Do I need water hammer arrestors?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Alan Waterman, Aug 21, 2021.

  1. Alan Waterman

    Alan Waterman New Member

    Joined:
    Mar 10, 2021
    Location:
    Merced, CA
    My house was built in 1998 on a slab. Water is M copper under slab and all original. It's possible the lengths under the slab could be L but everything that I can get to for fixtures has always been M.

    Solenoid appliances are clothes washer, dish washer, and ice maker. I also have a shower sauna but it's only use maybe once a year.

    How important is it to install water hammer arrestors? I don't have noisy solenoids or banging pipes but I'm not sure that means much.

    My ice maker spigot sprung a pin hole leak a few years ago which promptly shut off the water to my house so no damage but it was a bit surprising. I sweated on a replacement. I've had no other leaks and my pipes hold pressure for at least 30 minutes down to the PSI before I terminate the test. I only test after I've shut the hot water off, several showers to use up the hot water, and then flushing the hot water heater until the water is the same temp as the cold water so that decreasing water temp doesn't lower the pressure.

    Couple other slightly related facts. My water is neutral ph and 1 grain of hardness. I also have a phosphate feeder in an inline filter coming into the house.

    I used to have occasional water hammer from my well pump shutting off but about 15 years ago installed a Franklin VFD controller for constant pressure which has a slow start and stop which completely cured the banging of the pipe going into the house.

    So how important are water hammer arrestors and why don't appliances have them built in or do some in fact have them already.
     
  2. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    Some homes with a check valve at the water meter need the hammer arrestors. I'm not sure how important it is for a well system with a fairly large expansion tank. Perhaps someone else has experience with that.

    The copper looped in the ground will by type L. They don't make soft copper in M.

    Often is hammer is an issue, it will be noticeable. For a friend of mine, the banging pipes would wake him at night when the ice trays filled.
     
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  4. Alan Waterman

    Alan Waterman New Member

    Joined:
    Mar 10, 2021
    Location:
    Merced, CA
    In my case, none of the pipes really hang. The all go into the slab and only rise a couple feet out of the slab before exiting through the wall to their shutoff valves if they're stressed from water hammer I don't think I'd hear pipes banging around.

    I have an extra check valve after the pump above ground but that's 150 feet away from the house. The solenoids are small so the water hammer effect I'm worried about is pretty close to where their spigots are. Not worried about the effect traveling long distance for such small valves but am worried about the joints for the bend or so under the slab since those are still pretty close.
     
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    Water hammer can send some significant shock waves throughout the plumbing system. Your storage tank’s bladder can help, but arrestees work best when as close to the offending solenoid valve as possible. Note, most things like faucets and shower valves don’t close fast enough to require one, but note their installation instructions, as a few do!

    Pinhole leaks can be caused by various things:
    - aggressive water
    - over speed water flow, especially on hot lines
    - defective pipe
    - improperly made joints…you need to remove the flare or lip most tubing cutters make before making your joints at the fittings or that flare can cause turbulence…that over usually a long time can eat pinholes, often a series at the wavelength of the turbulence.

    You can consider water as incompressible so as it’s moving, it has inertia…stopping it quickly acts like a piston or hammer, banging against the end point, and any angles along the way of things that try to slow that piston down. Just like hitting a brick wall versus a big marshmallow. Dissipating the energy over some distance reduces the peak energy to something manageable.
     
  6. Alan Waterman

    Alan Waterman New Member

    Joined:
    Mar 10, 2021
    Location:
    Merced, CA
    So as to the original question, are water hammer arrestors needed on valves that feed solenoids as a rule of thumb?
     
  7. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    For valves controlled by solenoids, yes.
     
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