Moisture. How big a deal is it?

[Quad82]

I just picked up a used Wingshot. The PO said that it would leaked after a couple hours. So I got it at a good price. So I thought! You can hear air leaking at the air tube/barrel band. Easy enough fix. Pull the tank plug and replace the orings. Wrong. Seems he had already tried that. The tank plug had rusted to the tank tube at the threads. Yup, he stripped the threads cranking on the plug taking it out. No biggie. The inner tube looked fine. Called P A and bought a new plug with one-way valve already installed for $20 plus shipping. Easy Peary. Wrong again. It still leaked. But slower this time. You could still hear a faint hiss at the tube band just below the muzzle. So I tore it down again. This time I-really cleaned the threads of what I thought to be silicon grease and maybe a little rust color. By the time I had it clean enough to see the issue, we’ll take a look for yourself! The new air-tube will be here tomorrow. Anouther $150. Still I am ahead. But damn, not what I thought I was in for.
SO YES. Filter, filter, filter!

 

[Florida_Man]

Yowza. Do you think he primarily hand pumped it with no filter?

 

[Quad82]

Hard to say. I think the Wingshot came out in 2015? So 7 years of pumping without any water filter? I know when I found out about using a water filter. Had my first Mrod for about a year and only hand pumped. That is when I started modding. I opened up the rifle to add a larger transfer port and found a clump of rust in the air tube. Now I open each rifle about once a year or so just to clean and test for moisture.

 

[TheCurtster]

This is my pre pump air dryer experiment. 2x 24” long by 1 1/4” diameter PVC tubes, connected to make effectively a 4 foot tube. I’ll stuff the ends with cotton and fill the rest with desiccant beads. Total cost should be about $50.

 

[sd619223]

As a noobie, I’m reading lots of stuff regarding compressors, filters, tanks, SCBA, dive shops, desiccants, fire houses, etc. I want to be nice to my expensive new hobby, but how much moisture in our air is “too much”? With moderate usage (of our guns), moderate care (a desiccant filter on the pump), moderate humidity…. How long can one expect our guns to last before they develop the “mayonnaise” problem I’ve heard described (on a website trying to sell tanks and expensive pumps/filters). Is it really that big of an issue for a hobbyist shooter?

Thanks!

Curt

the question should be how much moisture is bad for the pcp. it would be wise to know what path the air takes from the bottle to the end of the barrel. then you can see what components could be exposed to moisture. stainless, brass, platic and marine grade aluminum would be safe i immagine. i found high humidity differences in the morning compared to mid-day and afternoon. with all the filtering devices offered, the more moisture removed the more resistance to air flow using any type of filtering medium. the little moisture that gets into your bottle should get blown out the barrel when fired down at the ground at low pressures easily. pull the gun apart once a year and check for moisture damage and clean if necessary.

 

[AlanMcD]

the question should be how much moisture is bad for the pcp. it would be wise to know what path the air takes from the bottle to the end of the barrel. then you can see what components could be exposed to moisture. stainless, brass, platic and marine grade aluminum would be safe i immagine. i found high humidity differences in the morning compared to mid-day and afternoon. with all the filtering devices offered, the more moisture removed the more resistance to air flow using any type of filtering medium. the little moisture that gets into your bottle should get blown out the barrel when fired down at the ground at low pressures easily. pull the gun apart once a year and check for moisture damage and clean if necessary.

I think the question on how much "moisture" is bad for a PCP needs to include a reference to the length of time between tear downs . . . .

It is important to understand that the state of "moisture" that causes issues in tanks and guns is liquid water, not water vapor. It is darn near impossible to get all water vapor out of compressed air, but it is fairly straightforward to drive the vapor level down below the dew point for a given pressure level - and then liquid water simply will not occur.

It is also important to know that ambient relative humidity is pretty much irrelevant in all of this - at "normal" levels (even in the desert) it only impacts how much water condenses out during compression. This is because of the fact that if we want to compress ~70F ambient air to 3000 psi and have no condensation occur in the compressed air once it cools down to the same ~70F, then the relative humidity of that ambient air must be under 1% (not a typo!). If the ambient air has any more humidity that that, and heated compressed air makes it into our guns, when it cools down then there will be water vapor that will condense in to liquid within the gun. Granted - we are not talking very much liquid water (likely less than a drop), but it can build up over time with every filling cycle. Some might be shot out - especially since as the pressure drops during shooting, some it will flash back to vapor and be shot out easily - but the more that is there the harder that will be to use as a solution to the problem. And that brings time between teardowns into the mix - the more frequent they are, the less liquid will build up as the amount resets with every degas and drying event.

To prevent the issue, one must actively "dry" the air charge before it gets into the gun. Personally, I expect there will be a lot of damaged guns out there (like the Wingshot) in the future from the proliferation of the small fast compressors that people are using without appropriate water vapor filtration . . . .

 

[Quad82]

To prevent the issue, one must actively "dry" the air charge before it gets into the gun. Personally, I expect there will be a lot of damaged guns out there (like the Wingshot) in the future from the proliferation of the small fast compressors that people are using without appropriate water vapor filtration

The other issue with these FAST compressors is you have no way to pre filter the air before it enters. They really piss out the water when bleeding between time-outs when filling even a small container.

 

[elwoodblues]

quit trying to pre filter and post filter , just feed your compressor Nitrogen NO WATER NO OXIDIZERS

 

[JimD]

The need to get the inlet air down to under 1% humidity pretty much tells you how successful a pre filter is going to be. I agree nitrogen will work, it cannot transport moisture. But I think the easiest and cheapest thing to do is to just get an additional filter that has an inner plastic cartridge and fill that cartridge with color changing dessicant. The color change is important in my opinion so you know when it is dry and when it is not. If it all changes color on one tank fill (improbable in my experience) then get a bigger one. You want some of it to still be dry at the end of the compressor run. If it is then the air in your gun is dry. The one on my Yong Heng is not very big but it takes over 6 refills of my 45 minute SCBA tank to get it more than half changed in color and then I change the beads out.

The other even cheaper and easier thing to do is to put your filters above the compressor so that any moisture that condenses as the air cools in the lines and even filters can run back down to the compressor where you can vent it. I vent every 5 minutes of run time on my YH and moisture comes out each time. That helps my filters stay dry.

Moisture in the air going into our airguns is not something to fear or spend a lot of money avoiding but it is not something to ignore either. A couple simple steps and your guns are not going to see significant moisture. (if you are wondering I mainly shoot my 3 P35s and to change the regulator I have to open the air chamber so I do inspect them from time to time and have never found water)

 

[AlanMcD]

quit trying to pre filter and post filter , just feed your compressor Nitrogen NO WATER NO OXIDIZERS

That's not really practical advice for everyone . . . many don't have easy or affordable access to N2.

It's not hard to filter properly - people just need to get the right stuff and then they are all set.

I could just as easily say this:
Quit messing with Nitrogen - just get a good appropriate sized rechargeable desiccant drier and then NO WATER NO ONGOING COST

The important thing is that people should be taking the appropriate steps to have "dry air" in their tanks and guns, be that Nitrogen, a huge pre-compression desiccant dryer, or a decent post compression desiccant dryer. Cotton filters don't cut it with air . . .

 

[Squirrelmageddon]

The important thing is that people should be taking the appropriate steps to have "dry air" in their tanks and guns, be that Nitrogen, a huge pre-compression desiccant dryer, or a decent post compression desiccant dryer. Cotton filters don't cut it with air . . .

I'm glad you mentioned a pre compression desiccant filter. Surprisingly you really don't need a pre filter as large as you think. These filters are lowering my air moisture levels from 70% RH to 10% RH and I can get about 25-30x 580cc 300 bar fills before I need to change the desiccant. It really really cuts the amount of water that makes it to the post compression filter. See that little blue 3" post compression filter in pic#2? I monitored the desiccant in it and pic#3 shows the desiccant saturation in that little post compression filter after 25 fills. I bet I could get 200+ fills before I had to change that desiccant out.

Before I started using a pre compression filter that little blue post compression filter wouldn't last maybe 7 fills on a humid Texas day.

 

[BackStop]

@Squirrelmageddon

"These filters are lowering my air moisture levels from 70% RH to 10% RH..."

How are you measuring this difference? What do you use to measure it?

I ask because you make no mention of the method you use to measure RH.

Thanks!

All my best!

Kerry

 

[elwoodblues]

10 % RH then compress to 300 bar i guarantee you have water vapor and lots more than you think

 

[BackStop]

10 % RH then compress to 300 bar i guarantee you have water vapor and lots more than you think

I am no expert on humidity, but I think many folks don't understand (and I may be showing my ignorance with this post) what Relative Humidity actually means. Without knowing the Dew Point, RH really means nothing.

The term "relative humidity" refers to the % of water that the air can retain at a certain temperature/dew point.

As temperature rises, the air can hold more water so 10% RH at 32F is a LOT drier than 10% RH at 80F.

The dew point is a good indicator of how much water the air can hold at any given temperature.

The way I look at it, for simplicity, is the dew point is the size of the vessel and the RH is how full of water that vessel at a given temperature.

The lower the dew point, the smaller the vessel, the higher the dew point the larger the vessel.

10% of a coffee cup is MUCH less volume of water than 10% of a bathtub.

Oh well, as I said, I am no expert on this, but this is how I look at it.

So, I ONLY pump (hand pump or CS4 compressor) when my hygrometers show that the RH is low compared to the dew point.

In the summer, I depend on the A/C to help and look for at least ~45%RH at 78F or lower.

Right now, my hygrometers show 32%RH at 67F indoors point with 33F dew point at 55F temp outdoors . That is really dry for my area.

Have never had a problem with moisture in my PCP airguns.

It is a fallacy to say that hand pumping causes more moisture in airguns. In fact, IMHO, if one pays attention to the above, hand pumping can be much drier than a compressor. JMHO and this is all my anecdotal humble opinion. (smile)

All my best!

Kerry

 

[AlanMcD]

@BackStop - your understanding of RH and dewpoint is correct, but @elwoodblues is not wrong . . . .

As you point out, there is a relationship between temperature, Relative Humidity, and dewpoint - change one and the others change. But the problem with them in our application is that they are all looked at at the same pressure, and we are dealing with changes in pressure. With that in mind, I prefer to work in terms of "absolute humidity" - specifically, the amount of water vapor contained in air under different conditions. This speaks to amount of water vapor that the air contains (thus the air charge temp has to be at or above the dewpoint for that amount to exist), and can be referenced as parts per million or grams per cubic meter. I like to use grams per cubic meter of air, all referenced at one atmosphere of pressure (meaning not a cubic meter of compressed air, even if reference as compressed) since it translates directly into the cubic centimeters of liquid water that could exist if it all were to condense out. for the rest of this, whenver I talk about grams of water I am meaning grams of water vapor in 1 standard cubic meter of air

Let's assume that we are dealing with the air you are feeding into your compressor being at 67 degrees F and at 10% RH. That would mean that every cubic meter of air can carry 1.5 grams of water vapor into your compressor. While that is far below the 5.4 grams that would be in air that that is 67 degrees F and 32% RH, or the 11.1 grams that would be in air that is 78 F and 45% RH, it is still too much for out needs without additional filtering post compression - which you do, so that is good.

Air that is compressed to 3000 psi and is at 67F can only hold 0.08 grams of water vapor - but here is the key thing: air coming out of a compressor is higher than that, and that higher temperature air can hold more water vapor. And that vapor will condense out later when the temperature drops to ambient, which in this case is 67 F.

I don't know how hot your air charge is, but it certainly is a lot higher than the readout on the compressors, given that the compressors have active cooling and the heat of compression is the source of the heat - the air charge must therefore be higher than the cooled compressor head.

Yong Hengs routinely seem to run above 50 C (and spike horribly is the water flow is disrupted), so maybe the air charge is 70 C or so? What does that mean? Well, 70 C air at 3000 psi can hold 1.2 grams of water vapor. Drop the temp to 40 C (since the CS4 seems to run slower and cooler) and that same air charge can hold 0.3 grams of water vapor.

Without additional drying, those air charges would result in roughly 1.1 and 0.2 grams of condensed liquid water ending up in the tank/reservoir for every standard cubic meter of air compressed. While that will vary by the size of the reservoir, that is probably about 15 fills of most tube PCP air reservoirs.

Somebody using your pre-filter (air at 67 F and 10% RH) feeding a Yong Heng would probably think they were in great shape from a water vapor standpoint because they likely would see nothing come out of their bleed points. But the reality is that all that 1.1 grams of water vapor that was in the air before compression will be in vapor form and make it into the tank.

A properly sized Silica Gel desiccant system will result in air that has no more that 0.07 grams of water water vapor per standard cubic meter, which should work well for most applications of room temperature shooting. For guns that will spend their life being filled and shot in temperatures below freezing, molecular sieve would be a better solution, as that would result in air with only about 0.006 grams of water vapor leaving the filter.

By the way, this all points the the fact that your pre-filter (at least on it's own) is no where near big enough to do the job by itself - the airflow must be just too fast through it. So it is good that you are using a post-filter too.

All this is why I say active drying is very important. But if set up right, there is zero risk of water getting into the tank or reservoir.

For my set up I use a Shoebox compressor and have a huge Wilkerson desiccant drier feeding it, and it gets the air down to where it should be (0.07 grams of vapor) as it flows very little air by volume, given that it is already compressed to 110 psi (and cooled and thus carries about 1.9 grams or so to the Shoebox).

 

[karl_h]

I’m a newbie too. Spent too much on an Airgun to mess it up. Started asking questions when I saw how much moisture I was bleeding out of my “field compressor”. I was told by Edgun west that since I’m in south Florida, I have little hope of keeping it moisture free. Luckily found a gas supplier and going to nitrogen. About $150 to rent a 300cu ft tank per year and $95 to fill. Plus about $700 for a 2 gauge regulator. It’s a 6000 psi tank. I was told I’d be able to use it til about 3000 psi. After that I’d need a compressor booster $700-$1000 to get the last 3000 psi out. We’ll see how long 1/2 a tank lasts me- probably not worth the expense for a recreational shooter.

Edgun west is full of it if they told you that, how many 10's of thousands scuba divers are in florida? How many fire depts? Breathing air has ungodly strict limits on moisture, guess what, it's easy to do. Use what the scuba people use to filter and dry their air and you will be fine. Use cheap hacks and you will be screwed eventually.

 

[AlanMcD]

Use what the scuba people use to filter and dry their air and you will be fine. Use cheap hacks and you will be screwed eventually.

Great advice right there. If I were not running my Shoebox compressors (I have two in great condition and plenty of spare parts) that allow me to dry the air after the first stage of compression (the shop compressor), I would be running either a Yong Heng or a CX4 with the output feeding into a coalescing filter submerged in ice water (to cool the air charge way down) and then through a good desiccant filter. This is the one I would buy - it would need different fittings, but I would always be able to source replacement media as it is a great dive compressor unit: https://nuvair.com/personal-filter-din.html

Then again, I could make my own filter and media, since I know what I am doing in this space . . . but if I did not have the expertise, I would definitely buy that filter.

 

[Richieg]

That's not really practical advice for everyone . . . many don't have easy or affordable access to N2.

It's not hard to filter properly - people just need to get the right stuff and then they are all set.

I could just as easily say this:
Quit messing with Nitrogen - just get a good appropriate sized rechargeable desiccant drier and then NO WATER NO ONGOING COST

The important thing is that people should be taking the appropriate steps to have "dry air" in their tanks and guns, be that Nitrogen, a huge pre-compression desiccant dryer, or a decent post compression desiccant dryer. Cotton filters don't cut it with air . . .

Here is a link that sell a couple different filters and some info. from the site.

Alpha In-Line Moisture Filter

When Filling a PCP airgun or airtank from a Shoebox, Alpha, Omega (or similar inexpensive high pressure compressor without a true water separator filter), a quality in-line moisture filter should be used to remove all oil, water and particulates from the air. This is an…

www.topgun-airguns.com

2. Moisture separation works best at High Pressure. When filling a tank with an inline filter, ensure the filter has some kind of the proper valving mechanism to allow the pressure to build up, prior to flow through the filter. The pressure needs to be held back up inside the filter to a point, and then allowed to flow through the filter media. (That’s the reason for the gold thing on the top of our filter). It costs us more, but without the proper valving, the air and moisture basically rushes over the media at low pressures, and doesn’t get scrubbed. Also the filter media needs a “dwell time” as well as high pressure to work best. Simply running air through a cylinder with a filter element doesn’t work well, and using loose packed beads doesn’t work at all. Make sure the filter has the proper valving to allow pressure to build up before the air runs through it.

 

[AlanMcD]

Moisture separation works best at High Pressure.

This is often stated, and is true with qualifications. In principle, for a given amount of either desiccant or chilling, the statement is true. But with an appropriately sized desiccant filter, or with a deep enough temperature of chilling, air can be "dried" (aka have the vapor level reduced) just fine before compression.

The main reason that it is "easier" to dry air after compression is because the act of compression itself drives much of the water vapor out of the air, and then also because the amount air flow is reduced significantly because the pressurised air is denser (ame amount of air, just with molecules closer together). This increases dwell time in the filter dramatically.

But those that say we can't dry before compression are just wrong, or at least misreading the facts.

 

[F6Hawk]

This is often stated, and is true with qualifications. In principle, for a given amount of either desiccant or chilling, the statement is true. But with an appropriately sized desiccant filter, or with a deep enough temperature of chilling, air can be "dried" (aka have the vapor level reduced) just fine before compression.

The main reason that it is "easier" to dry air after compression is because the act of compression itself drives much of the water vapor out of the air, and then also because the amount air flow is reduced significantly because the pressurised air is denser (ame amount of air, just with molecules closer together). This increases dwell time in the filter dramatically.

But those that say we can't dry before compression are just wrong, or at least misreading the facts.

So for moisture removal in general, and for owners of the CS4 in particular, what is the best way to reduce moisture? And what is the most cost-effective method?