GTA
Support Equipment For PCP/HPA/CO2 and springers ,rams => Support Equipment For PCP/HPA/CO2 => Topic started by: AlanMcD on February 19, 2018, 09:12:08 PM
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I thought I would share some of the results of some calculations on absolute humidity that I ran several years ago when trying to decide how to go about drying the air feeding my then new Shoebox Max. Hopefully this will clarify a very confusing topic for most people.
The confusion really stems from people referring to relative humidity all the time, as it really is a horrible metric to use for this purpose - given that we are looking at different pressure levels, we are basically destroying the ability to look at anything from a relative standpoint.
I prefer to use "absolute humidity," as it speaks to the amount of water vapor that is in a given unit of air, along with dew points at given pressures that equate to a specified absolute humidity level. As most of us know, as air is pressurized it "loses" the ability to hold as much water vapor at a given temperature - thus to retain that water vapor the dew point must rise as the pressure rises. If the pressurized air cools down, some of that water vapor will condense out into liquid water. This leads to an important point – at the dew point for a given air charge at any pressure, the “relative humidity” will always be 100% as the air is holding as much water vapor as it can – any more than that amount will condense out as liquid water.
To assist in understanding, I have complied all the information into a table attached as a pdf. What this shows is a series of columns indicating the dew points at different pressure levels, along with the amount of water vapor that would be in one cubic meter of air at atmospheric pressure. And here is the most important point in all of this: that “standard” cubic meter of air will always hold that much vapor regardless of pressure, provided that the temperature of the air charge does not fall below the dew point for that pressure and water vapor level.
This is what we are going for – “dry air” only means that the air holds sufficiently little water vapor that nothing condenses out into our tanks or guns after the air cools down after compression. The big question is “how much water vapor do we need to remove to make sure this happens?” It turns out to be quite a lot, as you will see when you study and begin to understand the data table. The bottom line is that no matter how low the humidity is when you run your compressors, there is plenty of opportunity for water to pass to our tanks if we A) allow a hot air charge to pass to the tank, and B) do nothing to capture the water vapor that is in the air charge either going into or coming out of the compressor. This matters because A) the air coming out of any compressor is guaranteed to be hotter than it will be after is sits in the tank for a while and B) without passing through a drying medium this air will be saturated with water vapor – in other words it will have a higher dew point than ambient for the tank, and condensation will occur in the tank when it cools down.
I will point out one thing here – all things being equal, it is always “easier” to dry air after compression for several reasons. The first is that the act of compression will cause much of the water vapor to condense on its own. The second is that with all that water vapor already removed the drying medium only needs to remove a smaller amount of remaining water vapor. Of course all things are not always equal – as in the case of a Shoebox where we have ready access to the air after the first stage of compression, and time spent compressing air into a post compression filter makes a slow fill process even slower . . . but I digress. Bottom line – air can be dried anywhere in the compression chain, even before it starts . . .
OK – onto the table. You will see that it is organized into sections. The first is about air as it goes through different stages of compression – for this I picked 68 degrees Fahrenheit to use for consistent data. The second section shows the same data for different drying mediums and standards, and the third shows the relevant data for other key temperatures, like running a small pancake compressor straight into a Shoebox, or running a Shoebox with no fan and the cover closed.
The important thing to note is the difference in the amount of water in the last column between different lines – this show the potential for water to condense in a tank out of each cubic meter of air we compress.
So enough words for now – review the table, think, and ask questions. And enjoy the learning process!
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If I understand your table.... if you use Silica beads the driest you can get is 0.07 g/CM.... but saturated air at 4500 psi contains only 0.06 g/CM.... Does that mean that at least in theory you can't get the air dry enough using Silica beads to not end up with a trace of liquid water in your tank at 4500 psi?.... I mean we're only talking 10 mg. of water in a cubic metre of air.... but does that apply even if you dry the air between the shop compressor and the Shoebox?....
Bob
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Good question, Bob. You are reading the table correctly.
I went through all this several years ago, and I figured I could beat that by a little bit by going big on the dryer so that the dwell time of the air in the dryer would be ridiculously long. After all, the dryer is rated to dry to a -45 dew point with a flow rate of 10 CFM, and I am flowing 0.1 CFM. I figured I would get a bit closer to -60 F or so.
Anyways, I opened up my Guppy this weekend after having put about 10 cubic meters of air through it, figuring that would tell me if I was correct based on how much water I found in it, and it was bone dry. So it must be in that range.
I keep my tank in my basement, and that is where I do most of my shooting and fills. It runs about 65 on average down there, and with no signs of water after 10 cubic meters of air clearly shows that I am beating the -45F ambient dew point going into the Shoebox.
Part of me wants to just swap the desiccant with molecular sieve 4A beads, but I really don't think it is necessary . . .
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I'm sure that I do not understand all of this correctly. Seems that the molecular sieve material in the high pressure flow is going to be much better than silica beads. Joe Brancato seems to have indicated that even the molecular sieve material is not going to absorb moisture that well if the air stream is not held in a "tightly packed" body of sieve material for a noticeable amount of time (hence his Pressure Maintaining Valve arrangement on the Alpha Filter). Bottom line-is the molecular sieve material in a Gold filter or a Diablo without PMV capable of absorbing enough moisture to improve the situation? And would silica beads before that point do any good?
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My pancake compressor has a 6 gal. tank which I drain regularly.... I then run my regulated 125 psi shop air through 25' of coiled hose (to cool), and into an inline separator/water trap, then into a 2 gallon holding tank, that has never had any water in it when I bleed it.... Between that and my ShoeBox I run two small inline Silica dessicant filters and I take them apart and dry them before the second one changes colour completely (I should do it as soon as I notice any pink, but I'm lazy).... I can just get one top-up from 3000 psi to 4500 on my Great White before having to bake the beads (250*F for 30 min.) to recondition them....
I just ordered a larger dessicant filter to replace the two inline ones.... because I'm getting tired of baking the beads every fill.... It is rated at 15 CFM, and of course my F8 is only about 0.15 CFM.... so like you the plan is to have the air sit in the dessicant much longer.... I guess I'll see how it works....
Bob
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So to summarize, its better to have a type of dryer/filter after the shop compressor before going to the Shoebox than to have nothing at all? Then add high pressure filter on the output like the Alpha filter?
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I have a Yong Heng with the small included filter and a large gold filter with molecular sieve. I always chill my filters before topping off my 88cf bottle. The small filter warms up in just a coupe minutes, but the gold filter stays mostly cool. The inlet side warms up some but half the shell and outlet side stay pretty cool. I may start wrapping it with ice packs.
I always find liquid water in the small filter after filling. I’ve only found slightly damp filter media on the inlet side of the gold filter. I never go more than two fills before changing out the sieve. I question the effectiveness of the sieve since the dwell time is quite limited.
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Alfonso,
I would summarize by saying that we need to be drying the air that we compress into our tanks. If we don't, we will easily be passing roughly a quarter of a cc of water vapor into our tanks in the hot air that will condense out into liquid water from each cubic meter of air we compress - no matter how much liquid water we are able to vent out before it gets to the tank. This will stay in the tank and add up over time with each fill.
That drying can be done anywhere in the path to the tank, as once the air is dried it stays dried. Silica Gel will do very well, but Molecular Sieve is best - and if using a Shoebox compressor the air can be dried equally well either before or after the Shoebox. Drying it before means the dryer will be saturated sooner as more water vapor will be in the air, but drying it after will result in noticeably longer fill times due to the need to fully compress air into the added volume of the filter and the slow fill rate of the Shoebox. Take your pick - you don't need to do both, but can if you want to.
If using an "all in one" compressor the only good option is to dry after compression, as there is so much vapor in ambient air - you would need a lot of dryer medium to fully remove all that vapor, and it would have to be regenerated often.
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Nice data. As more and more inexpensive compressors are getting out into the field without proper moisture control, I expect that we may start seeing a rash of tank failures due to corrosion. Hopefully, this will get caught during visual and hydro testing, and won't result in any catastrophic failures. Everything that we can do to raise awareness to this issue will pay off in the long run to keep our sport safe.
Another possible option for desiccant material is activated alumina. It has similar absorption properties as molecular sieve, but bakes out at a lower temperature, and may not have the reported corrosive properties of molecular sieve.
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In another thread, Alan mentioned degassing his guppy tank, and testing for any moisture. I think this would be good practice. Either done annually or between (2.5 years) the required 5 year inspection/test. Thoughts?
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What is the best recommended and cost effective way to do this low pressure side filtering?
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What is the best recommended and cost effective way to do this low pressure side filtering?
I think most will say, "the bigger, the better". Certainly, if you are filling large bottles or using a compressor that needs higher flow rates, big ones are better.
Alan posted a nice set-up that works well with SB compressors. It is larger than what I use.
I use this: https://www.harborfreight.com/38-in-desiccant-dryer-with-oil-removal-filter-69923.html (https://www.harborfreight.com/38-in-desiccant-dryer-with-oil-removal-filter-69923.html) about 3' from my CAT first stage compressor. I have a coiled line from the output of that filter, with two disposable filters, just prior to SB input. When I see the first one of the disposables change color, I swap out the desiccant on all three. I save the old, to bake out at a latter time. When I get 3/4 way through the current bag, I'll bake out the used.
I only fill guppy and 90ci tanks.
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What is the best recommended and cost effective way to do this low pressure side filtering?
Something like this:
https://www.ebay.com/itm/SMC-MEMBRANE-AIR-DRYER-IDG1-02-X192/172964248232?hash=item284578faa8:g:DZ0AAOSwk~ZZ~elh (https://www.ebay.com/itm/SMC-MEMBRANE-AIR-DRYER-IDG1-02-X192/172964248232?hash=item284578faa8:g:DZ0AAOSwk~ZZ~elh)
It's a membrane air drier with a 10 year life of daily use. No power use or media to regenerate. You have to make sure is has clean and oil free air or the membrane will become contaminated and stop working. The flow rates for that version will work with a Shoebox.
Taso
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What is the best recommended and cost effective way to do this low pressure side filtering?
I'll add this to the other replies. I have the Harbor Freight combined oil filter/water separator with small dessicant filter, and I added this immediately after it:
https://www.gamut.com/p/parker-hannifin-desiccant-dryer-4400-cu-ft-total-air-capacity-ODIyNDM2?q=716R140&utm_campaign=398131&utm_content=23022475&utm_medium=email&utm_source=Order_Confirmation_100617 (https://www.gamut.com/p/parker-hannifin-desiccant-dryer-4400-cu-ft-total-air-capacity-ODIyNDM2?q=716R140&utm_campaign=398131&utm_content=23022475&utm_medium=email&utm_source=Order_Confirmation_100617)
I'm using an Altaros booster, so there is another small water separator and dessicant filter that come after these. Once I got everything working properly, I was able to go from 3700-4400 psi with no change in color on the large Parker Hannifan dessicant dryer.
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I think that Parker-Hannifin is a great unit at a great price. I have the same basic unit made by Wilkerson on mine, and I am only now beginning to see a slight change in color in the beads in mine after 145 hours of run time of my Shoebox. I will probably dry it this weekend, and then I can report on the water weight I got out of it.
If you run one of these on the input side of a booster pump (be it the Altoros or a Shoebox) you will be in a good place for dry air - the first stage of compression will lead to condensing out around 90% of the water vapor, saving your dryer from having to handle all that load, and you will get the air very dry for much less cost than post compression filtration (plus no wasted time pressurizing that filter).
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I think that Parker-Hannifin is a great unit at a great price. I have the same basic unit made by Wilkerson on mine, and I am only now beginning to see a slight change in color in the beads in mine after 145 hours of run time of my Shoebox. I will probably dry it this weekend, and then I can report on the water weight I got out of it.
If you run one of these on the input side of a booster pump (be it the Altoros or a Shoebox) you will be in a good place for dry air - the first stage of compression will lead to condensing out around 90% of the water vapor, saving your dryer from having to handle all that load, and you will get the air very dry for much less cost than post compression filtration (plus no wasted time pressurizing that filter).
Thanks for the second opinion on that setup! I did a ton of reading before going the route that I did, but I'm still not COMPLETELY comfortable. When I have to fill in the summer, I'll be dealing with horrendous humidity here in North Mississippi. I guess I'll just keep a close eye on my desiccant in the big filter and stop if the color change approaches the top of the dryer, or maybe even 2/3 of the way up. The small desiccant filter in the Altaros unit has not changed at all, and the big desiccant filter has only changed color about 1/3 of the way up. That only happened when I had a leak on the Altaros middle stage line and ran the unit way too long. Now that I tracked that down, I don't even see a color change on the big filter (3700-4500 psi fill on Great White tank)--only on the little HF unit.
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Daniel,
The Altaros booster has two air systems tied into the single inlet. One system runs the piston for compression. The other system is the air used to fill your gun or air cylinder.
What you could do is supply fill side with dried air and the compressor side with unfiltered air. This would help the life of your desiccant. Or you could splice the drier into the fill side.
Taso
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Daniel,
The Altaros booster has two air systems tied into the single inlet. One system runs the piston for compression. The other system is the air used to fill your gun or air cylinder.
What you could do is supply fill side with dried air and the compressor side with unfiltered air. This would help the life of your desiccant. Or you could splice the drier into the fill side.
Taso
I didn't know that! I only see one input, and there's nothing about it in the manual. Do you have a link to instruction or video describing how to use the separate system?
It's not a big deal since I fixed the leak, but I would like to know how to use the option.
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So I started digging to find the threads where we discussed:
https://www.gatewaytoairguns.org/GTA/index.php?topic=123325.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=123325.0)
https://www.gatewaytoairguns.org/GTA/index.php?topic=135521.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=135521.0)
Taso
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So I started digging to find the threads where we discussed:
https://www.gatewaytoairguns.org/GTA/index.php?topic=123325.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=123325.0)
https://www.gatewaytoairguns.org/GTA/index.php?topic=135521.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=135521.0)
Taso
Now the thought of losing a 4500 psi tank worth $800 because of a failed 5 yr hydro is scary.
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What is the best recommended and cost effective way to do this low pressure side filtering?
I think most will say, "the bigger, the better". Certainly, if you are filling large bottles or using a compressor that needs higher flow rates, big ones are better.
Alan posted a nice set-up that works well with SB compressors. It is larger than what I use.
I use this: https://www.harborfreight.com/38-in-desiccant-dryer-with-oil-removal-filter-69923.html (https://www.harborfreight.com/38-in-desiccant-dryer-with-oil-removal-filter-69923.html) about 3' from my CAT first stage compressor. I have a coiled line from the output of that filter, with two disposable filters, just prior to SB input. When I see the first one of the disposables change color, I swap out the desiccant on all three. I save the old, to bake out at a latter time. When I get 3/4 way through the current bag, I'll bake out the used.
I only fill guppy and 90ci tanks.
I went to Harbor Freight last Sunday to check that specific dessicant /dryer but I thought it's really small and wonder if I can find a little bigger since I'm using a Great White tank 90 cubic feet.so I'm still in the search.
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Will this work. If you hook up like 3 or 4 of these in series?
https://www.a2zozone.com/products/silica-air-dryer?utm_medium=cpc&utm_source=googlepla&variant=574447973&gclid=Cj0KCQiAq6_UBRCEARIsAHyrgUy2kFmX7TW83gx5NMvPdQryWt__47nDZBhcvdsFX8dpspRLXFwdMB0aAp0qEALw_wcB (https://www.a2zozone.com/products/silica-air-dryer?utm_medium=cpc&utm_source=googlepla&variant=574447973&gclid=Cj0KCQiAq6_UBRCEARIsAHyrgUy2kFmX7TW83gx5NMvPdQryWt__47nDZBhcvdsFX8dpspRLXFwdMB0aAp0qEALw_wcB)
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For a 60 minute tank, then would look seriously at what Alan and Dan are using. if you mount it where it is not easily visible, then maybe add one of those inline at the input to SB.
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Will this work. If you hook up like 3 or 4 of these in series?
https://www.a2zozone.com/products/silica-air-dryer?utm_medium=cpc&utm_source=googlepla&variant=574447973&gclid=Cj0KCQiAq6_UBRCEARIsAHyrgUy2kFmX7TW83gx5NMvPdQryWt__47nDZBhcvdsFX8dpspRLXFwdMB0aAp0qEALw_wcB (https://www.a2zozone.com/products/silica-air-dryer?utm_medium=cpc&utm_source=googlepla&variant=574447973&gclid=Cj0KCQiAq6_UBRCEARIsAHyrgUy2kFmX7TW83gx5NMvPdQryWt__47nDZBhcvdsFX8dpspRLXFwdMB0aAp0qEALw_wcB)
I don't see a pressure rating for those filters. Make sure they can handle the pressure.
Taso
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Will this work. If you hook up like 3 or 4 of these in series?
https://www.a2zozone.com/products/silica-air-dryer?utm_medium=cpc&utm_source=googlepla&variant=574447973&gclid=Cj0KCQiAq6_UBRCEARIsAHyrgUy2kFmX7TW83gx5NMvPdQryWt__47nDZBhcvdsFX8dpspRLXFwdMB0aAp0qEALw_wcB (https://www.a2zozone.com/products/silica-air-dryer?utm_medium=cpc&utm_source=googlepla&variant=574447973&gclid=Cj0KCQiAq6_UBRCEARIsAHyrgUy2kFmX7TW83gx5NMvPdQryWt__47nDZBhcvdsFX8dpspRLXFwdMB0aAp0qEALw_wcB)
I didn't see a pressure rating. You want one that can withstand 125psi. It looks like it would hold a decent amount of desiccant, but didn't see that listed. Wondering if it is like the inline disposables, where the beads only fill a thin layer vs the whole cylinder.
PS: With shipping, Amazon Prime might be a better option at $20.
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I emailed the seller if that plastic case will hold 125 psi. I will look at those Gold filter at Ali express. Or have those contents poured into the gold filter instead.
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I emailed the seller if that plastic case will hold 125 psi. I will look at those Gold filter at Ali express. Or have those contents poured into the gold filter instead.
The gold filter is way overkill (psi wise) for the input side and then you would want a visible inline one downstream.
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How about this? Just replace the inside with the desiccant?
https://www.aliexpress.com/item/PCP-oil-water-separator-30-mpa-4500psi-310bar/32815274871.html?spm=2114.10010108.1000014.1.7cb13ae39ib21t&traffic_analysisId=recommend_3035_1_83054_iswinstore&scm=1007.13338.83054.0&pvid=ce25fa18-04f2-46ee-a659-acaa15b9f80a&tpp=1 (https://www.aliexpress.com/item/PCP-oil-water-separator-30-mpa-4500psi-310bar/32815274871.html?spm=2114.10010108.1000014.1.7cb13ae39ib21t&traffic_analysisId=recommend_3035_1_83054_iswinstore&scm=1007.13338.83054.0&pvid=ce25fa18-04f2-46ee-a659-acaa15b9f80a&tpp=1)
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That looks like the standard gold filter vessel that many have been using for the high side filter. For using it on the low side, to me, it is not worth the savings over what Dan and Alan are using. You are giving up the visual inspection capability and need to convert fittings to low side type.
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So I started digging to find the threads where we discussed:
https://www.gatewaytoairguns.org/GTA/index.php?topic=123325.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=123325.0)
https://www.gatewaytoairguns.org/GTA/index.php?topic=135521.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=135521.0)
Taso
Thank you Taso! I got my Altaros used, and it came with extra fittings for boosting from a tank. I never thought about using a second air compressor. Good stuff!
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Alan, I have a question for you.... Let us assume for a moment that the air in your 4500 psi SCBA tank is saturated at 68*F.... which means it contains 0.06 grams water per Cubic Metre.... Now, let's use that air to fill a PCP to 3,000 psi.... The pressure in the SCBA has now dropped slightly, depending on the volume of the reservoir on the gun, and you haven't added any water to the system, so does that not mean that the air in the SCBA tank can hold more water?.... So, if there was a trace of liquid water in the tank, should it not evaporate, at least partially, to re-saturate the air in the SCBA tank?....
More importantly, the reservoir you filled to 3,000 psi can hold much more water (50% more?) than the saturated 4,500 psi air you filled it with.... So, as long as you don't invert the SCBA tank, and blast liquid water into your PCP, shouldn't it be well below the saturation point at 3,000 psi.... I have heard people claim that as you fill your PCP, you are gradually accumulating water inside the reservoir.... I don't believe that to be the case if you are filling from a tank at a higher pressure, because my understanding is that air "dries" as it expands.... so even if your source air is saturated with water vapour, filling anything from that tank results in less than saturated air.... and zero chance of condensation, providing the storage (equilibrium) temperature is the same?.... Specifically, what would be the Dew Point of air at 3,000 psi that contains 0.06 g/CM water?....
Am I "all wet"?....
Bob
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Bob,
You have it correct. Even if water does accumulate in the tank as the air charge cools, no liquid water will end up transferring to our guns. While that is good news, we still need to keep the water out of the tanks to avoid corrosion there.
Unfortunately, the reverse is also true - when we begin filling our tanks up, if the air is not dried to the level we want at the highest pressure / lowest temperature situation for our tanks, the air charge entering the tank can carry more water vapor into the tank. Assuming we start filling the tank at 3000 psi, then at 68F that air entering the tank can carry 0.09 grams of water per cubic meter, leaving some to condense out as the pressure rises. But it is worse than that, because if the air is not dried before going into the tank, it will carry water vapor at whatever the temperature and pressure allows. At 3000 psi and 100F (probably typical coming out of most compressors, unless cooled very actively) the air will carry 0.2 grams of water per cubic meter, which leaves a lot to condense out when the tank is full.
Bottom line - we need to dry our air before it gets to the tank (or gun if filling directly). It can be dried anywhere in the airflow path through compression, but we need to get it dried.