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Thread: Oil Traps

  1. #1
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    Oil Traps

    I understand the reasoning of making risers look good but i have never
    Used 45s to bring the riser back over after my oil traps.
    My logic is the trap is to increase velocity and entrain oil so putting 2 45s right after each trap is counterproductive.
    Am i right on this? What is best practice? I have seen both ways and never had a clear cut answer. I never do it personally.
    Have you ever had a manufacturer say somthing on factory startup? Or is there a clear answers as to what is right or wrong? Im not wondering about opinions here. Who has definitive information on this?

  2. #2
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    Quote Originally Posted by HVACDreams View Post
    I understand the reasoning of making risers look good but i have never
    Used 45s to bring the riser back over after my oil traps.
    My logic is the trap is to increase velocity and entrain oil so putting 2 45s right after each trap is counterproductive.
    Am i right on this? What is best practice? I have seen both ways and never had a clear cut answer. I never do it personally.
    Have you ever had a manufacturer say somthing on factory startup? Or is there a clear answers as to what is right or wrong? Im not wondering about opinions here. Who has definitive information on this?
    You mean on a long riser with multiple steps of trap along the rise?


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  3. #3
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    Dupont Piping Handbook.

    RSES sam manuals


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  4. #4
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    Yes multiple oil traps.

  5. #5
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    That handbook didnt say anything and neither did the other one from what i saw

  6. #6
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    https://climate.emerson.com/document...us-5400002.pdf

    See page 18-22

    Shows no 45’s

    But - always go by the particular manufacturer’s guidance when available.


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  7. #7
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    Yes, ive seen stuff like this in literature. It doesnt say you cant use 45s.
    The pictures doesnt show 45s. I havent seen where manufactures have specified on this. Oil traps are a pretty general concept. I feel like there is a definitive and general answer. I just have never come across this information and hoping someone here would have.

  8. #8
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    Can add extra pressure drop, sure. Should you, no.


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  10. #9
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    Streel el 90s will move oil a small degree faster, 45s have a lower pressure drop but will hold slightly more oil. With single risers don't think much overall difference. On risers traps may be recommended at 10-20 intervals.

    Trane scroll installation does not want any traps and slope counter flow. This is because of low oil volumes and potential short cycling.

    I wrote Daikin/McQuay installation instructions to include traps and slope in direction of flow, but NO double risers for scrolls or shallow sump recips. Double risers can hold large volumes of oil starving compressors and cause slugging as loads change.

    Avoid short cycling and you are better off with slopes in direct of flow and less traps in risers.

    Short cycling was the #1 killer of scrolls in chiller applications, improper piped splits & miss application of HGBP valves round off the top 3.

    In ~ 20 years of piping reviews, recip, scrolls, & screws, only had 2-3 jobs needing double risers (~400' tels), then adding suction accumulators and discharge oil seperators. By reducing the vertical risers in most cases double risers can be avoided. Proper xtions are required to avoid oil restrictions, reductions only in downflow, increases only in horizontal w/slope.

  11. #10
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    Quote Originally Posted by ehsx View Post
    Streel el 90s will move oil a small degree faster, 45s have a lower pressure drop but will hold slightly more oil. With single risers don't think much overall difference. On risers traps may be recommended at 10-20 intervals.

    Trane scroll installation does not want any traps and slope counter flow. This is because of low oil volumes and potential short cycling.

    I wrote Daikin/McQuay installation instructions to include traps and slope in direction of flow, but NO double risers for scrolls or shallow sump recips. Double risers can hold large volumes of oil starving compressors and cause slugging as loads change.

    Avoid short cycling and you are better off with slopes in direct of flow and less traps in risers.

    Short cycling was the #1 killer of scrolls in chiller applications, improper piped splits & miss application of HGBP valves round off the top 3.

    In ~ 20 years of piping reviews, recip, scrolls, & screws, only had 2-3 jobs needing double risers (~400' tels), then adding suction accumulators and discharge oil seperators. By reducing the vertical risers in most cases double risers can be avoided. Proper xtions are required to avoid oil restrictions, reductions only in downflow, increases only in horizontal w/slope.
    This in no way addressed my question lmao. But ok.

  12. #11
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    Maybe you should post a picture then of what you're talking about .

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    First sentence addressed you questions. 45 or 90 has no difference in velocity except based on circumference due to oil volume in the line.

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    Quote Originally Posted by VTP99 View Post
    Maybe you should post a picture then of what you're talking about .

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    Quote Originally Posted by VTP99 View Post
    Maybe you should post a picture then of what you're talking about .
    Ugh idk how to add a pic. I tried.
    You have your trap every 10 to 20ft. Right after the trap you use a 45 to cone back to where your riser was so it will look straight all the up.

  16. #15
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    Quote Originally Posted by ehsx View Post
    First sentence addressed you questions. 45 or 90 has no difference in velocity except based on circumference due to oil volume in the line.
    Hes not asking about trap construction.

    Hes saying there is a trap midway up the riser, then asking if there should or should not be 45’s added to the downstream side of the trap to bring the riser back to its original longitude for lack of a better term.

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  18. #16
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    Quote Originally Posted by heatingman View Post
    Hes not asking about trap construction.

    Hes saying there is a trap midway up the riser, then asking if there should or should not be 45’s added to the downstream side of the trap to bring the riser back to its original longitude for lack of a better term.

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    This is exactly what i mean.

  19. #17
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    Don't think the difference in oil return would be measurable. More of an issue of space restraints than additional pressure drop.

    Cycles times need to be long enough to insure return oil. Best practice is keep it simple, minimum fittings.
    ASHRAE tables are the best reference for riser velocities and oil return.

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