[Vn_survivor_67-68]

I don't know if they seal well enough; or if they do--how durable would they be?

Here is a discussion of this system I found, by some pretty intelligent people:

http://www.greencarcongress.com/2006/12/valeo_in_develo.html

here is a snip from a post by "silverthorn" (75% down the page) that enlightens us on the spring tension dynamics:

Each valve is driven by a spring with a high force constant, whose neutral position is midway between open and closed. The resonant frequency for the valve + spring is somewhat greater than the maximum frequency at which the valve must operate at engine redline. When the valve opens or closes, it is not driven by electromotive forces. Rather, it's driven by the force of the spring, when the electromagnet that holds it open or closed against the force of the spring is switched off. It accelerates rapidly toward the neutral point, passes through that point, and then decelerates rapidly toward its other extremum. As it approaches the other extremum, the electromagnet at that end of its travel draws it with enough force to compensate for frictional losses, and then holds it. It continues holding until it is switched off and the next transition is initiated.

[Old Professer]

You left out the picture:

The part where he has two parents and a child on a swing;
each parent, in turn, grabs the seat and lifts it and then lets go - just like the electromagnets pull and release.

Can't you just see that lovely child, her hair being blown back and forth in the ever freshening breeze her proud mother and father have created for her?