Osma wavin AAV how do they work and how much is a new one

[James Salisbury]

Hi, I have an Osma Wavin AAV in my bathroom, was getting nasty wiffs from the stack. Decided to examine the AAV found that it doesn't seem to have a diaphragm, how do they work?

If I need a new one how much should I pay, rather than the list price shown at Plumb Center.

Thanks

James