Have you seen a sac like that before? It came from a Waterman 52 that clearly hadn’t been used for a long time. I’m not sure why it should be ridged in that way. Perhaps it helped to ensure that the sac did not stick to the pressure bar or the inside of the barrel. Strange that I shouldn’t have come across one of these before but I don’t remember doing so.
Sacs are quite confusing these days. There is the basic latex sac that we’ve used for most repairs for a long time. Then there are the sacs that we thought were silicone but turned out not to be, and there are David Nishimura’s true silicone sacs.
For me, the latex sac remains the default. Unless the pen is one of those colours that are greatly at risk of deterioration when latex sacs begin to decompose, I see no reason to use anything other than a latex sac. Latex sacs are by far the most flexible and therefore cause least stress on the filling system. Those sacs that we once believed to be silicone but have proved not to be don’t seem to have a place in pen repair any more, so far as I can see. Their place has been taken by Nishimura’s silicone sacs.
We are very fortunate that today’s sac manufacturers were able to resuscitate the process. Without sacs – and for a time their production had ceased worldwide – pen repair becomes very limited. Lever fillers, button fillers, Vacumatics, Touchdowns, Bulb fillers, Crescent fillers and a host more – most pens, in fact, would be unrepairable. Competition would be quite stiff for Onotos, Fords, Sheaffer plunger fillers and the like. Many of us might be limited to (shudder) the cartridge/converter!