I have not taken the valve apart. If the prefilter is external to the softener, then it doesn't have one.
I would love to take the valve apart to try to figure out what is going on, but I have absolutely no idea what is inside the valve or what I am looking for. That is one of the reasons I would like to see an exploded view of the valve. I am not too thrilled with Kinetico for hiding this information. Does any other company make a similar valve with an actual manual that could give me some idea what is in the valve?