This Respironics part is a spring-loaded valve which helps prevent the backflow of oxygen or water from the patient circuit in to the BiPAP or CPAP machine when the CPAP machine is turned off. Any backflow passes out of the circuit through the vents. When the CPAP machine is operating, the valve allows air to flow through the patient circuit. The vents are sealed to prevent flow out of the circuit. The inlet side of the valve is a 22 mm connector that fits on the outlet port of the BiPAP or CPAP machine. The outlet side of the valve fits a 22 mm connector on a bacteria filter or smooth inner lumen tubing. The minimum operating pressure is 2 cm H2O. Note: the Pressure Valve is not an exhalation port and does not vent exhaust gas during exhaustion.