Thanks Duncan,
That's slightly more complicated than I had hoped, but hey. One thing I noticed was that this method works for animating the maxClip but not for the minClip. Ho hum.
We are starting to realise that actually animating the pressure graph itself might be our best bet- fiddly as it may be.
Min and max clip animation tends to leave open ends to the tubes which is something of a worry, and at least you can control how the ends of the tubes are shaped to some extent with the pressure graph, or the width scale graph.
Never easy is it?