If you had an emulsion tube fitted into a "body"

What is needed to make it work and what passes through it?

And in use what does it do?

Is it a ballpoint pen with ink?

No Professor Its far more complex than that, (the entire item) and they all are custom made (in bulk)

PS In a way you are on the right track as you will see later

At least some inks are emulsion inks, which means that a ball point or fountain pen using that ink answers the question asked. Stenciling pens meet the conditions set forth in the question, too.

I know what your getting at DG
The liquid in Ballpoints is technically a gel
and the spreading is done by the ball( <--strong pointer )

You may know what I am getting at, but you missed what I said. Some inks are emulsions. Any ball point pen and any fountain pen using such ink meets the criteria set forth in your question. Stencil pens also meet the criteria. Your question has been answered. And THAT is a pointer, too.

After a little research, I'm convinced that my guess was wrong. I can't find anything about emulsions or "emulsion tubes" involving ballpoint pens. And then there's this:

quote:

What distinguishes a gel pen from a ballpoint pen is the gel ink which consists of pigment suspended in a water-based gel...By contrast, ball-point pens use a paste ink based on a solution of a dye solute in an alcohol solvent, and fountain pens use a dye solute in a water-based solvent.

Among other possible answers "Carburetor with fuel jet support structure" in cars.

....the fuel jet body is preferably provided with an O-ring upstream of the emulsion tube and inserted in the fuel passage bore in the support column. Thus, the air passage bore is reliably sealed at both upstream and downstream sides, and all the fuel in the fuel tank enters into the emulsion tube through the fuel jet to be mixed with the air, and flows into the outlet passage bore, whereby a stable flow rate of the fuel is achieved.

Ok We are after the wrong sort of emulsion tube here ...Lets try from an adjoining item (and you'll have the answer there is a "seat" where the liquid is admitted and another Tube to admit air (precision balanced)

By the way gel deposits in this area due to disuse is not a good thing

Bottom line ...The whole unit is often hiddem

At last!

I've dismantled and set up loads of these

They look complex but if you know the basics they come apart go back together logically

Motorcycle carbs are easy bar balancing them But when you find out how thats done its a few minutes work otherwise the engine runs Lumpily (at least!)
Is down as a Technician Job But I have the gauges and adaptor tubes and got those cheap through a trade page

What this comes down to is that it is another question in which we are to guess which correct answer Bedstor is thinking about. I don't know what you'd call it, but it isn't trivia. Occult games, maybe.

LOl In that case I shall post some Verbatim from my Mastermind quiz book over the next few days to balance things DG OK ?

Generally speaking, quiz books are worth their weight in paper. The proof of the pudding is in the eating. I just like to see credit given to people who come up with right answers, regardless of whether or not you had thought of the answer before. Of course, it would be best if you did the research before you posted, and asked a question that elicited only the answer you wanted.

Bedstor only one answer should fit your question. You have to built your trivia question accordingly. ( It seems simple but...) If not , you acknowledge your error and agree with the other answer.