- When fully opened the APL valve maintains a pressure of around 1.5 cm of H2O
- As we close the APL valve, the pressure builds up inside
- There is a safety overpressure release valve incorporated in modern APL valves, to avoid this rising to dangerous levels. This system starts opening at a pressure of 30 cm of H2O and fully opens at 60 cm of H2O and at this point, allows the gases to escape at a rate of 50L/ min
- When the patient inspires, the APL valve , if intact, should not allow entrainment of air from the environment
- As the modern reservoir bags are less compliant, compared to the older latex ones, the importance of overpressure relief valves has increased
- As the APL valve will always produce a small resistance to expiration, even when maximally loosened, it helps to maintain PEEP
The Lay Medical Man 