Drying agent

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JohanG

JohanG

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Dec 7, 2020
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Pietermaritzburg, KZNatal, South Africa
Hi All, i am using an in-line moisture filter between my compressor and airgun.
This is a generic type called airmega and uses Calcium Chloride and activated charcoal.
I have two questions for the chemistry fundi's amongst us:

1. Can one dry the CaCl2 and re-use it?
2. What can the CaCl2 be replaced with if you cannot get it locally?


filter.jpg
 
While the calcium chloride is used as a desiccant (and, ironically, in the production of activated charcoal), it's not a particularly good one. It doesn't remove much moisture, and readily releases it if the temperature rises only a small amount. The charcoal has no real use for us in air guns, as it's used to remove odors to make air more "breathable." I would suggest replacing it with silica gel or molecular sieve for much better moisture removal.
 
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Probably not South Africa but you'll get the idea.

Wisesorb 13X Molecular Sieve Desiccant Beads, 6 LBS Reusable Dessicant Dehumidifiers Desiccant Moisture Absorber https://a.co/d/8ZdQW4m

Dry & Dry (1 Gallon) Premium Silica Gel Blue Indicating(Blue to Pink) Silica Gel Beads Desiccant Beads(Industry Standard 3-5 mm) - Rechargeable(7.5 LBS) Moisture Absorber Silica Gel https://a.co/d/5j4FfFw
 
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Johan,
I'll add one thing, Biohazardman, a knowledgeable HPA compressor guy, once said if drying agents, or filters, are getting soaked, best to upgrade the system rather than spending time replacing or drying them out. I use a small cotton-filled filter (like a canary in the coal mine) before the M50 molecular sieve, it got soaked until I added a water-coalescing filter upstream, clean and dry since. WM
 
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I use the stock YH filter first. I want to keep oil out of my dessicant and it gets some water too. I really like color changing dessicant because it tells me what is going on. I get at least 6 tank fills before most of the beads change color and I change it out. I am using a fairly small filter with dessicant in it. But I think my setup with the lines running uphill to the filters helps and venting every 5 minutes helps. I know the venting takes out a significant amount of water. I don't even check the dessicant each run. Probably about every 3 runs. I keep a log sheet with the tank. I change the little white absorbent filter every run. I bought a bag of 100 from Aliexpress pretty inexpensively.
 
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Premium dive quality air compressors have both a coalescing filter and a drying filter. The coalescing filter is designed to remove up to 99% of the moisture from compressed air. The aftermarket coalescing filters do a great job and are much more efficient than a drying filter alone.

@JohanG, given the size of your drying filter, I agree with @rc4fun's recommendation of 13X molecular sieve. However I would suggest you specify that the 13X sieve in the smaller 8X12 bead size. The 4X8 bead size is twice as large so there are fewer larger beads and much more air space in your filter. The denser the beads are packed, the more effective the filtration will be in a smaller filter.
 
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TN_Yankee said:
What units are these sizes? The linked Amazon item states they're 1.5-2.5mm diameter.

Edit:
Ah - a quick search seems to tell me these are mesh sizes?

https://www.sigmaaldrich.com/US/en/support/calculators-and-apps/particle-size-conversion-table shows that the Amazon item above is the more desirable smaller 8-12 mesh (1.41 - 2.38mm) size.
Click to expand...
You got it. Smaller filters have more drying capacity using smaller 8x12 mesh size desiccant. I have an Alkin W31 and the beads are in an outer chamber while the charcoal for breathing quality air is in the inner chamber. If I substitute 4X8 beads it won't have nearly the same surface area for adsoption of moisture as it has with 8x12 mesh size beads. Most replacement clear plastic cartridges for dive compressors have a charcoal chamber with a divider and 4x8 desiccant beads. They work well in larger filters but less in a smaller one. The price is the same for both size beads so it makes sense to order the appropriate mesh size for repacking a filter. The photo below shows 13X desiccant in 4X8 mesh on the left and 8x12 mesh on the right.

beads.jpg
 
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