Flapper Valve 1.062 D .875 L with TPR Stem SIL BCG is a flapper valve that is made up of a data sensitive silicone material with shore durometer value ranging of 35 to 45. It acts as a tight seal for regulating gas flow for patients. It basically allows flow of fresh gas to enter the inhalation valve and exit the exhalation valve, inspiration or inhalation valve opens as patient Inhales and fresh gas enters the inspiration breathing hose to reach patient lungs.