SCR Summary required.

[daz]

I'm interested in a quick summary of the features/benefits/problems with SCR's.

Specifically depth limitations, scrubber duration, maintenance, issues and costs.

Any and all manufacturers and models.

Cheers,
Daz

[wreckweasel]

Daz,


IANTD did a review of most rebreathers in their last "nitrox diver" mag. Try contacting them.


/Z

[Muddweller]

I have an old atlantis, not had it long but am chuffed to bits with it, as for limitations, well depth limited to the MOD of your mix same as OC using nitrox and thats the only limitaion I've found. My bro uses twin 10s and I have a 4ltr, the other day we did an hour at about 12m i had used just over 60bar, my bro had used 60bar thats 240 litres compaired to 1600ltrs. Then theres the weight of the thing, about 22kg includin 3ltr pony. The scrubber is always warm after a long dive but until its winter I won't feel the benefit of breathing warm air until then.

When using a high FO2 theres a hell of lot less bubbles compaired with oc, when at 20m theres even less.

I like the simplicity of the unit, no electronics to go wrong, exept for the
loop monitor of course, what did suprise me is the amount of gooo in the exhalation bag after a long dive, yukk!

All in all its a good replacement for recreational oc gear but not for technical stuff (imo). Cost wise its probably the same running costs as you have less fills but you have to buy sofnolime.

Karl

[daz]

Cheers Karl,

Exactly the info I am looking for. Primarily I would be looking at the recreation diving area anyway.

I was quite interested in the differences between the Draegar units so your post is a good start as to what it can and can't do.

Cheers,
Daz

[NotDeadYet]

They work by adding a premixed gas at a rate that will maintain a ppO2 as you breathe the loop down. Because this means adding more gas than the loop can hold some of the excess must be vented every now and again so you get some bubbles.

The big downside of active SCRs is that there are no overt failure modes. If something goes wrong then you keep breathing until the loop goes hypoxic. They depend on an adequate flow of gas through a sonic orifice, with different orifices for different depths and gas mixes. These have to be preset on the surface and there is your first weakness. Gas flow depends on flow through the orifice being at sonic velocities. There is no filter so salt and debris can partially clog the orifice and reduce the flow. Weakness number two, gas still flows but not at a rate adequate to support life, you pass out and die while everything appears to be working. Also, as the gas flow is preset and not controlled by your breathing rate as in a passive SCR (or your metabolism in a CCR) you can overbreathe the unit if working hard, i.e. you consume O2 faster than its added, it becomes more of a risk the shallower you get. Weakness number three and again there are no warning signs.

I don't see the point of a RB for shallow diving, they take more maintenance than OC, they require more training, more discipline, more prep, more hassle and air/EAN isn't exactly expensive. On the plus side, the Draegers are extremely well made.

I wouldn't use one personally but if I did I'd certainly make sure I put some kind of ppO2 monitoring system on it.

[MATTBIN]

Does this link help, I havent had a chance to read it yet?

Rgds
Matt

http://crazy-rb-diver.com/html/what_...reather__.html