What is the purpose of the adjustable pressure limiting valve (APL) in the breathing circuit?

• A. To limit airway pressure by venting excess gas
• B. To measure pipeline pressure
• C. To provide a reservoir for gases
• D. To heat the gas

Answer: (A)

The adjustable pressure limiting valve acts as a safety device that keeps airway pressure from climbing too high by venting excess gas from the breathing circuit to the scavenging system when the circuit pressure reaches the set limit. It is normally closed during inspiration and opens only if pressure would exceed the chosen setting, preventing potential barotrauma. This component is not used to measure pipeline pressure, to store gases, or to heat the gas—its sole job is to cap peak pressure by releasing surplus gas.