"Stub Out" water hammer cushion


Old 10-19-16, 09:31 AM
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"Stub Out" water hammer cushion

Hi All, Hopefully an easy couple of questions here. I need to put an air cushion in our 3/4 inch copper that feeds both bathrooms. When it comes to air chambers, does bigger mean better....within reason of course. I went into our local Lowes to look at air chambers and they had your typical approx. 8 inch long air chamber made out of 1/2 inch copper for about $10....ouch ! But they also had one of the larger balloon type (for lack of proper term) that was actually cheaper, and it was much larger....probably 10 inches long and 1 inch in diameter. But is was labeled "Stub Out". So whats the diff between a stub out and an reg air chamber ? Will a "stub out" work as an air chamber ? And is it OK to just make your own chamber with some copper tubing by just capping it and save a couple a bucks ? Thanks for any help !!
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Old 10-19-16, 10:29 AM
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Not quite sure what a "stub out" is but I've made my own air traps. I have a underground 100' 1/2" copper line to a faucet near the pool. When the water was turned off it made a gigantic hammer in the house.

I installed a Tee where it comes in the house with a 15" piece of 3/4" copper pipe dead ended. It works well but I notice after several months a slight hammer comes back. Since there is no bladder... the air eventually gets absorbed/dissipated back into the water.
Old 10-19-16, 10:30 AM
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A stub out is just a piece of copper pipe with a sealed end. It's usually used at fixtures with the end sealed for pressure testing, then the end cut off and a valve soldered on.

If you want to use a simple air cushion, I would use a 12-18" piece of copper with a cap soldered. Add a few valves so you can isolate it and drain it occasionally because over the months, the air will dissolve into the water, and you'll no longer have a cushion.

They have newer water hammer arrestors that have a bladder inside them that won't fill up. Something like this:
Quiet Pipes Washing Machine Water Hammer Arrester-38600 - The Home Depot
There are different styles that can screw into a washing machine hose, under-sink stop, or be soldered into a main line.

BUT - often times water hammer has more to do with too-high water pressure. Have you tested your water pressure yet? Anything over 80psi is too high for residential plumbing systems.
Old 10-19-16, 02:25 PM
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This is the darndest water hammer thing. I could spend 10 pages explaning it, but i'll try a short hand version. bout 2 years ago the cartridge went bad in shower. Replaced it and all was fine. bout 6 months later new cartridge started leaking, replaced it, all went fine but pipes banged afterwords. been banging every since and we just lived with it. but we are selling our house and banging pipes is not a good selling point. i'm assuming that something re-positioned itself when I took the chrome ring off the shower fixture as it screws directly to the actual shower valve behind the wall and kinda pulls the valve when you tighten the ring. have gone through all the drills....drain water and re-fill....check all accessible clamping points & hangers.....water pressure is within specs. the banging is not consistent, might bang when a toilet is first flushed or when it shuts off, or both. you can work the cold water in any faucet within about 8 feet of it and it will bang when opening and closing, but again not consistently. it sounds as though there is a pipe somewhere that is just "teetering" back and forth because it has simply come loose, possibly when I took off the shower chrome ring. I have tried 5 holes in the wall to locate it and no luck. haven't even been close enough to really change the tone of the knock to let me know I was getting close. I had to drain the water to change a faucet the other day. no shut offs at the faucet so i had to off the main. turned it all back on and the pipes didn't bang. thought i got lucky. but i forgot that I hadn't opened up the other faucets close by to purge the air out. after i did that the banging was back. so thats why i'm gonna try and put a chamber in hoping it at least quiets it down enough. well, sorry for the book....but as you may imagine this problem is driving me nuts....LOL Thanks to all.
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