For a pneumatic transmission system for instrumentation purposes, if a pneumatic instantaneous flow indicator has a calibrated scale of 0 to 1000 gpm, what would be the actual measured instantaneous flow rate if the transmitted pneumatic signal pressure to the indicator is 9 psig, assuming the industry standard of 3 to 15 psig is used for instrument air?

Question

Accepted Answer

Option B: 500 gpm. The 3-15 psig range spans 12 psig. A 9 psig signal is 50% of the span (9-3=6; 6/12=0.5). Applying this 50% ratio to the 1000 gpm range results in 500 gpm. This linear relationship is standard for pneumatic transmission of process variables in shipboard instrumentation and control loops.