Most noticeable is the lack of fins of the overflow slits. To prevent overflow, the fountain pen has a hand operated shut off valve.
The feed is completely machined from Ebonite as you can clearly see in photo 3. In the following, I address the areas marked with red letters in photo 1.
At A is the contact with the nib and there three capillaries are ending. A detailed photo is following. The capillaries arrived there at the bottom of the air-canal, which is at the top of the feed.
In this case, the breather-hole serves its intended purpose. Many feeds have their air-canal at the bottom, for reasons I will talk about then, and their nibs still have this hole. About another purpose I have written in the chapter Nib Manufacturing.
B shows one of the hollowed out sections, which most probably are intended to absorb surplus ink. I wonder because there is no actual capillary to assist emptying these chambers.
At C is a chamfered away section, is allows the air to penetrate from the air-canal into the ink reservoir.
The stub at D sticks into the hole at the end of the section, which opens into the ink reservoir. It contains two ink capillaries, it is slightly flattened on top, and the larger flattening at the side runs out at C.
Photo 2 shows the front end at A, photo 1. At A1 you see the arrival of the two ink capillaries. At A2 is a narrow cut, which marks the centre of the feed, used to align the nib with the feed. At A3 is a third capillary, which runs along the bottom edge of the air-canal, starting at C, photo 1. This capillary is used to facilitate emptying of the air-canal of surplus ink. Any ink in the air-canal prevents air entering into the reservoir. This method is generally used to control ink flow.
It is plausible to assume that when the air-canal is somewhat filled, and all three capillaries supply ink to the nib, the writing will be wetter.
A4 shows the hollowed out section. With the green line, I marked the length of contact between the ink supplying capillaries and the nib.
Photo 2 shows details of the rear end. D1 shows the two ink capillaries and the flattened top of the stub. I am not sure what this is for; however, I find the capillaries very shallow. The cross section of the capillaries determines the amount of ink transported.
D3 shows the start of the third capillary, the air-canal drainage capillary. In German, this would be all one word. Don’t you love it? At D2 is the larger flat section of the stub and you can see how it runs out into the curved section at C, photo 1. Here is the trapdoor, the valve, which controls the air inflow to and the ink outflow from the reservoir, subsequently.
The photos have been generously supplied by Zollinger (username), a member of penexchange.de (… you can select the English version).
sketch 1 may look a bit daunting, it will make sense in a minute. The letters and number relate to the photos from above. G is the grip section. F is the outer diameter of the feed.
C1 is the cutaway part for the air to enter into the reservoir. C2 is the bit of C1 which goes through the hole in the section.
D is the stub that reaches into the hole in the section. D1 are the two ink capillaries. D2 is the flat part of the stub for the air to enter into the reservoir. D3 is the capillary at the corner of the air-canal.
And finally, X is the width of the air-canal and Z its depth. That was not too bad?
How it works
When the ink runs into the hole, it arrives at the part of the stub with the two ink capillaries D1 and gets sucked into them. The air-canal opening C2 is too big and a meniscus forms, preventing the ink to enter. It would be good if you could have open diagram 4 on page Application to the Feed.
As the ink gets drained out from the reservoir the vacuum in there increases and fights against the capillary force in the ink capillaries. This causes the meniscus at C2 to break, and a small bubble of air enters into the reservoir and reduces the vacuum. Ink can flow again.
If for whatever reasons (see Temperature and Air-pressure) the pressure in the reservoir increases and surplus ink is pushed into the feed it will be stored in the air-canal. When ink is needed for writing (or dropping) the ink in the air-canal is used first, and the capillary at D3 helps to empty the air-canal.
That’s what happens at the rear end. For the front end, I have to draw another sketch, for which I need to scout for more information.
If some information is missing, let me know. I am learning as I go.