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Burping In Eyedroppers Or Piston Fillers

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I think I understand why eyedropper-filled pens burp. At about 1/3 full, the air inside the eyedropper chamber expands and forces out some ink.


But why doesn't this occur with a piston filler?

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Usually there is a layer of insulating air between the internal and external chambers in a piston pen.


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A simple traditional ebonite feed must work hard to control the ink flow during significant temperature rises in the ink/air column in an almost empty 3 to 5 ml eye dropper barrel. The heat of the user’s hand causes the trapped air column to expand, pushing the ink contained under the air out. During winter, I must keep my Indian ebonite eye dropper half full for optimal function. I encounter increased ink flow (a wetter line) as a warning sign when my pen gets low on ink. Burping only occurs when I refuse to top up the ink.


Modern fountain pens have heavily finned feeds for buffering more ink and even piston fillers seldom have more than 1.5 to 2 ml ink capacity to control and minimize air expansion problems.


See https://www.fountainpennetwork.com/forum/topic/256177-pelikan-piston-filler-ink-capacities/ and https://www.fountainpennetwork.com/forum/topic/182350-ink-capacities/ for the ink capacities for some pens.

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I've been hearing this ink burping problem for ages, but for one who had used eyedropper and piston filler for decades I've never had this problem, even when ink level was somewhat low. I put it down to the kind of pen I had and the way I hold my pen. First of all I have a man size S hand, but actually I got a rather small palm and consequently long fingers. I tend not to grip the pen but cradle it. I suppose in this pose I never got the chance to actually heat up the pen enough to give the problem a chance. The other part being how good the feed actually feeds, that is feeding air and ink interchange.


That said I've heard enough stories about people using Pelikan and TWSBI having their pen burping ink so I guess Piston filler is not immune to that. Nor do some C/C though I doubt it had to do with the particular hand warming up the pen part.

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it does occur in older (or cheaper) piston fillers with simple feeds. Also in syringe and bulb fillers, and even, under extreme circumstances, in cartridge or converter pens. No pen can perfectly insulate the air inside whatever reservoir it uses from changes in the temperature of the barrel. The question is whether the feed has enough capacity to capture any ink that gets trapped between the expanding air in the reservoir and the nib.


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I did have this issue with my piston filling TWSBI Eco Fine untill i sent it in and they put a dryer feed unit in the pen, and i haven't had the issue since. So as others have said i think the feed plays a big role in controlling this. With wetter writing inks especcialy this was an issue for me.

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Bo Bo Olson

I've never had any problems with vintage and semi-vintage German piston pens burping. Never even read that before.

Can be wrong.... but I am not going to suddenly start worrying my cool weather German pens are going to go on strike demanding AC.

German vintage '50-70 semi-flex stubs and those in oblique give the real thing in On Demand line variation. Modern Oblique is a waste of money for a shadow of line variation. Being too lazy to Hunt for affordable vintage oblique pens, lets you 'hunt' for line variation instead of having it.

www.nibs.com/blog/nibster-writes/nibs-germany & https://www.peter-bo...cts/nib-systems,


The cheapest lessons are from those who learned expensive lessons. Ignorance is best for learning expensive lessons.



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