Desiccator Experiment Results…and what happened to my compressor

[Mole2017]

You might have seen my post last week about my shop compressor kicking the bucket, leading me to take a close look at my brass fill probe. The demise of the compressor was also the impetus to conclude an experiment involving this compressor that I started in April 2019.

Around March of last year, I discovered some moisture in the buddy bottle of my R10 and some moisture-related fowling of parts in the rifle itself. To tell the truth, it wasn’t clear then if the moisture was my fault or that of the previous owner, but it was disturbing. I cleaned things up and did two things towards prevention of a repeat occurrence:

• created a system to boost the air to my hand pump, hoping to gain both fewer strokes of the pump and less moisture in the air in the first place and
  
• loaded some silica gel into both the buddy bottle and the air compressor tank to further deal with moisture.

Here’s the system set up for pumping, with the now-deceased compressor:


Desiccation Experiment

The boost has been nice, but now that the compressor has died, it was time to check on the 325 grams of silica gel inside the compressor tank. I unscrewed the drain and dumped out what would come out. After drying, I recovered 252 grams of silica gel, meaning there are still almost 75 grams inside. I hear some of it still moving around, but I suspect some of it may be stuck to things. Here's the rusty debris that came out with my silica gel:



This compressor wasn’t new when I started this. I had already had it a few years and found rusty water in it a couple times when I drained it.

Anyway, the silica. Did it work? Well, after a year in the tank, what I dumped out weighed 275 grams before drying. Just 23 grams after a year of use and no interventions to drain the tank? I don’t go through a lot of air—maybe filled this thing a dozen times in the year. The compressor fills the tank to 110 PSI (or so) and I let it sit overnight and then use that air to fill my rifle until the tank pressure gets below 20 PSI. Since the regulators leaks so much, that is about 2 fills, or maybe 3 if I am lucky.

So, is 23 grams of water an accomplishment? Considering that the 252 grams of dry silica now weighs over 317 grams just from sitting out on my kitchen counter a little over 24 hours during some humid weather—absorbed 65 grams from atmospheric pressure air—I’d say it must have helped somehow. The inside of that compressor tank was bone dry—just dusty beads and rust flakes.

Did I mention it was dry and rusty inside? My silica gel was the normal pale colored almost-white beads but is now rust-orange, as shown in this photo (it goes to the bin next):



Compressor Postmortem

Speaking of rust, let’s turn this to into a public service announcement. Do you have an air compressor? Take a moment to drain the water and remember to drain it regularly or install something to do it for you. Do you have an old compressor? Think seriously about ditching it unless you know it was well cared for.

So, having a dead compressor, it was time to take it apart. But first, a look at the inlet side of my tank regulator:



Die cast metal does not like moisture. This part was mounted on the backside of the upper tank of the two little tanks that make up this unit. (Got and old, low cost compressor…?) This compressor might have been 10 years old and was used decidedly infrequently. I bought on sale for the small nail gun that the bundle included.

What was the cause of the failure? Not quite sure of the cause, but here is a picture of the mode of failure:



A contact on the commutator “ring” came off (I found it in the bottom of the motor housing). It actually ran in this condition but did weird things like “skip”, change speeds, and--just before I shut it off—stall outright for a few seconds at a time.

So, now a Makita MAC210Q has taken its place. This unit is doesn’t have intercooling and moisture traps like the big ones, so I plan to give it a load of silica gel too and see how that does. And it is so much more quiet! I used to start the other one and leave the room as fast as I could!

The Buddy Bottle

That leaves the buddy bottle. Inside my buddy bottle there is a piece of ordinary paper, rolled small enough to fit through the neck of the bottle and sealed with I think 6 or 8 grams of silica gel inside it. I don’t have plans to open that real soon, but I might be into the rifle valve and regulator areas later this summer and I’ll decide then how it may be doing. 6 grams is more than enough to hold the amount of water I had found that started all this last year.

And that’s my story. Not an option for everybody, but it seems to have worked for me. If I find myself with some time on my hands, I may cut the end of that compressor tank to see what I find--that would be good to add here. Feel free to describe what you are doing to control moisture.

[Doug Wall]

None of your pictures show up. One thing that you have to remember is that not all of the moisture from your boost compressor will end up in the tank! A lot of it will go through the hose. That's why painters, and Shoebox owners always have a desiccant unit BETWEEN the output of the first compressor, and the final unit. In general, it's a vary bad idea to put desiccant inside the tanks! You have very little control like that, and for the boost compressor, you could easily overload the desiccant inside, and end up with a muddy mess. If you get all of the moisture out of the hand pump feed stream, you don't need desiccant on the output side, or in the buddy bottle(or gun).
As you said, drain the boost compressor tank regularly, and something like this would be good on the output of the boost, so you can observe the indicating desiccant for color change.
https://www.ebay.com/itm/1-2-IN-LINE-DESICCANT-AIR-DRYER-FOR-COMPRESSED-AIR-PNEUMATIC-TOOLS-PAINT-SPRAY/192009639698?_trkparms=aid%3D1110007%26algo%3DHOMESPLICE.DISC%26ao%3D1%26asc%3D20200220090753%26meid%3Dd16cc691b2094738be39b4ade7d00277%26pid%3D100009%26rk%3D1%26rkt%3D1%26sd%3D402271953000%26itm%3D192009639698%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3Ddefault%26brand%3DUnbranded&_trksid=p2047675.c100009.m1982

[Mole2017]

Sorry about the pictures; I can only guess it is platform related as I'm using the GTA media folders to "host" the pictures and embed them with the post editor.

I'm not sure I follow your comments, so I'll see if I can recap. For sure, in large flow rate/high usage situations you will need more than I have done and inline as you describe. So, my approach is hardly a fire-and-forget solution for everyone. Silica gel by itself is not corrosive, but the blue colored stuff is. In fact, it is toxic too and banned in many countries. Fortunately, there are alternative indicating silica gels available.

My situation is a small dedicated compressor that gets run so infrequently that moisture collects so slowly as to make it hard to drain any. (If I ran it and used it a couple hours for a project, I could see some serious water starting to collect.) I wanted a way to capture it coming at these slow rates. Not having the option to tear my compressor plumbing apart to insert a drier, I put it in the tank, just to see. If my tank had one of those inspection ports, I would have put a bag or two of this in there.

That it captured and held 23 grams tells me it was accomplishing something (it adsorbed three times that amount sitting out in my kitchen). I'd be interested to hear what the adsorb and release behavior of silica is as the tank pressure varies; I haven't looked it up myself. For example, when first filled, the relative humidity is high and the silica adsorbs a bunch; but use some air, change the temperatures, or whatever, and the conditions change and the silica either tries to take up more moisture or lets some go, e.g. this chart.

The packet in the buddy bottle is the one I really would like to see. I did that one because I already had opened the buddy bottle and found a gram or two of water. It just has to keep me out of condensed water situations. If I open that and find a bone dry bottle, I'll consider it a success, and the results with this small compressor lead me to think it will work.

Given that some other GTA users hand pump without any moisture control devices and seem to be doing ok, e.g. this GTA thread, anything has a chance of being helpful. For what it is worth, hand pumping atmospheric air (i.e. no boost), can haul in a lot of moisture. Consider Ribbonstone's results discussed here.

[Doug Wall]

" Not having the option to tear my compressor plumbing apart to insert a drier, I put it in the tank, just to see"
I've never seen a compressor that you couldn't easily take off the output fitting to install a dryer/filter. If you wanted to, you could easily build a desiccant canister for the input side of the compressor as well, and keep a lot out of the tank. I have a small desiccant (about 7", around $30 on ebay) on the output of my Nomad II, that wouldn't be too bad on a boosted hand pump, that's a lot easier to check than pulling a tank valve off.
"Given that some other GTA users hand pump without any moisture control devices and seem to be doing ok, "
I have regular contact with a Crosman certified service station, and from what they tell me, virtually all of the leaking guns that they have come in, have internal corrosion from moisture, and have been hand pumped without desiccant.

[Ribbonstone]

Wow....you dug up that old post that made me a non-beliver (in my climate) of the Dry Pac.

Updated.
The Hills died from neglect....started using a chinese pump and figured I'd use it until it diedfor everything.It didn't die. Still working like 8 years later.

Compressor or (cheap Chinese)handpump.  Tend to silicone grease the internals of the rifle's air tubes (thin...like waxing a car) and not worry about moisture.

Still hand pump the little volume guns...and the 2K guns.  Only break out the compressor for big volumes or higher than 3K pressures.

Just had the oldest two apart (11 and 17 years)....no rust/corrosion in the pressure area of the air tube.

[AlanMcD]

I see your pictures just fine . . .

I will agree that putting desiccant in the tanks is not really a good idea.  I would not want them in any tank I use to feed an airgun, as desiccant beads can fracture when hit with liquid water, and that can release very fine abrasive particles in the air you are feeding into your guns.  I think it would be better to use a good sized desiccant filter in your airflow path to your hand pump, keeping the water out of it and out of your tanks in the first place.

Compressors are made to deal with condensation, thus the ability to vent/drain them.  While it is a good idea to drain them regularly, under regular usage the inside of the tanks get wet and stay wet - by definition of their duty, the inside of those tanks are subjected to 100% humidity their whole life.  And since it impossible to get "all" of the condensed water out when draining them, and any remaining water won't ever evaporate as the humidity in the tank is almost always at 100%, we know what that means - as do the tank manufacturers: the inside of compressor tanks always have some amount of liquid water in them.

Yes, eventually compressors will fail from corrosion.  My oil free shop compressor is about 26 years old and it still runs great - but it is darn loud.  It is no issue for feeding my Shoebox compressor in my workshop, as the shop compressor is in the garage and the air is plumbed into my house/shop.  But man it is loud when I am in the garage with it . . . and I expect if I replace it the reason will be that I finally decided to get a quieter compressor, long before its tank rusts through.

[UnderPressure]

How well did adding the additional stage (via compressor) work for hand pumping?

What did you notice most by doing this?

[Mole2017]

Thanks Ribbonstone! Yeah, when I found that post I knew that was data to keep a finger on and bookmarked it.

And Doug, yes, your observations are fair enough. Some people pump without desiccant and nothing happens. In 2019 it wasn't looking like I was one of them. Something on the outlet of the pump was doable and I have seen plenty of designs, including ones like yours posted this past January. But in a moment of Rube Goldbergness or just plain cheap opportunity, I popped it in the tank. I knew it wasn't going to come out conveniently, but here was an opportunity to find out. I forget the details, but I may have done the packet for the R10 bottle first and thought "why not?" and threw some into the little Campbell Hausfeld just to see what happened.

The Makita has somewhat better access to the tank plumbing, and the fitting for the metal pipe/tube from the compressor is twice the size of the drain plug and sure is tempting. The problem there is factory installed threadlock that I'm not sure I want to mettle with. But, again, here is a compressor that is going to do a lot of sitting around, so I might just give it the same treatment too. But I want to work out a better way to get the material in and out of the unit.

Alan posted while I was working on this reply. That "always at 100%" part was on my mind for both the buddy bottle and the compressor. Given the relatively low volume and an hunch about how much water I was dealing with, I figured it was worth a try. And that silica gel came out holding something like 10% of its weight in water, meaning, I think, (a) it was nowhere near full and (b) the tank wasn't at 100% RH either--maybe 20% judging from the charts. Win-win, except for some inconvenience.

I also though about the silica dust, but with the fine rust already in the tank I didn't think it was going to contribute much.

[Mole2017]

Russ, I like the boosted hand pumping a lot. It has been a while since I did a fill "unassisted" but the stroke count would end up as high as 160 strokes if I had let pressure get really low. 120 to 130 seems about right--40 strokes, take a break, repeat about three times for at least about 3000 PSI. At which point I often opted to call it done!

Now with a boost around 10-15 PSI (cheap gauges are hard to read...why does a pump with a 110 PSI limit have a 250 PSI gauge?), it is more like 80 strokes. You can boost at higher pressures to start, but I usually end up cutting back some near the end because it does become a little more work. The pump does warm up more; not too hot to touch, but warm. Taking a break helps with that.

If you boost, consider putting a cut-off valve on the compressor outlet. My line was threaded onto the compressor outlet, so I made the cut-valve part of that plumbing. It lets you shut of the air and take a few strokes to bring the pressures back down to "normal" before venting the hand pump and disconnecting the hoses. The Makita has a quick disconnect fitting already, so recycled my old compressor hose and the cut-off, adding a matching disconnect fitting to them.

[KnifeMaker]

Putting the beads in the tank is a sure way to super charge rusting. Huge mistake!  It will catch and hold the water against the tank and becomes itself, corrosive. And why the beads have to be change out regularly and dried. Putting it in the tank will greatly  increase rust on a grand scale!


Knife

[Mole2017]

Putting the beads in the tank is a sure way to super charge rusting. Huge mistake!  It will catch and hold the water against the tank and becomes itself, corrosive. And why the beads have to be change out regularly and dried. Putting it in the tank will greatly  increase rust on a grand scale!


Knife

Blue silica gel, yes, guaranteed, as it contains a salt. But plain silica? I'm still looking for data on that and haven't found any. By itself, it is chemically safe.

So, I'm going to postulate that there are two issues here. One is the old school blue indicating silica has given silica gel a bad rap, i.e. everyone thinks it a huge no-no to have loose silica beads in a tank. Two is that overloaded silica, i.e. soaking wet, is no better than wet sand and the water will lead to corrosion.

In fact, I just finished reading a paper that studied the addition of microscopic silica particles to improve the performance of coatings to protect steel from corrosion.

We have to remember how silica gel and molecular sieves work: microscopic porosity that literally traps water molecules. Both are chemically inert for our purposes. A chemist will have to chime in, but I suspect a water molecule trapped in a silica bead isn't going to be able to interact with metal that the bead is touching. I just spent some time looking online and found perforated steel cans that are filled with silica gel beads and used in gun safes. And you know what? some guy gave it a one star review after figuring out his wasn't made of aluminum, claiming that being steel it was doomed to rust out. One review did mention rust, but it was all over the can (outside) and his desiccant was already overloaded and past due to be recharged.

As for changing it out from time to time, yes, that is needed because the whole point is to have a place for the moisture to be trapped--once full, the silica gel and molecular sieve aren't doing anything for you. It is true that sealed in my tank like this I don't have a way to monitor moisture other than pull it out and check, which was part of the plan anyway. Since my compressor usage is actually quite low, I've actually had very little water to contain.

[KnifeMaker]

Yet you have shown the horrible results. Hello!

[Mole2017]

Yet you have shown the horrible results. Hello!

Don't forget this was a nearly 10 year old compressor. Water had already been in the tank at times prior to my experiment and rusty water had been seen in the past, i.e. rust was there before the silica was introduced (my mistake for leaving water in there long enough to do that).

This compressor has two tanks (shown in that first photograph); the bottom one is the one with the drain and that had held the silica. That is important because the upper tank is connected by a small bent tube (the new models have a fat straight stub between them). I can't remember how I held it while I loaded the silica, but I don't think any ended up in the upper tank. And I know there is no way it ended up in that regulator body.

It must also be remembered that water vapor in a tank doesn't conveniently condense at the bottom. It condenses on all surfaces that are cool enough to permit condensation. That includes all surfaces of the top and bottom tanks and the inlet side of the regulator. And each surface remains wet until a heat source sufficiently warms that surface or the relative humidity drops low enough to let things dry out.

This would explain the corrosion on the regulator inlet side. The outlet side was totally clean.

Judging by the moisture loading of the silica when I removed it (barely 1/3 of its capacity), relative humidity in this tank was about 20 percent and all surfaces would have been dry, i.e. not enough moisture to maintain active corrosion. (Everything I shook out was dusty and dry.) That's why we put this stuff in our gun safes and other storage systems. Silica gel packs are put inside new equipment and products so that environmental conditions during shipment and storage can't trigger condensation--the desiccant lowers the relative humidity and moisture dependent problems go away.

I'll try cut the tanks open soon and see if I can get some photographs. I predict some amount of rust on all surfaces in both tanks. It will be worse or at least different at the bottom of each tank where water would lay after rolling down the sides.

[Mole2017]

Rust report

Yesterday I cut both tanks open. I didn’t have a power tool that could do it safely, so I restrained it as best I could and went to work with a hack saw. These tanks are about 4.5" across, and the tank walls are 2 mm thick. I got lucky cutting where I did. Another 1/8” closer to the end I would have been cutting through twice that as the end caps are pressed in and welded to the cylinder that forms the body of each tank.

Other than some more rusty debris and the last of my silica gel, they are looking much better than I expected. In these two pictures, I had already dumped out the upper tank before cutting open the lower tank; no cleaning has been done:





Looks like I never had the full 325 grams of silica in there. That looks like a tablespoon of silica in the bottom of that lower tank, along with some of the "filings" from the hacksaw, i.e. a couple grams.  I must have miscalculated what I put in when I was drying and weighing stuff last year.

Anyway, the big surprise was the rust itself. The bottom tank is close to what I expected, except that the bottom of the tank is in really good shape. I was expecting heavy rust deposits where any water would have laid in the tank. The deposits on the sides are a fine coating rust dust (comes off with a wipe of the finger) with areas of "raised" rust blooms that are "glassy" and crusty (and mostly hollow, like bubbly blisters), not just big flakes of rust. Some areas seem to be benefiting, i.e. protected, from residual oils from manufacture or even overspray of the powder coating. Here is a shot looking at the “top” and far end of the bottom tank:



In that view you can see from left to right ports for the drain plug, a pressure relief, a small inlet from the compressor, a similar outlet for a pressure switch, and the tube going to the upper tank. Note the blue powder coating on the inside edge of that far end cap.

The upper tank had the weird stuff. I guess those "raised" rust deposits just grew bigger up there. Here's what that looked like:



And below is a view of the two ends. I've turned the two to be "topside up" so you can see that the rust grew wherever it wanted. Check out the powder coat overspray in that right hand piece from the lower tank. I still haven't figured out how that lower tank got powder coating inside it.



At first I wondered if the roundish glassy pieces were little corrosion "pearls" seeded with silica beads, but they are in fact mostly hollow. (I did find two silica gel beads up there, but they weren’t involved with anything, just rolling around.) Amazingly, these little “spheres” grew both up and down. Here’s a huge one (almost 1/8" in diameter) with a crack “hanging” in the end of the upper tank that I cut off:



Below is a picture of the remains of a couple that grew up from the bottom of the upper tank but that got their tops busted by sloshing debris while I manhandled the tank to dump my silica gel. The grey material is metal from the hack saw work. Incidentally the amount of rust debris on the loose in the upper tank was about the somewhat more than what I dumped out of the bottom tank through the drain plug port. It's piled in front of the two end caps pictured above.



Otherwise, it is just amazing to see how rust “grows” in these environments. This isn’t some backyard scrap pile; it’s like some little coral reef where a rusty spot starts and spreads where it can.



It is interesting to think of the dynamics here. Suppose the tank (with no silica gel) had been drained. The relative humidity would still be quite high inside and all it would take is a cool spell in my unfinished basement with a loose fitting door to the outside to let moisture condense on the sides and grow some rust and “flowers” until things warmed up again. It may be entirely possible the bottom of either tank never saw much moisture unless enough condensation formed to let some roll to the bottom in the first place. And that lower tank would benefit from its proximity to the floor to reduce cooling there. (Ever notice that a car parked even a couple yards from an outbuilding (not heated) gets a one-sided frost job in cold weather? That points to a difference in loss of heat by radiation.)

Summary

To recap, this tank is 9 years old (found the date tag on it). It was used occasionally for a couple years and then less frequently (like once a year?) until I hatched my plan to use it to fill the BSA R10 last year. I know the water damage happened before I introduced the silica gel. Seeing as the silica gel is completely uninvolved with any of the growths and scale in the tanks and how the bottom of the lower tank is also cleaner looking than the sides and top, I’d say the silica gel did nothing but good for the insides of this compressor tank.

Again, this is not a practical solution for just any situation. If you use your compressor enough that you would be able to drain something regularly from it, I think this stuff would get swamped. But I use mine about once every other month these days just for filling the air rifle. That's all I need it for unless I pull out that little pneumatic nail gun for a rare project to drive a half dozen or so brads.

I like the result so much I'm going to give the Makita a dose too. I've got a trick planned for that one--if I works, I'll add a picture here. What's neat about the Makita is I have this one new from the store: I think I can get before and after pictures of the inside by dropping an LED inside the drain port and holding my camera up to the hole for a picture of the back wall of the tank.

Finally, nobody has picked up on the fact that I did this to the buddy bottle on my R10 too, though that load of silica gel happens to be in a paper tube because I was concerned about silica dust there. That pack is there to keep the relative humidity down inside that tank too.

[KnifeMaker]

Wow! gotta wonder if a good powder coating inside would add any benefit.


Great job on the pic's!


Knife

[Mole2017]

If there was an easy way to do it without getting stuff in the wrong places, I'd treat the new compressor with something.

Whatever gets done, it has to be complete. If you look carefully at the picture of the cutoff end with the powder coat, the lower edge of the coating is pealing up (about 5 o'clock position). While looking for videos or pictures of the insides of people's air tanks, I did find one showing an epoxy spray coat being applied through a 2" inspection port.

And just for kicks, here's a video reminding us to not buy used compressors without checking a few things first:

[bear air]

Funny I should see this I just put together a dry air intake system for my new HPA compressor today using one of the little benjamin dessicant kits for their hand pumps. Ran it tonight and there was a lot less moisture when I did a quick bleed off while running it. I also noticed it had literally turned a bunch of the beads green when I was done. I plan on changing them out every time I run the compressor for an extended period of time.

[Doug Wall]

"Finally, nobody has picked up on the fact that I did this to the buddy bottle on my R10 too, though that load of silica gel happens to be in a paper tube because I was concerned about silica dust there. That pack is there to keep the relative humidity down inside that tank too. "

I actually did catch that here, but I thought it was a separate bottle
"I have a small desiccant (about 7", around $30 on ebay) on the output of my Nomad II, that wouldn't be too bad on a boosted hand pump, that's a lot easier to check than pulling a tank valve off."

[Doug Wall]

Funny I should see this I just put together a dry air intake system for my new HPA compressor today using one of the little benjamin dessicant kits for their hand pumps. Ran it tonight and there was a lot less moisture when I did a quick bleed off while running it. I also noticed it had literally turned a bunch of the beads green when I was done. I plan on changing them out every time I run the compressor for an extended period of time.

The little tiny hand pump desiccant packs are pretty useless on the input of a compressor. The key to desiccants working well is to have the air in contact with the desiccant for a long enough to have the moisture absorb. With those little ones, on a compressor, the air doesn't stay in long enough. Since this is on an input, the desiccant doesn't have to be in a pressure vessel. To make it effective, you can easily make a much larger one (say a quart size), with DIY components.

[bear air]

Thanks for the tip. This filter might be rather small but it really did capture a fair amount of moisture and turned a portion of the orange beads to green. I could also tell a significant drop in the moisture level when I did a quick purge on the high side. I figure every little bit helps. I wonder how much better two of them ran into a Y connector and then into the compressor would do. I do have it packed tight and also it sits upside down so the water beads towards the top/smallest part.