(This page published August 21, 2019)
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Fountain pens can leak, even when they are not broken. The preceding statement is a truism, as many users over the decades have discovered to their dismay. Uncapping a pen is not at all pleasant when you are rewarded by a splash on your hands, or your clothing, of ink that has leaked into the cap. Things were once much worse than they are today, since the invention of the comb feed and its descendants, but still pens leak. Various pen makers have attempted to build pens fitted with some sort of ink shut-off to prevent leaking, some — but not all — of which have worked. This article examines some of those systems.
The earliest ink shut-off this article looks at came from the mind of Benjamin J. Soper of Hoboken, New Jersey. Soper was one of the two principals in Soper & Sievewright, makers of the keystone fountain pen, which featured the ink shut-off described here (U.S. Patent No 663,590, issued December 11, 1900). August Eberstein‘s screw cap still being a few years away, cone-cap and straight-cap closures were the order of the day on everything except retractable safety pens, but Soper saw how he could use screw threads to good advantage on a straight-cap pen.
Soper started by threading the nozzle (callout B in the drawings, the part that held the nib and feed). He added a cork seal (callout e' ) just behind the threads to prevent ink from reaching the threads and leaking therefrom. On the back of the nozzle, he fashioned a conical valve (callout H) that seated against the edge of a hole (callout a) passing through a partition (callout A' ) in the barrel to seal the pen at that point. A pin (callout l) extended laterally from the top surface of the nozzle. A cutout (callout m) in the side wall of the cap fitted over the pin. When the pen was capped, screwing the nozzle down by means of the cap closed the ink path; when uncapping the pen, unscrewing the nozzle a couple of turns opened the path.
Because of the mechanism at the front of the pen, Soper designed a threaded blind cap (callout D) for the back of the barrel to facilitate filling from that end, with the valve at the front closed. The slot (callout p) in the blind cap allowed the user to use a coin or a key to unscrew the blind cap should it become stuck due to ink in the threads.
In 1917, after threaded caps and inner caps had become commonplace, Morris W. Moore, whose 20-year-old Moore’s Non-Leakable Safety Pen was still in production, came up with an iterative improvement on Soper’s design (U.S. Patent No 1,220,875). Instead of a pin engaging with a cutout in the cap side wall, Moore designed a screw-in nib unit with a square portion forward of the threads, to engage with a square inner cap. Operation of this design was the same as with Soper’s, with the square inner cap sealing the nib area when the pen was capped. Moore included no cork or composition seal, however, and it is likely that his pen, if produced as shown in the patent, would have leaked through the threads of the nib unit. Moore’s patent drawing shows the pen fitted with a Post filler.
Genius struck in 1905, the year George Sweetser, a mechanical engineer, tinkerer, and sometime vaudeville performer whose act was rollerskating in drag, invented the original plunger filler. Sweetser’s design, granted U.S. Patent No 813,534 on February 27, 1906, was so simple that only a single drawing and less than one full page of description were required, and it even provided for an optional ink shut-off valve. The design was so sound and reliable that it remained in production for more than half a century and spawned a handful of imitations, none of which lasted as long as the original.
The filler itself is described in Filling System Histories: Take the Plunge; here we are concerned only with the ink shut-off feature. As Sweetser imagined it, the front end of the plunger (callout f in the drawing) was a valve that would seat against a restriction in the section (callout f' ) to seal the passage between the ink reservoir and the nib. Sweetser sold his patent rights to Thomas De La Rue & Co., a London, England, printer of banknotes and postage stamps. His drawing was little more than a concept sketch, and when Onoto the Pen pen emerged from the De La Rue engineering department, the design was functionally the same but had been enhanced to work well and to be manufacturable.
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To shorten the excessive length of the front portion of the pen, the “piston” (callout d) became a cup-shaped rubber gasket (yellow in the colored drawing below). It was secured to a hard rubber plunger head (blue) by a shaft nut (green) that also served the function of the valve. The shaft nut was threaded and was staked in place by a transverse hard rubber pin.
The shaft nut/valve was conical on its end, as shown below. When the plunger was closed all the way and screwed down, the nut slipped into the section bore and fitted into a matching conical depression on the back end of the feed (orange). This shut off the flow of ink to the nib, preventing leakage if the unthreaded straight cap should happen to fall off. Although there was a bore of significant size in the center of the feed, the quantity of ink retained in the feed was still relatively small.
De La Rue exported Onoto the Pen in great numbers to Japan, and the pens proved very popular. Sweetser’s ink shut-off, independent of the filling system, worked so well that Japanese manufacturers, just entering the market, borrowed the concept for their own products. It quickly became a standard feature of virtually all Japanese eyedropper-filling pens, and it is still used in such pens made today. Shown here is a cross-section of a typical Japanse eyedroppr-filler.
The valve is increased slightly in diameter so that it seats against the back of the section, and the the section’s end is made conically concave to match the shape of the valve. In most of these pens, the back end of the feed is some distance forward of the back of the section, as shown here:
In a few instances, notably in older pens from high-level manufacturers such as Pilot, the feed was lengthened, made conically concave at its back end, and set into the section so that the two parts formed a continuous cone, as shown below. The net result of this improved version was a shut-off with no space between the valve and the feed when the valve was closed, allowing only a tiny amount of ink to remain in the feed, which could easy hold it.
As good as Sweetser’s ink shut-off was, it still had a downside: it was not automatic. The user must consciously screw down the blind cap to seal the pen and unscrew it a couple of turns before writing. Surely there was a better way! David J. La France and William P. De Witt certainly thought so. Before they cranked up production for their own De Witt — La France Pen Company, they bought pens made to their design by the Samuel Ward Company. These early pens were marked SaWaCo. One of them, pictured below, featured a surprisingly ingenious approach to shutting off the ink flow automatically.
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The operation of the ink shut-off is not at all obvious from the outside, but U.S. Patent No 1,340,277 shows the internals of this pen. The patent drawing is cluttered, however, and it might be easier to understand how the system works with the aid of a photo of the pen in its disassembled state.
As implemented, the gripping section was a straight cylinder, able to slide back and forth in the front of the barrel, but with its travel limited by a transverse pin (callout 31 in the drawing) that passed through the barrel. There was a “notch” in the gripping section (callout 30), with a slanted end (callout 32). As the gripping section moved all the way forward, the pin slid along that slanted surface and eventually prevented further movement. In so doing, it also kept the gripping section firmly locked against rotation.
The rubber seal shown in the photo was just a short length cut from a sac, glued to the nipple at the back end of the gripping section and also to the slightly widened area just to the left of the flange on the sac section in the photo. This sealed the ink passage, preventing leaking and protecting the spring that was outside the rubber seal. The sac section was fixed within the barrel, resting against the sac guard, which was glued in place. The feed channels (callout 24) stopped just before reaching the back end of the feed, and there was a small cutout (callout 25) inside the bore of the gripping section that was lined up with the end of the feed. When the pen was capped, the inner cap pushed the gripping section backward until the back end of the feed stopped against the front end of the sac section, making a seal there. Since the cutout was in the gripping section, the sac section blocked ink flow, and the pen couldn’t leak. When the pen was uncapped for writing, the spring pushed the gripping section forward, away from the sac section, and ink could flow between the sac section and the feed through the cutout in the gripping section.
On May 23, 1936, Anatol N. Andrews of Los Angeles, California, applied for a patent for his ingenious automatic ink shut-off design. U.S. Patent No 2,098,528 was issued November 9, 1937.
The principle of the design was that the section would be relieved so that a broad band of some elastic material (callouts 3a in the drawing) could be placed around it. A conical recess was made in the side of the section (inside the elastic band), and the ink path ran from the reservoir (with or without a breather tube, depending on the reservoir’s design) and then through the conical recess to a tubular path leading into the feed in the same manner as a breather tube. A ball (callout 10) was placed outside the band, fitting into the recess, and held in place by a conical hole (callout 11) in the barrel. With the cap off the pen, the ball protruded slightly through the barrel wall and did not depress the band far enough to close off the ink path. Capping the pen would force the ball inward, pushing on the band until it sealed the ink path, preventing ink from flowing.
It seems like a reasonable design, but this patent is a classic example of what can happen when a design is submitted without a working model. The thing simply didn’t work. The ink path from the reservoir to the feed had no provision for capillary fissures. The pen would behave much like pens of the mid-18th century, being prone to stoppages or to throwing blots when shaken to get it started. Fissures could be applied to the inlet and outlet sides of the ink path so that ink and air could pass, but adding fissures to ensure reliable flow through the section’s conical recess would prevent the band from sealing the ink path at that point. Figure out a way around that problem, and you would still be faced with the fact that there is no reasonable way to install the ball.
First-tier manufacturers were not sitting back and ignoring the problem. On May 18, 1936, Craig R. Sheaffer filed for a patent on an automatic ink shut-off. Although the design, as presented in U.S. Patent No 2,110,558 (issued March 8, 1938) seems sound, it had possible flaws (discussed in the next paragraph). I cannot find any evidence that it ever went into production.
The implementation of this design drew on Sheaffer’s experience with center feeds, as applied to the company’s lever-fillers and Vacuum-Fil plunger filler a couple of years earlier. The feed (callout 16 in the drawings) was bored (callout 19) from its back end to a point somewhat short of the end of the section. From there forward, it was hollowed out to provide space for a slide (callout 23). See Figure 3, to the right. Hollowing the feed out in this way removed material whose presence was essential to providing a capillary path between the feed channels and the feed’s comb cuts for buffering the ink flow.
Into the bore was inserted a small-diameter center feed (callout 20) with a channel and fissures to control ink flow. The center feed extended forward, stopping just before the nib’s breather hole. The slide, called a plunger in the patent, was fitted with a soft rubber block clamped in place at the end nearest the tip of the feed. The other end of the slide (callout 27) extended outward through a cutout in the underside of the feed, with a spring pushing on it to hold the rubber block away from the end of the center feed. It is not clear how ink would be kept from escaping along the outside of the center feed and thence through the opening in the underside of the feed.
Capping the pen (Figure 4) pushed on the exposed end of the slide, forcing the slide toward the section so that the rubber block in the slide plugged the opening at the front end of the center feed, shutting off the ink flow.
Anything You Can Do, I Can Do Better
At about the same time as Craig Sheaffer was working on his ink shut-off in Sheaffer’s Fort Madison, Iowa, engineering laboratory, Albert R. Stenersen was working on the Safety Ink Shut-Off in Wahl’s Chicago, Illinois, plant. Stenersen initially applied for a patent on October 25, 1934, but he amended his application on June 24, 1937, before a patent had been issued, by adding a filing for a related patent, and on January 3, 1939, he received U.S. Patents Nos 2,142,532 and 2,142,533. Like Sheaffer’s design, Stenersen’s used a slide operated by the cap; but there the similarity ended.
Rather than mucking around in the internals of the feed, Stenersen performed his surgery from the underside, and entirely within the section. The implementation shown here was for the Wahl Personal-Point nib unit. There were other implementations, with the requisite variations, for a section without an interchangeable nib unit and for the Wahl-Oxford twist-filling pen,
but the basic architecture was the same in all. Considering the rear portion of the feed, the part that fits within the section, the back half of this portion was machined flat on the underside, and two small longitudinal grooves were cut in the front half, so that the slide (callout 48 in the drawings) could move back and forth. A small recess was made for a compression spring (callout 49). The back end of the feed was made slightly conical to fit the conical end of the slide (callout 51, see Figure 8, to the left). The slide and the spring were assembled to the feed, and together with the nib, the feed was installed in the nib housing (called the bushing in the patent) with the small tab on the slide protruding from the front of the bushing as shown to the right.
Just behind the back end of the feed, a slight space away, was a rubber seal ring (callout 43). Capping the pen caught the slide on the edge of the inner cap and pushed the slide backward until the conical part of the slide lodged in the seal ring, shutting off the ink flow.
No, You Can’t
The principle was sound, and the execution was carefully thought out. The device performed exactly as it was designed to do, but manufacturers can sometimes overstate the value of their products, and such was the case with the Safety Ink Shut-Off. Wahl’s advertising claimed that pens fitted with the Safety Ink Shut-Off could not leak into the cap as other makers’ pens did. The U.S. Federal Trade Commission found that, contrary to Wahl’s claim, when the pen was capped, ink remained in the feed, forward of the shutoff valve. That ink could — and did, under certain conditions — end up all over the inside of the cap and, from there migrate onto the user's hands. Although the shut-off device did prevent leakage from the reservoir, that was insufficient to justify the claim, and on June 27, 1939, the FTC ordered the Wahl Company to cease and desist from advertising that its pens were leakproof until such time as they really would not leak. Unable to advertise the feature anymore, Wahl voluntarily chose to withdraw the device from production before the patents had even been granted.
On May 28, 1941, engineer Georg Ptak, a resident of São Paulo, Brazil, received German Patent No 706,476 for his clever design for an ink shut-off. He assigned the patent to A. W. Faber Castell, but it is unclear whether any pens were actually built to the design.
There are of course subtleties in the design, but the principle is simple. When the pen was not capped (Figure 1), a plunger running through the center of the feed was pushed forward by a spring so that the conical back end of the plunger, which was a valve (callout 5 in the drawings), moved away from the gasket (the valve seat, callout 12), allowing ink to flow to the feed. The plunger, whose shaft was also a breather tube, was then positioned so that the passage through the breather tube was aligned with a lateral hole in the floor of the feed channels (callouts 29 and 30). When the pen was capped (Figure 2), a pin in the cap pushed against the front end of the plunger, forcing it backward until the valve sealed against the gasket, which would be made of rubber or some similar elastomer. This action also misaligned the breather-tube passage from the hole in the feed, preventing any ink that might flow down the breather tube from escaping via the feed. To forestall others who might work around the patent, Ptak also described a version that did not have a breather tube.
The aforementioned subtleties revolve around ensuring that the inner cap sealed against the section at the same time that the plunger valve sealed against the gasket. The lengths of the plunger, the cap, and the section — and the location of the gasket — would need to be very precisely controlled. This could be done; but a better way was to spring-load the cap’s pin as well as the plunger in the feed, so that precision was not required. The valve could seal before the inner cap did, and the spring-loaded pin would hold the plunger at the proper point while the cap was screwed down a little further. To cover all his bases, Ptak also included a version with this design.
An interesting side note to Ptak‘s invention is that, like so many other inventions, it took advantage of existing technology. In 1903, William F. Cushman, one of the principals in the American Fountain Pen Company, makers of Moore’s Non-Leakable Safety Pen, patented a cap design (U.S. Patent No 747,948) with a pin that forced the Non-Leakable Safety Pen’s nib to retract if the user failed to retract it before capping the pen.
With the advent and subsequent rise of ballpoint pens, with fountain pen use declining, the need for protection against leakage diminished, and the appearance of new designs for ink shut-offs languished — but did not cease entirely. Let’s take a look at the system designed by Dante Del Vecchio (U.S. Patent No 6,250,832, issued June 26, 2001).
What we are looking at is the patent for Del Vecchio’s “Power Filler,” a feature of several Visconti pens in current production as of this writing. The filling system is a relatively ordinary plunger filler, but with certain modifications. We are concerned here only with the ink shut-off feature, which is an integral part of the filler and in fact does not really shut off the ink supply.
In any plunger-filling pen, when the plunger is all the way down (closed), there is unavoidably a small space between the plunger head and the back of the feed unless the front end of the plunger is made as an ink shut-off. In a traditional plunger-filler, the plunger head floats in the expanded area (callout 3A in the drawing) at the end of its travel. This design allows ink to flow freely from the barrel reservoir into the space between the plunger and the feed, and thence to the feed. Del Vecchio took advantage of the small space to create a pen with two reservoirs, a “supply” reservoir (callout 10 in the drawing) and a “reserve” reservoir (callout 3). The plunger head (callout 14) is made of an elastomer, and when the plunger is all the way down, the head seals against the tapered surface of the expanded area that is closest to the nib end of the pen. This creates the separate reservoirs, preventing ink from flowing from the reserve reservoir into the supply reservoir.
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The supply reservoir holds only about 0.8 ml of ink, roughly the same amount as a short International cartridge. Depending on its size, a modern feed can buffer approximately that amount, or a little more, of ink. The principle of the ink shut-off, then, is that if the supply reservoir happens to leak, the ink will be trapped in the feed, and no more can come from the reserve reservoir. Many users make a practice of unscrewing the filler knob to write, allowing the two reservoirs to function as one, and screwing the knob back down when finished, in the same manner as with a Japanese eyedropper-filler or Sweetser’s century-old original plunger-filler.
In the extreme case, this design carries a greater risk of leakage than the Wahl Safety Ink Shut-Off did, because a good shake, such as when the pen is dropped, can dump significantly more ink into the cap. In actual use, however, that scenario does not appear to have been a problem.
In 1937, Asahi Watanabe of the Namiki Manufacturing Company, Ltd (now the Pilot Corporation), received U.S. Patent No 2,070,461 for his plunger filler design. It was in essence an eyedropper-filler with a unique plunger filling system that included an ink shut-off in which the valve seated against the back of the section as in contemporaneous Japanese eyedropper-fillers. (The back of the feed was cut out conically, but it did not extend far enough back to provide a seat for the valve.)
Stepping forward about 60 years, we find Pilot engineers improving on Watanabe’s design. On May 22, 2000, Higano Masahide filed for a patent on a filler design. On November 27, 2001, he received Japanese Patent No JP2001328390 for the design that would become, with modifications that Masahide patented shortly thereafter, the internals of the Pilot Custom 823.
Masahide’s design is a further modification of Asahi Watanabe’s 1937 version, adapted to modern materials and manufacturing techniques. The valve on the front of the plunger (callout 25 in the drawing) is enlarged somewhat, and it seats on the conical back face (callout 24) of the section. The larger contact surface of the valve and the section‘s back face provides more area to make a reliable seal. As with Dante Del Vecchio’s design, there is a significant space, with slightly less capacity, between the valve and the feed; thus, the Pilot Custom 823 is also a dual-reservoir pen.
Thus ends our excursion into ink shut-off systems, at least for the time being. In the final analysis, these designs attempted to prevent catastrophic ink leaking, and some came closer than others; but nothing would, or could, prevent the ink already contained in the feed from leaking into the cap. And in the end, perhaps one of the most maligned fountain pen features in history wasn’t really as bad as it has been made out to be.
“In the Matter of The Wahl Company,” Docket 3836. Federal Trade Commission Decisions: Findings, Orders, and Stipulations June 1, 1939, to November 30, 1939, vol. 29, United States Government Printing Office, 1940, pp. 1228–1236. 
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.
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