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StillDragon Thermowell

I've had my eye on these Thermowells for quite a while. I somewhat recently emailed to find out what the dimension of the Thermowells are and this is the answer I received:

The entire piece is 1-7/8" long.
Half of the probe is 1/4" in diameter and the other half is 7/16" in diameter.
The "well" that accommodates the probe is a 4mm (1/8th strong) diameter and about 3/4" deep.
This depth is commensurate with the probes that are included with our thermometers but can also be drilled out an additional 1/4" if needed. The "well" can also be widened if needed to accommodate a larger diameter probe.

Well based on the description & the dimensions I drew the Thermowell. Here's what I drew.


Now I'm kinda confused and would love to have some clarification. Is this accurate? If so, why all the wasted space & extra material? Does all this extra material serve to conduct heat to the sensor and does not need to be drilled out (or shouldn't)? Is it made this way so that the customer can cut off the unused portion or drill it out in order to push the probe deeper into the Thermowell?


I was not expecting the Thermowell to be made this way. I suspect that no one really would. The only reason I emailed & asked about it was because there was not anything in the way of a description and it leaves everything to the customer's imagination.

I'll be ordering at least a few very soon because these are the first Thermowells I've found that actually fit 4mm sensors like the 3-wire RTD probes from Auber Instruments. Most others differ in ID and are much larger in ID.

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  • That's what they look like, your first pic. LoO probably drew them when he was stoned on acid. :))

    StillDragon Australia & New Zealand - Your StillDragon® Distributor for Australia & New Zealand

  • I drew it up in MSPaint and had it produced. I usually send them to the fittings factory to be welded into some of the bends, tees or reducers. They are made "fat" to help with the heat distortion of welding but it still helps to ream out the hole with a 4mm drill bit.
    The length of the "probe" end was sized to reach about the middle of a 2 or 3" fitting.

    It didn't occur to me at the time that DIYers would want to buy just the thermowell without the fitting but after a few requests we began stocking the loose parts as well.

  • do you have a 2" U with a thermowell? I have been looking for one of these!

  • Sure!
    Click here and scroll to the bottom of the page.

  • copper thermowells for the DIY guys would be friggin awesome

  • I agree with @NineInchNails I drilled mine out to look like his last picture.. I can see no reason for them to be made the way they currently are...

  • I agree with NineInchNails too.

    I just had the thermowells welded into my keg. I assumed that they were already like the third drawing. If I knew these were only partially drilled I would have had a half coupler welded into the keg and screwed in a threaded thermowell.

    I haven't decided if I will try drilling them out in place knowing that an off-center drill will result in another trip to the welder.

    This should teach me to double check even what appears to be obvious.

  • I don't think it will make a change in the reading even if you were to drill them out. The probe would still be touching the same piece of metal in the same position in the still.

    StillDragon Australia & New Zealand - Your StillDragon® Distributor for Australia & New Zealand

  • You may very well be correct punkin. If that's true then the customer doesn't need that other half which protrudes into the fitting ... that is unless that extra piece serves as like a conductor so to speak.

    It would seem to me that drilling it deeper would leave you with thinner material throughout the latter 1/2 of the thermowell and allow the majority of the probe to be extended further and be in more contact with the environment you wish to monitor. Maybe just a small advantage or perhaps none at all. I wouldn't know.

  • A thin wall thermowell will be more responsive to temperature changes than a thick wall thermowell. At constant temperature both will have the same readings. With changing temperatures the thermometer in the thick wall thermowell will be slower to respond.

  • The RTD sensors I use are sealed and don't need a thermo well.


  • I'm good to change the design on the DIY thermowell to whatever you guys want.
    Not sure I want to make 10 different ones though as I need to produce about 500 of each model to get them made cost effectively.
    Lets get a consensus of your wants and needs and see if we can perfect this.

    But on the ones that get welded into the fittings here, as we are doing now, I need to keep them as they are because they are supplied with the cheapo digital thermometer and a pack of thermopaste. If drilled deeper, the thermometer probe is very likely to get stuck and will break off inside the well by pulling on the wire.
    It's an elegant solution really, for $15 you get a thermowell machined and welded into the fitting and polished plus a pack of thermopaste and a cheap digital thermometer.
    It may not be a high end solution but it does give a very good indication of whats going on inside the still for very little money.

  • edited March 2014

    The RTD sensors I use are sealed and don't need a thermo well. Thermocouples are generally not sealed and DO need a thermo well.


  • Responsiveness is likely not an issue when you consider the thermal mass of the liquid, especially in the larger boilers. Suspect that even in it's stainless condom, the thermocouple will still respond fairly quickly in comparison. Lloyd's suggestion of the thermopaste is a great one, since if you have an air gap, that will have much more of an impact than the conductivity through the stainless.

    I've been worried about immersing some of my RTDs in hot, high-abv wash, or in vapor, since in some cases I don't know the material of the casing, and in the ones that I have that appear to be potted, I don't know what the potting compound is. I know there are some companies that make a teflon coated RTD that would probably be safe to use in either location, the next issue is finding a teflon housing and compression fitting, tapping out a triclamp cover, etc.

    The thermowell approach really is an elegant one from a durability and flexibility perspective...

  • @olddog said: The RTD sensors I use are sealed and don't need a thermo well. Thermocouples are generally not sealed and DO need a thermo well.


    I've been using these 3-wire RTD sensors from Auber. They do not require a thermowell. I could use compression fittings, but I would prefer to not have my sensors attached to my equipment in such a way that makes it less than convenient to remove. I also don't like the thought of removing my probes and having a hole in my boiler or holes in my fittings. Using thermowells seems ideal, no open holes.

    The probe on these sensors are 2" long. With the current Still Dragon thermowells my sensors can be inserted 3/4" leaving approx 1-1/4" of the probe exposed to the open air. This may not be a big deal, but if I drilled the thermowells deeper then the sensor would be almost completely enclosed. I really like the thought of doing that.

    I do not know if using thermopaste is critical or not. If I didn't use thermopaste then that would make removal of probes a breeze ... just pull em out. Probably only slightly less convenient if I did use thermopaste (pull em out and wipe em off).

    Using this type of probe would be nice if I could afford it! Just leave the probes installed and simply quick disconnect the wire. I'm not wealthy so I am excited to use the Still Dragon thermowells. They allow me to not require an expensive sensor for every location on every piece of equipment I want to use a sensor.

  • You could fit a plug and socket to the RTD sensor to be able to remove the cable. The requirement for RTD sensors is that the resistance on all 3 wires should be the same.


  • Nice cheap probes there NIN.

    StillDragon Australia & New Zealand - Your StillDragon® Distributor for Australia & New Zealand

  • edited March 2014

    @FullySilenced said: copper thermowells for the DIY guys would be friggin awesome

    I put copper thermowells in the last build I made. I fitted compression fittings into the column so the thermowells could be removed if the client wished to put a probe directly into the column with a silicon bung in the compression fitting.

    Easy build. Copper rivet in the end of a 1/4 inch tube. That was then soldered into successively bigger tubes.


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  • edited March 2014

    If you make the thermowells removable and fit them with a compression fitting it provides a bit more versatility. I increased my 1/4 inch tube up to fit a 10 mm compression fitting. The bit that passes through the depth stop is 8 mm tube so you could fit a 6mm probe. I built mine with 1/4 inch tube which takes a 4 mm probe.

    I put in 2 thermowells. 1 at the top of the vapour path, and 1 about 1/3rd down the column.


    They both fit with just a wrap of PTFE tape around the compression olive (which I actually soldered onto the tube) so as not to compress the tube for the probe.

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  • @myles I do admire your work sir...

  • From the standpoint of sanitation and ease if cleaning I prefer a welded solution. I have welded thermowells on my brewing equipment that use threaded attachments. I wish I had TC fittings on as the auber TC RTD is an elegant solution. I squeezed thermo paste into the thermowells and then ran the RTD directly into the compound. This appears to be pretty sensitive to temp changes, which I assume helps the PIDs be more capable of accurately controlling temps. From the brewing standpoint, I would want a thermowell to have the least impact on thermal conductivity as possible which means minimal mass and material selection. So, I would want the drilled out thermowell, I see that extra material only decreasing the probes sensitivity and when I'm trying to keep my mash stable to the degree, that is important information for my system so it doesn't over fire the element.

  • OK, after some thought about you guys' ideas I've ordered the following to be produced in both SS304 and pure red copper. It will take a couple of months to get and be propagated to your distributors.


    Not to scale but you and the machine shop get the idea.

    weld in thermowell2.png
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  • The copper ones should make @FullySilenced happy. Drill a 10mm hole, solder it in, squeeze a dab of thermopaste onto the cheapo digital thermometer probe and done.
    The SS thermowells will need to be welded in of course but either way it's a very cheap solution.

  • I think you will sell them with no issues ... ezflanges and themorwells to the same customer base.... and how many ezyflanges have been sold... dang... couple boxes maybe ... :D

  • Copper ones are a good idea. Maybe make them with a thicker probe so customers can drill them out to fit larger dia probes?

    StillDragon Australia & New Zealand - Your StillDragon® Distributor for Australia & New Zealand

  • I figure at least a metric ton of ez flanges have sold @FullySilenced. I haven't received any feedback yet on the new copper ez flanges but they should do OK.

    @punkin I think they really need to be purpose made and I opted to size them to the cheapo digital thermometer probe that's available through SD at very low cost.
    With luck, I'll have @olddog's controller soon and we'll have a new probe/fitting standard to accommodate. The minimum order of usually 500 pieces can be daunting at times but our customer base is big enough now to warrant that. It didn't take very long to go through the first 500 SS thermowells before having to reorder. The majority were used in the common SD fittings - end caps, bubble tees, reducers and bends. A few were made available for the DIY folks in USA but I'm not sure how well that is doing. I'd guess the copper ones, when they are available, would be easier for do it yourselfers.

  • The big problem is that there is such a variety of fittings for thermocouple and RTD sensors, this is the supplier I use and you can see the vast range available

  • Yes @olddog variety is a problem. We need to focus on just one or two sizes of threaded fittings if possible and adopt that as our standard. Else we will need too many different fittings to make and adding two or three bushing adapters together gets expensive and ugly.
    It could wind up being something like:
    2" 90 bend, for example, with a 1/2" half coupling welded in.
    Then a series of bushings that take the 1/2" down to 3/8", 1/4", 6mm, etc...

    Just thinking out loud until I have a chance to explore your controller.

  • 1/2" coupling fitted as your standard option. Reducing bushes in brass or stainless are standard items from other sources, so you don't really need to make those yourself.

    Your customers other option is to use a compression fitting, and pass the probe through a silicon or PTFE bung in the compression fitting.

    I actually use standard threaded to compression adaptors. On mine I cut a screw thread into the copper wall, and the threaded adaptor is screwed in and then soldered or brazed into place.

    If you can provide the 1/2" threaded socket - the customer has a lot of "off the shelf" options available, for actually fitting the thermowell or probe.

  • Good thinking Myles, that size can be adapted to fit virtually any size.

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