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Old 02-01-2006, 11:24 AM   #1
Uziel Gal
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Join Date: Mar 2003
Location: Chingford, London, UK
Exclamation ***Air system safety advice***

Compressed air/nitrogen and CO2 safety

Skipping straight to the conclusion for those with short attention spans, it is highly recommended that you only use CO2 in CO2 tanks, and only use compressed air or Nitrogen in air systems. Equally, only tanks manufactured for the purpose of storing propane should be used with the Tippmann C3.

As far as CO2 and air is concerned, only bottles that have been cleared for use by the paintball industry should be used to store and use these gasses. Tanks intended for the storage of other gasses should not be used, under any circumstances, unless the manufacturer of the bottle confirms their suitability for both the gas you wish to store, and for use in paintball. It is your responsibility to confirm that this is the case.

Any accident that occurs through the use of the wrong type of tank would be your responsibility, and knowingly using a tank unsuitable for the task it is being put to could constitute an offence if others are injured or property is damaged. If that doesn’t make you think twice, keep in my mind that you will most likely be the person closest to the tank if an accident were to occur. For your own personal safety, as well as the safety of others, you must ensure that the tanks you use are suitable for the task.

This forum is intended purely to provide information on paintball specific power sources, and as such, questions regarding the use of non-paintball specific tanks will not be condoned. Neither PBReview, myself, or other members of this forum will be held responsible for accidents caused by the use of tanks that are not intended for use with air, nitrogen or CO2. Our experience is based on the use of paintball specific tanks, and we cannot be expected to provide information on the properties of tanks intended for other gasses or applications, and neither can we conclusively say whether their use in paintball would be safe or not.

If you are absolutely hell bent on using a tank that has not been specifically cleared for use in paintball, consult the manufacturer, and the DOT, and comply with whatever their decision is.

Having said that, lets cover some specific examples: -

Can I fill a CO2 tank with compressed air?

This is a very common question. Of course, a CO2 bottle is designed to safely hold a certain amount of pressure. However, this does not necessarily mean that they are cleared for use with compressed air. Unless a CO2 tank actually has a “working pressure” marked on it, it is not considered suitable for compressed air use, and should only be used with CO2 – end of story.

CO2 bottles that are considered suitable for use with compressed air will generally be marked with two pressures – the working pressure and test pressure. The bottle can only be filled to the working pressure. This is often 1800psi, but can vary from bottle to bottle.

However, the suitability of the bottle to hold air is only one issue. Another thing to consider is that the fill pressure is lower than that of an air system, while capacity is the same as smaller air systems (48CI for a 20oz bottle) – this makes for a low shot count, making the use of air in a CO2 tank relatively pointless.

Another issue is the pressure in the bottle being unregulated, which as such may not be suitable for use with your marker anyway. While this may seem easily resolved with the use of an inline regulator, regulators often have a maximum input pressure of 1200psi, with many newer regulators only being rated for a 900psi input pressure. As such, not only does a CO2 bottle provide very few shots when filled with compressed air, it also has relatively few applications.

As such, the use of compressed air in purpose built, regulated air systems, and not in CO2 bottles, is strongly advised.


Can I fill an air system with CO2?

There are two types of air system to consider – one has a fibre wrapped bottle, the other uses an aluminium or steel bottle.

Fibre-wrapped bottles consist of a relatively thin walled aluminium bottle, which is reinforced by wrapping it with layers of carbon, glass or boron fibres solidified in a resin matrix. The problem here is that it is possible for the tank to freeze when used with CO2. This freezing can make the fibre/resin matrix brittle. With the possibility that the tank may be at it’s coldest when there is no gas pressure left in the tank, the aluminium inner core can contract as there is no pressure in the bottle to combat this. The combination of brittleness and the contraction of the bottle can eventually lead to the fibre wrapping and the bottle separating, seriously lowering the structural integrity of the bottle. The tank would almost certainly rupture if it were then filled with high-pressure air.

As such, fibre wrapped tanks should not be filled with CO2.

This brings us to aluminium and steel tanks, which would appear on face value to be perfectly safe to use with CO2, and as far as the tank itself is concerned, there should be no problems, as they are rated to a higher pressure than CO2 will achieve even at 100+ *F. However, there are again other things to consider. The regulator on an air system is not equipped with an anti-syphon tube, and they are not threaded to accept one. This means that liquid CO2 can pass through the air system regulator, which will damage o-rings and other seals, causing leaks, inconsistency, and possibly causing the full gas pressure to enter your marker or inline regulator. Not such an issue with the pressure of CO2, but if you then switch back to HPA, this is obviously more of a concern, as the full HPA pressure is much higher. If you’re lucky the LP burst disk will rupture before any permanent damage is done to your marker and/or inline regulator.

Why risk it? Use air systems for HPA only.

So could I not swap the regulator on the air system for a valve when I want to use CO2?

This would appear to be a solution, but can cause it own problems. Constantly switching valves is likely to weaken the bottle and/or valve threads. Damaging the threads will increase the likelihood of the valve breaking away from the bottle at a later date, causing the bottle to be launched under gas pressure.

Another consideration is whether you would have the right tools on the field to carry out this swap safely when you need to, and whether you would be able to guarantee that under field conditions you would be able to install the valve securely enough. If the valve isn’t secure, you risk the possibility of the bottle coming unscrewed from the valve.

The cumulative effect of multiple valve swaps is to increase the likelihood of an accident occurring with each valve change, and as such, should not be attempted. Unless your tank is equipped with a regulator that has been designed to be removed easily for transportation, valve removal should be limited as far as possible.


Burst disks

Having mentioned burst disks, lets look a little closer at those.

In it’s simplest form, a burst disk is quite simply a thin disk made of metal, most commonly brass. The disk is held against a hole that exposes it to gas pressure, and clamped in place with a nut that is drilled to allow air to escape if the disk ruptures. The thickness and material of the burst disk dictates what pressure it will rupture at. In the case of the high-pressure burst disk on an air system regulator, or the burst disk on a CO2 valve, the rupture pressure is designed to prevent the bottle being dangerously overfilled. The burst disk has a rupture pressure below the failure pressure of the bottle, but higher than the working pressure. So, the disk shouldn’t rupture often, but should fail before the bottle would.

Air system regulators are also often fitted with a low-pressure safety, often in the form of another burst disk with a lower rupture pressure. This will have a burst pressure higher then the output pressure of the air system, but lower than the fill pressure of the bottle. This is designed to protect your marker from being exposed to the unregulated fill pressure of the bottle if the regulator fails.

So, if your LP burst disk were to rupture, this means that there is something wrong with your air system. Do not be tempted to fit a higher rated burst disk or more than one disk, to stop the disk rupturing, as this could lead to your marker being damaged. Same goes for CO2 valves – use only one burst disk of the correct rating, otherwise your bottle could fail before the bust disk does.

Another thing to consider is when fitting a valve or regulator to a new bottle. Ensure that the high pressure burst disk on the regulator or valve is of a suitable value for the bottle you are using. If the burst disk has a higher pressure rating than the bottle, then it possible that the bottle could fail if overfilled, so make sure that your burst disk rating suit the bottle you are using.
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Gotta be a Scotch or a Kamikaze, none of those other weapons will faze me.

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Last edited by Uziel Gal : 04-29-2006 at 11:11 AM.
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