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Discuss Do Floplast Anti-Vac Bottle Traps Work? in the Fittings & Pipes area at

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  1. Reed

    Reed New Member

    I have bought one of these traps but there is no visible air admittance valve. Inside there is a narrow tube with one end in the water inside the trap and the other end going up to I'm not sure where. I cannot figure out how this is even meant to work.
  2. townfanjon

    townfanjon Trusted Plumber GSR

    I have never seen one on a flowplast , but that doesnt mean they dont make them , the antivac valve is a clearly on the top of the body of the trap and is approx 25 /35 mm diameter .
  3. Reed

    Reed New Member

    The whole point of my question is that Floplast say their trap is anitvac but it has no visible valve. Anything that is there is on the inside of the trap.
  4. Ch4 plumbing

    Ch4 plumbing Plumber GSR

    What makes you think its not working?
  5. rpm

    rpm Trusted Plumber

    If they say it works and it receives positive reviews then what`s your point? Or take it back and buy a McAlpine.
  6. Ray Stafford

    Ray Stafford Guest

    I haven't specifically looked at a Floplast one, but I have seen plenty of anti-vac traps without the external aav. They just have an internal air by-pass tube as you describe. More than one way of skinning the cat.
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  7. Reed

    Reed New Member

    The trap has been in place for about 8 hours; I have no reason to suppose that it does not work but i cannot figure out how it does work. One end of the "air by-pass tube" is below the water level in the trap. It's quite possibly something ingenious but if so then I really want to know how it works.
  8. Ray Stafford

    Ray Stafford Guest

    The point of an anti-vac trap is to prevent some downstream negative pressure from sucking the water out of the trap.

    In the trap that you have, there is way less water in the narrow bypass than in the main trap. If there is downstream negative pressure, it will suck the water out of the bypass first, and as soon as that is cleared, air can pass through the trap until the uneven pressure resolves itself. The the water seeps back from the main seal into the bypass and recreates the seal.

    At least, that is my understanding.
    • Like Like x 2
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