(This page revised June 22, 2012)
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In 1934, Sheaffer began selling pens with the Vacuum-Fil system. Sheaffer did not invent the system, however; the credit goes to an English mechanical engineer, tinkerer, and sometime vaudeville performer (doing a transvestite act on roller skates!) named George Sweetser. Sweetser sold the rights to his invention to Thomas De La Rue & Company in about 1905. De La Rue put the design into production in a pen model dubbed “Onoto The Pen,” and it was very successful in Europe.
First produced in 1934 on secondary-brand pens such as the WASP Clipper and pens bearing the Vacuum-Fil brand, Sheaffer’s version of the system (U.S. Patent No 1,983,682) appeared a year later on the company’s self-branded pens and continued in production the Touchdown superseded it in 1949. Wahl, Conklin, and Pilot of Japan also marketed pens with very similar plunger filling systems during the 1930s, and some modern Visconti and Pilot pens use plunger fillers with a technology boost to eliminate the problem of packings that can dry out.
The principal feature of the Vacuum-Fil is that it fills with a single operation of its plunger. An added advantage, because the mechanism occupies very little space, is that Vacuum-Fil pens have a very large ink capacity for their size.
In the 1930s, many pens had transparent barrels or sections to allow the user to see whether the pen was filled, and Sheaffer included transparent bands in the barrel of the Vacuum-Fil. The illustrations here do not reflect this feature. Here is a diagram of a Vacuum-Fil pen. (The illustrations depict a pen with its proportions altered for illustrative purposes.)
In the Vacuum-Fil system, the barrel is sealed at the back by a felt packing held within a packing unit that was assembled externally and press-fitted into the pen. The packing cup includes a threaded boss onto which the blind cap screws, and there are two semiflexible washers within the packing cup, one on either side of the packing. A larger rigid washer, the packing retainer, seats against the end of the barrel’s slightly smaller bore diameter to to retain the packing and washers in place without the use of adhesives:
The “piston head” comprises a hard washer whose front surface is slightly concave toward the center and conical toward the periphery, a pliable gasket, and a pointed cap-nut that squeezes the gasket into the hard washer’s concave center portion, forcing the gasket to assume a very slightly cupped shape:
Extending the plunger draws the gasket backward into the barrel. During this step, the gasket is cupped forward; cupped in this way, the gasket slides very easily, allowing water or ink behind it to flow past into the front part of the barrel. The next figure shows the pen with its plunger partially pulled up; note the forward direction in which the gasket is cupped:
Pressing the plunger down forces the lip of the gasket firmly against the barrel wall, flipping the gasket “backward” so that it lies against the hard washer. This flipping action is unique to Sheaffer’s design and causes the gasket to seal more quickly to create a tight sliding seal. (The hard washer forces the seal to remain tight by not allowing the gasket to cup too far.) As the plunger moves down, it forcibly expels the barrel’s contents. This action provides a very effective flushing/cleaning mechanism. Because the barrel is sealed at its back end, the plunger’s downward motion also creates a strong partial vacuum in the barrel behind the piston head. The next figure shows the pen with its plunger partially pushed down; note the flipped position of the gasket:
At the end of its downward travel, the head of the plunger escapes the bore into a slightly broader space; at the same time, the beveled end of the center feed pushes the pointed end of the plunger sideways. Pushing the plunger sideways ensures that there is a clear passage into the barrel, and outside air pressure forces ink in very rapidly. Here is a closer view of the section area, showing how the feed pushes the plunger aside:
In the earliest version of Sheaffer’s Vacuum-Fil, the cap-nut was not pointed, and there was no mechanism to push the plunger aside. (The feed had the usual flat back end.) Although that version did work, the passage for ink could be seriously restricted by the piston-head gasket, which was not under compression at rest and therefore filled, or very nearly filled, the space in which it sat. Sheaffer’s addition of the center feed solved this problem, and the system was very reliable.
A later version of the system, commonly seen in “TRIUMPH” point Vacuum-Fil pens from the 1940s, employs a modified version of an otherwise standard feed, shown here:
In this version, one side of the feed’s back end extends into the barrel far enough to engage the head of the plunger. This design, while it works just as well as the center-feed version, is less satisfactory because it impinges quite visibly through the clear area of a Visulated section, but it is also slightly less costly to manufacture because it requires less hand fitting.
Wahl’s version of the system differed by using a small pin, inserted crosswise through the threaded portion of the section, to push the end of the plunger sideways.
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