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Thread: Evacuation

  1. #1
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    Evacuation



    Dear Members,

    Is there any limit at which evacuation of any refrigeration system is carried out? Whether pulling the vacuum quickly with the help of high capacity vacuum pump will result in any other problems?

    There are some apprehensions that faster rate will lead to condensation of moisture inside the system (sometimes can lead to freezing also).

    Is it correct? If so, what is the limit?

    Cheers !!



  2. #2
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    Re: Evacuation

    Try this site - there are some useful tips:

    http://www.robinair.com/whois/protips/protipsframe.htm

    The secret of evacuation is to control the temperature, pressure (and hence the humidity) within the system.

    The use of small pumps at different locations around the systems is far more effective than one big one at one end.

    Use short, large diameter tubes instead of service manifolds and avoid schraeder valves.

  3. #3
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    Re: Evacuation

    Dear Argus,

    Thanks for the useful site reference.

    Site also gives the recommonded CFM ratings required for the sizes of refrigeration systems in tonnage.

    Any exepert in our forum can suggest the limiting value of this CFM. Our idea is to go for a quicker evacuation using a big vacuum pump to balance the cycle time. Under that situation, any suggestions...?

    Cheers !!

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    Re: Evacuation

    Hi Tad, personally its not good practice to use a bigger CFM vac pump as sometimes it will freeze the moisture, patience is a virtue the more rush in this bussiness can cause big problems

    regards Toosh

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    Re: Evacuation

    A nice 2 stage small unit will be fine for a smaller system. 1.5 cfm or 2.0 cfm.

    For large systems it would just depend on how large of a system you have.

  6. #6
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    Re: Evacuation

    Hi Tad
    Yes there is a limit - we usually pull vac down to about below 500 microns to about 150 microns, below 150 microns some oils will start to boil and deteriorate. Big pump, new oil, 3/8 - 5/8 evacuation lines, and accurate measurement gives the fastest result. The big pumps weigh almost twice as much. Ballast open till about 2500 - 1500 microns will speed up process ( Im suprised at how many techs don't use the ballast ). I also use a permanent magnet on any liquid line solaniods once I've pumped out the bulk via comp. I drain the oil while hot and fill it just before use - this avoids the accidental oil slick in back of van. Rate of pull down, vacume reached and vac hold test will indicate if any leaks exist. I'm pretty sure its normal if moisture is present, it turns to ice then sublimes to be drawn off as vapour. It also helps to isolate chwv if working on multiple chiller ccts to raise cooler temp - make sure their open before charging. In saying all that I wouldn't muck around with all this for a split. One more thing to check a pump warm with new oil from experience a new pump pulls 10 microns, a good one pulls 25 microns and a rooted pump pulls 50 microns.
    Hope this helps

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    Re: Evacuation

    Dear Tesla, Toosh and Bigjon,

    Thanks for your replies. They were indeed useful and clear my understanding.

    Cheers !

  8. #8
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    Re: Evacuation

    its interesting to see how other people from other regions apply a vaccum to a system..
    on systems larger that 1kw I use the triplevac method with dry nitrogen,
    (nitrogen charge to maximum ambient standing pressures of refrigerant used in system,leak test, purge and evacuate to 1000 microns.. Re charge system again with nitrogen, purge, then evacuate to 500 microns or below).. its by far quicker and just as effective as trying to control evacuation rates, otherwise we would all be carrying 3 different size vac pumps in our vans?

    this proceedure also depends on the quality of equipment and customer!!!

  9. #9
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    Re: Evacuation

    In Holland the amount of times one has to evacuate and purge with N2 is dependend on the charge that's going to be in there and is regulated by STEK (Dutch "law" on handling refrigirants).

    0 - 10 kg evacuate once < 270 Pa Standing time minimal 30 minutes

    10-200 kg evacuate twice <270 Pa, N2 in between to 0,05 bar Standing time after second evacuation minimal 1 hour

    > 200 kg evacuate three times, N2 in between to 0,05 bar Standing time ater last evacuation minimal 2 hours

  10. #10
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    Re: Evacuation

    *********** sorry double post.
    Last edited by BigJon3475; 14-09-2007 at 11:56 PM.

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