Depends on a lot of things, but I change them every time I disconnect them. Also change if they look worn or corroded. And definitely change if it's polybutylene.
PlumberFLMember since 12/31/15
Please elaborate: Does it always come out of the same faucet? Do you have a filter? What are your water lines made of in your house? What is the line that sup...
There are different brands of AAV's. Buy one with a lifetime warranty.