4-20mA 3-15psi ?
4-20mA 3-15psi ?
(OP)
We are replacing chilled water and steam valves that have pneumatic actuators. The steam valve operates between 4 and 8 psi. The chilled water valve operates between 9 and 13 psi. We still want to use pneumatic actuators, but we have an electronic control system that can drive both valves between 3 and 15 psi.
Any reason not to spec new actuators that operate over the full pressure range of 3 to 15 psi? I don't see why not, since we are trashing the pneumatic thermostats and using I/P transducers.
What do the experts say?
Thanks.
Any reason not to spec new actuators that operate over the full pressure range of 3 to 15 psi? I don't see why not, since we are trashing the pneumatic thermostats and using I/P transducers.
What do the experts say?
Thanks.





RE: 4-20mA 3-15psi ?
For accurate control of pneumatic actuators, you need to have positive positioners and high quality IP's not just any transducers.
Electronic control valves have so many advantages over the other way.
RE: 4-20mA 3-15psi ?
RE: 4-20mA 3-15psi ?
I assume the only advantage of the 5 to 8 and 9 to 13 psi scheme is that you can use one pressure source.
Or, maybe I should use one pressure source to be sure I never have both valves open?
I was thinking I could get better resolution over 3 - 15 psi.
Thanks for the fast responses, I actually need to make a decision tomorrow morning.
Any more thoughts?
Cheers!
RE: 4-20mA 3-15psi ?
RE: 4-20mA 3-15psi ?
All the 1970's 3-port heating valves eventually started to fail and the system was eventually converted to all electric actuators.
In your position, I think I'd specify 3-15psi actuators, but the 3-6/8-13 psi actuators worked fine. They had a very fast response and the room temperature graphs were flat lines for many years.
RE: 4-20mA 3-15psi ?
RE: 4-20mA 3-15psi ?
I understand the pros and cons of using electronics to control pneumatics from the perspective of a control technican and that of an operating engineer.
If all else fails, the watch engineer can pull off the control devices and apply supply air pressure (20 - 25 p.s.i) or use a Ben Casey (sphygmomanometer) to override complete system failure.
I particularly prefer devices that utilize a current signal over voltage or resistance as it pertains to ease of troubleshooting. My digital multimeter can measure current, voltage and resistance as well as generate a 0-30 mA signal.