What Keeps The pressure down?

triggerhappy · 02-27-2007, 10:42 PM

When you have you CO2 tank in your gun, what keeps the pressure from building up and blowing a seal or the gun if you are not using it but your take is hooked in?

Allfat · 02-27-2007, 10:53 PM

That is almost the same as asking why doesnt the tank blow if it is just sitting there. Everything is sealed up, just like it would be in a filled tank. The fact that it is under pressure and in an enclosed area keeps it from expanding continually.

Railgun · 02-27-2007, 11:37 PM

Yep..... Do you understand about vapour pressure? In the case of CO2 it is a gas at normal temperatures and pressure. But as you compress it there's a point where the gas condenses back to a liquid. When there's liquid in the bottle then the pressure in the open area of the bottle and all the parts of the marker is based on this balance and the pressure remains constant.

However the vapour pressure for CO2 is also temperature dependent. As it warms up the pressure DOES build. And this is why the pin valves have a burst disc for safety. Left in the sun on a hot day the pressure can easily exceed the burst disc rating and you get a snow show. But equally bad is what happens to the pressure in a CO2 bottle on a near freezing day when the system pressure can drop to around 300 psi. And as you shoot the need for the liquid to boil away to form gas draws heat in and the internal pressure due to the cold can drop the pressure down to 200 or less and suddenly many markers will stop shooting after a few shots until you stop and let the system "warm" up to whatever the cold outside temperatures will allow.

Walking_Target · 02-27-2007, 11:42 PM

yup

there was a 'Brass Monkey' game up here over the winter, wasn't able to attend myself, but it was said that any CO2 powered marker was shooting two, maybe three good shots before they got serious shootdown. (wind chill was at -36*C) they stopped playing after two games. paint wasn't breaking anymore, and that was the winter specific paint they were using.

Railgun · 02-28-2007, 09:24 PM

Oddly enough wind chill is GOOD for a CO2 tank. The wind moving over the tank will move the ambient mass over the tank and make the internal temperature recover faster than it would on a calm day. Wind chill is only a factor for skin where the passing wind evaporates the moisture in our skin and sucks the heat away as a result. It's this same latent heat of evaporation that causes the CO2 in the bottle to cool down and lower the pressure when you are shooting.

02-27-2007, 10:42 PM	#1 (permalink)
triggerhappy Active Member Join Date: Aug 2006 Location: California	What Keeps The pressure down? When you have you CO2 tank in your gun, what keeps the pressure from building up and blowing a seal or the gun if you are not using it but your take is hooked in? __________________ Bomb Hills Not Countries Kick A$$ Customs We go what you need "Well, I lost this finger playing paintball, and this one in an elephant stampeed, this one juggling rusty chainsaws,...... TriggerHappy's Feed Back

02-27-2007, 10:53 PM	#2 (permalink)
Allfat Active Member Join Date: Aug 2006 Location: Portland, OR	That is almost the same as asking why doesnt the tank blow if it is just sitting there. Everything is sealed up, just like it would be in a filled tank. The fact that it is under pressure and in an enclosed area keeps it from expanding continually. __________________ Probability is a math law, not an aiming technique.

02-27-2007, 11:37 PM	#3 (permalink)
Railgun MCB Member Join Date: Oct 2006	Yep..... Do you understand about vapour pressure? In the case of CO2 it is a gas at normal temperatures and pressure. But as you compress it there's a point where the gas condenses back to a liquid. When there's liquid in the bottle then the pressure in the open area of the bottle and all the parts of the marker is based on this balance and the pressure remains constant. However the vapour pressure for CO2 is also temperature dependent. As it warms up the pressure DOES build. And this is why the pin valves have a burst disc for safety. Left in the sun on a hot day the pressure can easily exceed the burst disc rating and you get a snow show. But equally bad is what happens to the pressure in a CO2 bottle on a near freezing day when the system pressure can drop to around 300 psi. And as you shoot the need for the liquid to boil away to form gas draws heat in and the internal pressure due to the cold can drop the pressure down to 200 or less and suddenly many markers will stop shooting after a few shots until you stop and let the system "warm" up to whatever the cold outside temperatures will allow. __________________ Model airplanes are cool too!

02-28-2007, 09:24 PM	#5 (permalink)
Railgun MCB Member Join Date: Oct 2006	Oddly enough wind chill is GOOD for a CO2 tank. The wind moving over the tank will move the ambient mass over the tank and make the internal temperature recover faster than it would on a calm day. Wind chill is only a factor for skin where the passing wind evaporates the moisture in our skin and sucks the heat away as a result. It's this same latent heat of evaporation that causes the CO2 in the bottle to cool down and lower the pressure when you are shooting. __________________ Model airplanes are cool too!

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