Italian to English Tech/Engineering Engineering: Industrial Boilers

this is part of the list of the technical specifications for a 'bollitore ad accumulo verticale'. There is 'altezza 1525 mm', 'altezza di ribaltamento 1640 mm'. There are various boilers in the range, and the 'altezza di ribaltamento' is about 8-10% more than the 'altezza' for each of them.
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'ribaltamento' comes up as tilting or folding over in other contexts, but neither seems to fit here. Any ideas as to what they're on about gratefully received.