Molded plastic pressure tank

A spin welded tank joint for joining two thermoplastic tank sections, comprising:

• (a) a male joint portion including a male bonding surface extending from a uniform diameter, external surface to a substantially radial end face;
• (b) an internal shoulder spaced inwardly with respect to said radial end face and joined to the radial end face by a tapered surface extending between the shoulder and the radial end face;
• (c) said male bonding surface diverging substantially inwardly towards an axis of said tank section and at least partially defining a cross section that narrows from said external surface to said radial end face;
• (d) said tapered surface being substantially shorter than said bonding surface and defining a tip-like region tapering at a greater rate than the overall narrowing of the bonding region;
• (e) a female joint section including:
• (i) a substantially uniform internal diameter segment defining an alighment surface cooperating with said external surface of said male tank section to align said sections during a bonding process;
• (ii) a bonding surface extending from said uniform diameter portion to a base surface of a recess defined between an internal lip and said bonding surface;
• (iii) said lip defined by a substantially radial end face spaced outwardly with respect to said base surface and connected with said base surface by a tapered surface;
• (f) one of said male and female bonding surfaces being crowned such that when said tank halves are initially assembled, contact between said male and female bonding surfaces occurs intermediate the uniform diameter alignment surface and base surface of said female tank section.