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What is a check flow valve?

John B_2
John B_2 Member Posts: 46
It's right after the air separator about fifty or sixty year old boiler set-up.

Getting new boiler and trying to make sure things are going to work as well as old system did.


  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Not the same as a check valve....

    A flow check valve has a heavier weight that can be adjusted anywhere from weighted closed to completely open (gravity circulation) and are typically used on boilers with immersed DHW coils, or large storage tanks that can allow their energy charge to flow via gravity into the heating distribution system, causing discomfort due to over temp, and energy waste.

    Not to be confused with a conventional spring or gravity operated SWING check valve, which are usually deployed where there are numerous pumps that can create back flow conditions. Regular check valves don't stop gravity flow in many situations.

    Attached is a picture of a gravity flow check valve.


    There was an error rendering this rich post.

  • John B_2
    John B_2 Member Posts: 46
    do you think it's there because of the large expansion tank

    above it?

    Will the system still need one if a newer bladder type is going to be used?

    The system has three zones with one pump each.
  • Brad White
    Brad White Member Posts: 2,398
    edited October 2010
    No relation.

    The flow-check valve as Mark said is a weighted check valve to "check" (stop) gravity circulation under normal circumstances, yet allows manual opening should your pump fail, so you can still get some heat.

    The expansion tank function is a buffer to absorb thermal expansion (usually about 4% of volume difference), when heated from cold fill to the 180F to 200F range. This expansion tank connection wants to be connected to the suction (inlet) side of your circulators while the flow check should be on the discharge (outlet) side of each circulator.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
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