Two things....

[rickyaifd]

I have been doing a ton of reading, and reading, and reading until my eyes have stopped bleeding... And there are two things that I've been looking at that I can't seem to find an answer for. 1) does the diameter of the lyne arm make a difference in distillation? I've seen some that are as skinny as a pencil and some that are as wide as a paper towel tube. 2) smaller-sized stills with a filling hole rather than a Lift-Off cap. You see that type of thing on the larger commercial stills oh, but I have yet to see it on a small home sized still. Is that even done?

[Twisted Brick]

There are a number of posts here that deal with your question. Just type in 'lyne arm size' or 'lyne arm diameter' to find them.

Here is a post from earlier this year that addressed a lyne arm that was like, 1/2" in diameter.

In your image, all of the vapor does (eventually) make it out of the riser into the 'lyne arm', after a period of turbulence. I believe this restriction creates pressure/surface turbulence in the boiler and less-than-ideal surface evaporation of constituents, not to mention a reduction in potential takeoff speed.

A smoother transition would be a pair of 90's tri-clamped to the top of the riser, then gradually reduced (3" - 2" - 1" - 1/2") with concentric reducers. If the still in your image is 3" or 4" it would be easy to see the cost-savings incurred by doing it the way it was.

Here's another view of the importance of looking at the still's overall balance and uniformity of vapor speed:

The arm diameter and taper, is more about maintaining a constant vapour speed as the vapour cools and shrinks. Run the same size tube all the way to your condenser and, at certain heat input levels, you will get surging and air gets sucked into your condenser by the shrinking vapour. The smallest diameter in your system will be a limiting factor in your MAXIMUM collection rate AT A GIVEN HEAT INPUT.

For a set heat input to the system, increasing the diameter of your tube will decrease your (potential) run times. You don't always want to run at full speed. In fact tube sizing has more to do with the balance of the system with heat input to maintain the collection rate that you want.

You can dramatically change your flavour profile by running too fast or too slow.