All files print best scaled to 125% For the steam valve file (top insert) you should print slightly larger at 126%.
I printed everything with a 10% infill except for the hinge assembly that I printed at 20% infill.
Assembly is required by using a plastic adhesive, for this I used Weld On - 16 or PLA 3D Gloop, but any similar adhesive will do fine. There are small slots in the middle ring that allow for the hinge to be glued in and stay in place.
The hinge has a very small tolerance, you may have to twist is loose just a tad, but out of the 4 times i have printed this is worked amazing each time. (125% scale) One option I have found is that you may have to split the hinge into objects and print each of the 3 parts individually with small supports.
The only supports I used were on the middle rings where the major overhang exists (where the hinge sits) but a well tuned printer may not need them