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  1. #1
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    piping of the liquid line



    hi all,

    hoping someone can enlighten me on something that bugs me.

    I work in the netherlands in the supermarket refrigeration industry, when we install the piping for a branch from the main piping we install the liquid line coming out of the bottom from the main piping, a t-junction pointing downwards. Can anyone give me a good explanation why?

    most of my colleagues come out with a half baked explanation or none at all and there is no mention of this practice in any of the books I have read and it is not something I learnt during my study.

    I have also seen in some supermarkets in England that the liquid line is just the same as the suction and is installed coming out of the top on the piping at a t-junction (for oil return in suction).



  2. #2
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    Re: piping of the liquid line

    I would assume that it is to ensure that liquid goes along the branch at full flow.

    This YouTube video of a Daikin refnet joint gives a good indication of what can happen.

    http://www.youtube.com/watch?v=HcyfweCquR0
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  3. #3
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    Re: piping of the liquid line

    thanks that is an awesome video, especially the third example.

  4. #4
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    Re: piping of the liquid line

    When having long liquid lines and solenoid valves than it is good practise to have the tee pointed down with one leg and use that leg to continue the main pipe. The straight going leg is for the local user (evaporator).
    The idea is first that the flash gas that is formed by pressure drop in the pipe (or heating of the liquid) is more evenly distributed amongst the evaporators. A second important quality is that the main pipe has many bends and therfore less problems with liquid hamer.

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    Re: piping of the liquid line

    Nico

    I think just the opposite. I think you want as few bends in the pipe as possible because each bend increases pressure drop and turbulance. Not mention more labor time to install. We do things with as few 90's as possible and liquid branches out the bottom as much as possible.

  6. #6
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    Re: piping of the liquid line

    That was practice in the day's that I did R22 DX systems Coorsman.
    As I said, taking the main from the bottom and the straight (or up) branch for the evaporator prevents the last evaporator from starving.
    You will agree with me that flash gas before the expansion valve is the pest for proper evaporator feed and should be prevented as much as possible, and I must agree that many bends are not very helpfull for that.
    However, I prefer all evaporators having some flash gas.... over few evaporators at the end having all the ****.
    The first would be not optimal working evaporators, the later would result in room conditions out of spec's and thus loss of production.
    So I do not agree with your idea, I would even prefer to branch from top than from bottom although that has the disadvantage of collecting all the dirt for the last evaporator.
    Non of this plays a role with properly subcooled liquid.

    btw, flash gas can also be seen for a short moment when a solenoid opens as it takes time for the liquid to accelerate, with a bit luck followed by a mini liquid hamer when the flash gas implodes.

    As for the liquid hamer I remember a cold room in a distribution center where we made the liquid pipe just as you normaly do, about 100m long straight pipe inside the cold room. The machine room was at one side of the building and the room had 8 evaporators controlled in four sections, room temperature 2C. We faced massive forces in the liquid pipe and failing solenoid valves at the last cooler due to liquid hammer(). We changed it to as what I have described with all those bends (not my idea, I was just ordered) and it did help to cure the problem. I presume that with all those bends the pipe will move in different directions, bends will stretch a bit etc. and in that way enough energy is redirected/lost to safe those solenoid valves.

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