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  1. #1
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    Vacuum pump CFM, does it matter?

    I was talking to someone that the CFM really relates to how fast it pumps the system down. Most technicians choose higher CFM pumps so that it trims the time they are with each customer. I'm looking at 3CFM pumps, 6CFM pumps and even 10 CFM pumps! We are talking maybe no more than 4 ton residential AC.....

  2. #2
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    I bought a 6cfm when i looked around. The 10 would be better for commercial jobs. The bigger pumps will freeze some of the moisture in the system. Hope that helps

  3. #3
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    Quote Originally Posted by bluescrew08 View Post
    I bought a 6cfm when i looked around. The 10 would be better for commercial jobs. The bigger pumps will freeze some of the moisture in the system. Hope that helps

    Not likely... Do you use your refrigerant manifold to evacuate?
    Gotta have the right tool for the job!

    Where is all the stuff MADE IN THE USA?

    "Thats what we do Troy. Incredible, Invisible, Imbelivable things. We are an Unseen, Unknown, Unvincible fraternity of craftsman.."

  4. #4
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    Rule of thumb is the cfm squared is how many tons of refrigeration it can do. So, residential 3cfm is ok...

    a 6 cfm is good for 36 tons.

    More importantly is your hose size and if your pulling through a schrader valve. A 1/4 hose will yield about .8 CFM. Thats right 8 TENTHS of a CFM! Do a couple searches here on proper evacuation techniques and micron gauges..

    I use a JB Platinum 7cfm. I highly recommend JB vacuum pumps. You get what you pay for.
    Gotta have the right tool for the job!

    Where is all the stuff MADE IN THE USA?

    "Thats what we do Troy. Incredible, Invisible, Imbelivable things. We are an Unseen, Unknown, Unvincible fraternity of craftsman.."

  5. #5
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    I find that the fewer CFM's the vacuum pump capacity - the less it weighs to carry - and the less space it take up in the truck. So far the smallest one I've found is 1.5 CFM. If there is any length of pull-down time difference between it and my 6 CFM pumps - it must be too little to get my attention.

    I have a feeling that the CFM Rating is measured with the pump pumping free air. That is not what this industry ever requires. What we really need to know is the 'below 3000 microns' pumping efficiency Rating. <g>

    PHM
    ------



    Quote Originally Posted by steppinthrax View Post
    I was talking to someone that the CFM really relates to how fast it pumps the system down. Most technicians choose higher CFM pumps so that it trims the time they are with each customer. I'm looking at 3CFM pumps, 6CFM pumps and even 10 CFM pumps! We are talking maybe no more than 4 ton residential AC.....
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  6. Dislikes skwoodwiva2 disliked this post
  7. #6
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    iIuse a 4 cfm, and only do 4 ton's and less. Works good for me, by the time i finish installing line set insulation, sensing bulb, and drain, plus wiring i'm at about 350 micron's.

  8. #7
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    I have a 1.5 cfm belt driven cast iron ancient pump at the shop that I use for all sorts of stuff. Its never been any slower than my other pumps. Its weighs 56 pounds without the cart I carry it on so it doesn't see much field work though.
    The only true knowledge is the pursuit of knowledge

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  10. #8
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    Quote Originally Posted by Poodle Head Mikey View Post
    ISo far the smallest one I've found is 1.5 CFM.
    Refco has a 1.35 cfm eight pounder they say will pull to 15 microns I've been eye'n
    No drain plug
    You tip it over to drain
    I have practice at that already lol



    Does yellow jacket still make a 1.5?

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  12. #9
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    If you are pulling through your manifold the smallest pump you can find will work just fine. If pulling through 1/2" hoses with the schraders removed and work on commercial units a 7 cfm will be nice . That is what I use and it is sucking down so fast I can hear the air rushing through the line set when it is switched on just as if I was pressurizing it with nitrogen

  13. #10
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    I use my Vacmaster 3 cfm. I also have a JB Platinum 5 cfm, but I think the Vacmaster is better. Both work great, though. I am never in any rush when pulling a vac. I will try to get the leak repaired or the line sweated back in first and get the pump running while I finish up the what is left.

    On new installs, if possible, I find that leaving the system on nitrogen over night helps speed the process greatly. New clean oil helps a lot too.

    With my JB, I seem to need to break with nitrogen more often than the Vacmaster.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  15. #11
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    I have a 3 cfm small cheapo rotary vane 2 stage from ebay that works as well as my yellow jacket bullet 6 cfm. I use 1/2 hoses and a yellow jacket evac manifold with a vg64 micron gauge. I have evacuated 5 ton units with long line sets just fine with the little one. It pulls low microns as long as the oil is clean.

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  17. #12
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    I really like this article.
    9. If I use a larger CFM pump, will I be able to pull a vacuum on a system faster?
    In most cases NO. Using a vacuum pump on air conditioning systems from 1 ton to 10 tons, you will not see the difference between a 3 CFM pump and a 10 CFM pump. For example, if you put a pump on a system and you notice within 2 minutes the pump quiets down and you cannot really feel any air leaving the exhaust. This means that there is no more CFM left in the system and you are now working with molecules. Thus, at this point if you replaced a 3 CFM pump with a 10 CFM pump, there is no change in vacuum or time.


    http://www.jbind.com/technical/faq-pumps.aspx







    1. My vacuum pump runs, but I cannot get a vacuum.
    The coupler between the shaft of the pump and the shaft of the motor is either broken or slipping. Make sure the set screws are tight on the flats of the two shafts.
    Back to top
    2. Why is it so important to change the oil often in my vacuum pump?
    The proper oil in a vacuum pump acts as a blotter and absorbs all of the moisture and non-condensables. As the oil becomes saturated with these contaminants, the efficiency of the pump is dramatically reduced. Maintaining clean oil in the pump ensures that the pump will operate at peak efficiency and prolong its life.
    Back to top
    3. Can I use any oil in my vacuum pump?
    No. JB Black Gold oil is extremely pure and non-detergent. Black Gold is hydro processed which means it goes through a series of catalytic steps rendering the oil extremely refined, more viscous, and more stable. The result is a clear mineral oil that will alert you to contamination sooner as it becomes cloudy or milky.
    Back to top
    4. Why is it important to change my oil when the pump is hot?
    As the pump cools, the moisture and contaminates start to separate in the pump and when drained, the contaminants cling to the walls of the pump. When you refill the pump with new oil, those contaminants will mix in with the new oil as the pump warms up resulting in the new oil quickly becoming contaminated.
    Back to top
    5. If I am always pulling a vacuum on clean, dry systems, is there a way to check my oil in the pump to see if it is contaminated and not have to change it so frequently?
    It is recommended that a micron gauge be attached directly to the pump and should pull to 50 microns or lower if the oil is clean. If the micron gauge does not pull to 50 microns, it is an indication that the oil is becoming contaminnated and should be changed.
    Back to top
    6. Other than pulling air out of the system, how does my vacuum pump get rid of the moisture in the system?
    Most two stage vacuum pumps will go low enough in vacuum and reduce the atmospheric pressure within the system, thus allowing boiling of the moisture at a lower temperature. Once the moisture is in a vapor form, it is readily removed by the pump.
    Back to top
    7. What is a gas ballast and how do I use it?
    On the initial pull of vacuum on a system, the gas ballast is open allowing the initial volume of air in the system to bypass the oil so as to not contaminate the oil immediately. When the pump starts to quiet down, close the gas ballast and the pump will start reducing atmospheric pressure in the system to boil the moisture and non-condensables.
    Back to top
    8. What is a blank-off valve?
    The blank-off valve acts no different than a water valve. Open it, and with the pump running you will get your desired vacuum. Close it, and with the pump running there is no vacuum.
    Back to top
    9. If I use a larger CFM pump, will I be able to pull a vacuum on a system faster?
    In most cases NO. Using a vacuum pump on air conditioning systems from 1 ton to 10 tons, you will not see the difference between a 3 CFM pump and a 10 CFM pump. For example, if you put a pump on a system and you notice within 2 minutes the pump quiets down and you cannot really feel any air leaving the exhaust. This means that there is no more CFM left in the system and you are now working with molecules. Thus, at this point if you replaced a 3 CFM pump with a 10 CFM pump, there is no change in vacuum or time.
    Back to top
    10. What is a micron?
    There are 25,400 microns in an inch. Therefore, with a compound gauge reading 0 inches to 30 inches, there are 762,000 microns.
    Back to top
    11. I have been using my low side gauge to pull a vacuum, is this wrong?
    YES. The low side gauge knows only atmospheric pressure and cannot sense moisture or non-condensables. A micron gauge is a heat sensing device that not only reads atmospheric pressure, but also measures the gases created by the vacuum pump as it boils the moisture. For example, if you were to pull a vacuum on an enclosed bottle of water, the low side gauge when pulling a vacuum will read a perfect vacuum. Using a micron gauge, it will immediately tell you with a high reading the you have a problem in you system.
    Back to top
    12. I have been pulling a vacuum on my system using a micron gauge and cannot get it down to a low reading.
    See FAQ #1. Another possibility is that some oil may have entered the micron gauge and is giving false readings. The remedy is to pour regular rubbing alcohol into the connector on the micron gauge, shake, and pour out (do not use a q-tip, rag, or any other material - use the liquid alcohol only). Do this about three times, then try to pull a vacuum with the gauge.
    Back to top
    13. I am able to pull a vacuum on my system, but when I blank-off, the micron gauge rises rapidly.
    Unless you are using JB`s DV-29, copper tubing, or flexible metal hoses, it is not recommended to use your existing manifold and hoses for blanking-off a system to check for leaks. Hoses work very well under high pressure. Vacuum is very critical in leaks, more so than pressure. All charging hoses, including the black hoses 1/4" or 3/8" permeate. Where the crimp is on the brass to the hose also has possible leak issues, and the gasket at the coupler is a major leak offender. The vacuum industry uses O-rings on most couplers. When you screw down on a gasket, it goes into many contortions and will not seal. When using an O-ring, you screw down on it to get a metal to metal seat and the O-ring lies around the lip of the flare giving it a positive seal.
    Back to top
    14. Can I mount my micron gauge onto the vacuum pump?
    It is not recommended to do so as you are reading what the pump is doing and not what the pump is doing to the system (see DV-29). It is suggested that you tee off on the suction side of the system and mount the gauge there.
    Back to top
    15. How low of a vacuum should we pull on a system?
    JB recommends that a system be pulled to at least 250 microns and held at least five minutes. On any polyester oils in a system, it is recommended to pull a much lower vacuum as moisture is very difficult to remove even with heat and vacuum.
    Back to top
    16. Why does the micron gauge slowly fall back and then start to hold after pulling a vacuum and blanking-off?
    The reason for this is there is equalization within the system. If you pull a vacuum lower, it will then fall back at a shorter range and hold.
    Back to top
    17. Why do I need to check the oil level when the pump is running?
    The reason for this is that if the vacuum is not broken before pumps are shut down the oil in the cover will seek the vacuum still in the cartridge and intake chamber. Then the oil level will drop in the sight glass and give the appearance of a low oil level. Then if the pump is refilled to the oil level line and the pump started, the oil that got sucked back into the cartridge and intake chamber will be kicked back into the cover and now you’ll be over filled and the oil will shoot out the handle (exhaust port).

  18. #13
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    Mar 2007
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    Quote Originally Posted by Poodle Head Mikey View Post
    I find that the fewer CFM's the vacuum pump capacity - the less it weighs to carry - and the less space it take up in the truck. So far the smallest one I've found is 1.5 CFM. If there is any length of pull-down time difference between it and my 6 CFM pumps - it must be too little to get my attention.

    I have a feeling that the CFM Rating is measured with the pump pumping free air. That is not what this industry ever requires. What we really need to know is the 'below 3000 microns' pumping efficiency Rating. <g>

    PHM
    ------
    Sorry to bump a old one. I couldn't find the latest post about the little pump but saw this the other day.

    The ones I've seen this small were only single stage. This one says 8.5 lbs two stage 15 microns



    http://coolstore.pl/product-eng-2440...S-M.html#close

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