Plumbing question

So our family is adding a bathroom to the house, and I noticed that on the copper cold water line, on the end nearer the sink, he added a short vertical pipe (~1 foot high) along the horizontal pipe run. The pipe is capped and otherwise inaccessible (it’s behind a wall).

Anybody know what this was for? My brother indicated that this is sometimes added to prevent the slamming noise (presumably from the ramjet of running water) that can occur when you shut off the faucet, but I wonder then why it wasn’t on the hot water line as well (I have photos of the plumbing at home and will check this evening).

It’s a shock absorber and it’s indeed there to prevent pipe banging. I’ve always seen it used on hot as well as cold water so I really don’t have anything useful to add.

A link.

The hot water doesn’t come from a separate street lateral, does it? No. There’s one supply line which feeds both supply to the water heater and the remainder of the cold water dwelling supply, so realistically the only water hammer arresting mechanism need be on the cold side.

That said, a 1 foot stub isn’t much to contain air-which is what acts as the shock absorber. All pipe stub arresters that I’ve seen are 2-3’ tall, and despite Levitt’s penny pinching, he put them on both hot and cold lines. :wink:

Oddly, I’ve only once seen a stub larger than a foot. Every place I’ve lived in has had multiple short stubs, rather than one big one. You can even buy pre-made stubs (talk about lazy!) here that are only 6" long or so.

There’s probably regional preferences at play here.

Wrong. Using that line of reasoning, you only need one for the entire city.

The usual cause of water hammer in a house is closing a valve very fast, creating a shock wave. This can happen on either a cold or hot water line, and both should be protected. A short stub of pipe is useless as the air inside dissolves in the water and the stub is soon waterlogged. The right way to do it is to install blader type water hammer arrestors on the pipe you want to protect. These use a rubber bladder to prevent the air from dissolving in the water. They come in different sizes and are sized depending on the number of fixture units that the pipe serves.

I checked my photos, and as suspected on this thread there are at least two such stubs on both the cold and hot line (didn’t notice the others; proof in case you doubted that it is a good idea to photograph everything before the builders put ont he drywall).

The stubs do look like ordinary copper pipe, so I suspected these do not include the bladder system Dag Otto mentions. I spoke to the plumber this morning, and he confirmed they are just stubs. He states that since they are going only to a sink, toilet, and shower, the bladder-type water arrestors are overkill; if there is a water hammer problem in the future, simply shut off the lines and drain the water by opening all the faucets (there is one faucet below the stubs); this will refill the stubs with air.

Here’s a link. They are really not that expensive. Of course, if you can remember to not close valves quickly, you probably won’t have a water hammer problem.

Now if we could just convince the solenoid valves in the dishwasher, washing machine, ice maker and lawn sprinklers not to snap shut… :smiley:

I’ll second that.

Saying the hammer arrestors is “overkill” is odd IMO. One system works and the other does not. :rolleyes:

Not that I’d worry about it, if you have a water hammer problem in the future you will want the arrestors in accessible locations anyway so nothing is lost, but nothing is gained by adding air chambers either.