The hump filler is basically a variation on the theme of the crescent filler in which the sac is compressed using a protruding element from a side opening of the pen. The element allows you to compress directly the rubber sac, the main differences between the variants of this filling system are the ways in which it ensures, more or less reliably, that the protrusion can not be pressed accidentally.
The system had some diffusion at the beginning of 1900, as an alternative to the success of the Conklin crescent filler, one of the best realized versions was the so-called Wawco filler conceived by William Welty (patent nº US-834542) and used for the pens produced by the latter both with the Wawco brand and with the other brands used by the company.
- Patent n° US-834542, of 1906-10-30, requested on 1906-02-23, of William A. Welty, Welty. Fountain pen.
- Patent n° US-916513, of 1909-03-30, requested on 1908-04-27, of William A. Welty, Welty. Self-filling Fountain-Pen.