Hmm, not quite sure that I fully understand that bit. I was assuming that you'd have an O-ring around the bottom of the main tank so that the "printing water" (in that tank) is completely separated from the "support water" (in the lower cylinder). You use up the support water, but the printing water remains fixed so you've got a constant volume of that. This should just result in the green cylinder/piston moving down, lowering the print bed into the printing water and resin.


Regarding the weight, there are two problems with making it really heavy. One is obviously that it'll be a pain to ship it - you might have to ask end users to attach big steel bolts or something to make it heavy enough. The other is that there'll be a lot of pressure in the support cylinder which makes it difficult to find a suitable valve setting. Still, it might be that this is just what has to be done to make it work. It'd be a small price to pay to get a nice printing platform.