Comfortgel FF to Nasal help

i'm relatively new to therapy, i have a respironics bipap st machine and have been using a comfortgel full face mask but due to inability to get used to it i purchased a comfortgel nasal mask from cpap.com, and i have a question. Situated within the elbow tube of the full face mask is a flap thing that opens when i inhale and closes when i exhale. When it closes it prevents my exhaled air from getting into the tubing that's connected to the machine, rather my exhaled air vents through a small hole right above the flap. And to me this seems like a good thing. keeps me from rebreathing my own air. Now i'm looking at my new nasal mask and there's no such mechanism whatsoever. if I put on the nasal mask and cover the end of the tube with my thumb and try to exhale through my nose, i can't. There's absolutely no type of venting whatsoever. Is something wrong with the nasal mask? i haven't connected the mask to the machine yet but it seems like a bad thing that, when i will exhale, all my exhaled air can only travel back down the tubing toward the machine. I've tried to determine if i could switch connectors between the two masks but i don't see any way to do that.

What's the deal? Does anyone know?

I'm not familiar with the Nasal model (the CG FF is my primary mask). In theory, the CPAP machine blows all the exhaled CO2 out the vent so you don't rebreathe it.

It MAY be the smaller volume of a Nasal makes that unnecessary, but ALL of the FF masks I've tried have an exhaust feature.

Looking at the Respironics site, I don't see an obvious vent on the CG Nasal, nor does the literature mention one.

I think I just learned something new! Thanks.

That flap is a mechanism on full-face masks to protect the wearer against asphyxiation if the blower fails. In other masks that interface with the nose alone, it is not needed as your mouth is not covered and you can breathe through it under the same circumstances. In a FF mask there are two ports: the exhaust port and a much larger anti-asphyxiation port. When air is moving into the mask from the blower, the flap covers the larger anti-asphyxiation port; without air movement, the flap comes down and one can breath through the port. Regarding the nasal mask exhalation port: without knowing what specific nasal mask you are using, I can't speak with any authority except to say it is probably much smaller that the equivalent on the FF mask. However, on exhalation the incoming air from the blower forces the CO2 out the port. When inhaling, any remaining CO2 is likely to be trivial.

JimW203