General Technical Question

[Nihontochicken]

I have a general technical question (hopefully not too ignorant). :blink: I read on another thread something about pulling out the original filler system and just filling the barrel with ink, using maybe a bit of grease on the threads to seal the barrel well. It would seem to me that as the pen was used, and ink drained from the necessarily unvented barrel, a vacuum would begin to form, limiting and finally stopping the ink flow to the nib. Is there perhaps enough air diffusion through the nib to equalize the pressure and allow continued use? If so, and an air bubble forms in the barrel in place of the used ink, then what happens when the partially filled pen is worn on a jet flight, as the ambient air pressure drops, and the air bubble in the barrel tries to push excessive ink out the nib? Are modern ink cartridges made of air permeable plastic in order to equalize the pressure?

[wdyasq]

I have a general technical question (hopefully not too ignorant).  :blink:  I read on another thread something about pulling out the original filler system and just filling the barrel with ink, using maybe a bit of grease on the threads to seal the barrel well.  It would seem to me that as the pen was used, and ink drained from the necessarily unvented barrel, a vacuum would begin to form, limiting and finally stopping the ink flow to the nib.  Is there perhaps enough air diffusion through the nib to equalize the pressure and allow continued use?  If so, and an air bubble forms in the barrel in place of the used ink, then what happens when the partially filled pen is worn on a jet flight, as the ambient air pressure drops, and the air bubble in the barrel tries to push excessive ink out the nib?  Are modern ink cartridges made of air permeable plastic in order to equalize the pressure? 

Ignorance can be cured. STUPID is foerver.

 

Yes, pens do allow air back in. It should be in a controlled maner.

 

What happens when the pen goes to altitude? If the conditions are just so, you buy a new shirt.

 

Air equalization in cartridge and cartridge converters are similar to eye-droppers. A small amount of air bleds back from the nib.

 

Ron

[Gerry]

Great questions Nihonto...

 

I'll try to answer them for you - but I'm certain that there'll be corrections from the peanut gallery...

 

Actually, the problem of getting air into the body of the pen is siilar in all other types of filler mechanism's, from sac fillers through cartridges and piston fillers. The air to replace the ink that has flowed out must travel up the feed next to the nib, to the ink chamber - wherever it is. Some pens have a filler tube for this, others have different channels cut into the feed, but all have to expect that the air slowly makes its way back to the chamber. Too fast a feed of air, and gravity will pull the ink down in a blob, too slow, and the nib starves, and writes dry. A sac is only a little different in that the flex of the sac allows some delivery of ink without air transfer back, but the resilience of the sac soon overcomes the vacuum and it also needs air.

 

Modern ink cartridges are somewhat permeable, but not enough to deal with air pressure. They are permeable enough that over years, the ink within can evaporate, leaving an empty (unopened) cartridge.

 

The aircraft problem does get lots of debate. Remember though, that all modern aircraft are pressurized, so the effective altitude change is never the real barometric altitude you would see at say 30,000 feet. I don't remember where they are normally set - but it has to be considerably less than 12,000 feet, normally thought of as where you need oxygen to assist in breathing (not enough air pressure to efficiently allow the transfer of oxygen from that rarefied air pressure through the lungs into the blood). So a pressurized aircraft would have to be pressurized to an altitude less than that. If I had to guess, it would be 8,000 or so, perhaps less.

 

If the pen is carried tip up, and the feed and nib aren't soaking wet, then provided the air channels in the feed are free, the slow change in air pressure should be accommodated with a small amount of air escaping through the channels into the atmosphere. This shouldn't precipitate a gusher in most pens.

 

HTH,

 

Gerry

[Michael Wright]

Controlling the air in the ink supply seems to be the heart (or guts, if you prefer) of FP design.

 

A technical description (with maths I can't follow, but that doesn't mean much) is in Geoff Roe, _Writing Instruments: A technical history and how they work_ 1996: ISBN 0 9529867 0 1. I got my copy from Pendemonium. It's fascinating, though he tends to regard the BP as the high point in writing technology.

 

Best

 

Michael

[Gerry]

You might look up this patent (Antonios posted it to the history forum under Waterman Patents) for info on feed design.

 

Feed Patent

 

The Air and Ink channels are clearly shown (#28 & 29)

 

Gerry

[Johnny Appleseed]

The question gets to the heart of Fountan pen design, and in fact fountain pens didn't take off until Lawrence E. Waterman and Frank Wirt found different solutions to the problem in the 1880s. Up until then it was just as you describe - a vacuum would develop in the ink chamber, a bubble would get drawn up the feed tube, and a big blob of ink would spill out the nib.

 

Richard Binder has a good overview of the problem and the development of the fountain pen feed in this article: Richard Binder - Feeds: Revolution, Evolution, and Devolution

 

Only one comment about Richard's article - and it is a minor qubble - is that he repeats the old Waterman Ink-blot story, which is considered a myth developed by the Waterman marketing people long after the death of it's founder. For more on the ink-blot story - David Nishimura - Waterman’s Ink Blot: More on the Birth of a Myth

 

John

[Nihontochicken]

Thank you all for your help. The Binder article was particularly enlightening. So, given that the ink volume need not be vented or otherwise pressure equalized except through a properly designed and fabricated nib, why aren't eye dropper supply pens more popular? Seems they aren't any more messy to fill than all the other systems, Sheaffer Snorkel excepted, and they must hold a whale of a lot more ink, with no volume "wasted" on the fill mechanism.

[Johnny Appleseed]

Well, EDs are having a small come-back in popularity - especially note all of those Dani-Trio ED pens, as well as Wality, Recife, etc. and ED conversion of cartridge pens.

 

However, there are downsides to EDs.

 

First, they are messy to fill - you have to use an eyedropper to get the ink into that little barrel, while holding the barrel upright - and be sure not to drop anything while you are doing it. Oh, and don't loose the eyedropper. Much easier to pull the lever (or push the button, twist the nob, etc), stick the nib in the bottle, release and go.

 

Second, because they store ink in the barrel, the heat of your hands (or through your shirt, or from a hot day) can cause the air in the barrel to expand, forcing ink out. Sacks offer some insulation that generally prevents this, and later pens that stored ink in the barrell (vacumatics, etc) often had breather tubes to allow air to vent. Not so with EDs.

 

John

Edited July 27, 2006 by Johnny Appleseed