wtf is a purge cannister solenoid

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07 F150 HD
im looking into getting a gc8 2.5rs and i checked out this one today that i had found and the cel was on

the guy said it was throwing a code saying it needed a new purge cannister solenoid, which in turn caused the car to go into limp mode, effectively ruining my test drive

but anyways

how much is this solenoid, what is it, what does it do, what causes it to break(is this indicative of another problem with the car) and what effect would this have on the car? would it smoke at all?

thanks much
 
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