Among all parts of fountain pens, feed is the last to be understood by human beings. It is also the most deliciated, sophisticated and the least talked about, due to its complications.
Low Ink Refill - draw ink from breather.
Low Ink Refill, is a term I invented to describe the feature of modern pens ability drawing ink from breather.
Benefit: possible to draw ink when ink bottle too low to merge up to the section; #8 or larger nibs prevails.
Manufacturers don't openly talked about this feature because LIR required precision in nib/feed/colar. Any weakest link of the chain result a failure of this feature. To preventing a soaring service rate, the makers just play safe and just keep you away from knowing of it.
More info will be there: https://shanghaiknifedude.blogspot.com/2025/01/on-low-ink-refill-lif-and-fountain-pen.html
video here. Enjoy.