ATF compatible sealed or liquid resistant pass throughs for 25 thermocouples? - Page 1
Forum section: electronics / projects

author: magicsmoke
author_rank: Regular Contributor
timestamp: March 13, 2018, 10:29:07 pm
content: Does anyone have any recommendations for pass throughs that would accommodate 25 thermocouples while at the same time not allow liquid through? The liquid is essentially at atmospheric pressure but is being flung around and sprayed. Ideally the pass through would be chemically compatible with automatic transmission fluid. I would prefer not to interrupt the thermocouple cable as that will likely cause temperature measurement errors. Any ideas?I have tried a simple port in the enclosure sealed with transmission sealant. It tended to leak as the thermocouple leads were moved and was frankly a pain to apply, set, and then remove.

author: Ian.M
author_rank: Super Contributor
timestamp: March 13, 2018, 10:44:48 pm
content: I suspect that potting the leads in a bulkhead pipe fitting using ceramic loaded epoxy so they can easily be removed from the port as a unit would be the best option.Otherwise you could make a bundle of the cables with no voids by smearing them with silicone transmission sealent then tightly wrapping them with silicone self-amalgamating tape then use a compression cable gland with a silicone seal.

author: magicsmoke
author_rank: Regular Contributor
timestamp: March 13, 2018, 11:02:52 pm
content: Quote from: Ian.M on March 13, 2018, 10:44:48 pmI like the first option you suggested but I also need to be able to pull the thermocouples back through the port when the item under test is removed from the enclosure. The thermocouples themselves are essentially permanently bonded to the item under test. I guess a two part bulkhead pipe might work where the pipe filled with the loaded epoxy could be unscrewed from the fitting in the bulkhead.Thanks for the second idea to. It is sort of close to what I have already been doing but sounds like it would seal better.

author: LaserSteve
author_rank: Super Contributor
timestamp: March 13, 2018, 11:22:46 pm
content: Places that sell supplies for research grade high vacuum sell what you want.Also companies like Ceramaseal.Expect sticker shock.Steve

author: Ian.M
author_rank: Super Contributor
timestamp: March 14, 2018, 12:15:52 am
content: Yes, the two part bulkhead pipe fitting solution would be pretty easy to implement.Mod a 22mm or 3/4" compression bulkhead plumbing fitting by reaming it out so the stop for the pipe is removed, and replacing the olive by a thick O ring thats ATF compatible, then pot the wires through a stub of 22mm or 3/4" copper tube so it slides out once the gland nut is slacked off.Another option would be to take a shallow rectangular diecast box as the potted fitting, drilling the bottom of it with minimum clearance for each thermocouple wires and potting them in place, then attaching it (with a gasket) to a rectangular cutout in the panel instead of its lid. Remove four screws and turn it 90 degrees and you can duck it though the cutout if its shallow enough in relation to its width.

author: floobydust
author_rank: Super Contributor
timestamp: March 14, 2018, 03:39:14 am
content: Conax Sealing Assemblies Catalogue.pdfsuch as HD series feed-throughs pdf page 18 of 22.For my own wires to feed-through; I've used Conax Buffalo graphite mechanical sealing glands. These are graphite disks with holes in them, you run your leads through and compress. The graphite squishes up against the conductors. It was to 5,000psi and quite expensive.Or you'd have to make your own seal with epoxy potting compound, like a hockey puck and then seal up against that.I hate ATF it's so messy.

author: jmelson
author_rank: Super Contributor
timestamp: March 14, 2018, 07:50:11 pm
content: Quote from: magicsmoke on March 13, 2018, 10:29:07 pmStrip a short length in the middle of the thermocouple wires, make sure they don't short together, and pot in JB Weld. They put engine blocks back together with this stuff, it holds against oil and coolant. So, a plate with 25 small holes and the thermocouples glued into the holes ought to work. If really no pressure, you could just glue the thermocouples in without the stripping, but the oil would slowly wick up the interior of the thermocouple wire jacket, which might not tolerate the oil as well.Jon