I'm changing out my fuel pump and found this thing sitting at the bottom inside of the gas tank. no idea what it is but I think it's some sort of valve.

 

Looks to be the roll-over valve for the CCP vent line on the sender unit.

RBob.

 

What RBob said. It also takes 2-4psi before it opens to relieve tank pressure which when it fails is likely the cause of so many posts about excess tank pressure when taking off the cap, or gas spewing out while filling the tank. New sending unit may be in order or can buy an external valve and put between tank and charcoal canister.

 

Thanks guys.