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.