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  1. #1
    Join Date
    Aug 2007
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    339

    Question Vac Pump: 6 cfm or 5cfm ?

    I'm looking to replace my Robarnair cool tech vac pump that was stolen that was a 6cfm. So I was looking at a flyer for johnstone supply that has a rob arnair vac pump that was on sale and it was a 5 cfm pump that was much cheaper than the one I had. My question is it worth me getting the 5 cfm? I'm only doing residental work.

    Thanks

  2. #2
    Join Date
    Jun 2006
    Location
    New Jersey
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    Quote Originally Posted by cook42 View Post
    I'm looking to replace my Robarnair cool tech vac pump that was stolen that was a 6cfm. So I was looking at a flyer for johnstone supply that has a rob arnair vac pump that was on sale and it was a 5 cfm pump that was much cheaper than the one I had. My question is it worth me getting the 5 cfm? I'm only doing residental work.

    Thanks
    You wont notice any difference between a 5 and a 6 cfm. Rule of thumb is pump cfm squared equals tonage. So a 5 cfm is good for 25 tons.

    If I was only doing resi work, then I would even go smaller to save on weight and money.

    Don't get caught up in the cfm thing. Evacuation time is more restricted by the ports than anything. With the money saved buying a small pump, buy a core tool, so you can pull the schrader, during evacuation.

    A 3 cfm pump pulling a vacuum with no schrader cores with smoke a 6 cfm pump trying to pump a vacuum with the cores in place.

  3. #3
    Join Date
    Nov 2008
    Location
    S.C.
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    931
    I'm looking at a 6cfm along with a micron gage. I'll keep an eye on this thread to see what the masters say

  4. #4
    Join Date
    May 2004
    Location
    Rapid City, SD
    Posts
    7,415
    I agree with the 3 cfm being better. Of course, I've only used 5 cfm when I was doing resi. I do mostly larger commercial stuff now and a 5 or 7 cfm is more than enough for 99% of the stuff we touch.

    I'd say stick with a name brand pump, go a bit smaller. Use the saved money to buy or build a vacuum rig. Someone here posted a lil write up of one a year or 2 ago. I suck at searches, but I'm sure someone can find it.

    Oh, get yourself a good micron gauge too!
    "If you call that hard work, a koala’s life would look heroic."

  5. #5
    Join Date
    Sep 2007
    Location
    Boise, ID
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    4,352
    Yep, I agree with the smaller CFM for smaller systems. Pulling a vac to fast on small systems can actually take you longer because it can freeze vapor in the system before it boils it off.
    If a nation expects to be ignorant and free, in a state of civilization, it expects what will never be. (Thomas Jefferson 1816)

  6. #6
    Join Date
    Mar 2007
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    wedged in freezer shelf
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    Quote Originally Posted by ascj View Post
    Evacuation time is more restricted by the ports than anything.
    Isn't the largest factor with a vacuum pump the static pressure of the oil ?

    Oil with a lot of moisture will raise the static pressure of the oil and not let you pull below a certain point regardless of pump size or time on a system.
    “If You Can Dodge A Wrench You Can Dodge A Ball”

  7. #7
    Join Date
    Apr 2007
    Location
    Mesa, AZ
    Posts
    120

    I Agree!

    Quote Originally Posted by Gib's Son View Post
    Yep, I agree with the smaller CFM for smaller systems. Pulling a vac to fast on small systems can actually take you longer because it can freeze vapor in the system before it boils it off.
    Absolute truth! Lots of threads pertaining to good evacuation procedures on this site. Favorites:
    1) Change oil after every good pull down.
    2) Heat indoor/evap coil (use defrost heaters if available in a defrost cycle to chase refrigerant out and keep everything from freezing)
    3) Remove cores, use heavy hoses and a true vacuum mainifold, INCLUDING MICRON GAUGE, etc...............

  8. #8
    Join Date
    Jun 2004
    Location
    Location:Raleigh NC
    Posts
    9,655
    Save the money get the 5 cfm If your doing Resi you don't need anything bigger.

    ANd get a good and I mean good Micron gauge
    If you help others then you are a Success

  9. #9
    Join Date
    Feb 2008
    Location
    Waffleville
    Posts
    10,339
    5cfm is good over 20tons
    If Guns Kill People, Do Pencils Misspell Words?

    http://www.youtube.com/watch?v=An2a1...eature=related

    Before we work on artificial intelligence why don't we do something about natural stupidity?

  10. #10
    Join Date
    Sep 2008
    Location
    Mesquite Tx.
    Posts
    374
    I have for years done chiller teardowns and pulled down to 600 microns overnight with a 6 cfm yellow jacket pump. Now, I would not use it for a machine that I knew had a high moisture level. Then I would get the 17 cfm rig. And I'm talking about chillers through 1500 tons. The key is being tight, and using the largest ports you can, as was mentioned earlier. If you have a 1/2" valve on it, you will be suprised how quickly you can get one down. Once you get moisture in the oil, your done. You cannot get a good vacuum with wet oil. Thats where the big pump with a large oil res comes in. 3 to 5 cfm should be more than enough for resi and most commercial work. And your right, big price jump at 6 cfm.

  11. #11
    Join Date
    Jun 2001
    Location
    San Diego, CA
    Posts
    1,149
    Isn't the largest factor with a vacuum pump the static pressure of the oil ?

    Oil with a lot of moisture will raise the static pressure of the oil and not let you pull below a certain point regardless of pump size or time on a system.
    Heck no! I've pulled under 100 microns with oil that must have been a year old, unsealed. Once your pump heats up the moisture in the oil goes out the exhaust port. Granted, that was an overnighter . . but 92 microns, held for an hour.

  12. #12
    Join Date
    Mar 2007
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    wedged in freezer shelf
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    Quote Originally Posted by gbfromsd View Post
    Heck no! I've pulled under 100 microns with oil that must have been a year old, unsealed. Once your pump heats up the moisture in the oil goes out the exhaust port. Granted, that was an overnighter . . but 92 microns, held for an hour.
    Good for you bro

    I've heard you can dry oil that way but why

    Do you know at what point you begin to vaporize oil out of a system ?

    I believe it is well above 92 microns
    “If You Can Dodge A Wrench You Can Dodge A Ball”

  13. #13
    Join Date
    Aug 2007
    Posts
    339
    Thanks guy's!! You've gave me some great feed back! I will be getting that vaccum pump from johnstone real soon! With that price you can't beat it!

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