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  1. #1
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    Nh3 screw oil temperatures


    After some opinions on oil temps compared to saturated condensing temperatures.

    With R22 have seen oil get saturated & foam with Freon when oil temp approaches saturated condensing temperatures.
    Have never seen it with ammonia, so does it matter?

    Any opinions welcome



  2. #2
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    Re: Nh3 screw oil temperatures

    I'm thinking ammonia has higher discharge temps preventing this occuring, where R22 is much lower!

  3. #3
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    Re: Nh3 screw oil temperatures

    I don’t think the foaming can be related to the temperature approaching saturated condensing temp.

    The oil pressure is much lower so this can’t be the reason for the foaming.

    Foaming is caused by saturated refrigerant mixed with the oil or worn oil pumps or opening of oil pump’s safety valve or high oil levels in recip compressors or opening of oil separator float valve (especially if mixed with liquid refrigerant).

    Pick the one that simultaneously occurred while reaching saturated condensing temp.

  4. #4
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    Re: Nh3 screw oil temperatures

    Correction I will rephrase foaming & call it saturated with refrigerant.
    In R22 screw this was happening causing oil pump cavitation, which in turn low oil pressures.
    Eventually oil pump is worn out due to this.
    Increase oil temp & all good.
    Ammonia is hotter by nature & not as miscible with the oil, so have not wittnessed anything like R22 sceanario with ammonia, but is it possible to anyones knowledge in a screw apart from a floodback or liquid injection not working correctly?

  5. #5
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    Re: Nh3 screw oil temperatures

    I had a case of refrigerant returning with the oil because someone (%&$#) connected the oil drain of an icemaker directly to the oil reservoir 10m below.

    It could happen on start up if the oil separator is allowed to condense refrigerant when the system is off.

  6. #6
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    Re: Nh3 screw oil temperatures

    Hi Ranger1
    historically had two R22 screws set with oil problems, both had oil issues with loading rates, the oil temps in separators controlled at +50'C higher than normal. During pull down both looked and reacted fine until at a particular point the oil in separator just flashed/foamed. Everything would point to separation and velocity rates through separator, the earlier/older unit had a larger separator fitted during commissioning at a huge cost. Result extactly the same. Thats when a slow/ really slow load rate was programed into PLC, to within design range and then rapid reponse loading activated. The later system was a GB set, similar problem on a spiral, so was a pull down condition every morning Load rate super slow, like 50 minutes to 100%. This unit was a close coupled gravity feed to evap., and an open flash econo., any minor hickup in operation sent everything ballistic and oil carryover, oil diff trip faults, rattly oil pumps the lot. I tried running higher SDT, lowering the injection rates controlled by discharge temps was probably the most successful, but solenoid was rather cyclic and ultimately did not want to screw the screw rotors, they both ran Suniso 4GS oil.

  7. #7
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    Re: Nh3 screw oil temperatures

    Apparently R22 can be volitile under certain conditions on some screw packages.
    I wonder if a "AMOT" type thermostatic valve would solve problem.
    Most Australian packages don't have "AMOT" type valve to date, unless imported Frick, Grasso, only seem to put them on Bitzer.
    It makes me wonder if a lot more packages should instal them on VFD drives etc.
    With a Mycom & some others the only limitation could be oil temps below 30 deg C.

  8. #8
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    Re: Nh3 screw oil temperatures

    Quote Originally Posted by Magoo View Post
    Hi Ranger1
    historically had two R22 screws set with oil problems, both had oil issues with loading rates, the oil temps in separators controlled at +50'C higher than normal. During pull down both looked and reacted fine until at a particular point the oil in separator just flashed/foamed
    Quote Originally Posted by RANGER1 View Post
    Apparently R22 can be volitile under certain conditions on some screw packages.
    I think you both may have had condensation in the discharge/oil separator at some point then a condensing pressure controls (like a fan cutting in) lowers condensing pressure which lowers discharge pressure and you reach saturation condition and the R22+oil mixture foams.

    Have you ever tried to measure pressure and temperature where your sight glass is?

  9. #9
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    Re: Nh3 screw oil temperatures

    Hi Ranger1
    volitile is a good description of what actually happens.
    Recently had a Frick XJS 120 that was liquid injected oil cooled, that was playing up being oldish 80K hours, and converted to AMOT and water cooled oil cooler, no problems and works a treat at -40'C SST. You might be onto something with the amot type regulator, it runs CPI oil. selected a +45'C amot

  10. #10
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    Re: Nh3 screw oil temperatures

    Dear Friends
    Hi , After reading your post i think that it would be better to tell you that i see some fake oils are filled in genuine trademarks. it means that if you want to buy oil , 1stly check that it is original or not.
    believe me that i have seen it and prove it to me that some case like your description happens and the cause was as i say. may be " fake China oil "
    regards.

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