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  1. #1

    Pulling faster micron vacuums.

    Knowing that using time to measure a vacuum is like using a clock or tape measure to measure weight, I am trying to pull micron vacuums faster.

    Does any one know if using two new 6 cfm vacuum pumps would pull down faster than one new 12 cfm pump? I have heard 2 was better. If it is how do you hook them up. We are putting in 33 new systems and the line run is only 30 feet of 1 1/8" and 1/2" on a 4 hp system. It is taking hours to pull down to 500 microns and costing me lots of OT. I am using a new NRP 6 cfm pumps and hooking one on the roof and one down below with 3/8" hose and have the shrader cores removed. Still takes forever.

    Would using two 6 cfm pumps be faster than one 12 cfm pump. Is there a better way to hook two pumps up? I don't mind hooking several pumps up if it would pull down to 500 faster.

    Any suggestions. Any help. The OT is killing me. Please help if anyone knows. What is the best way to hook up multiple pumps if that is the way to pull it down faster.

    Is one on the roof and one on the bottom fighting each other. Sould I have a vacuum trunk line and hook 2 or more pumps to a manifold with 3 tees? Series, parallel, will one suck the other oil out? Does it really matter where to put them. I just want to pull the system down quicker. Any one know a better way. Please help.

    Thank you,
    Aranon

  2. #2
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    Two 6 CFM pumps will move the same volume at one 12 CFM pump. Your best bet would be to parallel two 12 CFM pumps with 3/8" hose and pull the cores.

  3. #3
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    Yea, bigger hose to pump
    My doctor gave me six months to live, but when I couldn't pay the bill he gave me six months more.
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  4. #4
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    Big and short hoses would be your friend.

    Personally I'd think one pump on each end would pull down faster than one larger pump (or 2 pumps) at the same location, all else being equal.
    No real proof or facts to back this up though... anyone else?
    "If you call that hard work, a koala’s life would look heroic."

  5. #5
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    Are you reusing the old coils?

    Are you blowing out the lines with nitrogen?

    Are you flowing nitrogen while brazing?

    Are the lines left open for long periods of time, before they are brazed in?

    1/2" liquid line sounds too bg for 4 ton heat pumps.
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  6. #6
    Join Date
    Dec 2002
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    Tampa, Florida
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    706

    Try this.

    Believe it or not, your hoses may be part of the reason it is taking so long. Instead of hoses, use copper piping with flare ends to connect vacuum pump to system. Use a valve core removal tool (under-pressure type w/ side port) attach copper pipe to it. In Super-Market start-ups that is how we connect to the systems. One large vacuum pump is fine versus using 2 pumps.

    Changing the vacuum pump oil after each system pull-down will decrease the time it takes to achieve a 500 micron vacuum. The oil is relatively in-expensive, especially when you compare it to employee over-time rates.

    Using dry nitrogen to break the vacuum also helps reduce pull-down time.

  7. #7
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    Pulling vacuums too fast...

    http://www.youtube.com/watch?v=qDCaC4PKUBA.

    There is such a thing as trying to pull a vacuum too fast.

    You are pulling a vacuum on 4 ton systems. These are small systems. A 6 cfm vacuum pump is rated for a maximum of 36 tons, see how oversized it is for 4? Put your schraeder cores back in, use a regular manifold with 1/4" hoses. Turn on the pump and crack your manifold gages until the pressure begins dropping. When it is pulled down to 28" vacuum, open them all the way. Your vacuum will pull down real low. Pulling it down too fast actually freezes the water in the system and slows down evaporation.

    Save the core removal and 3/8" hoses for larger tonnage systems. I regularly pull my vacuums down to 150 microns no problem, even on old systems.

    Watch the video if you don't believe me.

    Also, you need non-permeable hoses, like Yellow Jacket plus II, or the black hoses. Otherwise hook up with copper like mentioned above.

    Just my 2 cents...

  8. #8
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    Another video...

    http://www.youtube.com/watch?v=BLRqpJN9zeA&NR=1

    I realize that this video is illustrating the point with an alcohol, but the triple point of water works the same way.

  9. #9
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    I missed the fact this is a 4 ton system, I'd agree with the guy above!

    The only time I really use 2 pumps (6cfm's) are on systems that are in the 30+ ton range, and even then I typically use just one pump. 1st because of the too fast possibility, and 2nd because I always only seem to have 1 pump on me when I run into those lol
    "If you call that hard work, a koala’s life would look heroic."

  10. #10
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    sems pretty techy for general....

    6cfm is morethan enough for a 4ton system!!!!!!!!!

    how about using a vacuum tree and ditching the manifold

    if this was pro forum i would go into greater details with you
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  11. #11
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    The OP isn't a pro mmber, and also hasn't responded to any post yet either.
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  12. #12
    Join Date
    Jul 2009
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    How many microns are you trying to achieve, 500?

  13. #13
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    Quote Originally Posted by beachtech View Post
    sems pretty techy for general....
    were generally techy, I've learned alot here today boys and girls. Never go to Resi. I'm only here for wasting time + a bonus grain of knowlege once in a while.....
    My doctor gave me six months to live, but when I couldn't pay the bill he gave me six months more.
    Walter Matthau

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