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primary-secondary tee alignment

designerHP Member Posts: 1
In a primary-secondary piping arrangement, how much pressure drop do you add if the outlet of the tees are not in the same plane. An example would be a horizontal main with one closely spaced tee facing down and the next facing to the side.


  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I am not a professional and do not really know, but I can guess.

    The whole object of closely spaced Ts is to have minimum (near-zero) pressure drop between the Ts irrespective of the flow rate through them. In the usual case, the stems of the Ts point down. and the tops are horizontal. In my system, with the size circulator I have and the pipe sizes I have, these Ts should be about 5 inches apart, and they are.

    Now if I put one in  in any other orientation, it would be sort-of like if I had a 90 degree elbow in there, only worse. If I do that, it is like adding that elbow. How much will that effect things? My piping there is 1.25 inch diameter. According to a table I have, the drop is equivalent ot 5.5 feet of copper tubing. So  there would be about 12x the resistance there should be. Basically, they would not longer be considered "closely spaced."
  • Gordan
    Gordan Member Posts: 891
    If I'm reading this correctly...

    Then the main/shared segment between the tees is straight, but the branch outlets of the tees face different ways. So, the pressure drop between the tees should not be affected.
  • Paul Rohrs_14
    Paul Rohrs_14 Member Posts: 80
    Closely Spaced Tee's

    Attached is a picture of a mini-tube injection system.   The circulator is pumping into the (reverse-returned) supply manifolds.   The upper tee on the right is my return, the lower tee on the right is my supply.   Worked very well.   The mechanical room was 100 feet away so I have a VSIM pump in the mechanical room that is supplying the closely spaced tee's.

    Full outdoor reset to this 12,000 sq/ft Space Heat zone.  (Slab on Grade - Autobody Shop)


  • Ironman
    Ironman Member Posts: 7,354
    edited June 2011
    Practically Speaking...

    I don't think there would be any significant pressure drop in the primary going straight through the Tee's. In the secondary, from bull to bull, there may be an increase. You would certainly have better mixing with the bulls pointing in different directions.

    Let me illustrate: If both the bulls were pointing to the right, and the velocity in the secondary was greater than the primary, you would actually have counter flow between the bulls and the right side of the pipe would be hotter than the rest of the pipe depending on the delta T between primary and secondary. I've experienced this often when there's an injection bridge and the injection pump is ramped up. That's when it becomes necessary to "throttle" the injection loop so there is no reverse flow between the Tee's.

    Now if the bulls were in opposite directions, and counter flow occurred, the water would mix better between the Tee's even though there were counter currents. You wouldn't have one side of the pipe hotter than the other.

    Just a wrench turner's experience. I'm sure Brad or Mark, or one of the other more knowledgeable men on here could give a better explanation.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    I don't think it really matters...

    So long as the rules of straight pipe fore and aft and closeness between the branch tees are followed, it will not make any difference. Technically speaking, if the tees are well before the secondary circulator, which acts as a blender, there should not be much stratification.

    I'm thinking the only thing you'd NOT want to do is use a cross for an injection fitting...

    And then, there is the Taco Twin Tee...


    Note the use of a baffle to avoid short circuiting.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
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