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Thread: Does trap size matter?

  1. #1

    Default Does trap size matter?

    I'm thinking of buying the Toto Dartmouth which has the G-Max flush. (We're tired of plunging.) My husband thinks the American Standard Champion will work better because it has a 2 3/8 inch trap opening compared to 2 1/8 inches on the Toto. Will the size difference affect the flush? Thanks!

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    Most trapways are 2-1/8" with the larger (3" or more) flush valves.

    That has been a good size.

    Some companies are using slightly bigger valves and trapways, mostly so they can say "bigger".

    Toto was about 15 years ahead of the others in coming out with the new design that has just recently been copied by others.

    Is bigger better, or is it marketing hype?

    There isn't that much difference between 2-1/8" and 2-3/8" to make much difference. You're talking 1/4".
    If you have waste leaving your body that is bigger than 2" in diameter, then maybe it does.
    Most people don't.
    The MaP testing is based on 7/8" in diameter waste.

    Both toilets use siphon flushing. Too much size, and you loose siphon. Otherwise there wouldn't be a limit on size.

    The biggest flushing problem I"ve had with a Champion in a friends home, was when the trip lever starts to wear in and it doesn't let enough water out of the tank to complete a flush. That has nothing to do with size though.
    I replaced the tank on that one, and so far it's doing the job. That also fixed the the leaking seal problem.
    I don't like how shallow the bowl is though. The deep part doesn't seem placed right.

    If size does matter to you, and it could with certain medical conditions which results in large than normal bowl movements, you could consider something in the 3" to 4" range, which the Caroma toilet uses. The Caroma uses a Wash down flush.

    The Caroma doesn't flush as much miso paste as the others at one time, but with the larger openings, you can drop bigger things through it.

    That all being said, most of the new toilets that use a 3" or larger flush valve and a trapway of 2-1/16" or larger will flush better than previous versions.
    Last edited by Terry; 01-27-2006 at 09:29 AM.

  3. #3
    In the Trades Bob NH's Avatar
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    Default Area matters

    "There isn't that much difference between 2-1/8" and 2-3/8" to make much difference. You're talking 1/4"."

    Flow rate is proportional to area for the same head (pressure).

    (2.375 squared)/(2.125 squared) = 1.249.

    The 2 3/8 unit has 25% more area.

  4. #4
    DIY Member RRW's Avatar
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    You guys are killin me. The area of a circle equals pi times the radius (1/2 the diameter) squared. there is a 20% difference between the two sizes in question. Regards, Dick

  5. #5
    In the Trades Bob NH's Avatar
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    Sombody needs a new calculator.

    Area = Pi x Radius squared = Pi x diameter squared /4

    Pi = 3.14159

    Area of a 2.375 dia circle is 4.43013

    Area of a 2.125 dia circle is 3.54656

    4.43013 / 3.54656 = 1.249

    Thatís 24.9% more area.

  6. #6
    DIY Member RRW's Avatar
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    You're right of course. The smaller is 80% of the larger which means the larger is 25% larger than the smaller. The % difference depends on which one you use as the base, and I used the large one which is not what we are trying to determine.

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