(This page revised May 25, 2022)
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This article first appeared in the October 2011 issue of Pen World Magazine.
The quest for fast and efficient fountain pen filling systems occupied many a brain back in the primordial past of a century ago. In the decade centered on the year 1900, most pen owners still filled their pens with eyedroppers. The only viable self-filling pen on the market was Conklin’s Crescent-Filler. And then, in 1905, genius surfaced.
In that year, a London-born mechanical engineer, tinkerer and sometime vaudeville performer named George Sweetser approached Thomas De La Rue & Company, Limited, with an offer to sell the rights to a plunger-operated self-filler for which he had recently applied for a patent. De La Rue, which had made its name as a high-quality printer of banknotes and postage stamps, saw the possibilities and made the investment, and the Onoto brand was born. De La Rue chose the Onoto name for its euphony, and because it wasn’t a word and so wouldn’t need translation into other languages; and the company marketed its first successful pen as Onoto the Pen.
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During the next half century, other types of fountain pens appeared under the Onoto name, but Sweetser’s plunger filler reigned supreme as the mainstay of De La Rue’s product line. Not only did it fill simply and easily, with one quick downstroke of the plunger, but it also delivered a forcible flushing action as the plunger went down. De La Rue marketed it all over the world and secured patents in various countries to protect it. In the United States, it received Patent No 813,534, issued in Sweetser’s name on February 27, 1906. The basic design was so sound that while other parts of the pen were improved over the years, the plunger system remained essentially unchanged.
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How does it work? Refer to the cutaway drawing below.
The entire barrel serves as the ink reservoir; cork packing forms an airtight seal where the shaft passes out through the back end.
As the plunger is pulled out, the plunger gasket (yellow) slides easily along the inside of the barrel. Any air or ink that is already in the barrel escapes past the gasket toward the nib end of the pen. But when the plunger is pushed down, the gasket presses against the barrel wall to form a good seal, and a partial vacuum builds behind the plunger head. Just before the plunger reaches the end of its travel (the position shown here), the gasket passes into a space where the barrel is larger inside, and outside air pressure forces ink past the plunger head into the barrel.
The shaft nut (green) is conical on its end. When the plunger is closed all the way and screwed down, the nut fits into a matching conical depression on the back end of the feed (orange). This shuts off the flow of ink to the nib, preventing leakage if the cap should happen to fall off.
Patent protection does not last forever. Sooner or later, if an invention is good enough, competition will rear its head. Onoto’s competition showed up in the mid-1930s, in pens made by several American companies.
Sheaffer’s initial version of the plunger filler was based on a design by Henry H. Polk (U.S. Patent No 1,926,405). Polk’s design did away with the ink shut-off feature. With a screw cap — as opposed to the Onoto’s slip cap — there was no need for an ink shut-off to keep the pen from leaking in the user’s pocket.
Polk improved the design of the plunger head by replacing Sweetser’s molded rubber cup with a simple flat gasket that was less costly and more straightforward to assemble into the plunger. To provide a reliable seal, he designed the plunger head so that the gasket would flop back and forth, as shown in the patent drawings below.
As the plunger is pulled up, the gasket flops away from the direction of travel, allowing air or ink to escape past it. When the plunger is pushed down, the gasket flops the other way. Polk put a conical disk behind the gasket to keep it from flopping so freely when going down, and this restriction forced the gasket to seal tightly against the barrel and create a good vacuum.
But Polk’s original design didn’t work out as hoped, and Sheaffer never produced it. Instead, the company put its energy into an improved version (U.S. Patent No 1,983,682, by Walter A. Sheaffer). Polk had designed four cut-out channels spaced around the barrel wall (callout 12 in the patent drawing), through which air and ink would flow when the pen was being filled or in use, but these channels were insufficient. Sheaffer’s modification opened up the entire circumference of the barrel, as in Sweetser’s original design. The enhancement worked.
First marketed under Sheaffer’s WASP and VACUUM-FIL sub-brands, possibly to avoid damaging the reputation of the company’s own branded pens should the system not work as expected, the pens did well in the market.
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One enhancement remained for Sheaffer’s system, however. For even better ink flow, the company implemented an extension to the back of the feed, designed to push the plunger head sideways as the operating knob was screwed down after filling (U.S. Patent No 2,158,615, by Howard S. Wright). The thinking was that the enlarged opening created thereby would provide better flow than an opening half as wide, even though the latter extended all the way around the head gasket, and Wright was right. About a year after their introduction, plunger-filling pens began appearing in Sheaffer’s Balance series.
Offered at the same prices as Sheaffer’s lever fillers, the VACUUM-FIL models became very popular. During World War II, when rubber was needed for vehicle tires and thus was on America’s list of critical war resources, Sheaffer ceased lever-filler production in favor of the plunger system, which used much less rubber.
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In about 1935, coinciding with a styling change on its superb Doric pen, Wahl leaped into the fray with its own plunger filler, called the One-Shot vacuum filler. Designed by Albert H. Stenersen (U.S. Patent No 2,142,531), this version also used a flat gasket, with several small holes punched in it and with corresponding slots cut into the nut that held it to the shaft. This arrangement allowed ink and air to flow forward more freely on the upstroke, resulting in easier action. The disk behind the gasket was flat, so that when the gasket lay against it on the downstroke the holes were sealed.
Like Wright, Stenersen used a device to push the plunger head sideways, in the form of a short crosswise rod inserted through holes drilled in the threaded portion of the section. Placed off center, the rod worked just as well as Sheaffer’s feed extension, and the restyled Airliner Dorics were successful in both lever-filled and plunger-filled versions.
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Conklin’s Nozac, introduced in 1931, was the first successful American piston-filling fountain pen. But it was costly to manufacture. Apparently, Conklin went looking for a cheaper alternative that wasn’t a lever filler, and the answer was a plunger filler. But there are only so many changes that can be made to a given concept, and Conklin’s plunger filler (U.S. Patent No 2,040,999), by Lloyd A. Kelley) was really the same as Sweetser’s original version in all significant respects, including its use of a molded rubber cup on the plunger head — except that Kelley omitted the ink shut-off feature. The Nozac Q.F. (Quick Filling) was a good pen, but it did not sell well, and today it is relatively rare.
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In Japan, the Namiki Manufacturing Company introduced its own Pilot plunger filler. Like De La Rue before it, Namiki secured patents in several countries; U.S. Patent No 2,070,461 was issued in 1937. In his design, Asahi Watanabe addressed some of the deficiencies of the Western versions. His plunger gasket was thicker and less flexible; and to provide a more positive seal against the barrel wall, it wiped against the wall with a cylindrical surface instead of merely an edge. Think of a hockey puck, but flexible enough that it can seal against the inside surface of a tight-fitting tube.
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Watanabe’s thicker gasket was not flexible enough to flop back and forth as Polk’s and Stenerson’s did. Instead, Watanabe made the hole (callout 4a in the patent drawings below) in the center of the gasket (callout 4) larger than the plunger shaft. As shown in the patent drawings, air or ink could pass through the gap between the gasket and the shaft, and the gasket could move along the shaft for a very short distance between two stop plates. The front stop plate had a crosswise channel (callout 6) machined in the surface against which the gasket rested, so that air or ink could pass freely on the upstroke; but the back stop plate had a plain flat surface that would seal the hole in the gasket on the downstroke. The result was a very positive action that produced a stronger vacuum than in Western versions.
All of these plunger fillers were discontinued before 1950. Sheaffer’s version was the last to go, eclipsed by the Touchdown in 1949. With the advent of the ballpoint pen, fountain pens were on the wane, and there was a long lapse before another plunger filler appeared on the market.
By the turn of the twenty-first century, devoted collector/users had reestablished the fountain pen as a useful writing instrument, and penmakers responded with new designs of all sorts — including plunger fillers.
Pilot of Japan (the Namiki company, renamed in 1938) offers the Custom 823, which is essentially similar to the original Watanabe design but with technology pops to bring it up to date. Produced in opaque colors and also as a “demonstrator,” the 823 is a popular, and very good, pen.
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Innovation continues, even in such “ancient” technologies as the fountain pen. In 2001, Visconti patented an enhanced plunger filler (U.S. Patent No 6,250,832), by Dante Del Vecchio) that featured a system with dual reservoirs. Del Vecchio’s design embodied features of several earlier designs, including Watanabe’s sliding gasket in the shape of a cup similar to Sweetser’s. With the plunger screwed completely down, the gasket seals the passage between the primary reservoir (relatively small, and adjacent to the nib) and the secondary reservoir (larger, occupying most of the barrel). Thus, to allow ink from the secondary reservoir to flow into the primary reservoir, the user unscrews the plunger a few turns. Del Vecchio’s thoroughly modern plunger has appeared in several excellent Visconti pens.
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What about all those vintage plunger fillers? Where are they? For a long time, no modern repairers understood how to repair their old-technology gaskets and shaft packings, and the pens went begging in the collector market. Today, with reliable techniques for rejuvenating them, they are enjoying a resurgence in the hands of users and specimen collectors alike.
How can you tell, when you are at a pen show, drooling over a plunger-filler on some dealer’s table, whether that pen’s filler is working? Here is a video that shows how to test these pens:
| Video © 2017 Mike Kennedy, used with permission. |
The information in this article is as accurate as possible, but you should not take it as absolutely authoritative or complete. If you have additions or corrections to this page, please consider sharing them with us to improve the accuracy of our information.
This article is also available as a chapter in The RichardsPens Guide to Fountain Pens, Volume 4, an ebook for your computer or mobile device.
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