On a nitrous system, what is in the bottle when the bottle gets low on (or runs out of) N2O?

thanks

Matt

 

AIR........when you take an empty bottle to get filled...it has air inside the bottle...As liquid nitrous is pumped into the bottle it compresses this air in the top of the bottle....the nitrous is siphoned out of the bottom of the bottle as it is used....leaving the air when it is empty

 

this is assuming you are not using a Nitrogen push system

 

thank you Ray!

 

AIR....... no.

Gas phase nitrous. If you fill the bottle the right way initially, you can get all the air out of it. The bottle cools as the nitrous level drops, because some of the nitrous has to vaporize, to fill the "void" left by the liquid nitrous that left the bottle. The heat of vaporization is removed from the remaining liquid nitrous, cooling it down.

 

Currect, If the line from the pump station is purged before filling it is common to have Gases nitrous left at the end of using up the bottle. However 99.9 percent of the shops I have seen fill bottles do not purge out the lines to the bottle they are filling and the end result is pushing air into the customers bottle each time it is filled.....

So if there is alot of clear pressure comming out of the bottle at the end odds are its more air than Gases Nitrous.
Dave

 

The volume of gas that the air in a line occupies at atmospheric pressure (~15psi) is SUBSTANCIALLY less than the volume it occupies at an "empty" pressure of say 600psi (i.e. 40 times less). Since Category C and D canisters are filled, in the case of N2O and CO2 (which store as a liquid phase under pressure) to only 2/3'rds their VOLUME capasity (hense the reason you physically can "overfill" a 10-pound bottle, yet liquids are not compressible)... you can see just how much volume of a canister must be N2O vapor (which is at 600 to 2000psi depending on the bottle).

Air may be in the gasous phase remaining in a bottle once the liquid has been pumped out, but it still accounts for a TINY amount of the gases inside. The insane concept of "emptying a bottle" before refilling it highlights this example. As mentioned, opening the valve gives you initiallly a very thick white cloud being ejected as all the remaining remnats of N2O liquid are expelled from the valve, tube, and cylinder walls. Eventually the pressure drops to a point where any liquid has completely evaporated and only "dry" gases are coming out... and it turns clear. That gas is STILL almost COMPLETELY N2O, and still under considerable pressure.

Left open long enough and you can get the bottle to atmospheric pressures where there is no driving force to expel nitrous from the canister... that still doesn't mean the canister is filled with air... it just means the nitrous in the canister is not under pressure, and any air-mixing will be due to passive diffusion along the small siphon path.

Worst case? the bottle was completely emptied, and a hose filled with air was used to connect the filling station to the canister. The result after a fill to 900psi and 10 pounds of nitrous means you have about 10 pounds of liquid nitrous, and a 900psi gasous phase above it providing pressure to push it out. The 900psi is in 1/3 volume of the tank, meaning the air that was in the tank acounts for (15psix3=45psi) ... 5% of the total gasous phase.

The gas above the liquid nitrous is 95% Nitrous (assuming 100% N2O being pumped into the tank... it's closer to 99.9% I suppose )... please don't vent tanks, you're just wasting N2O and driving up the price of your refill.

 

you learn something new everyday...thanks

 

im new to this but would it be wise to pull a vacum on the bottle before it is filled like oyu would an AC system and then have them purge their line before filling

 

Naw... ya'd just be wasting N2O. Leave what's in there alone, it won't affect your Nitrous system at all. venting the tank, or even going further to pull a vacume isn't nessesary.

If nitrous tanks were pressureized to say 30psi (like propane), then yeah, you could make an arguement for air being a decent % of the gaseous volume above the liquid... but even then you'd have to realize your not running off the vapor in the bottle... your running off the liquid being pressed through the siphon tube. You'd have to look at the solubility of O2 and N2 gas in N2O to figure out how much it dopes the "pure" liquid.... but without crunching the math I can tell ya it's gonna be MINNISCULE due to the small pressures and high temperatures were talking about in a N2O bottle (for comparrison, liquid O2 and N2 require MUCH higher pressures and MUCH lower tempertures to stay in liquid form). The pressure and temp of a N2O tank makes air-solubillity almost 0.

 

The time to consider getting the air out is on a NEW bottle, that will be full of air. Fill the bottle with nitrous, turn it upside down so the air pocket is over the siphon tube, and crack the valve.... very little needs to be vented. After that, nothing needs to be done.

 

thanks for the replys