Chilling PCP air cylinder before/during fill

[needmoretoys]

So if me chilling the cylinder to say 20 deg F is a bad idea then I assume that no one has ever filled their rifle out doors in the winter when the temperature was 20 deg F or less. As far as telling me to fill more slowly, I don't know how many times I have said that I'm filling as slowly as the AV valve allows. I do appreciate the comments, but I still don't see how chilling to 20 deg F is such a bad idea.

Well you should feel comfortable ignoring my advice as I am not qualified to speak to the mechanical engineering aspects of pressure changes with respect to temperature at fill.  There are people here who can speak to that and maybe they will chime in.  Motorhead is pretty smart about these things.  He seems to think condensation could be an issue.  On that I agree because when I pump up my Lonestar too quickly I get condensation in the pump.  I think condensation inside the gun is probably undesirable.  Frankly I don't know if cooling the tube would make that issue worse or better.

I would expect that because the air that is entering the pump is normal atmospheric humid air. The air that is used to fill the bottles at a paintball shop, fire station or wherever is supposed to be dried. If it isn't then there will also be water inside the bottle that they fill and it will likely get into the cylinder whether it is chilled or not. That is why AA says to use an air dryer on the inlet of a hand pump and not just pull in humid indoor air.

[needmoretoys]

Here is an interesting technical article:

http://www.vaisala.com/Vaisala%20Documents/Application%20notes/Dew-point-compressed-air-Application-note-B210991EN-B-LOW-v1.pdf

It appears that if air is not greatly dried that condensation will occur whether the cylinder is chilled or not (see Part 3). Now that I think about it, that is somewhat obvious, as just running a shop air compressor results in considerable condensation inside the tank. Of course, that is with undried outside air. Since a shop compressor only compresses to about 150 psi, compressing to 4500 psi will increase the moisture. Since the air cannot be completely dried at the paintball shop or firehouse (at least I don't think so), there will be condensation inside the bottle. The saturated air will then be transferred to the cylinder. When the air expands to atmospheric, the dew point will again drop, so no water will exit the barrel. It will evaporate first as the air expands.

Has anyone who has disassembled a PCP seen any evidence of moisture inside the high pressure area? Perhaps not, unless it is rust, as when you depressurize, the moisture will again evaporate.

In any case, I guess I will just pressurize as slow possible with my AV valve, leave everything connected for 20 or so minutes and again open the valve. Of course, this will require that all the various adapter connections are perfectly sealed. I guess I'll find out.

In ending, I still see no difference between chilling the cylinder to 20F and filling a cylinder that is 20F outside in the winter. The cylinder and the air inside it doesn't know the difference.

[William]

First of all when you keep chilling something below normal room temp (freezing) and then heat it up and keep doing it over and over again your are stressing the Air Tank's material it is made of, the more you do it the more likely it could fail.
I think if you kept it at the same room temp as you are filling would be fine, but not freezing and then UN-thawing it, that's where the problems begin. Metal expansion and fatigue set in and when it blows up in your face don't say you weren't warned! When you start putting several thousand PSI against something frozen and brittle, what do you think is going to happen!

Keeping it a constant temp will be a lot better! If you had a cooling tank to just keep the temp at say between 72 and 90* would be great.

Filling outside in the winter has nothing to do with it, everything is all the same temp as the surroundings.  This may not be good either in the long run due to the air heating up, but who knows!

William

[n2omike]

Condensation is irrelevant.  The air is going to stabilize at the same temp either way...  Moisture saturation in air is dependent on temperature.  Cooling the bottle will have zero affect on how much moisture reaches it.  Once the bottle temp stabilizes, it won't hold any different amount of moisture.

Freezing the bottle will only reduce the peak temp it reaches during filling, keeping it from losing as much psi as it cools back off.  I would do it if I were filling fast...  but I've just got a Shoebox, so it doesn't matter.  lol 

[needmoretoys]

Condensation is irrelevant.  The air is going to stabilize at the same temp either way...  Moisture saturation in air is dependent on temperature.  Cooling the bottle will have zero affect on how much moisture reaches it.  Once the bottle temp stabilizes, it won't hold any different amount of moisture.

Freezing the bottle will only reduce the peak temp it reaches during filling, keeping it from losing as much psi as it cools back off.  I would do it if I were filling fast...  but I've just got a Shoebox, so it doesn't matter.  lol

Exactly. However, if I were to do it again, I would buy either the Great White, Tiger Shark or Total Air Hog with flow control. My 2 AV tanks only cost $480 at the local paintball shop. They are actually Ninja tanks, regulator, valve and hose, but I believe that the AV tanks are actually the Ninja tanks. These Ninja tanks and fill station are for PCP guns and not paintball. I paid $238 each at the local dealer. They and the AV equivalent normally cost $300 each.

http://www.@#$%^.com/Ninja-PCP-3000-psi-Fill-Station-p/ninjafillmrod3000psi.htm

One of the flow control tanks would have been a better choice, but then they cost $750 to $884 for 1 large tank set.

Now that the pressure is down to 3100 psi (214 BAR) in the tank I filled from this morning, I did get a slow fill to 200 BAR with little warming. It only fell back to 195 BAR. However, when it's still at higher pressures, I can't get it to fill nearly as slowly and I lose more like 20 BAR unless I let it cool and top up.

[n2omike]

Condensation is irrelevant.  The air is going to stabilize at the same temp either way...  Moisture saturation in air is dependent on temperature.  Cooling the bottle will have zero affect on how much moisture reaches it.  Once the bottle temp stabilizes, it won't hold any different amount of moisture.

Freezing the bottle will only reduce the peak temp it reaches during filling, keeping it from losing as much psi as it cools back off.  I would do it if I were filling fast...  but I've just got a Shoebox, so it doesn't matter.  lol

Exactly. However, if I were to do it again, I would buy either the Great White, Tiger Shark or Total Air Hog with flow control. My 2 AV tanks only cost $480 at the local paintball shop. They are actually Ninja tanks, regulator, valve and hose, but I believe that the AV tanks are actually the Ninja tanks. These Ninja tanks and fill station are for PCP guns and not paintball. I paid $238 each at the local dealer. They and the AV equivalent normally cost $300 each.

http://www.@#$%^.com/Ninja-PCP-3000-psi-Fill-Station-p/ninjafillmrod3000psi.htm

One of the flow control tanks would have been a better choice, but then they cost $750 to $884 for 1 large tank set.

Now that the pressure is down to 3100 psi (214 BAR) in the tank I filled from this morning, I did get a slow fill to 200 BAR with little warming. It only fell back to 195 BAR. However, when it's still at higher pressures, I can't get it to fill nearly as slowly and I lose more like 20 BAR unless I let it cool and top up.

You can get the 90ci regulated Ninja tanks for $179.  They are also sold under other names such as Air Venturi.  The tanks are made in USA, and aren't bad for the price you pay.  I have one.  I also have a Joe B Tiger Shark.  The Tiger Shark is definitely a nicer piece, and doesn't need a separate fill adapter, but costs around $800 with all the bells/whistles.  Joe's small Guppy tank is a GREAT choice if you can fill your own, as it has the nice gauges, needs no fill adapter, etc...  and without the fill adapter, they aren't THAT much more than the Ninja + adapter. 

If a person does NOT have a Shoebox or something to fill with at home, I'd recommend biting the bullet and getting a big tank from Joe...  Maybe the Great White.  If you don't like hauling it around, you can also use it to refill a Guppy or Ninja sized tank...  as I use my Tiger Shark to fill my Ninja sometimes.  If you have to rely on someone else to fill who can do 4500psi, definitely save up for a big carbon fiber tank.

Good Luck!