How much water are you pumping into your PCP?

[lloyd-ss]

We've all experienced it at least once in a while.  You open the bleeder on your pump or tank and it squirts out enough water to clean your windshield.  Well, maybe not if you always get your tank filled at a scuba shop that has a good dryer on their air pump. But for those of us that use a hand pump or Shoebox, water can be a real problem.  Leaky check valves, rust inside the gun, corroded fittings.

Pumping air from atmospheric pressure (about 14.5 psi) to 2900 psi compresses it to one two-hundreth of its original volume, so in a way, you end up with 200 times as much water in the air.  And as the temperature of the air that you are pumping goes up, the amount of water it can hold goes up dramatically. If you pump your tank in the summer when the air temp is 95 degrees and the humidity is 95 percent, you'll be pumping 10 times as much water into the tank compared to doing it on a winter day when the temp is 45 and the humidity is 45 percent.  Picture that water dripping off your ice tea glass in July!

But if you are curious about how much water you are pumping, I made a spreadsheet where you can enter info about your tank or gun reservoir, and the pressure and air temp and humidity, and it will spit out   how much water ends up in your gun or tank.

I'd like to be able to share this spreadsheet (and some others that I have) without having to do a web based application ( I don't know how) so it was suggested that I try google docs. So, here is a link to the spreadsheet on google docs.  I don't know if the link will work or not, or if you must have a google account, so just give it a try if you are interested.  I didn't realize I already had a google login from youtube.  Go figure. 

Here is the link:

https://docs.google.com/spreadsheets/d/1_uc8opB2fTkjxd_MUfd6FTJaiLRVGNJ47OrMcXRb-eQ/edit?usp=sharing

Here is a screen-shot of the spreadsheet so you can see if it is of interest to you.  It will also do the conversions for all the different types of tanks: cc's for gun reservoirs and some bottles; cubic inches for paint ball bottles; cubic feet for scuba tanks; and minutes for SCBA air pack tanks.  Did you know there was going to be this much math in PCP's?



If it works, great, if not, let me know and we'll try and get it working for anybody who wants it.  BTW, you can only enter info in the blue blocks in the spreadsheet.  The yellow blocks are for the examples, and the green blocks are the results, and it is supposed to be protected so that you can't break it, LOL.  Or if anybody can do PHP or java programming, or VB, and has a server to put these spreadsheets on, and is willing to do the work, or has another approach, please let me know!

Edit- It appears to work, but it takes a minute or so to load.  After you change a value in one of the blue blocks, hit enter to update the screen. Lloyd

[triggertreat]

Great job on the chart Lloyd!  It appears to be working well for me (numbers are changing with different inputs).  So I'm thinking, what is the solution to remedy water in the reservoir?  If one held the gun straight up to let the water works its way to the valve then you could shoot it out easier doing so, maybe a few empty shots would do.  thoughts.

[Buldawg76]

Its working for me as well. I knew there was water going into my tanks and guns but did not know it was so much in high temp/humidity situations. I am wondering if the gun is filled from a tank say a 45 minute SCBA size that is allowed to set for at least an hour or more will the water fall out of the air and accumulate in the bottom of the tank so it does not readily flow into the guns reservoir if filled slowly. Or does it stay suspended in the air so it flows into the gun at every fill.

My tanks stay inside my air conditioned house but the shoebox is in the garage and I try to only fill on low humidity days but in summer here that's not ever possible. So if the tank is allowed to sit so the air inside it is at 75 degrees or so will that help when filling the guns. When at the FT range I have no choice with tank temp or outside conditions so just fill as slow as possible.

Any info on how to reduce the water going into the guns would be appreciated.

Mike

[lloyd-ss]

Thanks guys for trying the spreadsheet out and verifying that it works for you.
Getting the water out of the compressed air is the whole point I guess.  As far as getting the water to condense inside a tank, I am not sure how that works. Generally, cooling the air to below the dew point causes the moisture to condense and fall out of the air. Some people run their air lines thru refrigerators or ice buckets to help get the water out. But I don't know how the dew point relates to pressure.  I think the water that comes out of the bleed valve is condensing out because the air cools as it blasts thru the tiny bleed hole??  Then there are silica dessicants and molecular sieves to absorb the water. But looking at how much water is actually in the air in humid weather makes me wonder just how much of the water the dessicants can actually trap.  Sorry, but it looks like there are more questions than answers.

[Geoff]

2 micro liters per stroke   


seriously though, thanks Lloyd !

[grand-galop]

It works for me to...  Thanks LLoyd..   Now the laws of thermodynamics are UNMENSURABLES...   LOL  I always taught that liquids were not compressible..........   This is a good point to consider when you invest in a airgun and want to PRESERVE your investment... So those cheap HPA compressor need a bigger dryer to prevent the moisture...

[triggertreat]

I took my gun apart to replace the O-rings after a couple of years of hand pumping without any kind of dryer/filter attached.  I feared the worst from all of the reading I've done on the forums and expected rust city inside the reservoir.  To my surprise, it was clean, clean, clean without any rust at all.  I can only assume it was because I always pumped the gun up indoors and only outdoors in mild weather.  I also kept the pump and gun indoors and have my thermostat humidity setting set on 45% during the summer months.  I now am fortunate to have a tank and it is filled with clean dry scuba air from a dive shop so I have been rust free all along and thank goodness for that.  I also never overheated the pump in an effort to save the pump O-rings which has worked well too.

[Taso1000]

Lloyd,

Thank you for the spreadsheet!  I have a membrane drier that outputs air at ~4% rh.  So to fill my 30 minute tank I would get .2 teaspoons of water.  That is good to know because I have been considering making a high side water trap for my Shoebox and wasn't sure what volume for the trap would be necessary.  Cool!

But this air at 4500 psi still has water vapor pretty much at 100% humidity.  I think rh goes down as pressure drops and up as pressure rises.  I know that it has to be a lot less water vapor than when we started but how low does the relative humidity have to be so that we don't need to worry about corrosion?  I have not been able to find this.

Thank you,

Taso

ADDENDUM:  I just realized that my membrane drier puts out 4% RH at 100 psi.  Lloyd, How does that change the results or can a field be created for pressure?  I'm assuming your spreadsheet is setup for atmospheric pressure?

Thanks!

[moorepower]

I notice way more from my hand pump, FD chineese, than shoebox. I have a 1 micron filter on my shop ac and 2 desicant filters going in my shoebox. I use one of the paintgun ball filters before a filter with beads, and show 0 change of color on the beads. The tank is 120 gallons so the compressor almost never runs while filling. FYI, I have painter quality filtration coming out of the A/C before the shoebox. I actually am thinking of getting a dorm fridge off of Craigslist to house the Shoebox and a air conditioning condenser before the filters going in the shoebox. Plud it in a couple hours before I fill. It would not take up much more room than the Shoebox.

[lloyd-ss]

A lot of good info here.  I've taken guns apart that were totally crudded up with moisture damage, and others that were clean as a whistle.
A lot of water can come out of the drain on a shop compressor tank, so apparently, some of the water does condense out in the tank.  I use a couple of the disposable desiccant filters in series at the inlet to my shoebox and they will start to show color change after a few hours.  Sticking them in a 275F oven for 45 minutes will bring the color back to blue.  I think all the moisture needs to be removed before the air gets into the shoebox.  I've rebuilt a couple of shoebox compressors and both were pretty corroded in the area of the check valves on the end of the cylinders.  I have heard that if you make a chilled tubular dryer to use between the shop compressor and the shoebox, that the air should enter the bottom and come out of the top, and that filling the tube with metal beads (plated BBs for example) will give the moisture plenty of surface area to condense on.  Put the dryer tube in a fridge or ice bucket.  Once the water gets into the shoe box  its almost too late unless you have a dryer that will handle high pressure.  Remember that the actual air flow rate between the shop compressor and the shoebox is very low (moorepower says his large compressor doesn't even cycle on) so the air can linger for quite a while in whatever water removal device you have.  But that low flow also yields most of the cheap water extractor filters ineffective because they rely on some air velocity to drop the water out of the air stream.  There is a lot to it.

[Buldawg76]

I have my setup configured so my 5 gallon shop compressor is fed into a 33 gallon tank and then to the shoebox with a HPA molecular sieve on the output to the tanks or guns. I run the shop compressor to fill the big tank and then let it sit for 30 minutes to an hour so most of the moisture can fall out of the air and collect in the bottom of the 33 gallon tank  The 5 gallon tanks drain is fed into the same inlet to the 33 gallon tank so any moisture that is in the shop compressors tank is hopefully forced into the 33 gallon tank. I get about 2 to 3 tablespoons of water out of the 33 gallon drain after it sits and hopefully since I am pulling the air off the top of the tank it has very little moisture in it.

My shop compressor only fills to 125 psi so it does turn on about every hour of filling time and I wait the 30 minutes after it runs to allow the water to fall out to the bottom of the tank and drain it off. I have a water separator filled with sieve material on the inlet to the shoebox as well and it has not changed color yet either.

I have only had the sieve in the output for about 2 months. Before the sieve I would see a fairly heavy mist of water vapor when bleeding the pressure off. Now with the sieve I have a shutoff valve after the sieve to allow me to pressurize the high side before I actually start filling a tank or gun. It also allows me to retain that high pressure in the line and sieve so I only have to pressurize the sieve once during filling cycles of my tanks and guns. It takes 15 minutes to pressurize to 3000 psi with the sieve in the output line. Since the sieve has been in place I see no moisture vapor bleed out from the tanks release valve so I believe none is getting into my tanks. I have started filling my guns from the tanks only since they have no pressure release at the guns reservoir.

I have not checked the sieve yet since I have only filled my tanks twice since its been installed ( about 3 hours of fill time ). I have a 45 minute SCBA, a 90 ci/in tank, 2- 45 minute aluminum SCBAs that fill to 2500 psi and a 88 cu/ft scuba tank that fill to 3500 psi that I fill all at the same time.

I am using 13X molecular sieve in my filter since it is rated for just H2O absorption versus the 4A or 8A that also absorbs other gases. I use an oil free shop compressor so all I need to trap is H2O. If you use a oil lubed compressor then the 4A or 8A is a better choice IMO.

I am waiting on one of the Chinese compressor to arrive so I can fill faster and simplify my setup with less plumbing and equipment. 

Mike 

[Ribbonstone]

Guess I am...seems logical.

Do have the air tubes open now and again, and even the ones that have been pump filled for 10 years don't show any signs of corrosion/rusting.

Most pumps I've opened have a bunch of little glass beads  at the final output.  Not a whole lot, but they do collect some moisture, and much of what you see shooting out the pump when you open the bleeder wass collected on those beads.

So a decade now I've been pumping in sets of 50-60 pumps strokes, bleeding the pump, and disconecting for a cool down.  May take a few sets like that to fill a large air volume, but might be ne of the reasons I'm not seeing corrosion in the air tubes.

Certain can't get all of it.

Certainly cannot get all the moisture.

With two exceptions.

Opened up a brand new PCP and found some rust in the air tube....so it must have been "factory rust".  Am sure if I hadn't opened it when it was new, WHATEVER I was filling it with would have gotten the blame.

Often find some corrosion on gauge blocks, heavies beteen the sealing o-rings.  That area is not pressurized and is kind of open to the outside air (by way of the space where the gauge passes though the air tube).  Rain, mist , condwensation, etc. can get in from the outside world at that point.


If you want to be extra rust safe....silicon grease (real stuff...pure silicon please)the inside of the tube.

Yeah...I know...it will blow up.

Really?  How? Pure silicon grease, in a thin buffed in layer (like waxing a car) combusts?

What's on the inside of the hand pump, which has to produce MORE pressure than the air tube in order to fill it?

What do we leave snail tacks of when we silicon grease the o-rings on the valve and tank block and slide down the tube?

So...do as you see fit.  Oldest PCP has seen 14 years of pump filling without any rust/corrosion.

[Buldawg76]

I always add some silicone oil to my PCPs by way of the foster fill fitting about every 5th or 6th fill so that inside the tube, valve and barrel has a light coating of oil to help protect from corrosion. Never had any issue with combustion and do not expect any since there is never enough heat for it to occur like a spring piston gun will. In a spring piston gun you are compressing the small volume of air to 300 plus to 1 compression ratio is why they detonate on silicone oil. To put that into perspective a diesel engine use from 20 to 25 to 1 ratio to ignite the diesel fuel with heat of compression so a spring gun is using over 10 plus times that amount of compression which far exceeds the flash point of any silicone or other so called oils or lubes.

I have even tried marvel mystery oil which does not burn at gas or diesel combustion temps of 1500 to 2000 degrees. It will combust in a spring gun just like any other lube does.

Mike

[Christopher]

I hand pump for all my HPA needs so I'm not dealing with the same volume of air as you guys with a compressor or carbon fiber tanks and scuba tanks. The way that I manage moisture with my Benjamin hand pump is with a clear vinyl hose clamped to the air intake.  The hose is about 6' long and I put the end of the hose, the one not clamped to the pump, back into the rear of the freezer. Ever since I started doing this all of my moisture problems went away. By the way, not my idea, read it right here on the GTA somewhere. But just to prove how effective it is, just a couple of fills on a Marauder will cause apparent and visible condensation within the pump.  Which would no doubt result moisture in the air reservoir of the gun as well.

Nice work on the spreadsheet Lloyd

Thanks,
Chris

[Taso1000]

I remember reading about "one" and I want to emphasize "one" instance where there was an hpa air pump that blew up.  That pump was lubricated with motor oil as recommended by the manufacturer.

Found it:

http://www.gatewaytoairguns.org/GTA/index.php?topic=13977.0

My point is if this guy's pump exploded and it was connected to a rifle that had also been contaminated with motor oil, from the pump, it also could possibly ignite. 

Since I read that thread I've only used Krytox/ultimox and silicone grease in the air path.

So it "can" happen at the autoignition temperature.  But it would seem if we take every precaution to remove any lubricants that can combust a very prudent measure.

I can't imagine compressor oil manufacturers haven't taken this into consideration. 

Thank you,

Taso

[Ribbonstone]

No doubt it could auto ignite....have the remains of a Daisy 853 that was given a WD 40 spray "all over" (his words) and then pumped (no one really injured when the compression chamber split, but the shooter did admit to a bruised swollen hand from the pump lever kicking back).

Haven't found silicon grease to have that ability (although I'd be sure it was real silicon grease without additives).

[moorepower]

One thing I am seeing on guys setups, that I don't like, is running the air compressor thru a plastic line to the filter. The longer, larger diameter copper tubing, or metal pipe you can run it thru, the more water the filter will catch. Even if you get an a/c condenser inline it would be far better. I use a TP tool filter that is a housing that has a roll of tightly wrapped paper as my primary after being cooled with 3/4" copper tubing. I started out with 1/2" tubing and I would still get moisture in my sand blast cabinet, but after switching to 3/4" tubing all the water condensed, and I had no further issues blasting or coating. The ball desicant filters can be found at any place that sells paint supplies, even Harbor Freight for under $2 each, and I always used them when coating, and they are fantastic, and last quite a while. The key is cooling the air before the filter. I had a 25hp compressor feeding a 50 cfm pressure blaster fed by 2" black pipe, and even in 95f high humidity a 60' run cooled the air enough that a seperator and filter would keep out all water.

[AlanMcD]

Lloyd's excellent tool shows how much water condenses out of air as it is pressurized and cooled.  It is a good start, but it does not show how much water "gets into your gun" - it shows how much water is in the air that starts on the path to your gun.

Relative humidity is a bit confusing, as it is a measure of the percent of potential water vapor a sample of air can contain as vapor at a given temperature and pressure.  It tells you nothing about the amount of that water vapor.  For that, you need to work in absolutes . . .

So let's start with a cubic meter of air (~35 cubic feet) at atmospheric pressure that has a dew point of 68 degrees F (I will use that temperature for all examples that follow).  If the air temperature is higher than this, we have humid air, but no condensation within that cubic meter of air - at that temperature it will start to fog a bit, and below it condensation with start and water will turn to liquid.  But lets keep the air temp slightly above 68 so that we have that dewpoint.  Of course a dew point of 68 F is very humid air, but it works as a good example for those in humid climates.

At these conditions, that cubic meter of air will contain 17.5 grams (or ccs) of water as vapor.  Bet you did not know that it was that much!! So the question is what happens as we compress that air . . . .

When the air is compressed, it's ability to hold water vapor at a given temperature decreases quite dramatically - and as a result, the relative humidity of air once compressed (and as the temperature drops from cooling after compression) is almost always 100%. So as the air cools, much of the water vapor will condense out - and that condensed water will not make it into our guns (or tanks, at least for the water that condenses before the warm air enters the tank).

If we run that cubic meter of air through a shop compressor and run it up to 120 psi, but let it cool back down to 68 F, of the 17.5 grams of water vapor that was in the air at the start, all but 1.9 grams of it will condense out.  So we are left with 1.9 grams of water as vapor, and have 15.6 grams of liquid water left in the shop compressor tank.

Compress it again to 4500 psi, and let it cool back down to 68 F and now that same original cubic meter of air (having been "squeezed" down in volume from 1000 liters to a little over 3 liters) can only hold 0.06 grams of water as vapor - the rest has to condense out.

Of course, as we compress the air is hotter than this, so it can carry more moisture.  If we have air exiting the pump at 150 F at 3000 psi, it can carry 1 gram as vapor, so there is still a good bit left to condense out.

This is why it is so important to handpump in short sessions that allow for cooling.  The base of the pump acts as a heat sink cooling the charge air and thus condensing the water vapor out before it enters the gun (plus the cooler temps let the o-rings last longer).

And that is why we can run a Shoebox an generate dry air with a good desiccant in the path after the shop compressor - the shop compressor gets 90% of the water vapor out of the air (if done right, with cooled air feeding the Shoebox) and a good sized desiccant dryer gets most of the rest (at a rated -45 F dewpoint, only 0.07 grams of water are left in a stanard cubic meter of air).

I have used a Hill pump with Drypac for years, and switched to a Shoebox with a big Wilkerson dryer  on the input side for a few years, and I have never seen any signs of water in my guns or tanks.  As Lloyds calculator (and my numbers above) show, there is a lot of water in air that has to be managed, but it can be managed.

Oh, and don't think you get a free pass on this if you live in a "dry" climate - even air with a dew point of 32 degrees F has 4.5 grams of water in a cubic meter of air . . . and a dew point of 0 F will hold 1 gram of water, meaning continuous pumping will probably show no condensation, leaving the water to pass through the system (as air under pressure at 150 F can still hold that water vapor, with it condensing out later).

[Buldawg76]

Alan
So are you saying its better to try to remove the water vapor before it gets to a shoebox or other type compressor. Is it still a good idea to use a high side dryer like a molecular sieve filter as well or is a real good low side filter enough on its own. If the low side air is allowed to cool to outside temps before starting the shoebox that will remove say 90% of the water by condensation in the low side tank correct?.

What I am getting at is the setup I have using a 33 gallon tank to help cool the compressed air before it is fed into the shoebox is the right way to perform the removal of water from the air. I have a water separator with 13X sieve in it that is between the big tank and the shoebox to hopefully capture any remaining water that has not condensed out in the big tank.

Even with the above setup before I installed the high side filter there would be water vapor seen when bleeding off the high pressure air. After the addition of the high sidce filter I see no water vapor at all on the bleed off after filing my tanks.

Your thoughts.

Mike

[Taso1000]

Mike,

My opinion is that you need both.  The bulk of moisture can be removed easier between your shop compressor and the Shoebox.  The reason I say easier is because the capacity of silica gel and molecular sieve is low and it absorbs more at hpa pressures.  On the low side it would fill up very frequently and thus need to be changed or recharged frequently.  The membrane driers I found are good for removing the majority of the moisture on the low side.

On the plus side for us is that the Shoebox only draws .2 cfm.  So the dwell rate is high and the shop compressor doesn't have to work as frequently so the air has the time to cool.

Molecular sieve on the high side will remove the remaining water vapor.  A water trap would work well on the Shoebox outlet as well.  I think a tee and a nipple with a discharge valve will be good enough.

Taso