The Dunn Pen Company set its sights high.  Based in New York City, it produced a line of high-quality pump-fillers and backed them up with an extensive advertising campaign.  As it turned out, however, the company lasted only a few years, from 1921 to declaration of bankruptcy in 1924. 

Advertised as "the pen with the red pump handle", Dunns are filled by unscrewing the end knob then pumping up and down a few times.  Ink capacity was high and the mechanism strong and reliable, with no soft rubber parts and only one easily-replaced cork seal at the end of the barrel.

Dunns were made in a wide range of sizes from ladies ringtops to giants carrying #12 nibs.  Most have translucent red casein pump handles, but opaque orange handles without the screw-down feature are also common.  Quite a few Dunns were made with transparent barrels, most of which seem to be made of celluloid rather than Bakelite.  Dunns were not flashy pens; basic black was the rule, though a handful of pens with metal overlays are known.  Dunn also made a line of injector pencils which are usually found in gold filled metal.

An unusual feature of the pen shown above is the two-piece cap.  When the top portion is unscrewed, the nib is exposed, surrounded by a protective cage.  This permits the pen to be filled without risk of striking the nib on the bottom of the inkwell or bottle while pumping.

Link to Dunns for sale