It looks good. But why the single valve in the long run connecting the runs coming out of the tanks? There are (4) tanks and on the lines out, each has a valve. Then you have a valve in the center of the 4 lines out... Just curious but I don't see the purpose? I would think a union would be better for that location. (I recommend you add some unions throughout)? Just my thoughts. Very good detail by the way!
It's not done. The air system end up being more in depth. That valve is to isolate 2 bottles. So you can fill 2 or run off of 2.
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