causing the issue.

So if I have 4 faucets causing water hammer, you're saying I need 8 separate arrestors (hot + cold), even if some or all of them share the same upstream supply?

 

[Geofd]

Loose washers in the faucets can cause that also loose packing on valves will cause I loose washers on the valves under your sink can also cause water hammer

 

[dlukas]

Loose washers in the faucets can cause that also loose packing on valves will cause I loose washers on the valves under your sink can also cause water hammer

Thanks--I'm pretty confident it's not this, as it affects all fixtures in synchrony.

 

[CT18]

Water hammer usually occurs on quick closing valves. If you are getting a banging sound from just turning off a faucet then you may have issues with loose pipes. You should not need shock arrestors on every fixture. In the old days we would make them from 3/4" pipe a foot long with a cap.

 

[Twowaxhack]

Turn the water off slower.

 

[dlukas]

Water hammer usually occurs on quick closing valves. If you are getting a banging sound from just turning off a faucet then you may have issues with loose pipes. You should not need shock arrestors on every fixture. In the old days we would make them from 3/4" pipe a foot long with a cap.

Thanks. I was under the impression that banging due to a valve closing is water hammer? You're saying there's a difference between pipes banging and water hammer?

 

[Twowaxhack]

Thanks. I was under the impression that banging due to a valve closing is water hammer? You're saying there's a difference between pipes banging and water hammer?

It is water hammer but there’s always going to be energy dissipated into the piping upon water stopping abruptly. Loose pipes will help dissipate that energy before a water hammer arrestor has the chance to absorb that energy. So therefore the pipe must be secured.

 

[dlukas]

It is water hammer but there’s always going to be energy dissipated into the piping upon water stopping abruptly. Loose pipes will help dissipate that energy before a water hammer arrestor has the chance to absorb that energy. So therefore the pipe must be secured.

Got it, that makes sense. Planning to open up some walls and strap some pipes this weekend then :/

The thing I'm still struggling to understand is why the water hammer went away briefly when I drained my pipes, only to return a few days later. Any idea??

 

[Twowaxhack]

Got it, that makes sense. Planning to open up some walls and strap some pipes this weekend then :/

The thing I'm still struggling to understand is why the water hammer went away briefly when I drained my pipes, only to return a few days later. Any idea??

Sure, when you drained the pipes air entered the system and acted as an air cushion. After a few days the air gets expelled from the system naturally.

 

[Twowaxhack]

What’s your water pressure ?

 

[dlukas]

What’s your water pressure ?

70 PSI

 

[Do it myself]

You should reduce the pressure and install an expansion tank on the cold water pipe downstream of your main shut off. As the cold water sits in the pipes it can build pressure.

 

[dlukas]

You should reduce the pressure and install an expansion tank on the cold water pipe downstream of your main shut off. As the cold water sits in the pipes it can build pressure.

You're saying 70 PSI is too high? The internet seems to think that's within the range of normal (i.e. 40-80 PSI).

Can you explain what you mean by "as the cold water sits in the pipes it can build pressure" ? I'm getting the same banging effect with both hot and cold, fwiw.

 

[GReynolds929]

As the cold water sits in the pipes it can build pressure.

Wrong, this is nit why you want to have a thermal expansion tank. A clue to why is in its name.

 

[Do it myself]

You're saying 70 PSI is too high? The internet seems to think that's within the range of normal (i.e. 40-80 PSI).

Can you explain what you mean by "as the cold water sits in the pipes it can build pressure" ? I'm getting the same banging effect with both hot and cold, fwiw.

Water enters your house (well or municipal source) at a cold temperature, say 50F. Your house is at about 70F. So when you aren't using water, at night or while you're away, the water will heat up 20F and try to take up more volume. Since it's confined in a pipe, it will increase pressure.

 

[Twowaxhack]

Water enters your house (well or municipal source) at a cold temperature, say 50F. Your house is at about 70F. So when you aren't using water, at night or while you're away, the water will heat up 20F and try to take up more volume. Since it's confined in a pipe, it will increase pressure.

While that’s true, 20 degrees at the volume of water you’re dealing with isn’t enough to cause a pressure problem in a potable water system.