Sight gauge

I recently converted more 50L kegs into homebrewing vessels. Previously I was brewing with only one converted keg serving as both hot liquor tank and boiling kettle. That was very awkward, as I had to run off the mash into a carboy, then dump the HLT, rack the wort into the kettle, and then lift the kettle containing 6 gallons of very hot wort back up onto the burner. Not a good time.

Now I’ve got more kegs converted, so I’ve got two kegs serving as a dedidicated HLT and a boiling kettle. My 10gal Gott cooler continues to serve as a mash tun.

For the HLT, I added a second pipe-coupling to the side of the kettle, at a 90° angle to the drain cock, so that in a gravity-flow tower, the sight gauge would be facing me, while the drain cock led straight into the mash tun.

Gauge Tubing

I’ve seen plans on the net for sight gauges using plastic tubing, which has various problems with melting or sagging when hot, and clouding. I wanted to use a real glass tube, ideally borosilicate (“Pyrex”) glass. For this purpose, the tubing should be fairly heavy-walled, for strength.

Finding a source of borosilicate glass tubing was quite a challenge. Eventually I found a couple possibilities. I got six pieces of 3/8″ OD borosilicate tubing, 16″ long, for a very modest price, from Pegasus Glass in Cambridge, Ontario. They deal in laboratory glassware, and custom fabrications. They don’t normally deal in small quantities, so don’t bother calling them up to ship you a single piece. If you want a case, they’ll ship that, but not single pieces. They were willing to help me, because I’m local and I could just walk in.

Another possible source I found was Artistry in Glass, a London, Ontario web-store. They deal mostly with art glass, but they also sell Simax borosilicate tubing in small quantities. Apparently artists use it for making beads and stuff. And maybe also for glass pipes, I guess, though I hesitate to guess why someone would want a glass pipe…

If you want to search for your own suppliers, a couple search terms that might help reduce the huge volume of hits you’ll get for “glass” would be “lampwork”, “flamework”, or “beadwork”. It might also help to narrow the search using “COE 33” or “coefficient of expansion 33”, that’s the coefficient for borosilicate glass.


To protect a glass sight gauge from accidental breakage, they usually have some kind of windowed metal shield around them. I was able to mostly achieve that effect. In this, I finally found a use for the stainless steel dip-tubes that I removed from the 50L brewery kegs when I converted them. These dip tubes are about 9/16″OD, 1/2″ID. Using a 3/8″ID, 1/2″OD O-rings as spacers at the top and bottom, the sight gauge tube fits inside snugly.

The dip-tube can be cut to length easily using one of those rotating tubing cutters you usually use for cutting copper pipe.

Rickety jig for cutting window in metal tube

Of course, then you can’t see the glass sight gauge inside the stainless tubing. You have to cut a window. This was the hardest part of the operation. I assembled a rickety jig on my table saw top, using my sliding table. A rotary tool with a cut-off wheel was mounted to the sliding part of the table, while the stainless tube was mounted on the fixed part of the table. This was supposed to make it easy to make a couple parallel cuts in the tubing, and I would then clean up the ends with a small grinding stone. In practice, it was a bloody nightmare, consumed my entire stock of cut-off wheels (they kept breaking… wear a full face mask), but I got through it somehow. The result is quite decent.


I mounted the gauge glass to the keg using a 1/2″ MPT (male pipe thread) to 3/8″ compression elbow. In brass, unfortunately, but pickled to strip off the lead. The 3/8″OD glass tubing fits perfectly in the compression fitting, but rather than use the supplied brass compression ferrule (which would likely shatter the glass), I just used a pair of 3/8″ID rubber O-rings. The pressures we’re dealing with here aren’t great (just a 2′ water column open to the air.) I would have preferred silicone O-rings to withstand the heat, but they weren’t immediately forthcoming. The plain black rubber O-rings from Home Depot’s bulk bins have done fine so far.


To secure the top end, I just drilled a 1/4″ hole into the keg’s skirting, and installed a 1/2″ stainless steel eye-bolt. The dip-tube is slightly larger than that, so I had to enlarge the eye-bolt hold just slightly with my Dremel and a grinding stone.

Putting it all together is pretty straightforward. The brass elbow is installed into the pipe-coupling on the side of the keg. Put a 3/8″ID O-rings on the end of the glass tube, then the compression nut, then two more O-rings. Insert into the eye-bolt on the top, and the compression fitting on the bottom, and hand-tighten the compression nut. Slide the stainless steel tube down over the glass tube and through the eye-bolt so that it settles over the third O-ring at the bottom. Push one last O-ring over the top of the glass tube inside the stainless tube .

The only weakness in this assembly is that the stainless tube doesn’t really provide a lot of protection for the glass at the bottom end. Since it is not rigidly attached to the brass elbow, any force in that area will be borne by the glass tube, not by the stainless.


I cheaped out on the scale. I was in a hurry to get it ready for a brewing session. The scale is just a piece of white curtain rod. A couple small holes drilled in it, and secured to the sight gauge with nylon zip ties. I calibrated the scale manually, by filling the keg with 2L of water at a time, and marking each new level with a Sharpie. Cheap, quick, and dirty.

Unfortunately, my sight gauge does not read below 12L. I’m compelled to heat up at least 12L more water than I’m going to need to get accurate measurements.

My original plan was to have a second sliding reverse scale, used for measuring out specific amounts. It would have zero at the top and count up as the water level drops. You would start by aligning zero with the current water level, open the drain valve, and wait until the desired amount of water has been removed. I haven’t yet worked out how exactly to build this one. Perhaps attach it to the absolute scale with magnets.

Sketchup Model

Here’s a Google Sketchup model for the sight gauge. I’m not sure what use it is, but it was fun to make. Just don’t look too closely at the threads…

3 responses to “Sight gauge”

  1. Interested to know if you would like some more 50L kegs?

    Also, do you have any of the dip-tubes left, from the ones that were alreddy converted?

    Thanks for your time,


  2. FYI for anyone ordering from Artistry in Glass, They have a minimum $25 order plus shipping. I have enough glass for 24 boil kettles now.. so lots of spares.


Leave a Reply

Your email address will not be published. Required fields are marked *