I really wanted a sight glass on top of my packed column so I could play around with power and flooding condition. I've also read that when the glass begins fogging, it is a great indicator for onset of tails. My problem is that I'm cheap and I didn't want to spend nearly $100 on sight glass tube and the ferrule sight glass adapters still need ferrules soldered onto the column and triclamp adapters which drives the price up even more. Using a glass disc and a copper trap adapter,
you can get a functional sight glass for less than $25. Plus, I'm lucky enough to live locally to stores that carry these items so I could avoid shipping costs altogether
These have been mentioned in a few build threads here on HD and this particular thread here by OldvineZin is where I got the inspiration to try the trap adapter sight glass:
http://homedistiller.org/forum/viewtopi ... 50&t=59056
Materials:
1.5" Copper Trap Adapter:
Supply House or
Home Depot
1.75" x 3/16" Borosilicate Glass Disc:
McMaster Carr #8477K24
-128 or -129 FEP Teflon Encapsulated Silicone Oring:
McMaster Carr #9319K18
Harris Stay Brite #8 Solder and Stay Clean Flux:
Brew Hardware
My 3" column has a 3"x2" eccentric reducer on top of it because my LM condenser head is only 2" diameter. I decided a great place to attach my sight glass would be right there in the reducer where the top of my packing ends letting me watch the liquid pool on top of the packing. I figures the slant of eccentric walls would help me peer down into the column a bit better too.
In theory, you should be able to solder these trap adapters to any copper or stainless round section. Using a copper column tube would have allowed the use of a simple 1.75" bimetal hole saw and plain plumbing solder, but this slanted stainless reducer was a real bitch. In the end, I had to put the reducer in a compound angle vise to level the sidewall with the flat table, and then put everything on top of a flat rotary table on the mill because a hole saw wasn't working on the thick stainless. Finally I was able to manually machine a round hole in the reducer by spinning the rotary table under a 1/2" endmill. The only good thing about this approach was that I was able achieve a very tight slip fit on the copper reducer which makes soldering easier. The copper trap adapter has a round tube OD of 1.737" ... so a true 1.75" hole saw is oversize and would have left a bit of wiggle. (Which is really no problem for someone with good solder skills.)
Typically, people here have flattened the face of the trap adapter where the glass sits to give more of a sealing face. I chose a different approach and used a lathe to machine a stepped groove in the face of the trap adapter threads to hold a -128 size oring. I'm confident there's enough meat on the trap adapter to fit a -129 oring if you want. The oring will sit in the groove and the glass can compress the .103" thick oring with up to about .030"-.040" of squeeze to make a positive seal. I chose an FEP Teflon encapsulated silicone oring to give me both chemical resistance of teflon and the compressibility of silicone. However a solid teflon oring could be used if you want... it just won't compress as easily. The glass disc can be gotten from McMaster and the 1.75" size fits PERFECTLY in the brass screw ring of the trap adapter. I went with 3/16" glass thickness, but I'm sure 1/8" would have worked fine.
Next, I used a permanent marker to outline my excess copper inside the reducer and trim off unneeded portions. A bench grinder and then scotchbrite wheel made quick work of cutting through the copper.
and great write up and pictures..