Why doesn't the ink in a pen refill flow back if I hold it inverted?

[Benjamin_harsh]

Problem Statement: Why does the ink in refill won't flow back if I hold it inversely?

Why does the ink in refill won't flow back if I hold it inversely? What stopping it?

 

[BvU]

https://en.wikipedia.org/wiki/Capillary_action

But high viscosity is a big factor too

 

[Wrichik Basu]

Here is one good answer posted in Quora:
https://www.quora.com/Mechanical-En...ube-in-a-ballpoint-pen/answer/Raj-Sharma-1163

 

[sophiecentaur]

Problem Statement: Why does the ink in refill won't flow back if I hold it inversely?

Why does the ink in refill won't flow back if I hold it inversely? What stopping it?

My experience is that a ball point pen, left upright with the ball at the top will eventually leave the ball dry an it will no longer work. The cheap ones will not write many words upside down.
Papermate _TM pens have a pump arrangement that keeps pressing on a very thick wax / grease plug so that the ink reservoir gets smaller and avoids air getting in. They write upside down for ever.

 

[anorlunda]

In the 50s and 60s, the ink did run out of ball point pens. Unless you used one of those super nerdy pocket protectors, you would ruin several shirts per year.

Then at some point, they seemed to perfect it, and leakage from modern pens is less common. However, curiosity made me recheck amazon just now. Yes indeed, pocket protectors are still sold.