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Can anyone here downunda give me a source of gas for a subdriver ballast system. And just to make it a bit harder....I'm under downunda in Tasmania, tho we have most of larger mainland chains here....any advice or suggestions really appreciated.
I'm no authority but I considered the CO2 and N2O cartridges that you get from lots of places for a lot of uses. They're often sold as instant cycle tyre inflators (CO2/N2O), soft drink carbonation (CO2) and a whole host of other uses. Try googling for 16g CO2 cartridge, that should get you started.
The cartridges have liquid gas in them which is a big bonus when it comes to quantities (even the small cartridges have a surprising amount of gas in) but a big issue when it comes to decompression, since they tend to freeze if you dispense the gas too quickly.
To give you an idea of gas consumption (approximate numbers to give ball-parks):
CO2 liquid density is very close to that of water, at 20 deg C it's 1032kg/m3.
A 16g cartridge will hold about 15ml of compressed CO2 but that's at over 19 bar. You need two bar of pressure to overcome the outside water pressure at 10m depth so each cartridge can dispense 9.5 * 15ml or 140ml of gas at that depth.
At 2m depth you need 1.2 bar of pressure to overcome the water pressure which gives about 240ml of gas.
Depending on your sub characteristics (i.e. are you running a small sub?) this may or may not be enough gas. You can get much larger versions of these cartridges and if you have bigger subs you can use CO2 cartridges from welding stores. The refill cost on these is not low but it's not expensive either.
And, of course, if you can use some kind of air recycling method, e.g. snort (use the gas to get you to periscope depth and then snorkeled air to fill the MBT) or RCABS (use an air or water pump to inflate bladders/cylinders with water/air to change density) then your gas capacity only needs to be enough to vary your density and depth, consumption here would be very low.
Personally I don't like gas consumption systems, they scare me with the possibilities of out-of-gas errors, and I much prefer recycling systems. Using gas an emergency MBT purge, though, would be very useful and I've considered, but never implemented, this. It would be easy to implement as part of a fail-safe system, trigger it on loss of transmission signal and open a solenoid into the MBT from the gas cartridge. In these kind of emergency situations you wouldn't necessarily care about the freezing effect of the gas expansion although you would need to make sure the electronics were sealed to avoid water condensation when the air is cooled.
Don't be tempted to use CO2 on a sub driver- the gas tank isn't designed for those sort of pressures.
Perhaps the best chap to speak to about availability would be John Slater, as he's down under and runs Sub Drivers, although I believe he mainly uses them solely with snort these days.
Most people who use the gas system run with a little residual buoyancy, so should they forget how many times they've cycled the ballast system, you can let the boat rise in the way you would a dynamic diver.
Most people in the UK tend to use systems based on water pumps or piston tanks.
Don't be tempted to use CO2 on a sub driver- the gas tank isn't designed for those sort of pressures.
That's a good point that I didn't think to make clear. I'm talking about open-venting the gas into a water-vented ballast tank. The gas is stored at over 700psi so venting an unregulated CO2 cartridge into your sub-driver or unvented MBT would cause a rupture (at best).
One option would be to use the 'canned air,' office-supply stores sell 'em with the triggers and the tube/nozzles on the top.... A little bit of creative plumbing can make it a one-handed operation.
This was a matter of utilizing what was available, and, uh, lets say "cost effective."
Many thanks to all who replied.....being new to this type of system I've been a little unclear as to whether the gas tank actually contains gas or gas in a liquid form.....I'll follow up on your suggestions and start hunting around.
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