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Thread: difference between low flow and regular bowl?

  1. #1

    Default difference between low flow and regular bowl?

    Hi,

    Does anyone know authoritatively what the difference between a low flow and an older regular toilet bowl is? I know the tank is different, I just wonder if I can replace an old tank with a new 1.6 gpf.

    If you know, I'd really appreciate the info! Thanks in advance.

    -Rich

  2. #2
    Rancher
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    If you could do this, then just adjust the float to only allow 1.6 Gallons into the old tank... Try it, it won't work.

    Rancher

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    One reason many low-flow toilets got a bad reputation (and some still do) is that they didn't do the engineering to change their designs so they would work with the mandated low flow. There's more to it than just limiting the flow. Most of the new ones have a taller tank so there's still some water pressure when you flush and other small things.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4

    Default

    Thanks. That makes sense, that there would be engineering changes necessary to a-commode-ate (heh, heh!) less water. I guess I'll just ante up for the Toto Drake and pull the old toilet one ---- more ---- time ---- ugh! So sick of wax rings!

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Default tank

    Most companies designed their 1.6 tanks so you could not do it anyway. But if you could, the 1.6 gpf tank does not supply enough water to flush the old toilets properly.

  6. #6

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    Yes, I think you're right. Still, I'd love to know, from an engineering standpoint... what changes did they make in the bowl to make 1.6 gallons accomplish the same thing as 7 gallons? ... anyone... ???

  7. #7
    Homeowner geniescience's Avatar
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    i guess a good avenue for curious minds to explore would be to look deep into the bowls designed to bolt onto Euro style wall mount carriers. Like Duravit as one example.

    They were designed as "flush-down" technology right from start. They sort of trickle water down the sides and build up just enough momentum to push solids through.

    American style toilets were originally designed to use the "siphon" technique, which works well when water builds up a head, breaks through the pressure, and then relies on momentum in the pipe to suck forward everything behind it including a huge amount of extra water added "for good measure". I can remember seeing solids first float upwards for a number of seconds before then being pulled downwards disappearing fast along with a lot of extra water and making a lot of sucking slurping noises. Not a happy image or sound to remind you all of, in casual conversation, but since you asked, there's your answer.


    David

  8. #8
    DIY Senior Member SamC's Avatar
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    Default differences between low flow and regular bowl

    There are three prominent features on most recent low-flow designs, the combination pioneered by Toto. These were first used on one-piece Toto models, to improve performance with the low head pressure of the lower water level in the tank. Eventually they were designed into the two-piece Drake, and now most of the Toto line.

    1. Oversized flush valve: Toto used a 3 inch flush valve. This provides a 125%increase in cross-sectional area over the common 2 inch, and dumps the water much faster.

    2. Direct-fed jet: The water for the siphon jet is fed directly to the jet from the input at the tank through a channel or channels on the outside of the bowl, rather than branching off the front of the rim. This shorter, straighter, bigger channel provides higher pressure at the jet.

    3. Flex-trap: Toto added a second hump in the trapway, just before it exits. After the first flush, a pool of water remains in the lower loop, shrinking the size of the trapway for a stronger pull by the siphon, but without impeding movement of solids through it.

    Some or all of these features have been copied by other manufacturers for most of their recent designs.

  9. #9
    DIY Senior Member molo's Avatar
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    Toilet engineering.......begs the question, why do they still clog? Why not a
    4" trap way? Anyone?

    Molo
    "Any American who is prepared to run for President should automatically, by definition, be disqualified from ever doing so."
    Gore Vidal.

  10. #10
    Forum Admin, Expert Plumber Terry's Avatar
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    Caroma makes a 4" trapway.
    It has a very small bit of water in the bowl.

  11. #11
    DIY Senior Member SamC's Avatar
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    Rancher,

    There is a cutaway view at the Toto web site, complete with labels. It shows the older sled type flapper, but the idea is the same. You can see how the water branches to the rim and to the siphon jet at the input from the tank. You can also see the extra hump in the trapway, just before it turns down.

  12. #12

    Thumbs up Suck-cess!!! (in a toilet kind of way)

    Thanks, all! I took your advice to look at the Toto website and I found a great video of the whole system. I already trusted the information I got here that mounting the 1.6 gpf tank on the old bowl wouldn't work, but now I know why. Here is the url : http://www.totousa.com/innerbeauty.asp just click on the streaming video link.

    Now... Terry... a 4" trapway? Suppose one of the children fell in!!! Where will it end??? .

    Again, thanks everyone. I'm pickin' up my Drake 2 pc. today (replacing my 1968 Amer. Std.) and expect to be done by tomorrow.

  13. #13

    Default Postmortem & critique

    Hi,

    Well, I installed the Drake yesterday and it's way better than the old high flow. It is a little noisier than I expected, but I guess there is no way to have power and quiet at the same time. I'm also not crazy about the fact that, in order to get a full flush for solid waste, I have to hold the handle down until the tank empties. Does that seem a little hokey to anyone else?

    Question: the installation directions refer to 3 points of contact for the tank onto the bowl (two in the front... one in the back). The diagram shows these 3 points as being raised. The actual toilet does not have these 3 points raised and, in fact, I torqued those bolts down about as hard as I dare, and I still don't have actual contact between tank and bowl. Has anyone else recently installed a Drake and know what I'm talking about? Am I missing something, or did they just portray the points as being raised in the picture to illustrate where they are?

    -Rich

  14. #14
    Retired Defense Industry Engineer jadnashua's Avatar
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    The first person you find that can lay a BM that requires a 4" trapway...whew...not sure I want to see it.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  15. #15
    Plumber jimbo's Avatar
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    When they first went to 1.6 gallons, the manufacturers realized right away that 1.6 gallons of water was not sufficient to initiate the siphon action which is what makes a toilet work. The fix was to make the trapway smaller. This flushed well, but of course was prone to clog due to the small size.

    Your old toilet with a very large trapway...the 1.6 gal is barely enough to fill the pipe, but will not initiate the siphon to remove the waste.

    Toto was I think the first one to figure out that you could go back to a larger trapway if you could make the water go faster, hence the large flappers. After all, there has not really ever been a problem with 1.6 GPM flushometer toilets.

    There are fine points, but that is it in a nut shell.

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