Reducing moisture in compressed air (Cannot eliminate it?)

[Geezerhood]

Rather than hijacking it, I decided to start a new thread, inspired by the quote below from this thread on AGN.

If you really want DRY air you can get reconstituted breathing air but if you going to breath it for long it will dry all your airways out it is made of 79.1 %Nitrogen and 20.9 % oxygen these 2 components make great air EXTREMLY DRY. Nobody wants to breath it for long Too Dry. I've been in the compressed gas biz for the last 45 years and ALL the air separation plants for AirLiquide, Airco, Praxair, AirProducts have tried to MAKE air from those gases, they all had to go back to Compressors with filters and some driers for breathing air, So breathing air is NOT really dry the filters are for all the enviromental elements that come from compressing air

I have suspected exactly this as I have been learning about compressors. No matter what we do, there is going to be water vapor in our tanks, bottles and guns. It seems like the best you can hope for with a compressor is to reduce it to the point where you have the lowest amount of water condensing into liquid in your tank, bottle and gun. Nitrogen seems like the perfect gas for use in PCP guns, but it is quite expensive here, so not an option for me, so I will continue on with my compressors. A bonus on having a dewar (They don't call them tanks apparently) full of Nitrogen, you could also fill your tires with it and freeze stuff!

Perhaps if some gun maker came up with a rust (corrosion) proof or at least highly rust resistant PCP gun made of stainless steel alloys that would not corrode inside if moisture was present, they might have a winner.

Some questions for you elwoodblues or others.

1. Assuming we aren't injecting liquid water into the gun, what causes the water vapor that is in all the air we are putting into our guns, to condense out into liquid inside the gun?
2. What is the easiest and lowest cost method to verify the moisture content of the air we are putting in our guns?
3. What is the maximum moisture content percentage that would be considered "safe" as far as not causing corrosion?
4. Is a coalescing water trap the most effective method of reducing moisture?
5. How long would air need to be in contact with Synthetic Zeolite or some other product, to significantly reduce the moisture content? My guess is many times longer than simply passing through a small tube filled with it as it moves into or out of the compressor.
6. Is Synthetic Zeolite the best option for a final filter and does it or some other material actually do any good or is it a waste of time and money?
7. What are your thoughts on the cartridges at the last stage in line, filled with Silica Gel, Synthetic Zeolite and Charcoal? Seems like a gimmick to me.

 

[Miami Airgunner]

This is all just my opinion, some of it well supported, some of it probably less so, but here's what I think:

1. The ability of 'air' to carry water vapor depends mostly upon pressure and temperature, so an increase in pressure or drop in temperature can cause condensation. - The fact is that the air is hot going in, so it cools in the tanks, and that's the most significant and common event that leads to condensation inside the gun/tank.

2. I'd love to know, but suspect it would be industrial equipment, because to REALLY know, you need to look at water content at pressure. You could, of course, just measure the air you're compressing, both before you suck it in (I ALWAYS fill in my well air conditioned house, that's as dry as we can get in south Florida) and then I guess you could just blow some air out of a tank over a hygrometer that is the regular atmospheric kind. Just fill clear plastic bag from your tank with a line.

3. None. Reactive metal will always react more when there's more water. Also, just Oxygen itself will corrode metals. And, the best part? It happens even faster in most cases under pressure - the more pressure, the faster it can proceed. The best idea, IMO, is to simply limit water content in your air as much as possible within the limits of your budget and risk tolerance. Though, as many have said in other threads, they've done BAD things for years, and it's fine. You hear a LOT on these forums about failures of different sorts, and corrosion isn't a super common topic, so I suspect that for the most part, it's ok.

4. Multiple layers of water removal is best, as with most of these things, a pre-filter on the low pressure side with LOTS of volume of silica beads, water trap in line, and post-filter on the high pressure side.

5. Surface area and flow rate are key, and the time would depend on the moisture content of the air coming in. Overkill is great if you can tolerate it.

6. I'll let some person who's done more research/work/has experience with both answer this, as I have no idea and would love to know.

7. I love clean smelling air that is extra dry. See #4 . The only down side is more volume in the filter and line.

---

I think the easiest to control is the incoming air, A/C units remove a TON of water from the air, and a dehumidifer could do a lot more in a small room. After that, multiple layers of removal is best if you want overkill. Though, for me, my general plan is just to take reasonable precautions to minimize incoming water, fire the gun in a position to force water condensate through the system on a regular basis to prevent any real buildup, and I'm considering adding a fill or two of dry nitrogen once a year or so to clear out any remaining moisture, as it will help to suck out that water and keep things extra nice.

And also, aluminum forms a layer of oxide on it's surface that prevents oxidation in most cases, which is really good, because if it didn't aluminum and oxygen just LOVE to form aluminum oxide, far faster than iron rusts, just fortunately, it locks off the underlying material from further corrosion - meaning that most of our airguns are, for the most part, already fairly resistant to corrosion - and contrary to the name, stainless steel comes in a bunch of varieties, and not a one of them is genuinely impossible to corrode, just each has 'increased corrosion resistance' in specific environments. . And the stuff weighs a TON! I think my new Uragan 2 King is heavy, but it's a lightweight compared to anything that would be made using stainless LOL.

If you want a genuinely corrosion proof setup, it's probably a better idea is to coat or otherwise line the bottles, a PTFE liner seems like a good idea to me, but what do I know. .

 

[beerthief]

I have thought about this also . A LOT . but come to the conclusion that people have been shooting air for years and not many examples of serious results happening, SO i have the usual filters in place and just go on shooting . MY real concern started when i was shooting a springer on a rainy day 100% humidity and thought "im sucking that wet air into my new 97 " , everyone on here said i was not to be concerned, people hunt in the rain . at that point i quit thinkling about how to fix it .

 

[Miami Airgunner]

I have thought about this also . A LOT . but come to the conclusion that people have been shooting air for years and not many examples of serious results happening, SO i have the usual filters in place and just go on shooting . MY real concern started when i was shooting a springer on a rainy day 100% humidity and thought "im sucking that wet air into my new 97 " , everyone on here said i was not to be concerned, people hunt in the rain . at that point i quit thinkling about how to fix it .

You know, it's stuff like that which makes me usually own a DGAF version of everything I love. After all, it's great to have REALLY nice examples of things to love and use, but it's also just grand to have a mule you can go beat on without concern for it's well being, ensuring you never miss a chance to enjoy yourself because you were worried about hurting the equipment.

Onewheel? Yep. I have a specific board I'll ride through a river and toss down a cliffside, it's been built to do better at it, and I can afford to lose/damage it.

DSLR? Oh yeah! Of course, I have several "dumb stuff" bodies and lenses

E-Bike? Just bought a fantastic RAD Bike on special for $480 to my door, brand new... I won't ride my $5000 bike in the rain, but you can BET I am going to test the $500 one just to see how dumb it'll let me be. I can afford to lose/damage it.

I have a .30 Hatsan springer, and a Vectis that I've chopped the hell out of for fun, and various mods - they are both perfect for doing anything dumb. I and can afford to damage them. . They have both seen more than a few rainy days on the backyard range, and are still great. Thinking I may get some cheap low power springer for this sort of stuff as well, since I really don't need to always be smashing paintballs with 20-40 FPE LOL.

 

[beerthief]

You know, it's stuff like that which makes me usually own a DGAF version of everything I love. After all, it's great to have REALLY nice examples of things to love and use, but it's also just grand to have a mule you can go beat on without concern for it's well being, ensuring you never miss a chance to enjoy yourself because you were worried about hurting the equipment.

Onewheel? Yep. I have a specific board I'll ride through a river and toss down a cliffside, it's been built to do better at it, and I can afford to lose/damage it.

DSLR? Oh yeah! Of course, I have several "dumb stuff" bodies and lenses

E-Bike? Just bought a fantastic RAD Bike on special for $480 to my door, brand new... I won't ride my $5000 bike in the rain, but you can BET I am going to test the $500 one just to see how dumb it'll let me be. I can afford to lose/damage it.

I have a .30 Hatsan springer, and a Vectis that I've chopped the hell out of for fun, and various mods - they are both perfect for doing anything dumb. I and can afford to damage them. . They have both seen more than a few rainy days on the backyard range, and are still great. Thinking I may get some cheap low power springer for this sort of stuff as well, since I really don't need to always be smashing paintballs with 20-40 FPE LOL.

Why buy a cheap low power springer when you can buy a HW30 from Kral for the same $$ ? still shoot paint balls .

 

[Chickenthief]

1) If you have a sponge the volume of a gallon with 10% water in it, now compress that sponge 10 times, the moisture is the same but it is now in a container 10 times smaller. So now it will fill every pore of the sponge. Compress that 10 times more and you have water everywhere. And if you continue it only accumulates.

Same in compressed air. It only get’s worse if you do nothing about it.

But at some 150bar~2200psi’ish you’we reached 100% humidity even for bone dry Arizona air and water will collect at the bottom of the moisture trap built into the compressor. A desiccant filter will remove most of the remaining high pressure moisture. If you’re still at 30-50% moisture at 3000psi then dilute that 10 times to 300 psi and you’re at 3-5% and then down 10 times to 30psi and you’re at 0.3-0.5%.
2) Tough to do
3) I would guess under 50%
4) Yes, it always work and dont need replacing.
5) Many diving compressors does over 100gallon of air every minute and adhere to EN 12021
6) Look at what the diving compressors uses in their filters!
7) The charcoal is to remove odd taste as the air is inhaled nothing more.

EN 12021: https://www.breathesafety.com/technical-blog/what-is-en12021-and-why-do-we-air-quality-test.html

Compressor Filter System Theory - Scuba Engineer

High Pressure Breathing Air Compressor Filtration System Design author:- Stephen E Burton BSc(hons) C.Eng, MIET - Email to:- [email protected]

scubaengineer.com

I hope this helps you a little.