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  1. #1
    Join Date
    Mar 2004
    Location
    Vancouver, Canada
    Posts
    148

    Question

    When I was in tech school I was told to never ever adjust the calibration on the gage set. Apparently it will ruin them. We were told to make note of how much they were out and make the adjustment in our heads.

    My richie set was so much out on the high side that I had to adjust it. When I screw the plastic cover on the front it alters the reading and throws it out by 5 to 10 psi.

    Is it common to have to adjust every day or so due to varying atmospheric pressures? Was he right should I just leave it? Is it common for the adjustment to go out simply by screwing back on the cover (pressure change?)
    Is there a brand that is better quality?

  2. #2
    Join Date
    Mar 2004
    Location
    Vancouver, Canada
    Posts
    148
    Great tip on drilling the hole. I wonder if the bellows are better since they may not go out of adjustment so easily. Thanks for the tip.

  3. #3
    Join Date
    Nov 2003
    Posts
    501
    I like the hole idea also.

    Make sure that the screws in back are tight, or it will go out of calibration at the drop of a hat.

  4. #4
    Join Date
    Feb 2004
    Location
    Western New York
    Posts
    1,053
    Originally posted by dorrmann
    Make sure that the screws in back are tight, or it will go out of calibration at the drop of a hat.
    Or the drop of a gauge set!
    Experience is what you have an hour after you need it.

  5. #5
    Join Date
    Aug 2002
    Location
    Orange County CA
    Posts
    1,084
    I third the hole drillin'
    thing.

    Also, if you swing the gauges over your head holding them by the hoses,they will reset also.

    It looks really cool too!

  6. #6
    Join Date
    Nov 2003
    Posts
    501
    Originally posted by NedFlanders
    Also, if you swing the gauges over your head holding them by the hoses,they will reset also.
    ??? Are you serious?

  7. #7
    Join Date
    May 2004
    Posts
    12,152
    Never heard of that one either. Funny but I carry mine over-the-shoulder. Nice when you get hung up on the ladder and don't have a free hand.

    Does anyone else use the brass backed guages? I switched from plastic because of the starting post.

  8. #8
    Cut open a pot compressor. See what's inside. Remember it for the rest of your life.

    Then forget about ever doing it again.
    As to everything else we work on, plan on opening it up and making countless adjustments .... for the rest of your natural life!

    Give your instructor a break. If this is his, or her .. only wrong point, (I pray), they will do just fine for you.

    Unless your instructors are very very good at what they do .. you will come to hate them, in time. Especially once you learn the truth after you leave school.

    I am not against schools, only against wrong teaching methods.
    And there are a few of them out there. Be wary of them.
    demonstrate respect at all time for your students and teachers, but challenge them one and all!

    If they take offense, the hell with them. They are losers!!!

    Tell em to get a life! Seriously!


    Your education is NOT being paid for by any of them. You are doing it yourself. And you deserve the best that can be delivered! Bar none!


    A good instructor is worth their weight in platinum! Treat them as such. You may not remember who taught such and such classes during high school or grade school ... but I guarantee you WILL remember your instructors in HVAC/R for-ever!!!


    Have that teacher who said to calculate in your head ...have them sign on here..... WE'LL SET EM STRAIGHT!!!

    Dice will bore em a new ...... uh ....Dice will harass em good!

    (if they dont behave)

  9. #9
    Join Date
    Mar 2004
    Location
    Vancouver, Canada
    Posts
    148
    I've had the greatest respect for this teacher due to his no nonsense, get to the point style where you better have an answer for a question when you come to class. Years of experience and great in the shop. Each and every one of us liked and respected him.

    I actually think he was more concerned with us greenhorns wrecking his shop suppies.

    More great advice R12, its such a basic tool that i have admitably neglected.


  10. #10

    Calibrating Gages

    Calibrate the gage by pulling an absolute vacuum on it and adjusting the needle to 29.92 "Hg. If working correctly the gage will zero at 14.696 psia athmospheric pressure (sea level) or will register less than zero as the altitude increases.

    Now you're set for 100% accuracy.


  11. #11
    Join Date
    Sep 2002
    Location
    Hampton Roads, Virginia
    Posts
    1,627
    Too many Techs. worry about calibrating gage to zero, doing that in itself is pointless, it needs to be check at at least two different pressures and atmospheric, if it is not within your tolerances ditch it. Personally I have a good professorially calibrated gage that I connect to my manifold and connect both to my nitrogen regulator and check my manifold gage like that.
    "There are 10 types of people in the world.. those who understand binary, and those who don't."

  12. #12
    Join Date
    Jul 2001
    Posts
    310
    Variable

    Question - why would you want to calibrate to an inaccurate spot on your gauge to begin with? If you look at the gauge accuracy %, through the scale, I thought the vacuum area was almost the most inaccurate area. Refrigerant pressure at two different temps would seem to be the way to go.

    DaleP

  13. #13
    Join Date
    Mar 2003
    Posts
    127

    calibrating manifold gauges

    Zeroing and calibrating gauges are not necessarily the same thing. Of course, if you go to the beach, hold them down by the ground, and the weather is just right, then you can calibrate them at zero psig.
    Try this. Find a virgin refrigerant cylinder (we all know the recovery cylinders have non-condensibles permanently installed), hook up your gauges to it (this implies purging all air out of the hoses), and read the pressure. Next, take the temperature of the cylinder (down where the liquid resides). Use an insulated probe or an IR thermometer. If the temperature and pressure readings you just took do not agree with the saturation PT chart for that refrigerant, at that pressure, at that temperature, then make them agree. And I don't mean by heating or cooling the cylinder.
    "Calibration" is making an instrument agree with a known standard. Your PT chart is that standard. It is the law (physics). Finding a refrigerant which will allow you to calibrate your gauge somewhere around the mid point of its scale would be ideal. We are taught that bourdon-based gauges are inherently inaccurate at the extremes of their scales.
    So, this inherent inaccuracy of the gauge's operating principle, the fact that it is a cheap gauge anyway, the fact that it states on the packaging a +-5% accuracy, the fact that you are going to tell the gauge what to say whenever you want to, all lead us back to square one...which is to say, pull that hose off, set the sucker on zero, and get back to work!
    "Knowledge is what you get when you read the directions. Experience is what you get when you don't." --Unknown

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