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DIY Homemade Thermowell

I would expect this topic to have multiple posts by the same person showing us how to do something. If there are pictures, let pint_o_shine know and he can host them for you.

DIY Homemade Thermowell

Postby NineInchNails » Wed Mar 12, 2014 10:48 pm

I'll try to keep this as short & sweet as I can. I have been trying to find a really good thermowell that is:

#1 Effective!
#2 Inexpensive
#3 Readily available
#3 Versatile
#4 Easy to use and no tools required. Just insert sensor/probe and pull it out. No thermal grease.
#5 Easily customized to fit my needs
#6 No compression fittings. Thermowell can be left in or removed & plugged.

Most that found online were quite expensive, bulky, made out of really thick material. I own a couple, but the inner diameter is too large for 4mm probes. Their inner diameters also varied which I thought was strange. I was seriously considering the Still Dragon thermowells, but I wanted something that could be easily replaced or modified. I also needed different lengths so I just had to make them myself.

One trip to the local Ace Hardware store I picked up a 1/2" npt brass plug ($3.29) and a 3/16" OD x 12" long brass tube ($1.29). Total cost for materials = $4.58. If you get a few plugs you could easily make a few thermowells. Any size plug would work.
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I drilled a hole through a hole dead center of the plug using a 3/16" drill bit. I cut a piece of the brass tube to the desired length.
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I sanded the end of the tube, sanded inside the plug, fluxed both surfaces and inserted the tube into the plug. I bent a length of solder to form a small ring and slid it over the tube. I heated up the brass plug with a propane torch until the ring of solder melted.
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I then dipped the end of the brass tube into some paste flux, snipped approx a 1/4" long piece of solder, shoved it into the end of the tube, held the end of the tube against some steel and torched the end of the tube until the solder melted. I spit on it to cool it then cleaned up any rough edges.
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I flipped it around and used a countersink bit to bevel the hole. You can use a larger diameter drill bit.
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DONE! ! !

Here's a pic showing how tight a 4mm RTD probe (or 4mm thermocouple) fits inside this tube. No thermal grease required. It fits like a glove!
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I made a 2nd thermowell for a LONG K-type thermocouple I had lying around.
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I would have preferred 3/16" OD copper tubing, but NONE of my local stores had any in stock :( Copper tube would have been ideal, but brass will work just fine. They're so cheap I'm sure I'll be making more as needed.
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Re: DIY Homemade Thermowell

Postby vadiia » Wed Mar 12, 2014 11:44 pm

Awesome!
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Re: DIY Homemade Thermowell

Postby punkin » Thu Mar 13, 2014 1:48 pm

Really neat NIN, i moved this to Teach Us so it wouldn't get lost.
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Re: DIY Homemade Thermowell

Postby varocketry » Sun Sep 07, 2014 9:01 pm

9InchNails or any senior member:

Ok, so what is the purpose of the thermowell? Is it to protect the thermocouple from direct exposure to the vapors?

Why not simply insert the thermocouple through the hole in the plug?
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Re: DIY Homemade Thermowell

Postby NineInchNails » Sun Sep 07, 2014 9:32 pm

Yes, you could just drill a hole in a plug and stick the thermocouple in the hole. Now you have potential for vapor to escape. Yeah you could pack wads of flour & water paste around the thermocouple to seal that. Long term ... I think messy and what if you could simply leave the thermowell installed and stick your probe in there whenever you want.

Let's say you wanted to monitor your boiler temp or let a PID controller control your electric element, bring it up to temp and maintain that temp without fluctuation. You do not need to have a dedicated thermocouple attached to your boiler. You can pull it out and monitor your vapor takeoff temp in your reflux head if your want. There are a lot of practical uses for a thermowell. A thermowell enables you to remove your thermometer/thermocouple at will, does not directly expose your thermometer/thermocouple to the environment you are measuring and upon removal of your thermometer/thermocouple it will not leave an open hole.
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Re: DIY Homemade Thermowell

Postby bentstick » Tue Oct 14, 2014 7:20 am

Thanks for this NIN I have one in use for a couple of months in my boiler
It is what you make it
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Re: DIY Homemade Thermowell

Postby 3d0g » Tue Oct 14, 2014 12:15 pm

For a more semi-permanent mount with a liquid tight RTD, simply soldering a brass nut works well too...

Image
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Re: DIY Homemade Thermowell

Postby Eucyblues » Wed Oct 29, 2014 2:33 am

A simpler approach which works well for me is to get a brass set bolt -10 to 12mm dia about 25mm long (threads all the way to the head) - and a nut

Drill a blind hole in the centre of the bolt head the same depth as the length of the metal tip of the probe - diameter sized to provide a push fit for the probe - be careful here - too loose and it won't work - too tight and you won't get the probe back (I use the digital thermos with attached probes from eBay - accurate enough for me) - use a bit of lube the first time to make it easier to get the probe in and out.

Mine was a little tight to start with but now it's perfect - slips in snug and slides out easily

Drill a hole in the boiler (or still column if that's what you want it for) and fix the bolt in place with fibre or epdm washer/s - tighten securely

Away you go - the temperature is being read at the wall of the vessel or in my case, the head of the column- but unless there are peculiar circumstances in terms of temperature uniformity, the results will be good

If you're worried about leakage with a side mount below liquid level in your boiler, you could use a (very) long bolt from the top - the depth of the hole for the probe still only needs to be the same length as metal tip of the probe

The thermal conductivity of brass is high enough to provide a quick response through the mass of the bolt.

My head temp monitor reacts to draughts passing the column from open windows and doors
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