Why I started using a desiccant filter, and why you should too.

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Argh, I am currently window shopping https://www.nuvair.com/products/filtration/personal-filter-din.html for the LC-110. My problem is I keep undulating between the agreement of everything said above as it applies to compressed air and physics but then it logically conflicts with our data set regarding failures due to moisture incursion. IE: Do we really need 100% clean, dry, breathable air in the air guns or is a nominal amount of moisture acceptable?

We have folks hand-pumping with no filtration at all and we don't have reports of failure.

We have folks using those tampon style filters which saturate quickly and do not fully removal water vapor and no reports of failure.

With regard to the LC-110 and other systems such as the shoebox, which are specifically designed for air gun use it's hard for me to assert that additional filtration is required and the engineers have done some odd cost-benefit analysis and determined that they're going to provide us with an inadequate filtering product because of cost reduction.

... ugh ... I hate to spend $200 on something that isn't needed. The decision for additional filtering would be a no-brainer if we had forum reports of failed airguns due to moisture incursion *coupled* against a fill method. Or reports of moisture related failure at all. One would think the whole airgun tank/tube gas expansion during the shooting process and subsequent fill process as the pressures vary from 250 bar to 150 bar would be sufficient to adsorb any moisture and expel it during the shooting process.

All said, thank you all for the dialog and discussion, I'll keep reading this thread for sure.


 
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My question and Tom Kaye's response:



"I hope you don't mind my contacting you regarding this issue Tom. We are having an ongoing discussion at Air Gun Nation of whether or not we should have a desiccant filter attached to our compressors to keep moisture out of our PCP air tanks and there is a lot disagreement. But none of us are experts. Would you be willing to chime in and help answer this question? I'm not asking for a dissertation, just a short simple answer. Thanks, Tony"

"Hi Tony,

One of the reasons we have a shop compressor feeding the Shoebox is because most (but not all) of the water will condense out in the shop compressor tank before it goes in the Shoebox. So compared to a normal 3 stage compressor we have less water overall. If you want to put a desiccant filter between the shop compressor and the Shoebox that is even better but most of the work has been done by the shop compressor. 99% of our customers do not use a filter. Most who do live in a pretty humid place and have a particular worry about water. If you want to be 100% sure then you have to go with a high pressure filter like Brancato’s.

Tom"

Since my Shoebox is inside my residence I must conclude that a desiccant filter is unnecessary. That becomes particularly true given the expense of Joe Brancato's HP filters. Tom's info is applicable to the Shoebox only of course and is uniquely unhelpful to owners of other brands. Was this exercise any help at all? What do ya think fellas?


 
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Absolutely, it was very helpful to me, and I don't think anyone in this thread has been wrong. From a logical aspect:

I think we're running into an emotional concern about water ingress and water damage, a logical proof of water condensing based on pressure and temperature, and an observation that additional filtration is not necessary based on failure rates *unless* you're like mtnGhost pumping in the fog. In the interior of a home where the relative humidity is 55% or less I don't believe additional filtration to be necessary.

Have I proven anything? Nope, it's just a hypothesis based on the above input and the observation that there are no failure rates of air guns observed with reasonably engineered compressors/filtration systems.

All in all, looks like everyone is correct depending on their viewpoint and objective. This has been a good and educational thread and if James wants to perform additional filtration or encourage others with physics fact to consider filtration good on him. Perhaps I should change my stance from "disagree" to neither disagree nor agree since depending on case both situations can be correct.


 
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I decided to take a look at the desiccant filter I've been using between my Shoebox and buddy bottle this evening. Take a look at what I found. On the left is the color changing desiccant from the gold filter. On the right is unused desiccant. The unused stuff is a deep blue. The used stuff is kind of violet to pink. Proof enough to me to keep using this filter. Hopefully the colors as posted here will be accurate enough to see the marked difference. Glad I checked now.
1584145672_8579841815e6c2508deb522.23919263.jpg

 
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Thank you for this, I am in full agreement with your findings regarding indicator color change. Those are silicia indicator beads, I believe?

What specifically and emperically did they indicate other than color change? How much moisture did they eliminate? How much of the eliminated moisture would cause a problem with an air rifle? Which air rifle would have that problem?

Thanks again this is great data and field testing, much appreciated and thanks for sharing!
 
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Good questions that are not going to be easy to answer. I'll use the desiccant filter for now and check my PCPs air cylinders say in a year or so. That's about the best I can do. You would think this information would be around somewhere, from airgun manufacturers at least. If there is I haven't found it and they are not telling otherwise. It feels like we are the only people asking these questions. Given the dangers inherent in these designs we need to do better.
 
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Thank you for this, I am in full agreement with your findings regarding indicator color change. Those are silicia indicator beads, I believe?

What specifically and emperically did they indicate other than color change? How much moisture did they eliminate? How much of the eliminated moisture would cause a problem with an air rifle? Which air rifle would have that problem?

Thanks again this is great data and field testing, much appreciated and thanks for sharing!
Click to expand...

It looks like Flintstone is using silica gel beads with cobalt chloride as the color change indicator to show that the beads have become saturated and can no longer adsorb additional moisture. Deep blue = dry. Pink = saturated. In general, I've learned that silica gel holds a weight of water equal to between 30 and 40 percent of its original weight. So, 30 to 40 grams of water per starting weight of 100 grams dry beads. He' could weigh those beads before and after drying (regeneration) to give us an idea of the actual amount of water. When mine gets to that point, I will weigh it before and after as well, and share the data. Thanks for sharing the pictures, Flintstone! And thanks for your continued participation as well, LMNOP. Life and work are very busy for me right now, but I am continuing to research this issue and it's possible effects.

James
 
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I decided to take a look at the desiccant filter I've been using between my Shoebox and buddy bottle this evening. Take a look at what I found. On the left is the color changing desiccant from the gold filter. On the right is unused desiccant. The unused stuff is a deep blue. The used stuff is kind of violet to pink. Proof enough to me to keep using this filter. Hopefully the colors as posted here will be accurate enough to see the marked difference. Glad I checked now.
1584145672_8579841815e6c2508deb522.23919263.jpg
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@ Flintstone.

That silica jell stuff is recommended for low pressure use and is supposed be less efficient at higher pressures. I would only use it on the inlet side of my booster. For your high side, I recommend that you get some 13X molecular sieve. That is the recommended media for high pressure filters. You can salt the MS with a small amount of the colour changing silica jell to give you an idea of when it needs changing. I agree with James that the best place to filter is on the high side but for different reasons than all that mumbo-jumbo about dew points and temperature changes. It can't hurt to feed the booster with the driest possible input air if only for the benefit of the inside parts of the pump.
 
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I decided to take a look at the desiccant filter I've been using between my Shoebox and buddy bottle this evening. Take a look at what I found. On the left is the color changing desiccant from the gold filter. On the right is unused desiccant. The unused stuff is a deep blue. The used stuff is kind of violet to pink. Proof enough to me to keep using this filter. Hopefully the colors as posted here will be accurate enough to see the marked difference. Glad I checked now.
1584145672_8579841815e6c2508deb522.23919263.jpg
Click to expand...


Do you keep the output hose capped air tight when not filling? If you don't then the moisture in those beads could be from the normal air in the room. Try putting some of those bright blue beads into an unsealed box and let them sit in the room for for the same amount of time.
 
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He' could weigh those beads before and after drying (regeneration) to give us an idea of the actual amount of water. When mine gets to that point, I will weigh it before and after as well, and share the data. Thanks for sharing the pictures, Flintstone! And thanks for your continued participation as well, LMNOP. Life and work are very busy for me right now, but I am continuing to research this issue and it's possible effects.
Click to expand...

James, this is a great idea. Weigh the filter before a fill cycle, weigh the filter after, the difference would be the adsorbed water weight. Great discussion and no worries with work and life taking up time, that's the way it's supposed to work :) Us Interent forum folks should be lowest priority.

All the best to all and thanks for this topic!
 
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Oh, and thanks for the tip Eaglebeak. You don't have a reference that can be found on the internet by any chance. I don't have a problem with switching to 13x molecular sieve. It doesn't cost that much. Since this discussion has started I think we should aim for a reference work that all can use.
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There's lots of info online. This one is a good start. https://www.agmcontainer.com/blog/desiccant/selecting-desiccant/ 
 
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For anyone with a dive compressor, or just wanting to learn more about the process of producing clean, dry, high-pressure air, this is a good read:

https://www.scubaengineer.com/high_pressure_compressor_filtrat.htm

I haven't yet found anything about silica gel not working well at higher pressures. I did find info that it works better at higher relative humidities and temps below 77 degrees F. Molecular sieve seems to be preferred for its better performance at the filter tower temps encountered in tropical areas as well as at lower relative humidities, which is the case as the air is dried as it passes through the desiccant media.

James
 
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How little moisture is good enough?

Is'nt it fine as long as water vapor does'nt condensate within the rifle?

If someone need extra dry air for winter hunting/shooting then maybe a booster and bottled air from the diving shop?

After all thats what you're paying for there, right?

Or if you go all in then nitrogen.



And for all the compressor guys not wanting a booster then cut in between first and second compressor stage and feed it regulated air/gas at @100-150psi. No biggie.

Shoot if you have scuba gear then it regulates right down to atmospheric pressure and can be fed directly to the compressor inlet.
 
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For the present I'm going to use the desiccant filters I have now. That is, silica gel filters on both the input and output side of my Shoebox and keep closer track of the number of hours on it. And note silica gel saturation as well. Seems to me that the references especially from AGM Container clearly state that we want to keep moisture out of our PCP airguns. Didn't I see evidence of air cylinder corrosion from moisture somewhere Iceman? I thought it was here on AGN but I'm not sure.
 
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