[FrankJ]

Largely conjecture here since I am not on the rules, committee... But the pneumatic rules seem to be written to keep the pneumatic system safe with minimal knowledge by the volunteer inspectors. (Absolutely no dig intended for the many volunteers who freely give their time & cannot be experts in everything.) But it makes very difficult to source parts that meet the literal interpretation of the rules.

KOP parts are by definition legal. A part identical to but not the same part number, mfr may not be legal. For example only a specific battery is legal although it a standardized battery with many equivalents. Same with regulators.

In the past we have used regulators downstream of the Norgren 60 PSI regulator for elements that needed a lower pressure. I believe we used a Norgren, so it was legal by definition, but the inspector did not look that closely at it. Having somebody able to clearly explain how the robot works is helpful to the inspector. What ever makes their job easier makes the inspection go smoother. At least that has been my experience.

Back in the day pneumatic controls where used extensively where electronic do an easier & better job now. Pneumatic PID controllers are still used in places where it is inconvenient to use electrics. Pneumatic valve actuators are still pretty common. Controls & actuators typically run on lower pressure (around 20 PSI). Instrument regulators are generally able to set a lower pressure, better quality & more precise that a GP regulator, but they both do the same function. Probably easier to find a First legal instrument regulator because of the lower working pressure.