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  1. #1
    Join Date
    Apr 2008
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    South New Jersey
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    78

    Confused pneumatic calibration theory

    I came by a johnson t4002-203 pneumatic t-stat pissing its branch pressure. i know i need to get a pneumatic gauge and adapter to start , however its been so long since i stepped up to this plate i dont remember anything. Can someone please give me a good brief refresher on pneumatic cal. theory Perhaps some steps to start to do it right?

  2. #2
    Join Date
    Nov 2001
    Location
    Seattle, WA
    Posts
    7,756
    Do a search on this site of pneumatic controls and you will find a link to Honeywell Grey manualy of pneumatic controls. Johnson Controls may also have some training material on their site.
    "The American Republic will endure until the day Congress discovers it can bribe the public with the public's own money.
    - Alexis de Toqueville, 1835

  3. #3
    Join Date
    Jul 2008
    Location
    Puerto Rico
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    29
    Make sure you know your sensor temp/psi range, actuator spring range and your 0-15 PSI gauge. The idea is to adjust everything up at half the system pressure range, (7.5PSI if a 6 to 9PSI actuator). If your measured variable (sensor), is at setpoint, you should have half the system pressure range on the branch output of the controller. Controller output is linear! Good luck!

  4. #4
    Join Date
    Mar 2008
    Location
    NY NY
    Posts
    181
    Pneumatic control thermostats are direct acting (increase in the output with an increase in temperature) or reverse acting (decrease in the output with a decrease in temperature).

    You will need a adapter for the thermostat , pneumatic gauge and the Johnson’s thermostat tool.

    As mentioned in the thread the output at set point is half the spring range of the actuator.

    You can tee the gauge into the branch line at the actuator insuring the accuracy of the control signal.

    The tee port becomes the adapter in this case.

  5. #5
    Join Date
    Apr 2008
    Location
    South New Jersey
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    78

    Smile

    Ok thats just the help i wanted Thank U! This site is great

  6. #6
    Good video showing how to calibrate a pneumatic thermostat at Removed Link
    Last edited by Chris_Worthington; 12-28-2010 at 05:37 PM. Reason: Removed Link

  7. #7
    Join Date
    Nov 2001
    Location
    Seattle, WA
    Posts
    7,756
    The one thing I might add is that sometimes the thermostate/controller is controlling between items such as a hot deck/cold deck or hot water valve/chilled water valve and in that case you do not calibrate for the mid range of either, but the mid range of the control system, which should still be around 7.5 psig.

    In the above cases there will be a dead zone within the spring ranges of the operaters where nothing is to happen untill there is a call for heating OR cooling.

    So you need to know your individual control application before you can actually know the best way to calibrate.
    "The American Republic will endure until the day Congress discovers it can bribe the public with the public's own money.
    - Alexis de Toqueville, 1835

  8. #8
    Join Date
    May 2002
    Location
    Baton Rouge, Louisiana
    Posts
    3,877
    Was it with the branch line on or off? Dont forget a tstat will seem like its out of cal and bleeding by when you could have a diaphragm with a hole in it.
    Quote Originally Posted by MatrixTransform View Post
    very soon it is you that will be pwned

  9. #9
    Join Date
    Feb 2009
    Location
    Northeast
    Posts
    342
    I have more than once had a diaphragm that did not leak with a quick jump from low to high pressure, like when you turn the setpoint adjustment, but will leak when the pressure slowly builds like when the room gradually warms up.

    Bill

  10. #10
    Join Date
    Oct 2010
    Location
    Baton Rouge, LA
    Posts
    1,113
    I find with 25 year old VAV boxes that some will not have a fan but will still have a damper inside and two actuators. Alot of times people will work on the outside but miss the ones on the inside. So you will have 25 year old pneumatic lines inside the box leaking or a leaking diaphram.
    If you're too "open" minded, your brains will fall out.
    Artificial intelligence is no match for natural stupidity.

  11. #11
    Join Date
    Nov 2005
    Location
    Captive DDC Customer
    Posts
    108
    Quote Originally Posted by billcontrols View Post
    I have more than once had a diaphragm that did not leak with a quick jump from low to high pressure, like when you turn the setpoint adjustment, but will leak when the pressure slowly builds like when the room gradually warms up.

    Bill
    Bill, I have one that seems to have started doing that. I figured, the bladder gets in a certain position in the actuator head, a hole in the bladder opens and stays open until a dramatic increase in signal happens, the bladder will then pressurize. The actuator strokes open at varied different signal thresholds depending on the speed of signal increase. This damper actuator is located in a nearly unservicable location 20' above a busy stairway... the economizer works well enough to ignore the problem. so far.

  12. #12
    Join Date
    May 2007
    Location
    New Orleans, La.
    Posts
    141

    Pneumatics Theory

    Send me you email address and I will send you the JCI pneumatics control manual.

  13. #13
    Join Date
    Jul 2001
    Location
    Canada
    Posts
    1,810
    Pneumatic control thermostats are direct acting

    There are also REVERSE acting Pneumatic thermostats as well

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