I couldn't follow everything you wrote.
However, I'll just point out that a mid position valve may well
stay in the mid position if you just remove all power from it.
To keep the valve in mid-position, the motor is fed with DC
to lock the rotor. This magnetises the yoke which can continue
to hold the actuator against the spring if you just remove the
power (although the holding force is very weak and it will
probably release if you touch it). In normal operation, a tiny
AC current is leaked through the motor when it isn't operating
to degauss the yoke, and ensure the spring returns the actuator
to its resting position.

--
Andrew Gabriel