One never knows what might be lurking on a table at a pen show. This unprepossessing black hard rubber pen caught my eye with its unusual shape and obvious quality. On closer inspection, its imprints identified it as a very early Conway Stewart, but not a model I recognized.
The screw cap has an imprint with an arrow at its top to show which way to turn it to unscrew, another typically early feature. The feed is notable, consisting of two flat fingerlike projections, with a narrow rectangular projection below. The projections are so flat they reminded me of the Wirt safety, and sure enough there is a axial post inside the cap that extends under the feed when the cap is on, making contact with the rectangular projection, which can slide back and forth. Clearly it was originally spring-loaded, and the post would push it down and seal the central hole in the feed when the cap was fully tightened.
Once I got home, I took a look at Steve Hull's Conway Stewart monograph, Fountain Pens for the Million. Sure enough, on page 15 our mystery pen appears: The Conway Pump-Action Pen. At the time the book was written no actual examples were known to the author, but the engraved illustration turns out to be an accurate depiction in all details.
Coincidentally, on the same page there begins a discussion of how Conway Stewart made no pens of their own from the company's founding up through 1909. Elsewhere it is noted that a substantial number of pens sold by Conway Stewart during their early years were American-made. Could this pen have been a Wirt product? The shutoff valve and the ventless nib certainly point in that direction.
The reciprocating valve on Wirt safeties is different, as it uses a weight rather than a spring. The flat feed is gold and one-piece, not hard rubber. Just as was the case with stylographic pens, a weight is less likely to break than a spring. Though our Conway does not appear to have seen a great deal of use, its gold spring had broken (a replacement was made from corrosion-resistant stainless steel).
Wirt's patent was issued on December 13, 1910 as US978419. Actual manufacture and sale started earlier -- judging from advertising and trade journal mentions, around the time the patent application was submitted on October 31, 1908.
The Wirt safety patent is written rather narrowly, making quite specific claims for a metallic feed and the form of the valve. No mention is made of alternative feed materials or the possibility of using a spring, so while the Wirt design is tantalizingly similar, it is also sufficiently different that the Conway's design may well be covered by another patent entirely which I have not yet been able to identify. Perhaps that patent is British, as a close examination of all the US patent databases turns up nothing.