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Thread: Vacuum relief on cold water feed?

  1. #1
    DIY Senior Member vtxdude's Avatar
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    Default Vacuum relief on cold water feed?

    I can't remember what it is called but usually on the cold water feed to the water heater there is an extra brass piece that I think the plumber said is a vacuum relief something or other.

    When he put in the new water heater he said that they were no longer required. It was attached right to the cold water feed on my water heater but now I have just the straight copper pipe.

    Is this needed? Reason asking is that pipes seem a lot nosier now when a call for water is initiated such as washing machine or if WH is refilling etc


    Thanks

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    Plumbing Designer FloridaOrange's Avatar
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    Was your old model a bottom fed unit?
    Matt
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    Retired Defense Industry Engineer jadnashua's Avatar
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    I don't know what the NH code is, but Nashua requires them on installation along with a tempering valve. Was a permit pulled and an inspection done? That would tell you for sure what was required. The vacuum breaker should(at least in my limited experience) have no affect on the sound of water running.
    Jim DeBruycker
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    DIY Senior Member vtxdude's Avatar
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    Im talking about the brass fitting here off the cold water feed



    Plumber said no longer required


    What is it's purpose?


    Here is pic of new piping





    Tempering valve? You mean the T/P?
    Last edited by vtxdude; 01-13-2010 at 02:43 PM.

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    Plumbing Designer FloridaOrange's Avatar
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    Down here it's only required for a bottom fed unit.
    Tempering valve is not a T&P.
    Matt
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    DIY Senior Member Runs with bison's Avatar
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    For process vessels typically a 150 psig rating was good enough to rate a vessel for full vacuum as well. Since the water heater relief is set to that I really doubt vacuum protection is necessary. For my process equipment design group it was customary to spec anything requiring moderate pressure (say 75 psig+) at 150 psig and full vacuum as there was little to be gained savings wise from lower pressure rating and it made the overall design simpler and more robust. Vacuum relief devices posed a lot of problem when boiling ether, gasoline, and other light hydrocarbons.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Vacuum will collapse a vessel more easily than pressure will blow it out. Regardless, if it is required by code in your area, you put one in if you want to pass.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Illinois Licensed Plumber SewerRatz's Avatar
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    Is your water heater installed in the basement? If not is there any plumbing fixtures lower than the water heater?

    Here they are required if the water heater is installed above any other plumbing fixture. This way it will prevent vessel from collapsing if the water where turned off at the meter and someone opened a fixture.

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    DIY Senior Member vtxdude's Avatar
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    It is in the basement.....the plumber said used to be a requirement but is no longer..maybe different requirements for Nashua vs Merrimack? Who should be able to confirm? Water Dept?


    So the absence of this should cause any difference in pressure or cause more of a clicking noise at the meter (knocking noise at where meter is tied into the j-horn when water is being drawn) Seems like faster meter spins for washing machine, toilet, shower the louder the knocking noise..it is only at the pipe attached to meter...can post pic later to clarify
    Last edited by vtxdude; 01-14-2010 at 04:03 AM.

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    Illinois Licensed Plumber SewerRatz's Avatar
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    Best person to contact to confirm if it is not required is the plumbing inspector from the building department of your city or town. Not having a vacuum relief valve will not affect how your meter is working or water pressure. It is a safety device to prevent a vacuum from collapsing the tank if the city shut of the main and someone opened a faucet below the heater.

    Quote Originally Posted by vtxdude View Post
    It is in the basement.....the plumber said used to be a requirement but is no longer..maybe different requirements for Nashua vs Merrimack? Who should be able to confirm? Water Dept?


    So the absence of this should cause any difference in pressure or cause more of a clicking noise at the meter (knocking noise at where meter is tied into the j-horn when water is being drawn) Seems like faster meter spins for washing machine, toilet, shower the louder the knocking noise..it is only at the pipe attached to meter...can post pic later to clarify

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    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by jadnashua View Post
    Vacuum will collapse a vessel more easily than pressure will blow it out.
    Yes, and that is why it takes about 10x the internal pressure rating (150 psig) to achieve the 14.7 psi external pressure (vacuum) rating.

    I don't think I've ever lived anywhere that required vacuum breakers on the hot water tanks. I wonder if that is because the municipalities I've lived in three widely separated states typically have not had residential boilers? From what I've gathered here the design pressures of these residential boiler shells appear to be lower and therefore probably at risk of vacuum collapse. The boilers I've worked with have been industrial ones producing 600 - 1600 psig steam.

  12. #12
    Moderator & Master Plumber hj's Avatar
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    Default vacuum valve

    Even where they are "required" the actual installation of the heater would determine whether it is necessary. Usually they are more of a nuisance that anything because they can develop leakage through the port.

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    HVAC Jah0983's Avatar
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    Hi all came across this thread and have been trying to get a ? answered. Is this an older style vacuum relief valve? Is it replaced by the watts N36-M1? Thanks in advance for any response!
    Last edited by Terry; 02-05-2011 at 11:08 AM.

  14. #14
    Forum Admin, Expert Plumber Terry's Avatar
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    We would "guess" that it's a vacuum relief valve.
    Some places like to see them on electric tanks to prevent the elements from running dry and burning out.

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