Filling Mechanism
From WikiPenia for PenBoutique
The earliest fountain pens were mostly eyedropper fillers - that is, the pen was essentially an empty reservoir which one would fill with an eyedropper. This was a relatively awkward and messy process, though the absence of complicated mechanisms meant that an eyedropper-filler could hold much more ink than could a self-filling pen of comparable size. As a result, eyedropper-filling pens constitute only a tiny fraction of pens made today.
After the eyedropper-filler era came the first generation of mass produced self-fillers, almost all using a rubber sac to hold the ink. By various mechanisms, the sac could be compressed and then released in order to empty and fill the pen.
The Conklin crescent filler, introduced c. 1901, was one of the first mass-produced self-filling pen designs. The crescent filling system employs an arch-shaped crescent attached to a rigid metal pressure bar, with the crescent portion protruding from the pen through a slot and the pressure bar inside the barrel. A second component, a C-shaped hard rubber ring, is located between the crescent and the barrel. Ordinarily, the ring blocks the crescent from pushing down. However, when it comes time to fill the pen, one simply turns the ring around the barrel until the crescent matches up to the hole in the ring, allowing one to push down the crescent and squeeze the internal pen sac.
Following the crescent filler came a series of systems of increasing complexity, reaching their apogee in the Sheaffer Touchdown and Snorkel systems. With the introduction of cartridge pens by Waterman-Jif, though, many of these systems were phased out in favour of convenience (but reduced capacity). Today, most pens either utilise piston-fillers or cartridges, although the latter can usually be converted to piston-fill with the use of a convertor.
The piston filler, first introduced in the original Pelikan of 1929 (although the concept was from Croatia), was somewhat of an anomaly in an age of sac-filling pens. The idea was a simple one: merely twist a knob at the end of the pen, and an internal piston will drive up and down the barrel, forcing ink out or in. While the capacity of these pens was not comparable to some of the better sac systems, and certainly not the eyedropper pen, they offered convenience only second to the cartridge. The reason for their lacklustre capacities is the size of the piston unit. In order to effectively drive the whole way down the barrel, some of the earlier models had to devote as much as half of the pen length to a complicated system. The advent of telescoping pistons has in some respects remedied this, but piston fillers are still sometimes foregone today in favour of older methods.
