Click Here for AirGunHome.com Main Page AirGunHome.com: THE Worldwide Airgun Forum

Air Gun Home Forum Index » General Air Gun Questions and Topics » Safety and CO2 Bulk-Filling    View previous topic :: View next topic  Safety and CO2 Bulk-Filling   Posted: Sun Oct 18, 2009 8:10 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC I am curious how you guys determine the proper amount of CO2 when you are bulk filling a gun.... I'm not talking about connecting a remote bottle that you had filled at a paintball station (they know what they are doing).... I'm talking about filling something like a 22XX or QB78 where you are using the main tube of the gun to hold the CO2.... I assume that everyone knows that CO2 fills should be done by weight.... A 100% fill is 7/18 oz. CO2 per cu.in. of reservoir.... As an example, the tube on a 2260 measured from the front of one of Joe's extensions to a typical bulk-fill adapter is about 9" long.... since it's 3/4" ID, that works out to about 4 cu.in.... so the proper CO2 fill would be 1.5 oz, or about 44 grams.... ie about half what an AirSource cylinder holds.... Here is a chart showing the pressures CO2 can develop: You will note that overfilling by just a third (ie 2.0 oz. instead of 1.5 oz. in the above example) will result in the pressure rising to about 2000 psi at room temperature.... So 'fess up, you guys.... how many of you that are bulk-filling guns (or your own tanks) have an accurate scale, use it, and do the math to make sure you aren't overfillilng?.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Sun Oct 18, 2009 8:30 pm sniper Silver Status Member Joined: 28 Nov 2008 Posts: 3752 Location: Star, Idaho i can't' help you at all bob! there! happy now? i have another headache! _________________ I believe in gun control, If there's a gun around I want to be controlling it.......   Posted: Sun Oct 18, 2009 11:02 pm kanyon Silver Status Member Joined: 09 Aug 2008 Posts: 1582 Location: New Zealand Hey bob you got a moden version of that chart.. *F / oz etc...what the hell are they.... I want to build a HPA version when the co2 ones competed... Yer could use the fill and run approach... then poke it with a LONG stick.... Pete   Posted: Sun Oct 18, 2009 11:13 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC Quote: Hey bob you got a moden version of that chart.. *F / oz etc...what the hell are they.... I have no idea what that means.... I'm not asking how I should fill, I would do it by weight.... I'm just curious how many people are bulk-filling by weight or if they are using the Quote: fill and run approach... then poke it with a LONG stick.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Mon Oct 19, 2009 4:18 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC Here is a bit more information from warpig.com about properly filling CO2 bottles and guns: Quote: How much liquid is in a "full" tank? Why not fill it up? A "full" tank contains about 34% liquid CO2. If it is filled any more, the CO2 will become very sensitive to temperature changes, with a small increase in temperature causing a large increase in pressure. This is a dangerous situation which is avoided by only partially filling the CO2 bottle. One cubic inch of water weighs 0.577 oz and the specific gravity of liquid CO2 is 1.977 gm/cc so one ounce of liquid CO2 has a volume of 0.877 cubic inches. CO2 bottles generally have a full-fill to volume ratio of about 2.57 cubic inches per ounce of CO2, so that one ounce of CO2 will take up 0.877/2.57 = 34% of the total volume of the bottle. The figure of 68% is often quoted as the volume of liquid in a full bottle, but this error probably stems from translating "ounce" into volume using water as the standard. Water is 1.00 gm/cc, or about half the density of liquid CO2 so that if a CO2 bottle is filled to its rated capacity with water, it will be 68% liquid by volume. Since a properly filled gun is only one third (34%) full of liquid CO2 and a dangerously overfilled one would be only half full of liquid.... I'm betting a lot of people are overfilling their bulk-filled guns.... either accidently or on purpose.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Mon Oct 19, 2009 10:00 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC Here is what I concluded from analyzing the graph.... If the gun is at 70*F, it is possible, in theory, to overfill it by 13% if the source tank is at 70*F and by 17% if the source is at 80*F This amount of overfill could produce 2000 psi at temperatures of 98*F to 103*F respectively.... If the gun is at 60*F, it is possible, in theory, to overfill it by 22% if the source tank is at 60*F and by 26% if the source is at 80*F This amount of overfill could produce 2000 psi at temperatures of 81*F to 90*F respectively.... If the gun is at 50*F, it is possible, in theory, to overfill it by 28% if the source tank is at 50*F and by 32% if the source is at 80*F This amount of overfill could produce 2000 psi at temperatures of 70*F to 75*F respectively.... In order to accomplish these complete fills, the gun and source would have to be allowed to equalize to the temperatures stated.... Under normal filling conditions, the source cools during the filling process, and the gun initially cools (due to the initial CO2 evaporating inside) and then warms.... Therefore, filling in a relatively short period of time and at room temperature, is unlikely to cause a serious overfill.... It is clear, however, that if the gun is filled when it's temperature is only about 50*F there is a serious risk of overfilling it with disasterous results.... Even at 60*F the gun could receive a significant overfill if the gun and tank are left connected until the temperature stablizes.... When it comes to safety when bulk-filling with CO2.... it would appear that "Cool ain't cool".... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Mon Oct 19, 2009 10:40 pm Slavia Moderator Joined: 31 Mar 2008 Posts: 4382 Location: Waseca, Minnesota, USA Have I got this right: The simple case is that the pressure used to push a pellet is vapor pressure, and the liquid CO2 is just sloshing around in there like water. Except at a certain point (the "critical point") the liquid stops acting like the water in your glass and becomes a "supercritical liquid." Which means it is a liquid that acts like a gas, expanding lots for very small changes in temperature. So the pressure at that point isn't just vapor pressure, but the (supercritical) liquid itself trying to blow things apart. So you have to leave enough space so things don't get ugly. Close? http://en.wikipedia.org/wiki/Supercritical_carbon_dioxide http://en.wikipedia.org/wiki/Supercritical_fluid _________________ ¡Listo! ¡Apunte! ¡Fuego!   Posted: Tue Oct 20, 2009 11:11 am rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC Sort of.... I don't have a great understanding of supercritical fluids either, but I think this phrase: Quote: Which means it is a liquid that acts like a gas, expanding lots for very small changes in temperature. would be better turned around: It is a fluid (both gasses and liquids are fluids) that acts like a liquid which is completely filling the container, where a small change in temperature causes a big change in pressure (because liquids are basically incompressable). In ideal gasses, the pressure is directly proportional to the (Kelvin) temperature.... ie a 20*F change in temperature only changes the pressure about 4% at room temperatures.... "Supercritical" is about as far away from an ideal gas as you can get.... The best way to visualize what is occuring is to think of what happens when water freezes.... If you have a sealed container full of water and freeze it, it expands only about 10% and yet can develop pressures high enough to break metal pipes with ease.... Water is the most dense at about 40*F, so over a 10*F drop in temperature the pressure skyrockets.... Not the best example, because it involves a state change from liquid to solid, but I can't think of another common example.... If you look at the straight horizontal lines in the lower part of the graph, that is how CO2 guns are meant to operate.... Those lines are the "boiling point" at the various temperatures, where the CO2 in the tank/gun is both liquid and vapour, and each shot slides you to the left along that line as the container empties.... The pressure stays the same, as long as the temperature stays the same.... Above 88*F, there is no longer any regular liquid CO2 left in the tank/gun.... To the left, all the CO2 is a gas.... To the right, it is a "supercritical fluid" where pressures skyrocket as the temperature increases.... CO2 tanks are designed to be filled by weight.... Exceeding the 100% fill.... or storing a properly filled tank at above 120*F.... puts you in the "supercritical fluid" region of the graph.... where a small increase in temperature causes a huge increase in pressure.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Tue Oct 20, 2009 12:40 pm Slavia Moderator Joined: 31 Mar 2008 Posts: 4382 Location: Waseca, Minnesota, USA Quote: The best way to visualize what is occuring is to think of what happens when water freezes and Quote: can develop pressures high enough to break metal pipes with ease Or engine blocks, or those little glass bottles that milk came in for school lunch (betraying my age here). While the CO2 is a supercritical fluid (and not a solid as in the case of water), this does help me understand what's happening. The point is that it is an uncompressible fluid that expands rapidly for small increases in temperature, and there better be enough space or things will go kablooey. Quote: I don't have a great understanding of supercritical fluids either The daughter's boyfriend is a chemistry major, so it's time for an e-mail. Besides maybe being able to explain the molecular basis for all this, there would be an added benefit. He may become more at ease with the knowledge that I now have a reason to allow his continued existence. (Only kidding; he's a fine young man.) _________________ ¡Listo! ¡Apunte! ¡Fuego! Safety and CO2 Bulk-Filling     Air Gun Home Forum Index » General Air Gun Questions and Topics You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum All times are GMT - 5 Hours   Page 1 of 1   All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First  Select a forum Main Forums----------------AirGunHome Q&AGeneral Air Gun Questions and TopicsPicture GalleryTarget Shooting: Casual, Fun and CompetitionHunting, Pest Control, Varminting People/Events/Airgun Issue Discussion----------------Introduce YourselfThe BS TopicClubs/Events/Regional/Political Airgun Issues Maintenance, Modification and Reviews----------------RiflesPistolsAntique, Collector and Novelty AirgunsBB GunsPellets/AmmoOpticsAccessoriesAirgun Smithing Buy, Sell or Trade Forums----------------For SaleWant to Buy   Note: If you are seeing "Please enter your username and password to log in." Your browser cookies have been reset or you need to register to access the topic in question. Use the 'Register' button near the top left of this page. Click Here for AirGunHome.com Main Page Powered by phpBB © 2001-2004 phpBB Group Partial Styling Supplied by Vjacheslav Trushkin Themes Database.