Results 1 to 13 of 13

Thread: Is this normal for vacuum gauge to rise slowly when valved off?

  1. #1
    Join Date
    Jul 2018
    Posts
    9
    Post Likes

    Is this normal for vacuum gauge to rise slowly when valved off?

    I pulled my vacuum gauge down to 200 microns.

    I then valved off the gauge with two Appion valve core removal tools. I did not hook up anything to a HVAC unit.

    The vacuum gauge will slowly rise from 200 to 700 after 15-20 minutes and slowly keep rising.

    Is this normal because the rubber seals and valves will just leak slowly and because of the very small volume of space between the two valves? To me this makes sense and also what someone mentioned on youtube. Nothing will be 100% seal proof.



    OR is my gauge faulty and leaking or something leaking that shouldn't be?

  2. #2
    Join Date
    Apr 2003
    Location
    Greenback, Tennessee
    Posts
    1,121
    Post Likes
    Vacuum decay test Standards vary slightly depending on the source but, IMO if it is still below 1000 microns after 10 minutes, that is a clear test passed indication.

    If there were an leak or moisture of consequence it would have rose way more than that.
    -Marty

  3. #3
    Join Date
    Jul 2019
    Location
    Oklahoma home its in the name
    Posts
    7,422
    Post Likes
    Quote Originally Posted by m singer View Post
    Vacuum decay test Standards vary slightly depending on the source but, IMO if it is still below 1000 microns after 10 minutes, that is a clear test passed indication.

    If there were an leak or moisture of consequence it would have rose way more than that.
    I believe he is just testing his tools not on a system.

    Sent from the Okie state usin Tapatalk
    "Is this before or after you fired the parts cannon at it?" - senior tech

  4. #4
    Join Date
    Jan 2020
    Location
    Winnipeg Canada
    Posts
    1,155
    Post Likes
    A slow rise like that usually indicates either system pressure equalizing, or moisture in the system.
    Often times I'll vacuum on the suction side of a new system and install my micron guage on the pressure side.
    When my guage hits 500 microns hooked up this way, I shut down my pump, Often times after 20 minutes my guage will be down around 450.
    If I hook my guage up to the port I'm sucking out of, when I do the decay test the levels rise.
    You don't squat with your spurs on.
    And you NEVER put the torches away before pressure testing.

  5. Likes R600a liked this post.
  6. #5
    Join Date
    Apr 2003
    Location
    Greenback, Tennessee
    Posts
    1,121
    Post Likes
    Quote Originally Posted by R600a View Post
    I believe he is just testing his tools not on a system.
    I did not catch that. In that case I would say his tools are are very leak free but, his pump should be able to pull much lower than 200 microns.
    -Marty

  7. Likes R600a liked this post.
  8. #6
    Join Date
    Jul 2019
    Location
    Oklahoma home its in the name
    Posts
    7,422
    Post Likes
    Quote Originally Posted by m singer View Post
    I did not catch that. In that case I would say his tools are are very leak free but, his pump should be able to pull much lower than 200 microns.
    I agree.

    Sent from the Okie state usin Tapatalk
    "Is this before or after you fired the parts cannon at it?" - senior tech

  9. #7
    Join Date
    Sep 2008
    Location
    VA
    Posts
    4,228
    Post Likes
    With the old Appion VCRT’s I used to be able to get down to a 0 decay rate pretty frequently unless it was an old system repair vacuum or existing tubing. Since, I’ve purchased two new sets of the newer Appions with the magnet end, and I rarely ever get down to 0 decay rate. Even bought a new BluVac + Pro to make sure it wasn’t the gauge, and it shows the same as my old one.
    "The only true wisdom is in knowing you know nothing" Socrates

  10. #8
    Join Date
    Jul 2018
    Posts
    9
    Post Likes
    Thread Starter
    Quote Originally Posted by m singer View Post
    I did not catch that. In that case I would say his tools are are very leak free but, his pump should be able to pull much lower than 200 microns.
    I'm not sure but if I put my CPS micron gauge directly on my vacuum pump, I can pull down to below 5 micron very quickly.

    If I use a yellow jacket charging hose, and attach the micron gauge to the end of the hose, I can pull down below 200, but it is very slow and the lowest I got was 170.

    I'm not sure if that is normal or if I need to use a vacuum rated hose.

    I'm thinking its not my gauge or pump because I can pull down to below 5 microns when attached directly to my vacuum pump.

  11. #9
    Join Date
    Jul 2018
    Posts
    9
    Post Likes
    Thread Starter
    Quote Originally Posted by mgenius33 View Post
    With the old Appion VCRT’s I used to be able to get down to a 0 decay rate pretty frequently unless it was an old system repair vacuum or existing tubing. Since, I’ve purchased two new sets of the newer Appions with the magnet end, and I rarely ever get down to 0 decay rate. Even bought a new BluVac + Pro to make sure it wasn’t the gauge, and it shows the same as my old one.
    Maybe you can share your opinion. When I ran a nitrogen test at 300 PSI on a mini split. I used my yellow jacket gauge set for this, I also used an appion valve core removal tool to connect the 1/4" hose to the 5/16th.

    The pressure would stay at 300 PSI for 5 to 10 minutes, but very slowly drop a PSI or two PSI. I used a bubble test on everything and couldn't find anything. I even used a bubble test on my manifold and appion valve core removal toll and didn't see anything.

    Should you expect any PSI drop with a nitrogen test?

    Is this normal for a little drop in nitrogen test with time, maybe because of the manifold gauge set?

    When I did my vacuum test on the system, I pulled a vacuum to 200 microns, and it would maybe rise to 220 microns after 10 minutes. It seems like there isn't a leak, but the nitrogen test seemed like it would just continue to drop very slowly with time.

  12. #10
    Join Date
    Jun 2021
    Location
    Vermont
    Posts
    17
    Post Likes
    No you really shouldn't be dropping psi at all unless its left overnight and with a significant temperature drop.. Did you bubble test your hoses? If your hoses are used and if you crank on them alot the rubber gaskets can wear and you'll leak through your hoses. It could be a scenario where the rubber blows out under pressure but seals when in a vacuum. Also bubble test your manifold. I've had the 4 valve Titan leak through the sight glass before.

  13. #11
    Join Date
    Apr 2003
    Location
    Greenback, Tennessee
    Posts
    1,121
    Post Likes
    Quote Originally Posted by iDred View Post
    I'm not sure but if I put my CPS micron gauge directly on my vacuum pump, I can pull down to below 5 micron very quickly.

    If I use a yellow jacket charging hose, and attach the micron gauge to the end of the hose, I can pull down below 200, but it is very slow and the lowest I got was 170.

    I'm not sure if that is normal or if I need to use a vacuum rated hose.

    I'm thinking its not my gauge or pump because I can pull down to below 5 microns when attached directly to my vacuum pump.
    I agree. That is an indication that your pump is likely fine and that your hoses or its connections are leaking. On change outs I can often pull a whole system down below 100 microns.
    -Marty

  14. Likes R600a liked this post.
  15. #12
    Join Date
    Apr 2003
    Location
    Greenback, Tennessee
    Posts
    1,121
    Post Likes
    Quote Originally Posted by iDred View Post

    Should you expect any PSI drop with a nitrogen test?

    Is this normal for a little drop in nitrogen test with time, maybe because of the manifold gauge set?
    I don't put much faith in N2 pressure drop tests unless the drop is large enough to indicate a 100% for sure leak ie more than just a # or 2 or the test is left over night with temperature change accounted for. Typically pressure will change slightly for a few minutes after the N2 charge even on a system with no leaks. Temp equilibrium needs to be reached and pressure needs to equalize throughout the volume.

    Also Mitsubishi recommends 600 psig for a pressure test. IMO if you cannot see a flare leak with Big Blue and 600 psig you can 100% for sure that you do not have one at least at that time.
    -Marty

  16. #13
    Join Date
    Sep 2008
    Location
    VA
    Posts
    4,228
    Post Likes
    Quote Originally Posted by iDred View Post
    I'm not sure but if I put my CPS micron gauge directly on my vacuum pump, I can pull down to below 5 micron very quickly.

    If I use a yellow jacket charging hose, and attach the micron gauge to the end of the hose, I can pull down below 200, but it is very slow and the lowest I got was 170.

    I'm not sure if that is normal or if I need to use a vacuum rated hose.

    I'm thinking its not my gauge or pump because I can pull down to below 5 microns when attached directly to my vacuum pump.
    I agree with m singer, you will have some drop initially from pressure balance and temperature adjustment. Also, don’t forget if your using a digital pressure gauge you could see electrical drift. I almost alway see my FP probes fall slowly on a psi test unless they’ve been on for a while, but typically the leak rate slows as time goes by. The little gasket needs to be really tight as well.
    Standard hoses are cut, you may want to view some of Jim Bergmann’s videos or Yellow Jacket University video. I believe they explain this. Standard hoses have small slices for expansion and strain relief, so they are not air tight.
    "The only true wisdom is in knowing you know nothing" Socrates

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •