Read any Honeywell catalog on control valves and most likely you will end up with red eyes and possibly a bald spot on top of your head from scratching it in frustration.

Let’s see…Stem up to close, Stem down to close, reverse acting, direct acting…..ARRRGGG, I just want a normally closed valve with a pneumatic actuator with a 8-13 psi spring range!!!

The easy way….Call Stromquist and Company they know what I want… Yes, but there is a lesson being taught here so I need to do my job.

Pneumatic Control valves are inherently spring return and modulating valves, always opening and closing the valve to whatever location the temperature controller deems correct to maintain proper conditions in a controlled space. For this reason when we get to the electronic portion of this article the actuators will be modulating and spring return.

Pneumatic Globe Style Control Valves and Actuators:

Valve Action = Stem down to close. This means that the valve body is Normally Open and the actuator would have to push the stem down to close the valve.

Valve Action=Stem up to close. This means the valve body is Normally Closed and the actuator would have to lift the stem up to close the valve.

Directing Acting Actuator =Stem up.  This means with an increase of air pressure the actuator will pull the stem up

Reverse Acting Actuator =Stem down. This means with an increase of air pressure the actuator will push the stem down.

So in the field if you need a normally closed pneumatic actuated valve you would need to pick an N/O valve (stem down to close) and a RA (reverse acting) actuator; this will fail closed (stem down) on a loss of air pressure. If you need a normally open pneumatic actuated valve you would need to pick an N/O valve (stem down to close) and a DA (direct acting) actuator; this will fail open (stem up) on a loss of air pressure. Having said that; remember that pneumatic valve action (not fail position) is dependent on the action (DA/RA) of the thermostat AND if you are doing cooling or heating (hot water or steam will also change things). Final selection of the pneumatic actuator will depend on the spring range you need and the body size and close off pressures needed. This paragraph applies only to Honeywell, as other manufacturers do things differently (most manufacturers have true NC and NO valves and use only DA actuators). Proper valve sizing and actuator selection is vital with today’s temperature control systems for proper control and tenant comfort. If you are unsure of which valve/actuator combination to select just call the professionals at Stromquist and we can “walk” you thru it.

Electronic Globe Style Control Valves and Actuators:

Thank goodness the valve bodies for the electronic applications are the same as the pneumatic applications so the Valve Action for the electronic control valves will remain the same as the pneumatic control valves.

Care must be taken in the selection of the spring return modulating actuator. The first consideration is the close off pressures necessary in the system so an electronic actuator with the proper torque can be selected.

As I was reading through the specification sheet of the spring return actuator I noticed in the application and features section of the sheet the statements “reverse/direction action” and “An internal selector plug can be used to reverse the direction of action.” DANGER!! DANGER !! Honeywell is NOT stating that the valve can be normally open or normally closed by changing the selector plug. The changing of the selector plug can and is used to reverse the action of the CONTROL SIGNAL only.

The decision of a normally open or normally closed valve is based on the direction the actuator drives the valve stem (up or down) on power failure.

I hope this has cleared a little of the mud away when selecting Honeywell globe valves with pneumatic and electronic actuators. Goodness knows we need our eyes clear and our hair intact.

Even with all the great new technology in HVAC controls, there are still many pneumatic buildings out there.  If you happen to be someone who has to work on pneumatic controls, you know it can be frustrating when you have a problem with the system.  Here’s a good troubleshooting procedure from Jerry Condiff, the instructor who teaches a great pneumatics class for us here at Stromquist every year.  Jerry has been in the HVAC controls field for over 30 years and really knows pneumatics.

Pneumatics Troubleshooting Procedure

Start at the thermostat or controller.  Check to see if the thermostat will put out a high pressure by turning the set point to its minimum setting.  The pressure should be high on the output gauge.  If not, try adjusting the calibration screw. 

If no air noise is distinguished, check to see if air is present in the supply line into the thermostat (this will require removing the stat from the mounting bracket). If supply air is present but there is no air bleed noise or output pressure, the restrictor is plugged or the nozzle at the bleed port is dirty.  Check and clean the nozzle or clean out the restrictor.

If there is no pressure output but air bleed noise is present, check for an air leak behind the mounting bracket.  Check the air hoses that are connected to the mounting base for deterioration.  Check Honeywell stats for broken plastic air nipples in the back of the mounting base.

If no air leaks are found, plug the branch line of the stat with a jumper hose connected from the supply line to the main or supply to the stat.  If pressure builds on the branch gauge, the branch line of the controlled device (valve, damper or pressure switch) has a leak.  You may also make up a tool consisting of two 5/32 lines and a barbed gauge tee and a 30# pressure gauge.  Connect one end of the hose to supply and the other to the branch port on the mounting base. If you do not read any pressure on the gauge, the branch line has a leak.  If pressure builds, the stat is bad and will need to be replaced.  Use a squeeze bulb and gauge to check controlled device diaphragm for leaks.  If no leaks are present, the branch line hose has a leak and needs to be replaced. 

This procedure may not cover every potential issue you run into with your pneumatic system, but it should at least be a good start, and I hope you find it helpful.  Happy troubleshooting!

1. Determine the throttling range for your control system.  Let’s use 3-13#’s as an example.
2. Next measure the ambient temperature at the thermostat with a precision temp meter.
3. Adjust the setpoint knob on the T Stat to the current ambient temperature.
4. Pull the branch line off the T-Stat and T tap a gauge between the T-stat and branch line.
5. Adjust the calibration screw in the T-Stat until the branch PSI reads zero.
6. Now adjust the calibration screw in the opposite direction until the branch pressure reads mid range. In this case our differential  is 10#’s of pressure, so (13-3)= 10(diff) /2 or 3+5 = 8 psi.
7. Verify the box damper and reheat valve(if applicable) are both closed. Fine tune if needed.
8. Remove your calibration gauge and replace the branch line back onto the T-Stat.
9. Adjust the T-Stat to the desired setpoint.

Your T-Stat is now calibrated…

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