|Filling Instructions: Blow-Fillers|
The blow-filler is the simplest pneumatic-filling pen design possible. One blows through a hole at the end of the barrel, thus emptying out the ink sac. When the pressure is released, the sac expands and fills.
Blow-fillers were sometimes offered with an accessory rubber bulb, as shown in the picture above, which permitted the pen to be filled in a more dignified and hygenic manner.