Which connects the compressed air source to the control devices?

• A. Supply line
• B. Return line
• C. Exhaust line
• D. Pilot line

Answer: (A)

In pneumatic systems, the path that directly feeds pressurized air from the source to the control devices is the supply line. This main feed carries the compressed air (often after it’s filtered and regulated) from the compressor to valves, cylinders, and other control components so they can operate. Without the supply line, the control devices wouldn’t receive the pressure needed to function.

The other lines serve different roles: the exhaust line vents air to atmosphere when devices release pressure; the return line provides a path for air back in some circuits; the pilot line carries a smaller air signal to pilot-operated devices. But the essential connection from the air source to the control devices is the supply line.