Temperature dropped, winter’s here and you still want to play ‘Ball? Can’t afford an
HPA/nitrogen system, or just can’t find HP air or nitro supplies? The answer is easy, and only
costs a few dollars.

First, a bit of background about CO2:
CO2 can exist in three states: Solid, liquid, and a gas. Let’s ignore the ‘solid’ state right now, and focus on the two we have to deal with in Paintball. Under normal atmospheric temperatures and pressures, CO2, or Carbon Dioxide, is a gas. It makes up a small portion of the normal air we breathe, and plants use it like we use oxygen. When compressed, or pressurized, CO2 becomes a
liquid. In the tank, at ‘room’ temperature, some of the liquid vaporizes, turning into a gas, which takes up more room. This action increases the pressure in the tank. Once the pressure reaches around 800 psi (pounds per square inch), no more liquid boils off to become gas.

When some of the pressure is relieved, say, by firing your paintgun, some of the liquid vaporizes to produce more gas. This “boiling” action, just like boiling water on a stove, requires heat energy. The boiling point of CO2 is in the -200 degrees below zero range, so normal temperatures like we live in are more than sufficient to boil off liquid CO2. However, the boiling action takes some heat out of the air, and even itself, so it cools off. The cooler the tank and liquid, the lower the pressure inside. The more you shoot, the colder the CO2 gets, which means the lower the pressure. If you happen to be playing during a 75 degree F day, there is plenty of ambient heat to keep the tank warm, and therefore the pressure up. If you happen to be playing below about 30 degrees, the already-cool day, combined with the self-refrigerating action of the CO2 means your tank loses a lot of pressure, and takes a long time to ‘recover’, or warm back up.

Now, short of adding additional heat to keep the tank warm, there is not a whole lot one can do about this, it’s simply the nature of the beast, and we have to deal with it. However, there is one other thing that can force liquid to vaporize, and that is to remove the pressure. CO2 cannot remain as a liquid without pressure, unless it happens to be around two-hundred below outside, and by that point, you’re not going to want to play paintball anyway. So, let’s take the point where the liquid vaporizes, out of the tank and move it into the valve of the paintgun. Along with that, lets forget about applying enough heat to boil it, and simply remove the pressure. Sound easy? It is, and it’s a proven concept. It’s called “Going Liquid”. Tippmann used it as far back as 1988 to keep their early SMG-60 full-auto paintguns running, and without a drop in velocity.

How it works:
The liquid is many, many times denser than vapor. As I recall, the expansion ratio of CO2 is something like 3000%. In other words, a given volume of liquid, for example one cubic inch, will expand into 3,000 cubic inches of gas/vapor. What this means is, there is an enormous amount of potential energy, or “stored” energy in liquid CO2, much more so than in already-vaporized CO2. The more you expand the gas, the less energy it has per given volume. This is why some people refer to “over-expanding” CO2; doing so simply robs it of useful potential energy.

So, let’s cram that full-power, high-octane Liquid into the valve. When the gun is fired, the valve is opened momentarily, which allows the pressure to drop way, way down. Since the liquid cannot remain a liquid without the pressure, it “flashes” to a gas almost instantly. The valve only lets out a tiny amount of liquid, but because of the tremendous expansion ratio, it quickly becomes much more gas than the valve could have let through. Because of this, there is more than enough energy, in the form of expanding gas, to operate the Paintgun. And, since the expansion to gas does not take place in the tank, the cooling action is greatly reduced, and transferred to the valve, where it has little effect. As long as there is sufficient pressure in the tank to force the liquid up the siphon tube, and there is still liquid available, the marker will keep running, usually with no drop in velocity.
Converting to Liquid:
The conversion is as easy as installing a siphon tube to an existing tank, or buying a premade siphon tank. A “Siphon” tube, also spelled “syphon”, is merely a flexible, weighted ‘dip tube’, like a straw, connected to the pin valve, inside the tank. The weight on the bottom end of the tube keeps it immersed in the liquid no matter what position the tank is in. (Except inverted, or upside down.) Fill it like usual, slap it on like any normal CO2 tank, and go play. Whoops, no, sorry, it’s not quite that easy.... Since you need to keep the CO2 as a liquid, you need to minimize the excess space that could cause the liquid to expand.
So here’s a quick list of guidelines for running Liquid:

#1: Remove any expansion chamber you may be using. Since an E-chamber is intended to reduce the amount of liquid passing through, one should not be used.

#2: No remotes. It is very difficult, if not impossible, to get liquid all the way from the tank, through the remote line, and into the valve consistently. Even with a very small-inside-diameter remote, like the old “Slinky” type, you end up getting several shots of liquid, then a bunch of gas, than a few shots of liquid again. Needless to say, this leads to terribly inconsistent velocities. Liquid CO2 must be run on-gun.

#3: If you use a bottomline, minimize the amount of tubing, hoses or connections between the tank and the ‘gun’s valve. A good suggestion is to switch to a “Micro Line” type hose, since the internal diameter is very small. Don’t worry, it will still flow plenty of liquid. Try to leave off things like filters, quick-disconnects, and long coiled-up hoses.

#4: No regulators or check-valves. If liquid passes through either of these, and you stop shooting long enough to let it expand, even slightly, the internal pressure can and will shoot WAY up, causing all sorts of problems, and a very dangerous situation.

Will it work on any ‘Gun?
Now then, we have the basics of Liquid operation in mind, now, you probably want to know how to use it on your particular paintgun. Okay, first off, unfortunately, not all paintguns can utilize Liquid CO2 operation. Almost all pumps can, along with most blowback semi-autos. However, several markers, including some of the top-of-the-line ones, cannot be run on liquid for various reasons.
For example, the Automag has a regulator and sensitive internal seals which are damaged by liquid CO2. Velocities and internal pressures would be astronomical, and very unsafe, not only for you holding it, but the guy you’d be shooting at.
The Autococker also has a regulator which controls the pressure fed to the ‘pneumatics’, the cocking mechanism. While the valve and bolt systems can easily accommodate liquid use, the pneumatics would be unreliable at best, damaged at worst.
Other markers which have a regulator built-in, or used to regulate velocities, such as the Equalizer, Desert Fox, Shocker, Typhoon, Blazer, Sovereign and Automag RT, similarly cannot use liquid CO2, and could very easily be damaged by it.

Some ‘guns that can use liquid include the Pro-Am/Pro-Lite/MiniLite, Raptor, F-1/2/4 Illustrators, Spyder, AlleyCat/ThunderCat/BobCat/Puma, VM-68/PMI-3, Icon/Z-1/Mega-Z, Master/Combat, Stingray 1&2, Mirage, BlackKnight, and probably several more I’ve missed. Even some of the older discontinued ‘guns will take liquid, like the Storm, the Blade, SMG-60, 68-Special, Poison, and Patriot 1&2.

However, there are a few exceptions to the rule. For example, Tippmann’s Carbine uses a unique “floating valve”, and the seals between the receiver and the valve don’t take well to the freezing action of full-time liquid. As I write this, rumor has it TP is working on a newer, less troublesome valve, so we’ll see what the future brings. Also, there are a few markers that come with an expansion chamber from the factory, like the VM-EXE. If at all possible, the expansion chamber should be removed.
(Note: The new Carbine valve was released, called the CVX: It withstands liquid perfectly.)

Setting it up:
For the most part, switching to liquid is as easy as slapping on a siphon tank. When you go to chronograph it, you’ll want to take a few shots to get the liquid up into the valve, then chrono to get a correct reading. You can tell the marker is getting liquid in the valve when you see a large ‘cloud’ of vapor or “snow” when it’s fired. On a warm day, you’ll want to pre-charge a warm ‘gun before chrono’ing. To do this, hold the bolt knob all the way forward while screwing on the tank, or opening the valve. When heavy vapor or snow starts coming out, release the knob and/or cock it. It should then be chilled, fully charged with liquid, and ready to play.

If its fairly warm, say 50 degrees or higher, you’ll need to occasionally fire three to five shots every couple of minutes to keep the valve flooded with liquid. If you run siphon on really warm days, like 60 degrees or higher, you’ll have to really lean on the trigger to keep it up to speed. However, for the most part, if its below 30 degrees, shoot it and play like it’s still summer. Between games, you’ll actually want to keep the tank cool; not cold, or frozen, but cool. Don’t set it in the direct sun, or on the dash of your car with the defroster going.

To get the proper chrono readings depends on individual guns. Markers using a “choke” type velocity adjuster, such as the Pro-Lite, may not have enough adjustment to keep the velocity under 300 fps before the adjuster bottoms out. In that case, you might want to try cutting the mainspring a tiny bit to get the velocity down. Be careful, don’t cut too much, and it’s a good idea to have a spare on hand before cutting. The same applies to markers that use mainspring adjusters to regulate the velocity, like Spyders. If you back it out all the way, and it’s still shooting ‘hot’, try clipping a turn of the mainspring. Finally, there are the ‘guns that have no trouble regulating velocity, like the Mirage, because it’s mainspring adjuster has plenty of travel, and the VM-68, because of the ‘choke’ adjuster in the bolt, which can be almost completely closed, and the extra, smaller, holes in the valve body itself.

There are some ‘guns which also have adjustments for the amount of gas used to blow the hammer back. The Indian Creek Designs markers have an easy “recock” adjustment on the side, right next to the velocity adjuster. In this case, ICD recommends closing the adjustment completely for use with siphon CO2. Also, the Brass Eagle Raptor has a sort of ‘hidden’ adjustment, under the grip frame, just behind the front grip-frame mounting screw. The brass ‘plug’ there can regulate the ‘recock margin’; screw it in for less gas to recock the hammer, out for more. You’ll have to experiment for best results, but try a turn back from all the way in to start.

Other tips for cold-weather use:
Along with the siphon tank, and proper velocity regulation, you can do a few other things to set your marker up for good, reliable, cold weather use. You’ll want to use a thin oil, since the marker actually becomes very cold when run on liquid, and many normal “warm weather” oils will “gel” or get thicker, which slows the action down. I prefer KC TroubleFree oil, and Palmer’s paintgun oil is pretty good as well. Gold Cup thickens considerably in the cold, as do some Teflon-based oils, like Tri-Flow and 1-Shot. In a pinch, automotive Automatic Transmission Fluid works reasonably well in the cold, and a quart bottle lasts forever and a day, for about a dollar. No matter what lube you choose, use it sparingly. The more oil inside, the more it can gum up the works when it gets cold. Lube everything with a light coat, and wipe off the excess.

Liquid CO2 can act like Liquid Nitrogen inside a cold paintgun, causing even temperature-resistant polyurethane O-rings to crack or shrink. It’s not a bad idea to keep a few extra ‘rings and seals on hand anyway, moreso under the punishment of intense cold.

Some lightweight blowbacks take quite a beating from liquid CO2, since a much larger burst of air is delivered, which slams the hammer back, often a bit harder than it needs to be. Smaller markers, such as the Spyder and Illustrator lines, should be checked frequently for additional wear-and-tear, and any worn parts should be replaced before they become a problem. Also, especially on the Spyder, keep an eye on the pins in the grip frame; they tend to walk out at the most inopportune moment under the additional battering.

Lastly, after a fast cold-weather game, Don’t stick your tongue on the barrel!

A few extra details:
The number of shots you get per tank goes down a bit with the switch to siphon, but not greatly. If your marker got around 400 shots per tank before, if it’s set up right, it should get around 350 or better on liquid.