Desiccant canster filters

[Andrew Robinson]

Hey guys and gals,

Getting ready to start machining the desiccant canisters for my gas handling systems and wanted to get a little feedback on filter material. Filter material is actually a poor choice of words. This part is actually just a felt buffer between the desiccant and the perforated plate supporting the desiccant material stack. Felt is the material of choice it seems in the industry, however, I am trying to get a little more detailed information on it. Specific felt? Chemically treated vs untreated? Seems there are a few options out there that are all used in this application. Does anyone have any direct experience in this area that would know the benefits one way over the other?

Thanks,
Andrew

[dylan hume]

Regarding the felt in the desiccant canister's, do any commercial desiccators contain something like this as well? I have a stainless steel desiccator and was hoping to use it as the start of my vacuum chamber, welding the top on and additional ports directly to the sides. It looks like the link below:

http://www.amazon.com/Stainless-Chamber ... B00GME37C6

[Andrew Robinson]

I don't think you quite understand what I am talking about. What you just linked to is a vacuum chamber used for degassing epoxies. Please do some reading first and create a post if you have a question.

Bump

[Dave Xanatos]

I'd be wary of felt purchased from local hobby stores, etc. Probably treated with stuff that would outgas until the sun goes dark! But I'm only guessing. I'm sure others will chime in here.

I had the opportunity to look at an actual drierite cannister that was used in some sort of lab setup. It was all being sold at the MIT Flea market. This cannister was huge easily 12" long by 3" diameter; it would probably have taken all my deuterium gas just to fill the unit! What they had between the retaining screens and the actual drierite compartment looked more like compressed fish-tank filter fluff than felt. It was coarser/rougher feeling than felt for sure.

Fortunately, though, the dessicant compartment in your fuel line is NOT under high vacuum. It should be D at atmosphere, so the outgassing of other non-treated materials should be minimal.

[Nick Peskosky]

Dave is pretty spot on in his description. I utilized one of the drierite glove box dryers shown here https://secure.drierite.com/catalog3/page5.cfm when I was working on OLED fabrication with the physics department of the Academy. The felt really doesn't serve any purpose aside from acting as a screen to prevent the individual desiccant granules from sifting down to the supply side of the cylinder. In addition to the previously suggested felt, you could substitute a fine SS mesh to accomplish the same task and minimize purity issues altogether. For my D2 drying system, the wet gas is fed through a borosilicate U tube with drying connectors. The top of the U tube is stoppered off and the glass gas feeds are small enough that I don't have issues with the desiccant spilling into the supply or outlet.

[Andrew Robinson]

Thanks Nick, that's a fantastic idea. Originally I was planning on machining a perforated support plate for the felt pad. I guess I could always increase the perforation density to eliminate the need for the pad all together. I guess the only concern left would be small fractured bits sifting to the bottom and falling through. Under normal operation and care this should never be a problem, but it's still something we should consider. Thanks for the input.

[Andrew Robinson]

Thanks for the replay as well Dave. Yes I would think out gassing should not too much of a concern. You hit exactly what I was concerned about regarding standard felt. I would still like to find out exactly what material is used in these containers. Might do some searching for replacement filters for laboratory gas dryers. Thanks again!

[Dennis P Brown]

I have taken exactly one (fairly large) drier canister apart (15 inches long, and 3 inches in diameter - all welded steel; a bear to cut open); besides the desiccant, it used a fiber-glass like pad (only one end) and some type of fiber glass "fiber fill" to prevent the desiccant from entering either gas feed tube at each end of the canister ( the stuff does look a lot like the aquarium stuff that Dave mentions. But this stuff was really a glass fiber.) I salvaged the canister and desiccant (all the fiber material was contaminated) and I did simply use aquarium fiber fill to seal each of the ends so the desiccant is contained in place. This stuff appears to handles the 120 C temp heating cycle I used to recharge the dryer and holds the desiccant in place preventing any dust or other small particles from entering my high vac system.

[Andrew Robinson]

Thanks Dennis. Have any pictures to share?

[Dave Xanatos]

Since the filter medium is glass fiber, I wonder if fiberglass insulation could be used? I know nothing about any treating of that material, I just know it comes in pink and yellow And I have a lot of it in my garage. I'll have to look that up.

I also like the idea of the fine SS mesh.

[Andrew Robinson]

Since we're on the topic. Steel wool comes to mind as well.