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how to calculate resistance (head?) for a 180 degree turn return 3/4" pipe

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iexpl
iexpl Member Posts: 48
Like @EdTheHeaterMan posted in this photo, how to model the resistance for these 180 degree turns of the copper pipe? What happens if this is a PEX pipe? Is there some specification somewhere I can look at?

Many thanks.

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  • Jamie Hall
    Jamie Hall Member Posts: 23,426
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    Same as two close 90s, or close enough as doesn't matter.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    mattmia2
  • hot_rod
    hot_rod Member Posts: 22,251
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    Call it 2- 3/4 90 ells
    Usually if the sweep is a 4" radius or more in 1/2" pex it is not considered in head calcs.
    8D typically, so 3/4 copper or pex would be a 6" radius
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    jtcz
  • iexpl
    iexpl Member Posts: 48
    edited April 18
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    I see. So, with a 6" radius for 3/5 copper, I would need the supply pipe 1 ft off the floor to give the 6" turning raidus. Do I interprete it correctly?
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,328
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    Hi, My understanding is that if the radius of the bend is five times (or more) the diameter of the pipe, the water no longer knows it's changing direction and the friction loss is only equal to the length of the pipe.

    Yours, Larry
  • iexpl
    iexpl Member Posts: 48
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    Thanks @Larry Weingarten @hot_rod @Jamie Hall for answering. So, if I do not want 1 ft high baseboard off the floor, I will have to curve the turn with smaller radius, I just model it as 2 90 degree elbows, which adds 2 ft head each with the total of 4 ft head, right?
  • Jamie Hall
    Jamie Hall Member Posts: 23,426
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    Got it
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 22,251
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    long sweep copper ells would have a lower pressure drop. You may find charts with the EL of longer sweep ells. I suspect the sweep ell may be 1/2 the flow resistance of the typical copper ell?

    I doubt you would get enough of a sweep radius inside a typical fin tube enclosure to get 0 pressure drop. If that is where you are headed?

    I don't remember where the radius number comes from. Either the Copper Tube Handbook bending section 4, or maybe the REMS tube bender tech sheet. I don't know there is an exact multiplier??
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Sylvain
    Sylvain Member Posts: 147
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    You might have enough space to do this with a large enough radius:

  • GGross
    GGross Member Posts: 1,065
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    iexpl said:

    Thanks @Larry Weingarten @hot_rod @Jamie Hall for answering. So, if I do not want 1 ft high baseboard off the floor, I will have to curve the turn with smaller radius, I just model it as 2 90 degree elbows, which adds 2 ft head each with the total of 4 ft head, right?

    The copper 90's do not add 2 feet of head, they add 2 feet equivalent pipe length. Make sure when you are adding the fittings that if the value of the table you are looking at says "equivalent length" you are not counting that as feet of head or you will end up with a massive pump
    mattmia2dkoAlan (California Radiant) Forbes
  • hot_rod
    hot_rod Member Posts: 22,251
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    like this
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mattmia2
    mattmia2 Member Posts: 9,735
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    What are you trying to accomplish? Unless you are dealing with a monoflo system or something only very rough calculations are usually necessary especially with adjustable ECM circulators.
  • iexpl
    iexpl Member Posts: 48
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    I am trying to get rid of the monoflo Tees by connecting pipes directly due to pepetual imbalance of the monoflo system. @mattmia2


    @hot_rod thanks for the illustration.

    @GGross thanks for the head up calculation for the pump. I am a layman and need some understanding of this.
  • mattmia2
    mattmia2 Member Posts: 9,735
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    use regular tees and put a balancing valve in the main between the tees then you can use the balancing valve to effectively make the monoflo orifice whatever size you want.
  • iexpl
    iexpl Member Posts: 48
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    @mattmia2 are these balancing valves self adjustable? This is a rental unit and no one is there to adjust the system :-(
  • mattmia2
    mattmia2 Member Posts: 9,735
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    You only have to do it once. I don't see what you're going to do with math that doesn't involve 100 inputs that are pure guesses.
    iexpl