Well, if this is the feed you're talking about, here are the pics of one I have, along with the drawings from the patent filing.
These are "much later" feeds for the 9xxx series of nibs. I haven't found any on later 1xxx and 2xxx nibs.
And here's the blurb that accompanied the drawings:
856,881. Reservoir pens. ESTERBROOK PEN CO. April 2, 1957 [April 9, 1956], No. 10694/57. Class 146(3). A fountain pen comprises a feed-bar having an internal duct wholly within its body extending through its entire length and communicating at one end with the ink reservoir, the duct providing communicating capillary ink and air channels in juxtaposed relation of which the ink channels are located on that side of the air channel nearest the nib, the feed bar also having a transverse slot of capillary dimension underlying the nib and communicating with the capillary ink channels. As shown the feed-bar 10 is formed of extruded plastic material of circular cross-section having an internal duct of U- shaped cross-section which provides a capillary air channel (15b) and ink channels (15a) of slightly greater capillarity. The transverse slot (17) of greater capillarity than the ink channels 15a is cut in the upper part of the feed bar and intersects the ink channels to convey ink therefrom to the underside of the nib. A longitudinal capillary groove 21 is also provided on the upper surface of the feed-bar underlying the forward end of the nib and is intersected by the slot 17. Semi-annular capillary grooves 18 are cut in the underside of the feed-bar to serve as overflow chambers for any excess of ink which has been fed to the underside of the nib through the channels 15a, slot 17 and groove 21. When the pen is inverted the ink in the grooves 18 returns to the reservoir along the feed passages mentioned above. The air channel 15b is blocked in front of the slot 17 by a plug 22 of metal or plastic, air being fed to the channel 15b via the open front ends of the ink channels 15a. In a modification annular capillarygrooves extending completely round the feedbar replace the grooves 18, and the groove 21 extends backwards beyond the front end of the nib-section. A method of making the feed-bar is described wherein a blank of material extruded with the internal duct therein is held horizontally by a member which enters the air channel 15b at the front end of the blank while a notch 30 is cut in the rear end of the blank. The notch 30 is then used to key the blank in a holding fixture while the front end thereof is bevelled and rounded and the grooves 18, 21 and the slot 17 are cut. The nib and feed-bar may be assembled in a sleeve to form a removable insert which is screwed into the nib section.
#17 is a razor-thin cut into the top of the feed. Apparently, that's where the ink flows up to the nib.
I still couldn't figure out how the thing worked, even with the explanation. Maybe someone else can interpret and translate it into third-grade .... sure is a departure from the old Waterman-style fissure-feed.
Edited by Hobiwan, 25 August 2013 - 23:32.