Parker boasted the Vacumatic to be the first self-filler without a sac, which was not entirely true. However, the filling mechanism was an innovation.
By using a diaphragm rather than a sac, the whole barrel could be used as an ink reservoir. The mechanism worked similarly to earlier button fillers. When the plunger was depressed, it compressed the rubber diaphragm and forced air out, creating a vacuum. When released, ink was drawn into the barrel.
There were three basic models manufactured with the Lockdown filler. If you examine the barrel imprint, you will find one of the following model names:
Click the imprint that looks like yours
