CO2 bottle angle

[Lee]

I'm using twin 5l bottles which take up a fair amount of space and I have found that the best 'fit' is at slight down angle with the valves at the bottom end (see pic) Does anyone know if this will have any impact on making the valves more or less likely to freeze up?

[GlenR]

You would need to put a dip tube in it to pull gas through or you will freeze up whatever is downstream of the bottle with liquid (i.e. valve or regulator)

[maddox10]

Why using 2 3.5kg bottles? That's a lot more than any other heavy, most have 2kg on board, and some do have 2 x 2kg.

[Lee]

I'm using 5 actuators - 3 x pistons for weapons and 2 x rotating for self righting

[maddox10]

That is all low pressure. At best suitable for 10 bar.

7 kg of CO2 is 3500 liters of gas.
A double acting 100*200 ram @10bar uses 30 liters per double action. (this is Killerhurtz/Terrorhurtz powerlevel)
Unless you have the rare Norgren Hi Pressure series that can handle 16 bar. Then it is 50 liters.

The biggest Rotary Actuator I have seen in 24 years of work in that branch is close to that. And that was at least 30 kg heavy to close the 12" Hastaloy ball valve.

[Yatcatcher]

To Hijack this thread...

Freezing valves seems to be an ongoing issue with CO2, mainly on high flow systems. We tried CO2 fire extinguishers with and without the plastic 'straw' that is screwed into the bottom of the valve. Upside down and right way up and it seemed to make little difference at the low flow levels through a standard 1/4" extinguisher valve orifice. When we started using buffer tanks and higher flow rates then we froze everything up. Make of that what you will Grin!


The hijacking is to do with the rules on heating the CO2 supply. If we used (say) a glow plug in a block of aluminium attached to our valves to stop it from freezing, would that break the rules? Or attaching the valve to an overworked ESC perhaps?

[maddox10]

Straight from the rulebook.

9.14 Heaters and Boosters
Pneumatic systems using heaters or pressure boosters are not permitted.

[Yatcatcher]

.

Hi Maddox, yep that is what I understood, to phrase the question a little more specifically;

Would a system designed to prevent icing necessarily be considered as a CO2 heater (it is, but not there for extra performance)? The second part of the question is; would using heat produced in one area of the robot to warm the CO2 valve be considered illegal? Could perhaps be a thorny issue for layout?

[Lee]

My vote would be that its legal if your battery pack and or ESC is next to your CO2 valve. Heaters tend to be electric blanket type gizmos that you run when the rest of the bot is powered down (like the tire blankets used in F1) which an ESC is not. There is also no rule to say we cant used liquid cooled electronics (such as you find in gaming PC's) so who's to say if the CO2 is cooling the ESC or the ESC is heating the CO2?

[terry]

I would keep the esc and batteries away from the bottle my setup dosent get very warm and there is too much frost/ice on the bottle during fights anyway. the batteries are probably in a metal box anyway so the heat will do nothing to the bottles.
My motors get the hottest in the system but I still wouldn't bother moving them closer , the only thing I would do is try and get lots of bottle surface area to freeze up.

[maddox10]

@ Lee

CO2 needs a lot of heat to evaporate.
The few watts the ESC provides in heat are like a mosquito pissing in the sea.
The complexity as well the vurnability of such a setup won't pay off.

@ Yatcatcher.
It all depends how the techcheckers interpret the setup. But any kind of deliberate active heating is prohibited.

[Yatcatcher]

.

Grin, not trying to get around the rules. Just find this rule could be interpreted in different ways.

So for example if the aim is to prevent a valve from freezing up in use different methods could be used;

- bolt the valve to a heat sink of some kind, maybe with some fins.
- Use some electronic heating of some kind which only heats to ambient temperature
- Use heat from other areas to heat the valve through positioning / fans

Two of these would be legal and the other one not, even though they all in effect add heat to the valve / CO2 system.

Other solutions, the cooling comes from the gas expanding and one of the places that happens is where the gas leaves the system, still under some pressure. So using a pipe to allow the system to vent at some distance from the valve area can help. Certainly allowing the system to vent near the valve will cause condensation and freezing to occur to a greater degree.

One final thing (and it may be our imagination), but we switched from getting our pub CO2 bottle which we used to recharge our system, filled at the local welding shop to a fire extinguisher supplier, and the gas seemed to contain less water?!?!

[maddox10]

Talking as a tech checker with some knowledge about CO2 setups I can write this.

Using fins to gather more heat from the enviroment, perfectly passive. No problem there according the rules.

Active heating restricted to ambient temperature still is active heating.

Fans to suck out the cold, should work, if designed well. And ain't active heaters.

On the idea to expand gas away from the valve. It could work, but will degrade performance due long piping. At least for the first flips.
I don't see a direct advantage, as the energy hungry transition between liquid and gas should happen in the main bottle or between main bottle and buffertank. Not between buffer and main ram feeding valve or even after main feed valve.

Water in CO2 bottles. It's potentialy deadly. If you notice that, don't use the feed bottle, return to supplier, and ask for a refund. Check your setup thoroughly.
Check all pressure parts on corrosion, and clean them. If pitting of inner surfaces is noticed, let the parts be rechecked by professionals that can provide official certificats.
Be warned, most of the time they will recommend scrapping.

[JeremyCuss]

I am at the point at which I need to decide whether to slope the CO2 bottle up or down or leave it horizontal. I have a full pressure system. Above the CO2 bottle I have 2 horizontal buffer tanks, each feeding a ram inlet valve. My intention was leave the CO2 bottle horizontal. On opening the isolation valve liquid will transfer to the buffer tanks and evaporate until the pressure balances. On opening the inlet valves the pressure in the system will fall and feed gas (and some liquid) to the ram. I have taken on board the point further up this thread that it would be good to direct the cold exhaust gas away from inlet valves. Any suggestions or advice would be welcome.

[maddox10]

You could add an "up tube" in the main tank. A dip tube bend so it will take gas when the bottle is in a normal position.