The spring is heated by the coil in the bottom of the can. The coil is powered by the same circuit that powers the fuel pump--which is triggered by the ECU.
I recall that there is actually no air path from the can to the upper part, the valve, so making the can seal airtight is a bit of overkill. I remember that the valve itself was reasonably airtight, at least in terms of air leaking into or from the can.
Still, I RTV'd the seam when I did this repair to the AAR I was using...
--DD