I had several requests for photos of the filling system so here they are:
The following is from Richard Binder's website:
How It Works: As you can see, the spring tries to force the sac protector (and the rest of the “cartridge”) forward, extending the Snorkel tube. The blind cap and Touchdown tube prevent this.
Next, the user extends the Touchdown tube. A partial vacuum builds up, but the sac protector keeps the sac from distending. As the Touchdown tube reaches the end of its outward travel, air enters the barrel through the hole near the threaded end of the tube.
The user immerses the tip of the Snorkel tube in the ink and then presses quickly down on the blind cap. This restores the Touchdown tube to its rest position, compressing air as the tube travels. The compressed air squeezes the sac. The following illustration shows the pen at the instant just before the pressure is released by the dimpled groove when the Touchdown tube reaches the end of its travel; note the squeezed sac.
When the Touchdown tube reaches the end of its travel, pressure is released. As the sac resumes its normal shape, external air pressure forces ink into the sac.
Last, the user screws down the blind cap again. The threads on the Touchdown tube engage the threads on the sac protector, drawing the “cartridge” backward against the spring. The Snorkel tube disappears into the section, and the user returns to writing.
Is It Working Right? To test a Snorkel, fill it with water. Aim the filled pen in some harmless direction. Extend the Touchdown tube and then depress it quickly. If all the seals are working right, the pen will shoot a stream of water that can travel about six feet (2 m).