OK for shower head but not for tub spout?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by OldPete, Apr 17, 2007.

  1. OldPete

    OldPete DIY Senior Member

    Messages:
    186
    Location:
    NJ
    As per Uponor/Wirsbo documentation:

    When doing a shower/tub valve -- you can use PEX for the hot and cold supply and for the leg that goes from the shower head but NOT to the tub spout.

    Ok, why?
  2. UPEngineer

    UPEngineer New Member

    Messages:
    6
    Well I will take a stab at this because I used pex to install my Delta shower/tub combo.

    Whenever I fill the tub using the tub spout I get water trickling almost a run.

    A quick call to Delta confirmed that since I used PEX (1/2" pex instead of 1/2" copper) the inside diameter of the pex is different that copper. It is just enough that it restricts the water flow to the spout.

    She said since my valve is filling faster than my spout can empty due to the small restriction, I get what is called shower rise. The excess water only has one place to go which is path of least resitance which is up and out my showerhead.

    ANyways, hope that makes since.

    If I would have used copper from the valve to the tub spout I would have been ok.
  3. OldPete

    OldPete DIY Senior Member

    Messages:
    186
    Location:
    NJ
    Ah. Ok... well, what if a person uses the shower/tub valve with the shower port plugged (say, for a whirlpool application)...

    ? :) Thanks, Pete
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,003
    Location:
    New England
    The spout is connected to the supply pipe. Pex is flexible. Your spout will flop around if you happen to press on it if you could get a good seal. Spouts are designed for either screwing onto a soldered threaded adapter, or a compression fit on the outside of a rigid pipe. You have neither of those options with pex, not counting the fact that it is smaller on the inside for flow purposes than the equivalent sized copper pipe. Run the outlet from the valve with copper - you'll be much happier when it doesn't end up leaking or flopping around.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,631
    Location:
    Cave Creek, Arizona
    Pex

    Why are you being stubborn? It is too small for the line to the spout with a shower, and it will also be too small when you try to fill a "Roman" tub.
  6. OldPete

    OldPete DIY Senior Member

    Messages:
    186
    Location:
    NJ
    I'm not being stubborn (not sure if you're talking to me) -- but here's the part I don't understand.

    If you 1/2" AquaPex feeding the hot and the cold. And you turn the valve all the way to cold. Based on simple physics, won't the flow from which the water is coming (the 1/2" supply) match the 1/2" line from the valve to the spout (or shower) -- or what ever you direct it to?

    As far as the shower is concerned... you could argue that the water restriction at the head won't allow more than 'x' volume to pass, so why not use 1/2" lines. On the spout end of things, I suppose you could argue that when you have both the hot and cold "full open" -- now you are asking two 1/2" lines to run out one 1/2" line. However, the same would be true with copper. 2 into 1.

    ProPex fittings are larger when it comes most Pex. So you don't get the usual restrictions.

    As far as it "flopping around" -- I don't get that. The Pex goes into a drop-ear elbow (that is threaded)... that drop-ear elbow is screwed to the wall, just like one would be for copper -- the pex would be secured with talon/clamping...

    Sooo?
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,631
    Location:
    Cave Creek, Arizona
    pipes

    Your basic mistake is assuming that the valve are "full size" so all the water in a 1/2" pipe is going into the tub. Most valves have openings which are much, much smaller than 1/2" diameter, so the flow from each of them will be less than a 1/2" pipe, but combined they may equal a "full sized" 1/2" pipe and more than a 1/2" PEX line, which is really only about 3/8", and if you remember your geometry, reducing the diameter of a circle causes an IMMENSE reduction in the area and thus the volume.
  8. OldPete

    OldPete DIY Senior Member

    Messages:
    186
    Location:
    NJ
    So you're saying the restriction occurs at the valve. If the orifice at the valve is much smaller and then it "opens" again to 1/2" (at tubing) -- then why would it matter?
  9. can't pour it out fast enough

    without rereading everyone's remarks and adding the most likely intonation that they all meant for their words to be read by, I'll say NO to you and hope I'm right.

    The I.D. (inside diameter) of 1/2" pex suppy pipe is far far too small to carry the stream that a typical person expects a tub spout to pour out when they want to fill a typical large tub like a "roman" tub.

    Carrying capacity of the pipe.

    I'll bet 100:1 that this is the reason why the manufacturer wrote "not for tub spouts" and didn't explain why.


    David

    edit:
    And the fittings too, have way too small openings. Because it's pex.
    Sorry I didn't add that in the equation above.
    Don't shoot me.
    -d
    Last edited: Apr 18, 2007
  10. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,631
    Location:
    Cave Creek, Arizona
    opening

    You are confusing a short restriction with a long one. Going through the faucet, the water can "speed up" through the faucet opening due to the venturi effect. It is when it has to flow through a longer, small pipe that flow resistance occurs.
  11. mamato2girls

    mamato2girls New Member

    Messages:
    9
    Location:
    Arkansas
    I want to make sure I did the right thing this weekend when we installed our pex system in our new house. In the master bath we have a roman faucet that has 1/2" pex running to the hot & cold sides, directly from the manabloc. In the girl's tub/shower I ran pex to the valve, used pex to run to the shower head, & copper to run to the tub spout. That is what the directions appeared to suggest. They were only pictures, with no words, only measurements here & there. I guess they assume that installer usually know what they are doing & aren't soccer mom's like me!
  12. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,631
    Location:
    Cave Creek, Arizona
    directions

    If they use pictures they don't have to worry about which language to print the directions in. The problem is that the people making the drawings have probably never tried to follow them afterwards, or better yet, given them to someone else to follow to see if they are intelligible.
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