How to seal thermowell on SS fermentor?

[kevin1911]

I treated myself to one of these https://www.angelhomebrew.co.uk/en/...onical-fermenter.html#/83-cooling_option-none stainless fermentors from Angel Homebrew, and decided I wanted a thermowell in it to put the temp sensor from my temp controller. It turned out to be harder than I thought to drill a hole in stainless steel, and now after deburring the hole is not quite round. This means that when the thermowell is fitted, with rubber seals on each side, there's very slight leaking of the liquid out. It's JUST possible to stop the leak with the absolute precise preload on the seals, but once the fermenting liquid is under any sort of pressure I fear it will start spraying everywhere.

So I'm thinking of how else I could seal the gap between the thermowell thread and the fermentor wall. I'm considering using a food-grade silicone sealant such as Dowsil 786 Food Grade Sealant. I was wondering if anyone else has used this, and is it likely to work?

Any other suggestions?

Thanks!

 

[Richie_asg1]

Have you got a photo of the thermowell? Is it fully threaded or has it got a flat shoulder to seal against?

I used TN coated cobalt drill to start then went with a step drill which was the same as it was thin plate. Standard two flute twist drills will leave your hole lobed on thin sheet.

You could use a dowty seal, which is a steel ring with a rubber inner. You can tighten them so the inside deforms and fills any gaps. The steel ring prevents the seal squishing out. Or you can use soft copper or aluminium washers. They deform and will seal tighter than a rubber seal, but no good filling threads.

You could try PTFE tape as well. The stuff sold for gas fittings is thicker if needed. PTFE is inert unless you burn it.

 

[kevin1911]

 

[kevin1911]

This is the drill bits I used - two-flute as you guessed! Took me ages to file away the burrs.

The thermowell came with a large metal washer but I've set this aside as there was very little thread to attach the nut.

A dowty seal could be just the ticket - do you know what type I need to avoid the rubber giving off-flavours to the beer?

 

[Richie_asg1]

In use the rubber will be hidden inside the seal so you won't see it.
If the outside large nut is part of the thermowell, then you can just put one dowty seal on that, and add a light smear of silicone on the threads, then assemble using the nut on the inside with no washer. The outside seal will be good enough, and the silicone on/in the threads will prevent them filling up with wort/crud.
When you are done give it a very good wipe over inside with a cloth to remove excess. You may find holding the nut still with a spanner and turning the outside to tighten easier and you won't scratch the shiny.

 

[foxbat]

If the curvature is not too pronounced you might be able to replace the round o-rings with flat nylon gaskets. Since the ring part is much wider and less prone to deform when you tighten against it you should get a good seal. Silicone gaskets are also available and will deform more easily to match the curve of the surface when you tighten up the nut against it. Both types are available on ebay for a couple of pounds.

 

[BeerCat]

These can be a pita as i found out. I would put a SS washer on each side and use plumbers tape. If it still leaks flat silicone rings are available. Works a treat on mine and i have a wonky hole.

 

[kevin1911]

Thanks all! I've got some dowty seals on order, and will look to get some flat silicone ring/gaskets too to try various combinations. Beercat - in what order did you assemble the seals and washers? I presume it was nut-washer-gasket-wall-gasket-washer-nut?