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.

 

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!

 

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.

 

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

 

Good video showing how to calibrate a pneumatic thermostat at Removed Link

 

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.

 

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.

 

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 laying:to ignore the problem. so far.

 

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.

 

Pneumatics Theory

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

 

Pneumatic control thermostats are direct acting

There are also REVERSE acting Pneumatic thermostats as well

 

What makes you think it's bad because it's bleeding it's branch?

 

so what would happen on a reverse acting pneumatic thermostat with an increase in temperature?

 

R.A thermostat output pressure will decrease on temperature rise.