I hadn’t given breather tubes a second thought until I unexpectedly ran into one in a 1951 Park Parkette. I got to thinking “what are breather tubes and why are they only in some pens?”
What is a breather tube you ask? Welp, it is added to a filling system whose mechanism will not completely fill the ink reservoir with one cycle of compression and vacuum.
The breather tube is a thin tube inserted into a hole in the back end of the feed and extends into the ink reservoir; it permits complete filling in pens that require multiple operations of the filling mechanism.
They also control the airflow within the barrel, thus immediately balancing the pressure of the air inside the ink reservoir with that of the external air, because the breather tube provides a way for air to transition between inside and outside, thus reducing or eliminating the tendency of leakage at high altitudes, sometimes!
What? How does it work?
When a filler mechanism is engaged, it pushes air out of the reservoir up the ink channel in the feed and out through the breather hole and slit in the nib. The nib of the pen is submerged in ink, as the compression stage ends, a vacuum is created and the evacuated air is replaced with the ink drawn up through the same channel in the feed.
Breather tubes require modification to the feed. A hole is drilled into the reservoir end of the feed, in to which the breather tube is inserted. Perpendicular, a “blowhole” is added via the ink channel or the dorsal side of the feed connecting with the breather tube hole.
A breather tube (26), effectively extends the ink channel deep into the reservoir. Thus, when the filler mechanism is engaged, the air is forced out through the tube and the “blowhole” in the feed (16). The vacuum draws ink up the ink channel into the blowhole. As the blowhole is attached to the breather tube, the distance ink travels is farther so a better vacuum is created. As ink exits the breather tube it fills the reservoir while maintaining a vacuum. Once the ink level in the reservoir reaches the end of the breather tube (A), the vacuum is equalized and the pen is “full.”
This sounds great – right, well it does come with a significant aggravation. The breather tube makes it difficult to completely empty the pen thus cleaning the reservoir is problematic.
Not all breather tubes address the issue of leakage and excess ink flow associated with high altitudes or air travel. The Parker patent 2,400,768 claims to address this issue. Breather tubes extending to the rear of the ink reservoir are prone to leakage caused by air pressure differential. The aft opening of these excessively long tubes is submerged in ink until the reservoir is almost empty – when carried nib up. The pressure differential associated with altitude changes causes the higher pressure in the reservoir to force ink out through the breather tube. Who knew patent applications could be interesting to read?
Contemporary Pens with Breather Tubes
Basically, any pen with a fixed squeeze filler, which is pretty uncommon, will use a breather tube, such as many of the Hero, the Bahadur, and the Dux models.