in most control systems, you will run anywhere from 60 psig on up to 100 plus depending on how the distribution piping etc was designed. its very commonplace for the distribution to be at say 100 psig and get reduced by floor or zone to 20 or less. USUALLY the relief device is at the downstream of the prv and sometimes contained within, especially for honeywell prv's. most commercial controllers will be damaged at either 25 or 30 psig. in addition, this air should be clean down to about 3 microns, especially on the newer(plastic) controls which contain very small orifices. the valves talked about requiring 60,80 or even 100 pound air to the cylinder are used extensively around here on comercial jobs, even though most wholesalers refer to them as industrial valves. the position of an end device is determined by its normal rating i.e. normally open means thats how it is as it comes out of the box. you apply air to close it.