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Thread: Vacuum Readings After Isolation

  1. #1
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    Vacuum Readings After Isolation

    Recently I have been testing my vacuum rig and I'm not happy with the results. Fieldpiece VP85, Appion 3/8 hoses, Appion VCR tools, BluVac gauge. When I pull vacuum rise after valving off is ridicules. So I thought my VCR or hoses were leaking so replaced all gaskets and rebuilt VCR. Same issue valve off pressure continues to rise. If you go online and watch Appion video they say pressure should stop before 200 microns when testing tools. Mine don't. I pulled a vacuum on recovery cylinder to 250 microns valved off pressure rose to 1600 then stopped. Repeated 5 times same result. I'm starting to call bullshit on people who say vacuum shouldn't rise after isolation. Has anybody pulled a vacuum and have it stay after a small rise say 100 microns etc. I don't think its possible. I'm so feed up with this I might power purge with refrigerate and not vacuum at all. Any suggestions?

  2. #2
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    It will go up after isolating the pump. It will then stabilize. If it slowly gcontinues up then theres something wrong.

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    I'm sure there will be plenty of people on here who disagree with this, but I don't read too much into vacuum readings. I've just personally experienced too many cases of false positives (and your example illustrates that well, assuming you don't have a leak somewhere).

    The problem is that oil, rubber, etc all off gas under a vacuum and that skews the reading. I do use a micron gauge and I do watch it rise but I just don't over analyze it. I feel the point of a vacuum is to remove moisture. I use nitrogen to test for leaks. A micron gauge isn't able to distinguish between what it is sensing...it could be molecules of literally anything and have nothing to do with air getting into the system.

    Personally I'd maybe put some nitrogen pressure on everything and confirm you don't have a leak somewhere. If you don't have a leak, and that could very well be the case, then I would just learn to not over analize micron gauge readings.

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  4. #4
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    Quote Originally Posted by JayMan7 View Post
    I'm sure there will be plenty of people on here who disagree with this, but I don't read too much into vacuum readings. I've just personally experienced too many cases of false positives (and your example illustrates that well, assuming you don't have a leak somewhere).

    The problem is that oil, rubber, etc all off gas under a vacuum and that skews the reading. I do use a micron gauge and I do watch it rise but I just don't over analyze it. I feel the point of a vacuum is to remove moisture. I use nitrogen to test for leaks. A micron gauge isn't able to distinguish between what it is sensing...it could be molecules of literally anything and have nothing to do with air getting into the system.

    Personally I'd maybe put some nitrogen pressure on everything and confirm you don't have a leak somewhere. If you don't have a leak, and that could very well be the case, then I would just learn to not over analize micron gauge readings.

    Sent from my SM-G960U using Tapatalk
    I somewhat agree. Get it down to 500...…...Isolate everything and wait. Comes up to 1500 but holds...………...Run the pump again, how quickly it pulls down says a lot.

    There could have been a small moisture issue or just a pocket that didn't move as fast as you wanted!

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  6. #5
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    So. I will pull down until I hit 120 microns or so. When I valve off I will rise to 250-350 then hold. If I valve off at 200 microns I will rise to roughly 1000 microns. It's kind of the same as if you were to measure from the pump. There is a significant difference but the same principle. When vacuuming you will see those micro leaks as bubbles.
    What I mean by that is you pull to let's say 300 microns the that bubble hits and it climbs to 450. It will work it's way down to 300 again and just continue to do that. Bigger leaks act similar at higher micron levels but those are "generally" audible under nitrogen pressure.

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  7. #6
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    When I first upgraded to the Mega hoses and quality vacuum gauges, I had something similar. But it didn't stop losing vacuum. Heard about new hoses out gassing, thought maybe that was it.

    Took a few months to realize the recovery tank had a leak.


    Quote Originally Posted by colnago View Post
    Recently I have been testing my vacuum rig and I'm not happy with the results. Fieldpiece VP85, Appion 3/8 hoses, Appion VCR tools, BluVac gauge. When I pull vacuum rise after valving off is ridicules. So I thought my VCR or hoses were leaking so replaced all gaskets and rebuilt VCR. Same issue valve off pressure continues to rise. If you go online and watch Appion video they say pressure should stop before 200 microns when testing tools. Mine don't. I pulled a vacuum on recovery cylinder to 250 microns valved off pressure rose to 1600 then stopped. Repeated 5 times same result. I'm starting to call bullshit on people who say vacuum shouldn't rise after isolation. Has anybody pulled a vacuum and have it stay after a small rise say 100 microns etc. I don't think its possible. I'm so feed up with this I might power purge with refrigerate and not vacuum at all. Any suggestions?
    I do a triple evac with nitro to remove non condensables.

  8. #7
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    Quote Originally Posted by Zamoramax View Post
    So. I will pull down until I hit 120 microns or so. When I valve off I will rise to 250-350 then hold. If I valve off at 200 microns I will rise to roughly 1000 microns. It's kind of the same as if you were to measure from the pump. There is a significant difference but the same principle. When vacuuming you will see those micro leaks as bubbles.
    What I mean by that is you pull to let's say 300 microns the that bubble hits and it climbs to 450. It will work it's way down to 300 again and just continue to do that. Bigger leaks act similar at higher micron levels but those are "generally" audible under nitrogen pressure.

    Sent from my SM-N960U using Tapatalk
    120 microns is hard to get. I have gotten that low before but sometimes it doesn't seem possible. If you have your micron gauge as far away from the pump as possible (so a discharge port for example) and you have a 5 ton used system with a massive accumulator how long are you running your pump? And yes I'm aware that big hoses and appions speed up the process...that's what I use.

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    Quote Originally Posted by JayMan7 View Post
    120 microns is hard to get. I have gotten that low before but sometimes it doesn't seem possible. If you have your micron gauge as far away from the pump as possible (so a discharge port for example) and you have a 5 ton used system with a massive accumulator how long are you running your pump? And yes I'm aware that big hoses and appions speed up the process...that's what I use.

    Sent from my SM-G960U using Tapatalk
    On a previously operational system its dang hard to achieve. On a virgin install I will achieve 120 microns in roughly 20-30 minutes. With that said on a service where it was operational it can take hours to achieve that level. In that situation I will look for the previously stated "bubble". If it's not there and I'm at say 400 microns and it's taking forever inching it's way down(a micron every 3-5 minutes) I will see where it holds. Most conventional brands only ask to hold below 1000 microns for something like 10-15 minutes if I'm remembering correctly. So as long as I'm holding below 1k I generally call it good. Still that level can take anywhere from 1-4 hours in my experience.

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  11. #9
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    For grins and giggles, replace your hoses with copper tubing and flare nuts. Rubber is permeable, so at the lower end of the vacuum you can have less leaking thru the rubber.

    I had some old hoses at the school house that made it impossible to hold a vacuum. Replaced with copper tubing and problem solved. I did persuade the boss to buy new hoses after that demonstration.

  12. #10
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    Yes I've experimented with copper vs rubber and the difference is amazing

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  13. #11
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    Any pic's with real life scenarios.

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  14. #12
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    Thread Starter
    Good points, will try the cooper piping as an experiment. I did notice once when I left vacuum overnight and went back next day when I valved off it raised a little then stopped. I’m wondering if longer is better when vacuuming. I know with these new tru blu hoses the thing is speed vacuum down in 30 minutes but maybe longer is better but who has the time for that. Going forward I am going to be watching the leak rate on my gauge if it’s 0.0 or 0.1 I’ll assume system is good. All these systems are used systems not new installs. But still vacuuming down recovery tank I’m thinking it should hold.

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