Model of a spherical tank. These are used for LPG, LNG, Butane, Propane or any other liquified (pressurized) gas. This tank is 75mm in diameter and can be used in various scales like N (real world volume 900m³), TT or HO scale (real world volume 137m³).
For printing efficiency the bottom of the sphere is open, the cap for the opening is provided and can be glued into place, resting on 8 small protrusions inside the sphere.
Spherical tanks (officially Horton Spheres) are used because the round shape has the lowest possible surface area to volume ratio and because this shape will distribute the stresses evenly. A cilindrical tank holding an equal amount of pressurized gas will need about double the amount of steel of a spherical tank.