a Q about water-hammer arrestors and flushometer toilet

talley_sue_nycJune 20, 2011

I live in a 5-floor, 10-unit self-managed co-op. No "management agency," just a co-op president with lots of power. Built in 1920.

I'm on the 2nd floor; the Prez is on the top floor (5). She said that when we flush our toilet, with its flushometer, that she gets really bad banging. Water hammer, I'm assuming.

Her solution is for all of us who still have the 1920s flushometers to have to replace it with a tank the next time it breaks, instead of simply repairing it. Given that we have an 8" rough-in, I really don't want to go there.

But of course, the water hammer isn't good for the pipes, nor should she have to live with the banging every time we flush.

Apparently this happens on the other side of the building, in the other line of apartments (or else I'd think it came when she did a gut remodel, complete with new pipes, about 13 years ago). She says it's been a while, but I'm thinking it couldn't have been THAT horrible, or she'd have been complaining big-time 16 years ago, when we had middle-of-the-night wakings w/ babies and pregnancies, or right after her remodel, when Kid No. 2 was born.

I haven't had a chance to ask if there's an air cushion that should/could be reinstated. Wouldn't they have known about water hammer, and air cushioning, in 1920, when our bldg was built? And installed something, since the building was full of flushometers? (20 of them in the building originally)

But I'm wondering--would it do any good to install a water-hammer arrestor on the pipes behind our wall?

(I think I can access the pipes *above* the tile through the plaster wall, and then cover it up w/ either a decent skim-coat job, or by hanging the cabinet back up. If I could put the arrestor on the cold-water supply line there, would that help? Not the tallest point in the system, but above the only flushometer in that line.)

How hard is it to install an air cushion for the stack? Would it go on the roof?

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You got it. In Ma this code now. If I am correct a flushometer requires a 1" line which supplies a large volume of water quickly. I would venture to guess that someone along the line removed the suppressors during a reno.The stack you mention is a vent for the drain lines which are not pressurized
A simple way to find out the culprit is to have each unit flush and when you hear the hammer you have found the unit.This is an issue I would have all the owners get on board with.If a water line lets go because of this hammer you are going to have more than one owner upset. I believe at the time your building was constructed fine thread brass piping was used (as compared to soldered copper). The brass fittings tend to deteriorate over time, coupled with the hammer and one of these large lines lets go on an upper floor , well I think you get the picture. Putting in toilets with tanks may exacerbate the issue , the feed on those is a 1/4" . Not only will the likely hood of hammer go on unabated but you will hear the sound of the toilet tank filling. Good luck

    Bookmark   June 21, 2011 at 9:21AM
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Adding (or replacing) water hammer arrestors would be a lot easier.

    Bookmark   June 21, 2011 at 10:50AM
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As an example, in the master-bath line, my apartment is the only one on our side with a flushometer. When we flush, and only when we flush, there is big banging up on the top floor. The plumber called from the top floor and had my DH flush our toilet while he was listening, so there's no question but that it's the flushometer.

And it doesn't happen for the other toilets. So it's the large volume of water from the flushometer.

I'm assuming water hammer. Would it be anything else?

Apparently the noise of other toilets filling isn't really an issue. The walls are pretty solid; you'd have to be IN the bathroom to hear your own toilet filling, so I would imagine you'd have trouble hearing other people's toilets in our building.

Hence the proposal of making us replace our entire toilet w/ a tank should our flushometer break.

Brickeyee, about the arrestors: Can I put one above my toilet, on the cold-water supply line? Or does it have to go all the way on the top floor?

I can get into my wall above the tile without a lot of pain, but the top-floor tenant can't do that without messing up her floor-to-ceiling limestone-covered walls. I would have assumed that in her renovation, her architect & plumber would have put the arrestors in along with all the new pipes.

I haven't been able to find out for sure when this got bad enough to become an issue; she would probably tell me it has always been like this. Whether it has or not.

    Bookmark   June 21, 2011 at 1:23PM
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talley sue,

Could be a couple of things, but first what is the water pressure at the water meter? Water hammer is caused by excessive water pressure. If you have excessive water pressure, a shock absorber would help, but it needs to be installed between the last two fixtures on the CW piping and sized for the number of plumbing fixtures on the entire system.

If the piping has come loose from it's supports you will get movement in the piping (This is not water hammer). If the piping supports were nailed instead of screwed in, they could have worked themselves loose. You would have to determine where the piping is loose and resecure it.

Hope this helps,


    Bookmark   June 22, 2011 at 1:37PM
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Hmm. I don't think the entire building's water pressure is too high--the folks on the top floor always complain that their showers have very, very low pressure.

As for the pipes coming loose--that's probably not going to help my ultimate cause, because the only way to deal w/ it would be to bust through people's tiled walls. (The only person who ever hears the banging is the lady on the top floor; no one else hears it, which makes me think it's that the banging, whatever it is, is happening in her walls.) And they'll all say, "I'd rather you just replace your toilet--it would be easier." Nothing else seems to cause the banging--just the flushometer.

So since the flushometer is the only culprit, I was hoping I could install something specific to it, the way arrestors are often installed right next to washing-machine valves to protect the rest of the system.

(there are washing machines in our basement, and they don't cause this problem, btw.)

    Bookmark   June 23, 2011 at 7:56AM
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"Water hammer is caused by excessive water pressure."

Water hammer is caused by pressure spikes produced when the moving water is forced to stop suddenly.

If you have higher pressure that can translate into faster water movement, and adding a fast closing valve makes it worse also.

Unsecured pipes do not help at all, since they can move with a much smaller momentum change.

The hammering and movement can result in damaged lines (cracks) and leaking.

If there are units between yours and the victim unit, you might check to make sure the victim is not from unsecured pipes.
The closer to the source the worse the problem should be, the further away the less.

A water hammer arrestor close to the flushometer may be the needed fix.

    Bookmark   June 23, 2011 at 10:28AM
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It's definitely the flushometer--because when we flush it, the banging happens.
There isn't particularly high water pressure in the building, and certain the pressure dwindles as it rises toward where the pipe banging is heard. Nobody else hears it. I don't hear it (floor #2), my upstairs neighbor doesn't hear it (floor #3), and I think she only hears it on her top floor (she's a duplex, so #4 and #5).

She did a mega-bucks renovation, complete w/ architects and incredible plumbers, about 13 years ago, and I would imagine that her pipes are secured. She's absolutely NOT going to bust through her limestone tiles to look at her pipes (though I think she does have photos of the interior before the walls were put up). It would be better to break through my plaster walls above the tile.

My big question is, is it sensible enough to consider? Can I install the arrestor about 3 feet above the T-joint that leads in to the flushometer, off the vertical pipe? Will it help w/ any surges or stoppages that are happening because of the flushometer, or must it be on the horizontal part of the pipe after the T-joint itself?

    Bookmark   June 23, 2011 at 1:16PM
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You know, I've been thinking about this:

"The closer to the source the worse the problem should be, the further away the less."

The banging happens in the unit that is as far away from me as it is possible to be.

It is, in fact, the end of the line--we have a one-pipe system, so the supply pipes go up, but they don't turn around and come back down (why she didn't add a return pipe for our side of the building in her reno, I don't know.)

I wonder if that "end of the line" bit explains why she gets the water hammer and other people don't. If she's getting the "end of the line" water hammer, if there was supposed to be an air cushion at the top of the single pipe and something's gone wrong.

    Bookmark   June 23, 2011 at 7:39PM
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I started out trying to give technical advice as to what the problem is(in this post), forget about it. The problem is hers, she sounds like a piece of work. Put the toilet in properly and go from there. Undoubtedly the problem is in her unit. Sometimes its better to bite the bullet.

    Bookmark   June 24, 2011 at 7:04PM
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LOL, jonnyp.

    Bookmark   June 27, 2011 at 8:48AM
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