advice on PEX system valve and hammer arrestor details

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by jono604, Nov 9, 2011.

  1. jono604

    jono604 New Member

    Nov 1, 2011
    vancouver, BC

    I have installed a new Trunk-and-branch PEX system as part of a bathroom remodel (3/4" trunk, 1/2" branches to supply the fixtures)
    It's a simple bathroom with, toilet, single sink, tub/shower (single mixer valve)

    I'd like some advice on a few things:

    1 - installing hammer arrestors in this system
    a) is it necessary?
    b) which fixture branches should get the hammer arrestor?

    2 - installing shut off valves on the branch supply lines to the shower mixer valve
    a) is it necessary? Is there any code requirement for this?

    any advice would be appreciated.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    In a bathroom, most fixtures do not need hammer arrestors at all. Now, some shower valves specify them in the installation instructions, and if your valve does, then you should install them. You get the 'hammer' effect when quickly shutting water off, the inertia of the moving water then pushes the pipe and it bangs into something making noise. On most typical valves used in a bathroom, you usually can't turn them off fast enough to require a hammer arrestor. Some toilet flush valves shut off quickly, and one there might help, depending on the toilet you choose. Most don't need one.

    You do not require individual shutoffs for any of the lines, and especially on a shower, most plumbers would not look for one. If you want to put some in, fine, but it isn't required. You'd normally install one for the toilet and the vanity, though. While you can use a compression shutoff valve directly on pex if you get one with the internal reinforcment ring, it's better to stub it out to copper and anchor it in the wall so it has some regidity and you aren't flexing it when trying to open or close the valve.

    If the shower is also a tub, keep in mind you should NOT use pex on the outlet side of the valve, at least to the tub spout. If you do, you WILL have needs to be full bore ID of metal...pex's ID is quite a bit smaller than copper or brass.
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  4. jono604

    jono604 New Member

    Nov 1, 2011
    vancouver, BC
    Thanks for the feedback Jiim

    I'll take a look at the fixture specs and see if any of them require a hammer arrestor.

    For my toilet and sink I'm planning to terminate in a copper stub-out elbow like you mentioned. I like the rigidity of this for the shutoff valves.

    Thanks for the advice on the valve outlets. I was planning to run copper to drop-ears for the tub spout, shower-head and hand-shower.

    Would you recommend using copper between the mixer valve and diverter? I'm using a three way diverter that directs the mixed water to one of the three tub/shower outlets.

    Would you supply the mixer directly with pex or would you use some type of copper connection?
    I was thinking of putting a PEX barb fitting on the inlets to the valve and going straight in with PEX. I would use some 90deg bend strain-reliefs on the tubing and strapping to the framing to avoid loading the fittings.

    Last edited by a moderator: Jan 28, 2014
  5. Tom Sawyer

    Tom Sawyer In the Trades

    Nov 29, 2010
    I have run into that several times in the past couple of years. It seems there are quite a few plumbers out there that have a problem reading the directions. Under the new IPC water hammer arrestors are no longer required.
  6. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona
    PEX usually has enough "flexibility" that it will absorb most "water hammer" effects. Unless the hammer arrestor is installed RIGHT AT the source of the hammer it will be ineffective. Most tub/shower valves are serviced without removing the trim plate so any "intergral stops" are never seen or used.
  7. ssimacdonad

    ssimacdonad New Member

    Jan 28, 2014
    I had a problem with hammer originating from automatic washing machine water shut-off valves. The machine is late-model with electronic controls. I live in a condo with PEX piping and I have been extremely concerned that the hammer (i) will annoy my neighbours and (ii) might cause a line rupture somewhere in the system. So I purchased two hammer arresters made by LynCar for about $20 each (don't know if the brand really matters) and installed them at the wall valves in the laundry room. Some slight improvement but still noisy and worrisome. THEN I read this thread and noted that I should install them as close as possible to the source. So I moved them to the washing machine end of the (stainless steel braided) connection hoses. PRESTO!!!! quiet as a mouse! Thanks for your help!
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