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Thread: shower mixing valves intentionally restricted?

  1. #1
    DIY Member ginahoy's Avatar
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    Default shower mixing valves intentionally restricted?

    A relative just did a bath remodel. His tub spout flow rate is significantly lower than with previous bath. Before the remodel, his tub fill was 7 gpm, but now it's only 4.5 gpm, so it takes much longer to fill the tub. His other bath has same setup as the bath he remodeled. He confirmed it's 7 gpm (eliminating the possibility there's a pressure issue).

    The salesperson at the hardware store told him all of the mixing valves available today are more restrictive than the ones installed in his home 15 years ago, so replacing the valve with a different brand / model won't help the flow rate. Is this true? Here's a link to information on his mixing valve:

    mixing_valve.pdf

    One other possibility - his home has PBT pipes. Fortunately, no problems with that. But the plumber switched to 1/2" PEX under the bathroom, so there's about 6' of PEX between the transition and the mixing valve. The pex ID is 0.475" compared to 0.50" for the PBT. Surely this wouldn't cause a nearly 40% reduction in flow rate?

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    Moderator & Master Plumber hj's Avatar
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    There are a LOT of places where the flow can be restricted, and since they are cumulative, the final pressure/volume can be severely affected. The PEX AND its fittings will be a restriction, although that short length should be minimal. THe "stems", however, have VERY SMALL openings in them for the water to flow through, which is where most of your restriction is occurring. Then the water has to work its way through the diverter which is another "pinch point".
    Licensed residential and commercial plumber

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    DIYer, not in the trades LLigetfa's Avatar
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    Ja, probably a case of "all of the above". Pressure balance spools need to sense pressure differential and use some of that differential to exert control so they could have a slight limiting factor. That said, they and the entire rough-in are not all created equal. If you go to a reputable supply house, you can find assemblies designed for the larger soaker tubs but one would not likely plumb those with 1/2" pex.
    Last edited by LLigetfa; 12-31-2011 at 06:09 PM. Reason: typo

  4. #4
    DIY Member ginahoy's Avatar
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    Thanks for the replies. After transitioning to PEX, there's a pair of T's for the cold and hot water lines to supply the tub and vanity sink. One suggestion I made was to transition from 1/2" PBT to 5/8" pex before the T's. But that's not going to buy much if he's got add a transition back to 1/2" to mate up with the shower mixing valve. I don't imagine anyone makes a mixing valve designed for 5/8".

    Quote Originally Posted by hj View Post
    ...THe "stems", however, have VERY SMALL openings in them for the water to flow through, which is where most of your restriction is occurring. Then the water has to work its way through the diverter which is another "pinch point".
    But wouldn't this have been the case with the old valve? Or are mixing valves available today more restrictive than what was commonly available 15 years ago? Did older valves not have pressure balancing?

    Maybe the simplest thing would be to replace the pex and valve with 3/4"...

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The type of pex fittings can make a difference. Many tub/shower valves have two outlets...a smaller one for the shower and a larger one for the tub. If it was plumbed backwards, it might be restricted by trying to force the water out of the shower port. Since a showerhead is already restricted to a max of 2.5g, using a smaller port to it isn't an issue, but could be when trying to fill the tub. Also, if they used pex to run from the valve to the tub spout, that would account for some of it. If they did, that often causes other problems, too.
    Jim DeBruycker
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    DIY Member ginahoy's Avatar
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    Quote Originally Posted by jadnashua View Post
    Many tub/shower valves have two outlets...a smaller one for the shower and a larger one for the tub. If it was plumbed backwards... if they used pex to run from the valve to the tub spout...
    Neither of these is an issue. My brother (the homeowner) measured exact same flow rate from shower riser (without head), and he confirmed the spout plumbing is 1/2" hard pipe, although I'm not sure what it is.

    Also, he told me he didn't think his valve is pressure balancing. See pdf linked in my OP... it has separate hot and cold controls.

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    If the install is inspected with a permit, a replacement generally requires an anti-scald technology valve...he did himself a disservice by not putting one in, and it is likely to be an issue whenever it comes time to sell the house. Plus, they mandate these for a reason...they are safer for especially children and older folks, neither of which can handle potential hot water without injuries as those in the middle.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member ginahoy's Avatar
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    Quote Originally Posted by jadnashua View Post
    If the install is inspected with a permit, a replacement generally requires an anti-scald technology valve...
    I plead ignorant. If anit-scald is universally required by code, then wouldn't any valve he might have purchased have anti-scald?

    Also, are you referring to my comment that the valve doesn't have pressure balancing? I have no idea if those terms mean the same thing, but I was only speculating about it not having pressure balancing because it has separate hot and cold controls. I was under the impression, perhaps mistakenly, that pressure balancing is only possible with single-lever temperature control. Please correct me if I'm wrong. I'm not a pro.

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    DIY Senior Member kreemoweet's Avatar
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    Code-compliance is of no concern to most retailers.

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    Moderator & Master Plumber hj's Avatar
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    IF your drawing is for YOUR valve, then there is NO pressure balancing unit, and since they are 1/4 turn valves their design is NOTHING like one from 15 years ago.
    Licensed residential and commercial plumber

  11. #11
    DIY Member ginahoy's Avatar
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    Quote Originally Posted by hj View Post
    IF your drawing is for YOUR valve, then there is NO pressure balancing unit, and since they are 1/4 turn valves their design is NOTHING like one from 15 years ago.
    Yes, that drawing is the valve that was used. Looks like that's the culprit.

    As an aside, there are other ways to provide anti-scald protection. A mixing valve such as the Honeywell AM1 series can be installed at the water heater. I see that in situations where the water heater is set to a higher temperature to supply potable hot water to a hydronic fan coil in the air handler.

  12. #12
    Moderator & Master Plumber hj's Avatar
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    There are remote pressure balancing units that are installed to the lines going to the faucet, in fact, I have two of them I am trying to get rid of. The heater mixing valves do NOT provide pressure balancing function, so if the cold pressure drops the shower user will STILL get a "slug" of extra hot water, (or vice versa if the hot pressure drops), which he/she was not expecting, and could result in injury if they were to "recoil" from it. Pressure balancing is NOT entirely to prevent scalding, it is to maintain a constant temperature of the water coming out of the valve. A thermostatic valve at the heater could ONLY do that, if it were set to the ideal shower temperature so that the user ONLY turned on the hot side.
    Last edited by hj; 01-01-2012 at 10:48 AM.
    Licensed residential and commercial plumber

  13. #13
    DIY Member ginahoy's Avatar
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    Quote Originally Posted by hj View Post
    Pressure balancing is NOT entirely to prevent scalding...
    Yes, I understand that. I was speaking to an earlier comment.

    In this case, my brother specifically required separate hot and cold water controls. I can relate to that. I absolutely HATE single lever valves that don't allow for separate control over the volume. My preferred valve has two levers -- one for temperature and one for volume. I had one like that in my last house (Delta). Not sure if it was pressure balancing (installed in 1999), but I never had any problems if someone flushed the toilet.

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    DIY Junior Member butleraudio's Avatar
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    Hi All, I am ginahoy's brother. Thanks for all your comments and suggestions. Let me answer a few issues here.... I did not pull a permit, there is no concern here for anti-scald and/or pressure balancing (I purchased the 3 handle to avoid pressure balancing), and the T is installed correctly where the HOT valve is on the left. I use a $2 shower plastic head that I can drill out with a 3/4" bit. My existing (2nd) bath filler is a cheap, plastic face, 1994 model, 2 handle unit, with the shower diverter in the tub spout. (the location where I still 7GPM)

    After seeing the water flow thru the new mixing T body with all 3 stems removed, (unit was being flushed for debris) I am convinced the stems are the main issue restricting the flow. I can assure you that the flow rate was at least if not more than 7 GPM with the stems removed.

    My questions remains: are tub fillers regulated (and WHY)? Is there a modification? and/or, How do I get 7+ gpm at the tub filler and shower riser? Can it be done with 1/2" pex?

    I guess I can use 1/2" shut off valves and a tub spout with a built in shower diverter.....

    here is a link to the actual unit purchased:
    http://www.amazon.com/Three-handle-S...619653-1875551

    butleraudio
    Last edited by butleraudio; 01-01-2012 at 11:42 AM.

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    DIY Junior Member butleraudio's Avatar
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    found this paragraph from and KBIS article linked below:

    "In a tub/shower installation, the diverter between the tub and shower is found after the mixing valve. Currently, tub spouts do not have maximum flow standards; they have minimum flow standards. If the DOE’s new definition is adopted, tub spouts and showers units would have to have a 2.5-gpm combined maximum flow rate at 80 psi. This also contradicts current plumbing codes, which specify a minimum for a tub filler to be 2.4 gpm at 20 psi."

    link: http://www.hospitalitydesign.com/kbb...head-976.shtml


    So now a new question arises: can my diverter stem be clogged with debris that would not be obvious upon first inspection? (the flow rate between hot and cold is equal, so I don't suspect the hot/cold stems in the debris scenario...or I could still have debris in all 3 stems) I DO know that construction debris has been found in all my other faucets/aerators during the course of plumbing construction.
    thanks, butleraudio

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