Hydro-pneumatic pressure vessel and diaphragm assembly method

An expansion tank for storing a pumped liquid under pressure, the expansion tank comprising:

• an outer shell including a first dome-shaped section and a second dome-shaped section joined with one another to form an internal volume defined by an inner surface of the outer shell;
• a seal ring having an inner circumferential surface and an outer circumferential surface between a first end of the seal ring and a second end of the seal ring opposite the first end, wherein:
• the outer circumferential surface is disposed against the inner surface of the outer shell and forms a depression extending completely around the outer circumferential surface, the depression defined between the first end of the seal ring and the inner surface of the outer shell, and
• a primary stress reliever is formed between the inner circumferential surface and the outer circumferential surface at the first end of the seal ring;
• and
• a diaphragm including an enlarged lip disposed around an outer circumference of the diaphragm, the enlarged lip being disposed in the depression between the outer circumferential surface of the seal ring and the inner surface of the outer shell so as to sealingly divide the internal volume of the outer shell into a first fluid-tight section and a second fluid-tight section,
• wherein the primary stress reliever is configured so as to flex radially inward toward the inner circumferential surface in response to pressure from the diaphragm.