Bursting CO2 SMB's?

[Gary K]

I'm getting confused

so, if the SMB is say 8L capacity and the CO2 canister 0.02L capacity

8/0.02 = 400bar pressure in the CO2 canister?

[Gary K]

Originally Posted by triplefin

slight deviation here folks - Gary where did you get your yellow one, its on my 'to purchase list' and assume you looked around so thought I'd save myself the work

LDS Jane

[gobfish1]

Make shore you ask for the ones that don’t go bang at the surface

[MixedUp]

Originally Posted by warmwaterdiver

I'm getting confused

so, if the SMB is say 8L capacity and the CO2 canister 0.02L capacity

8/0.02 = 400bar pressure in the CO2 canister?

Gary don't forget the DSMB is being filled to more that 0ne ATM, not sure how many but lets say it is 5 then the cylinder is "only" 80 bar.

Steve

[Lou]

Originally Posted by warmwaterdiver

I'm getting confused

so, if the SMB is say 8L capacity and the CO2 canister 0.02L capacity

8/0.02 = 400bar pressure in the CO2 canister?

Yes. That's the right thinking. I think. Except the SMB will hold a bit more than 1 bar's worth but not much.

[Gary K]

Steve, but if I test it on the surface at 1 ATM

I've got to fill a 8L space from a 0.02L device

surely its got to be at 400 bar?

[MixedUp]

Originally Posted by warmwaterdiver

Steve, but if I test it on the surface at 1 ATM

I've got to fill a 8L space from a 0.02L device

surely its got to be at 400 bar?

No because if there is no dump valve the pressure inside the blob will increase untill the pressures are equal, same as decanting from one cylinder to another (remember your belending course Gary? )

And also the blob is "elastic"

Steve

[matt_scubaguy]

Slight deviation but watch these at the surface a chap in our club did burst his DSMB with the CO2 cartridge but it went off with the DSMB still rolled up with a strap round it. It made quite a bang lucky no ones hand was on it at the time.

Matt

[jb2cool]

Originally Posted by warmwaterdiver

I'm getting confused

so, if the SMB is say 8L capacity and the CO2 canister 0.02L capacity

8/0.02 = 400bar pressure in the CO2 canister?

I don't think it quite works like that as the CO2 is in liquid form inside the cartridge. Essentially the maths is correct but the pressure will be lower as the CO2 has changed state.

[Janos]

Originally Posted by warmwaterdiver

I'm getting confused

so, if the SMB is say 8L capacity and the CO2 canister 0.02L capacity
8/0.02 = 400bar pressure in the CO2 canister?

Yes. If the cannister is 0.02L. If it's a bit larger (say 0.04L) then it's only 200bar.

Originally Posted by Steve Jones

No because if there is no dump valve the pressure inside the blob will increase untill the pressures are equal, same as decanting from one cylinder to another (remember your belending course Gary? )

Eh? When the cylinder opens, the pressures inside the blob and the cylinder will equalise. But this is not what we're interested in.

Because the blob is not a fixed volume (it possible to have a half filled blob) then the cylinder needs to be matched to the maximum volume of the blob. If there is not enough gas in the cylinder then the pressure in the blob & open cartridge will be the same as ambient.

Think of a balloon. One breath into will inflate it so much. If you take it down to 10m then the baloon will half in volume because it is non rigid.

I would have thought that the gas in the cartridge is just enough to inflate the blob at 1atm. I bet if you let it off at 10m, the blob will only be half full.

Janos