From what I have seen, pressure is NOT our friend. While I am aware of the fact that our machines create negative pressure to suck ink out of the heads in the direction of printing, I am not yet aware of how much pressure. And I know no pressure is ever applied in reverse, by the machine at least.
The last head that I performed an autopsy on showed evidence of pressure damage. I am the only one who applied pressure to that head, and I was very gentle. The current strategy I am developing avoids any pressure in any direction.
The weakest part of an X900 head is the chamber deck floor. Beneath this floor, which is so thin it's actually transparent, is a sealed reservoir that runs the length and width of the entire deck. Too much reverse ink flow pressure, applied to a clogged chamber wall, pulls the chamber deck away from the surface of the printhead face - which causes it to collapse into the sealed reservoir.
The X900 machine sucks ink through the head in the direction of printing, which I believe is safer because the chamber deck gets pushed up against the face of the printhead, which it is already in contact with (the top of each and every chamber wall is actually glued to the printhead face).
This is a work in progress, I only started this morning. Take a look at this X900 PRINTHEAD REVEALED
page and you'll get a better idea of how the chamber deck can collapse with negative pressure drawn into the printhead face.