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  1. #1
    Join Date
    Oct 2010
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    Australia
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    Vacuum fitting recomendations



    G'day all,

    I'm doing some experimentation looking at the outgassing of various thread sealants. To do this I'm trying to hold a vacuum under 100 microns on a brand new recovery cylinder. I'm having trouble holding a vacuum however.

    Now, as I do this as a hobby, most of my kit is cheap E-bay garbage excepting :
    - All ball valves are CPS
    - Valve core remover / isolation valve is a CD3930
    - Vacuum gauge is a Fieldpiece SVG2

    As an asside, I had a "cheap" chinese vacuum gauge which measured in "Microns" and when I put it up against the SVG2 it turns out the cheap gauge plumets toward absolute vacuum somewhere around 2000 microns on the SVG2. The best part is I paid more for the cheap gauge 2 years ago than I did for the SVG2.

    Connecting the SVG2 directly to my Vac pump using a small 1/4" copper hard line gives me about 37 Microns (when it's nice and hot with fresh oil). Putting any of my valves between the pump and the SVG2 gives me about the same base reading, but when I close the valve to isolate, the SVG2 steadily increases until it's off the scale (> 2000 microns). So that indicates to me either my flares are leaking or the ball valve is leaking. The flares look clean, have a decent looking seating surface and are torqued properly. Replacing the hard line with any of my hoses gives the same but slower results (more volume in a hose I guess).

    I've seen vacuum grease advertised around. Should I be using that on the connectors?

    My hoses are cheap e-bay specials (but with new CPS gaskets). Can someone recommend me some real hoses that are likely to hold < 100 microns vacuum?

    Are there ball valves that are Vac rated?

    Basically it appears I've reached the limits of my cheap-o gear and I'm looking for some affordable real-mans gear.

    As another observation, I've been using my vac pump (cheap e-bay 2 stager) on and off for the last 2 years, but probably with a combined run time of less than 24 hours. When I started this little exercise I was getting ~200 microns vac from it. After about 3 days of continuous running and a couple of extra oil changes I now see 37 microns. Obviously it needed a good run-in.



  2. #2
    Join Date
    Aug 2006
    Location
    england
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    43
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    Re: Vacuum fitting recomendations

    Have a look on YouTube for a guy called "HVACrat" he has a lot of videos about getting a good vacuum level, with some product reviews etc.
    Mostly found in Oxfordshire, UK :)

  3. #3
    Join Date
    Oct 2010
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    Australia
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    Re: Vacuum fitting recomendations

    Just the sort of info I was after. Ta!

  4. #4
    Join Date
    Feb 2007
    Location
    UK
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    Re: Vacuum fitting recomendations

    BradC,
    The best hoses to use for vacuuming is actually not hoses... As you have noticed...
    Properly flared 1/4" copper pipe will do a much better job. (or 3/8" or 1/2", depending on your connections)



    Also, sometimes the vaccmeeters/gauges themselves are leaking. This will normally not be noticeable when the meeter/gauge is connected to a system, but will be huge when just on a hose.
    (never used the SVG2 myself so I wouldn't know)

    If you think that it's your valves leaking, pull a vacuum on your cylinder then shut the valve and remove the vaccpump then put a balloon over the end of the hose/pipe. You will soon see if the valve is letting by as the rubber will be pulled inwards.

    Last edited by The Viking; 15-01-2012 at 08:54 PM.

  5. #5
    Join Date
    Oct 2010
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    Australia
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    Re: Vacuum fitting recomendations

    Quote Originally Posted by The Viking View Post
    If you think that it's your valves leaking, pull a vacuum on your cylinder then shut the valve and remove the vaccpump then put a balloon over the end of the hose/pipe. You will soon see if the valve is letting by as the rubber will be pulled inwards.
    Gold. What a brilliant idea!

    Looking at the youtube vids recommended above, he puts nylog on _everything_. I suspect my gaskets are leaking, so even using just a ball valve between the pump and the vac gauge still leaks vacuum.

    I was going to say it's my fault for cheaping out on e-bay crap, but to be honest I only got into refrig so I could install my own mini-splits, but now I'm hooked I need better gear!

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