In the years after the First World War there was a scramble to find a successful method of ‘self filling’ a fountain pen. Sheaffer’s lever filler led the way and, of course, their version was denied to everyone else. All sorts of methods of compressing a latex sac were offered to the public with varying degrees of success. Only the Conklin Crescent filler lasted and even that eventually died away. Waterman created a version of the lever sufficiently different that Sheaffer could not successfully claim it was a copy of their design. Parker re-thought the whole process of flattening the sac and created the button filler.
These two sac fill designs dominated fountain pen design for many years. Which is the most efficient? Which proved the most popular then and among vintage pen fanciers now?
There’s an aesthetic consideration. The button filler provides an unbroken barrel and a different coloured blind cap may echo a clip screw and/or a section. Until it becomes worn and loses its plating, Waterman’s box lever may be seen as a handsome interruption to the plain or patterned barrel. That design has been copied many times, by companies such as Conway Stewart, Wyvern and De La Rue.
There is another, less visible issue with lever fillers. Waterman designed a swing pressure bar that met the sac quite flat and squeezed the air out very efficiently. Conway Stewart used a similar system, perhaps licensed from Waterman. Other manufacturers adopted the j-bar which is cheaper but addresses the sac at an angle and does not compress it so well. Mabie Todd pens use their own version of the j-bar developed to be more effective.
It is generally assumed that Parker designed the button filler to avoid Sheaffer’s patent and that is undoubtedly so but as a result they created a very efficient system – or a couple of systems, one transferring the pressure of bending the pressure bar to a screw-in section, the other applying it to the button aperture.
I have heard those who occasionally repair a pen say that they dislike the button filler because it is a more difficult repair. There may be a little more to it but of course it isn’t more difficult. In the hands of the user, I would say it is a little easier to fill, though there isn’t much between them. Which system do you prefer, and why?