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Another BFP question

ChrisJ
ChrisJ Member Posts: 16,233
edited November 11 in Plumbing

Ok I've been curious for a while, and I keep forgetting to ask.

What's the difference between a dual check with atmospheric vent, and a RPZ back flow preventer? Isn't the vent the reduced pressure zone?

By dual check with vent, I mean such as this one commonly used for boilers :

https://www.supplyhouse.com/Watts-0063190-BBFP-1-2-IPS-Backflow-Preventer

Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 24,556

    Belt and suspenders. The reduced pressure zone valve has, in between the two check valves, a zone with a differential pressure relief valve which is set up so that if the pressure in that intermediate zone approaches the supply side pressure, the relief valve will open and discharge to a drain.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Intplm.
  • ChrisJ
    ChrisJ Member Posts: 16,233
    https://forum.heatinghelp.com/discussion/comment/1819443#Comment_1819443

    Isn't that what the atmospheric vent on a vented dual check does?

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Jamie Hall
    Jamie Hall Member Posts: 24,556

    Not really — think about it. That vent is not operational under any normal operating condition (if it were, you'd get wet). The reduced pressure zone is.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ChrisJ
    ChrisJ Member Posts: 16,233
    https://forum.heatinghelp.com/discussion/comment/1819455#Comment_1819455

    I guess you must be right.

    But I'm still not understanding the differences between them. Can you explain?

    All of the videos just show how the dual checks and vent function in a RPZ but not really what the reduced pressure zone is about or why it works.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Intplm.
    Intplm. Member Posts: 2,155

    @ChrisJ

    I'll take a wack at this.

    A reduced pressure zone device (RPZ) has two check valves that are independent of each other and have different spring tension. In the device, the checks are commonly "in series". These two checks can also be referred to as zones.

    The third zone per se is called the reduced pressure zone or chamber within the device.

    The chamber is designed to work at a pressure that is (lower) than the water pressure but high enough to maintain an adequate usable pressure downstream.

    The checks have different tensions. The first check is usually weaker than the second check and will usually be the first to fail and make the device discharge. This can also happen if the second check fails.

    A dual check with atmosphere vent uses the water pressure. When lower pressure flows through it, it simultaneously shuts the check and opens the vent.

    Hope this helps. Really racked my brain on this one. It has been a long time since I described these things.

    I think I got it right.

    mattmia2ChrisJ

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