1908 W.A.Sheaffer applied for a patent on the first lever filler. Basically it was an eyedropper, that sucked up ink by a rubber sac – a simple system, fast and reliable.
The lever (1) moves around a fixed pivot mounted in the barrel. By lifting up one end of the lever the other moves downwards and compresses the rubber sac (2) inside by means of a metal strip (3), thus creating a vacuum. By pushing the lever back the rubber sac takes it's former shape and sucks in the ink. The sac helps to prevent flooding by reducing an increased pressure caused through higher temperatures. The only disadvantage is that the rubber sac tends to harden over a time of 5 to 10 years.