Air shifters - c02 vs nitro

[84z28]

So I know c02 tanks are lighter than compressed air/nitrogen, but I've seen the problems that paintballers have from c02 guns. The o rings freeze up, the gun starts leaking and eventually stops firing. Not the best thing for an airshifter on a car. Nitro is a little heavier, but safer in my mind and more consistent. So my question is. Which teams out there are using c02 and which are using nitrogen, any problems you have experienced? Thanks.

[84z28]

So I know c02 tanks are lighter than compressed air/nitrogen, but I've seen the problems that paintballers have from c02 guns. The o rings freeze up, the gun starts leaking and eventually stops firing. Not the best thing for an airshifter on a car. Nitro is a little heavier, but safer in my mind and more consistent. So my question is. Which teams out there are using c02 and which are using nitrogen, any problems you have experienced? Thanks.

[Patrick]

searchy mc search

http://fsae.com/eve/forums/a/tpc/f/125607348/m/40560747...10475911#27010475911 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/4056074731?r=27010475911#27010475911)

-Patrick
RPI Alum
Jet Propulsion Laboratory

[84z28]

yeah I've read that before, but I was still wondering if anyone has had trouble with freezing o-rings or destroying the solenoids from c02?

[GreatfulDeadHead]

Its not a huge difference for this purpose. Paintball guns freeze up because a) they use more air to fire the paintball and b) they fire faster. The air shifter in the car uses a LOT less air. A paintball gun has to use C02 to fire a projectile and recock the gun. The airshifter just has to move a couple inches. So there's less cold air moving throught he system and it'll freeze up much slower. Second, paintball guns on a really old, bad C02 system will still get about 10 to 15 shots in a very rapid succession (3 secs) before freezing up. If you slow down the firing rate a bit or get a better system, you can fire almost indefinitely without freezing up. So unless you constantly use 10 shifts per second, you will be fine. I would just check the O-rings every once in a while. You also will get some heat from the engine warming up the tanks if you shift a lot.

However you are right about the consitency of nitrogen. On a paintball gun you can have 10-15 fps fluctuations on the paintball speed with C02 while it'll be aroune 2 fps changes with Nitrogen from shot to shot. So you have minor changes in the force put out eacht time.

My team will probably use Co2 if we use that system since i got many spare c02 tanks from paintballing. The tanks are cheaper and its just easier to deal with. If you want to use nitro thats fine. If weight is a concern and money isn't they make carbon fiber nitro tanks for paintball guns. Since most of these shifter systems can accept paintball tanks you could go that route

EDIT: i forgot, lube it up regularly. Well oiled o rings and parts are a big key. Paintball oil should work ok since its more resistant to freezing up.

[Erich Ohlde]

we have run an air shifter since 97, i've been around since 04 and I have never seen our CO2 system freeze up. Occasionally we will have an oring swell up and we will replace it.

[mtg]

There also *may* be slight heat production around the area of the C02 bottle.

At FSAE-West this year, one school that came through my tech inspection queue had their Nitrogen bottle for the shifter within 1/4" of the headers. They probably wouldn't have had any "cold" issues even if they were using liquid nitrogen in that bottle. They had to fix that to pass tech, btw.

[Bill Kunst]

Um,
Stop me if I am wrong, but the freezing is a direct effect of the depressurizing of the gas. All the gases, when depressurized will end up cooling their related systems. The only time heat is produced, or released, would be if you were pressurizing gases. Nitrogen will get cold as well, but the size of the molecules are smaller than CO2 or O2 and therefor have much less expansion related pressure changes (i.e. when it gets cold it doesn't lose as much pressure). I may be crazy, but I may be right.

[Corey H]

I am curious to what brand of shifters everyone is using, or if they are home made. A couple of years ago we ran an electric Pingel Shifter but everyone was complaining about not knowing when it shifted or being able to get back to neutral. Just wondering if this is a common problem, or easily solvable. Thanks

[mtg]

Bill, the heat production I was talking about comes from the engine; every air shifter I've seen in an FSAE car is in close proximity to the engine.

[GreatfulDeadHead]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Bill Kunst:
Um,
Stop me if I am wrong, but the freezing is a direct effect of the depressurizing of the gas. All the gases, when depressurized will end up cooling their related systems. The only time heat is produced, or released, would be if you were pressurizing gases. Nitrogen will get cold as well, but the size of the molecules are smaller than CO2 or O2 and therefor have much less expansion related pressure changes (i.e. when it gets cold it doesn't lose as much pressure). I may be crazy, but I may be right. </div></BLOCKQUOTE>

you are right. With nitrogen though, its not a problem for the reason you mentioned, but also since nitrogen liquify's at a lower temp. The problem of "freezing up" comes from having liquid CO2 in the components, not it simply being cold.

[Wesley]

As long as you put some semblance of an expansion chamber inline, you shouldn't have a problem.

We just made one out of aluminum for the '07 car - it also functioned as our tee for up/downshift lines.