Redesign Of The Eyedropper System

[P.A.R.]

It seems like one of the main quibbles about eyedropper pens is their potential to burp ink once the ink level is low enough that the air bubble trapped inside can expand due to temperature change.

 

I spent about fifteen minutes drafting this:

http://sphotos-a.xx.fbcdn.net/hphotos-prn1/61931_10200175139325844_1457209927_n.jpg

 

This is focusing primarily on the filling system, so I didn't bother (or want to attempt) drafting a nib, feed, and cap. Another time, perhaps.

 

Anyway, here's a section view to give you a better idea:

http://sphotos-a.xx.fbcdn.net/hphotos-snc6/217925_10200175139485848_597768115_n.jpg

 

Essentially, there would be a barrel that holds ink within the outer barrel of the pen. The air pocket might reduce the tendency for the air inside the inner barrel to heat up. Even though this reduces the size of the capacity from a traditional eyedropper, it would still hold a pretty decent amount and have the advantage of being virtually maintenance free (having no moving parts.)

 

Thoughts?

[ddustinn]

Seems like a good idea, but I'm not sure how practical it would be to manufacture.

[P.A.R.]

If you made the inner barrel like long cartridge that is plugged by the back of the feed, it might not be too difficult to manufacture. The outer barrel would more or less serve as a holder.

[Lloyd]

I find that, as long as the feed is sufficient, I don't get any burping. For example, my Edisons have never burped on me.

[Dillo]

Hi,

 

While that is a nice idea, I prefer a system where the barrel is compartmentalized. There is a small reservoir that is connected directly to the nib and a large reservoir 3-4 ml behind it that feeds ink into the small reservoir 0.7-1 ml when a valve is open. This reduces the effective reservoir size to a size that is more manageable for the feed.

 

I don't know if there are many eyedroppers actually made this way though.

 

Dillon

[Brian C]

Why not just make the barrel thicker and reduce the open area? I've always thought that a custom pen with a really thick barrel, just enough room inside to mimic the diameter of a converer would be cool. Sturdy feeling also.

[Scribblesoften]

PAR some input on your idea. If I understand correctly, you would put the ink the the outer compartment in the picture, the blue part. This would allow the center of the pen to act as a heat sump. Yes. Why not put the air or vacuum in the outer compartment. The would allow the air to insulate the inner compartment. If you used vacuum, you would, in effect, have a small thermos. I also might be concerned with the practicability of filling just the outer compartment and not the inner. These comments are not offered in the spirit of negativity. I always want to see new concepts.

[bbbiswas]

I find that, as long as the feed is sufficient, I don't get any burping. For example, my Edisons have never burped on me.

 

I agree. My Edison Herald Grrande too has never burped. My Ratnamsons Supreme, Newtonpens Big Burly and Big Black Ebonite and Bexley Imperial and Jitterbug have never burped. All these are based on traditional and simple barrel.

But my Vishal Gajendra has burping problem in spite of the thick ebonite being a good thermal insulator. I think the problem comes because of improper balance between feeding and breathing. I think Edison, Bexley and Newtonpens know the trick.

[P.A.R.]

Why not just make the barrel thicker and reduce the open area? I've always thought that a custom pen with a really thick barrel, just enough room inside to mimic the diameter of a converer would be cool. Sturdy feeling also.

 

This is may be true, but not everyone might like the increased size/weight necessary for that design. I probably would

 

 

PAR some input on your idea. If I understand correctly, you would put the ink the the outer compartment in the picture, the blue part. This would allow the center of the pen to act as a heat sump. Yes. Why not put the air or vacuum in the outer compartment. The would allow the air to insulate the inner compartment. If you used vacuum, you would, in effect, have a small thermos. I also might be concerned with the practicability of filling just the outer compartment and not the inner. These comments are not offered in the spirit of negativity. I always want to see new concepts.

 

I meant to say that the green section would be filled with ink, the red would house the nib and feed, and the blue would act as insulation, as you suggest.

 

Hi,

 

While that is a nice idea, I prefer a system where the barrel is compartmentalized. There is a small reservoir that is connected directly to the nib and a large reservoir 3-4 ml behind it that feeds ink into the small reservoir 0.7-1 ml when a valve is open. This reduces the effective reservoir size to a size that is more manageable for the feed.

 

I don't know if there are many eyedroppers actually made this way though.

 

Dillon

 

Would this be accomplished by making the red section a bit longer?

 

I shall attempt to redraft today.

[bgray]

Well, before you design this based on heat, you should realize that an eyedropper burping really has nothing to do with heat, unless you are talking about a real extreme temperature change. Certainly not when going from room temperature to being warmed up in your hand.

 

I had a good conversation with Richard Binder about this a while back, and this is what we concluded....

 

It has to do with a very large capacity and the dynamics of a gas.

 

Once the ink levels start to get low, volume of air has a big effect. It's simply the elasticity of a gas versus a liquid. A pen with a smaller capacity can stave off the burping problem better, given the same feed design. Early lever fillers, with simple feeds lacking buffering capacity, had more of a problem than modern ones.

 

The feed wants a column of ink above it in order to maintain flow control. When that column isn't present at the end of a fill, burping can happen due to a huge presence is a gas, which is "elastic" in both directions....compression and vacuum.

Edited December 2, 2012 by bgray

[P.A.R.]

Well, before you design this based on heat, you should realize that an eyedropper burping really has nothing to do with heat, unless you are talking about a real extreme temperature change. Certainly not when going from room temperature to being warmed up in your hand.

 

I had a good conversation with Richard Binder about this a while back, and this is what we concluded....

 

It has to do with a very large capacity and the dynamics of a gas.

 

Once the ink levels start to get low, volume of air has a big effect. It's simply the elasticity of a gas versus a liquid. A pen with a smaller capacity can stave off the burping problem better, given the same feed design. Early lever fillers, with simple feeds lacking buffering capacity, had more of a problem than modern ones.

 

The feed wants a column of ink above it in order to maintain flow control. When that column isn't present at the end of a fill, burping can happen due to a huge presence is a gas, which is "elastic" in both directions....compression and vacuum.

 

So there would be increased air pressure on the inside of the reservoir and lower pressure outside the pen, causing the ink to move out of the feed? What causes that difference in pressure, however?

 

Well, before I read that I had already drafted a second design using a different program and slightly different approach...

 

http://sphotos-b.xx.fbcdn.net/hphotos-ash4/1330_10200179224707976_486301100_n.jpg

 

http://sphotos-b.xx.fbcdn.net/hphotos-snc7/320685_10200179224747977_531095814_n.jpg

 

If it's not based on heat change, would the narrowest inner barrel shown (second from the left on the bottom row of components) help prevent burping?

Edited December 3, 2012 by P.A.R.

[bgray]

The problem is just inherent to large ink reservoirs.

 

Do some "Mythbusting". Put a pen in the fridge so it cools down thoroughly. Then fill it about halfway. Then put it back in the fridge so the ink will also cool.

 

Then take it out and let it warm up. Probably angle the nib downwards about 10-15 degrees to make sure that the air is trapped away from the section. Then whatever happens regarding temperature will for sure be a result of the air pocket expanding.

 

This an extreme situation, and would just prove the concept that heat can indeed make a pen burp. I'm guessing that going from 30-some degrees to 70-some degrees will indeed effect the air pocket enough to make the pen burp.

 

The real-life test of this would be to do the same thing, but go from 70 degrees up to about 98 degrees. This would mimic a pen being warmed in someone's hand. I'd be willing to bet that with a modern feed, you wont have any issues. And remember that getting the entire pen to 98 degrees is probably overkill. When someone has been holding a pen in their hand for a while, I'd be willing to bet that the internal temperature of the pen never actually reaches 98 degrees.

 

Just make sure that the temperature change is not fast, so you are mimicking a real situation. Modern feeds are pretty effective at containing burps, and also properly exchanging air for ink as needed.

 

//So there would be increased air pressure on the inside of the reservoir and lower pressure outside the pen, causing the ink to move out of the feed? What causes that difference in pressure, however?//

 

Just a simple jostle could cause this. The act of writing is enough that the ink will move around inside. With the huge volume of air being "elastic" or compressible, you can reach a point where the ink jostling has enough effect on the air that the vacuum is lost at the very end of the fill. Then it burps the very last bit of ink.

 

But remember that this is not a huge problem, in my opinion. I can't remember anyone ever telling me that Edison eyedroppers are burping. It doesn't happen that often. The bottom line, when you are at about 1/4 capacity, fill the pen.

Edited December 3, 2012 by bgray

[mhosea]

Hmmm. What Richard said makes sense. I was just observing the ink pooling in the Lucite feed of my ED-converted Parker VS after it had heated up in my hand. This was easily corrected by pointing the pen up and unscrewing the section, then putting it back, but if I hadn't noticed, it might have burped. It's a good feed, IMO, but it doesn't have the excess capacity of my modern feeds. Since I don't need the 3ml or so ink capacity that it has, I'm thinking now that it might be best to reduce its capacity. Now I just need to figure out how to do that in a way that is reversible and doesn't make it harder to clean.

[tmenyc]

I find that, as long as the feed is sufficient, I don't get any burping. For example, my Edisons have never burped on me.

And also in agreement with Brian, I have converted my little Kaweco sport classics to ED and never have a burp, no matter how little ink is in the barrel; good to the last drop.

Tim

[Conker]

Let's put a couple of numbers into this from a physicist's perspective.

Assume a 2mL capacity barrel with 1mL of ink in it and let's warm this up from 60F to 80F. The Gas Laws tell you that this will cause a 4% increase in the air volume. (Ink is incompressible compared to air). Without a feed in the design, 4% of 1mL will cause quite a big ink blob as it comes out.

As Brian and others point out, today's feeds are able to adequately buffer these sort of ink volume ranges.

If you follow Brian's example of stepping out of a meat freezer at -20F into a hot area at 90F then the Gas Law will tell you what ink volume your feed design must buffer for this temperature swing. Anyway, there is always a long time constant involved in real life for these temperature swings to additionally buffer ink movement.

[Joe in Seattle]

I may be the only person for whom an Edison as ED burps. YMMV

 

I'm content to use it as C/C as I like to change ink colours frequently.

[lovemy51]

this is why i also stay away from ED's -and i own a couple, mind you. my Airmail 444 is my fav.

[bgray]

I may be the only person for whom an Edison as ED burps. YMMV

 

I'm content to use it as C/C as I like to change ink colours frequently.

 

Probably not the only one! Remember that most people who convert to ED understand the burp risk. So maybe no one bothers to report this back to me, and it's a little more common than what I realize.

[Lloyd]

I wonder if the fact that my EDs have F-XXF nibs that there is less flow potential for burping.

[mhosea]

Since I don't need the 3ml or so ink capacity that it has, I'm thinking now that it might be best to reduce its capacity. Now I just need to figure out how to do that in a way that is reversible and doesn't make it harder to clean.

 

Last night I remembered I had some small-diameter, thick-walled polypropylene tubing that I had bought for a different project. It was small enough in diameter to fit in the barrel, so I cut it to length and also cut v's in the ends so that the ink could always flow around either end. When the barrel was full of water you could turn it upside down without dumping it, so I roughed it up a bit and cut a slit along its length. Don't know if that helped. I just thought I'd make it a little feed-like. Ultimately it reduced capacity from 3ml to 2ml. I filled the pen with 1ml of ink. The feed often looks dryer now (it's Lucite, so I can easily see how saturated it is), but it writes the same. I haven't been able to make it want to burp yet, but it remains to be seen if the ink can be used up effectively or whether it will stop feeding before that because the ink gets hung up somewhere.