what is a vacuum relief valve for?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by northman, May 14, 2007.

  1. northman

    northman New Member

    Messages:
    31
    Location:
    Washington
    on a water heater/expansion tank installation?

    Looking at the Watts site to size an expansion tank, they show a vacuum relief valve installed at the water heater. What is the purpose? Is it necessary or are they just trying to sell parts?


    Greg
  2. Peanut9199

    Peanut9199 Customer Service Manager Plumbing Wholesale

    Messages:
    875
    Location:
    Ontario, Canada
    "Vacuum Relief Valves are used in water heater/tank applications to automatically allow air to enter into the piping system to prevent vacuum conditions that could siphon the water from the system and damage water heater/tank equipment." and no you don't need it.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,268
    Location:
    New England
    My city requires them on new installs along with a tempering valve. My guess is to prevent what may be heated water that has sat for awhile in the water heater from being sucked back into the rest of the potable water. Since all of the water is supposed to be potable, not sure why, but as I said, it is code in my city.
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,054
    Location:
    Cave Creek, Arizona
    vacuum vent

    If the heater is in an upper floor level or attic, then the negative pressure created by a broken pipe draining the heater could collapse the walls of the heater. In this case, the installation requires a vacuum vent to relieve the negative pressure. It is not required if the heater is in a basement or first floor because those installations cannot create high negative pressures.
  5. Required on most commercial applications regarding restaurants, nail shops, beauty salons, where chemicals/cross connections are possible above mild.
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,054
    Location:
    Cave Creek, Arizona
    valve

    Those applications do not require a vacuum relief valve, they require backflow prevention devices, and the higher the possible contamination level, the more sophisiticated the device has to be.
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