Which control system requires a compressed air source?

• A. Pneumatic valves
• B. Electronic sensors
• C. Bubbler controls
• D. Float switches

Answer: (C)

The key idea is that bubbler level controls use a compressed air supply as the actual sensing signal. In this setup, a small tube is placed into the liquid, and air is pushed down the tube. The pressure in that submerged line, which comes from a compressed air source, increases with liquid depth. A regulator and sensor translate that pressure into a level signal that the control system uses to maintain or regulate the process. Without a constant compressed air source, the bubbler can't generate the necessary pressure signal, so it can't measure level or drive the control actions.

Electronic sensors and float switches operate with electrical signals or mechanical buoyancy and don’t depend on air pressure to sense level. Pneumatic valves are actuators powered by compressed air, but they aren’t the sensing method in the same way a bubbler is. That reliance on a continuous air-pressure signal for sensing is what makes bubbler controls the best fit here.