Water hammer question

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by gagecalman, Dec 6, 2017.

  1. gagecalman

    gagecalman Member

    Joined:
    Nov 25, 2016
    Location:
    Baltimore, MD
    I am on city water at 80 psi. No PRV. No expansion tank on water heater.
    I have water hammer when the toilet is flushed.
    My new water meter was making a loud tapping sound when the water was running.
    The city came out and replaced it with a straight piece of pipe.
    They sub the installation out so I don't have a meter now.
    With the meter removed I don't have water hammer.
    What happened?
    Thanks,
    Jim
     
  2. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    I don't know what happened. Clearly the meter had a noise-generating problem. It could be that pulling the meter removed a check valve also. I don't know why that would have impacted the bang that occureed when the toilet fill valve shut off. You could add a water hammer arrestor near the toilet if the bang comes back. Or you could try a different fill valve. Is the Korky "Quietfill" valve slower to turn off? Maybe.

    If you get a check valve back in there with the new meter, you will need to add a thermal expansion tank if you don't have one already.
     
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  4. gagecalman

    gagecalman Member

    Joined:
    Nov 25, 2016
    Location:
    Baltimore, MD
    Thanks for the reply.

    I was wondering if the meter had a check valve built into it. I don't know how to find out.

    I have the Korky valve. I actually prefer them over the others.

    I was trying to decide if I should install a PRV. I am at 80psi without one. I didn't know if reducing the pressure would help with the hammer.
     
  5. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    I think a PRV is a potential failure and noise point. It would require you to have a thermal expansion tank unless you both get a "bypass" PRV and have no check valve on the incoming water.

    If you have a check valve, a pressure gauge would see a large rise in pressure after using much hot water, such as taking a shower, and then stopping using any water for a half hour while the WH heats the water back up. If you have such a rise, you will need a thermal expansion tank, which will give the expanding water somewhere to go.

    You might be able to get rid of the water hammer at the toilet by partially closing the stop valve.
     
  6. LLigetfa

    LLigetfa DIYer, not in the trades

    Joined:
    Feb 6, 2011
    Occupation:
    Semi-Retired
    Location:
    NW Ontario, Canada
    Was the noise at the start of water flow or when the tank was full and the valve shut off? Did it happen on every flush? If it was not on every flush and at the start of flow, possibly the pressure was higher than 80 PSI due to a lack of an expansion tank.

    Sometimes there can be a resonance due to a certain length of pipe run that creates a perfect harmonic and the water meter may have had a checkvalve that set off that resonance.

    As @Reach4 suggested, partially closing the angle stop could mitigate it. I would not reduce the pressure with a PRV.

    I don't understand how you can no longer have a water meter. Do you have flat rate billing instead or is this just temporary? If/when you get another water meter and if it has an integral checkvalve, then I suggest you install an expansion tank.
     
  7. gagecalman

    gagecalman Member

    Joined:
    Nov 25, 2016
    Location:
    Baltimore, MD
    Thanks for the replies.

    The pipes would "bang" every time either of my two toilets would stop filling. Now that the meter is removed they don't bang.

    I could actually hear it if I turned a cold water faucet off quickly. No noise now.

    I will check the pressure after hot water use to see if it rises above 80psi.

    The lack of a meter is temporary. The city subs this out. I don't know when they will replace it.

    Can there be a check valve built into the meter? The meter is in a vault and I didn't see a seperate check valve when they were disconnecting the meter.

    At what pressure is it recomended to install a PRV?

    Thanks again.
     
  8. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    Yes.

    I don't think it is certain that the change in water hammer requires a check valve. Having the water meter determining whether you experience water hammer is a surprise to me. I don't know what does this. I think it would be something adding momentum to the water flow. My suspicion is that a thermal expansion tank would stop the effect.

    There are many instances of people reporting PRVs making noise.

    Code says you should have one above 80.
     
  9. LLigetfa

    LLigetfa DIYer, not in the trades

    Joined:
    Feb 6, 2011
    Occupation:
    Semi-Retired
    Location:
    NW Ontario, Canada
    If there is no meter, then the expansion would just backflow into the city main so I would not expect to see any rise in pressure. If the new meter includes a backflow preventer, then how much expansion raises the pressure (if at all) depends on several factors. Some toilet fill valves could actually open slightly to bleed off high pressure. If there is a humidifier with a float valve, it too could bleed off pressure.

    As for the hammer on close, the only plausible explanation I can come up with is where the pressure wave reflects back from the backflow preventer and other fixtures at the ideal harmonic to arrive and amplify at some place in the plumbing. Anything that changes the "tune" of the plumbing such as partially closing the angle stop, adding an expansion tank, or adding a hammer stop could change the end result.
     
  10. gagecalman

    gagecalman Member

    Joined:
    Nov 25, 2016
    Location:
    Baltimore, MD
    Just an update.

    Still no meter. No PRV.

    No hammer.

    Pressure is at 78psi with everything off. Goes down to 75psi with something on.

    50 gal electric water heater. Two showers taken. Pressure stayed at 78psi while the water was heated back to temperature.

    I don't know when they will install a meter.
     
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