There are two ways to check a one way valve on a Kirby Morgan Dive Helmet or BandMask®. The one way valve should be checked prior to the start of diving or every 24 hours if in continuous use.
Oral One Way Valve Check -Test the one way valve for proper operation by blowing and sucking (cycling) on the umbilical adapter. No gas should be drawn through the one way valve. If you are able to suck any air through the one way valve, it is not working properly and should not be used.
Low Pressure One Way Valve Check -With the bail-out bottle connected to the emergency valve, no gas should escape through the one-way valve when the EGS valve and cylinder valve are opened.