Combined Primary Rebreather and Back up RB (BOB) dsv

Drmike

One problem with using a BOB is the need to verify its working (not flooded) and or keep it active during the dive.

I have found that the need to remove the primary dsv from the mouth and insert the bob one to be enough of a pain to do during busy dives that Im not encouraged to do so, also far more importantly (as I learnt the hard way) taking a perfectly working dsv out of your mouth can add problems/risk if you flood your primary (or bob) in the process.

So I looked at the design of a dsv that houses both loop dsvs.

trouble is they become too big and heavy and unpractical.



Then I hit on a very very simple solution.....


Its a bit of a cheat but here it is


1) Use a Panorma Nova FFM
2) Primary DSV goes in mask front p-port as normal
3) BOB dsv* goes into one of the side P-ports in mask


During the dive to verify the bob is working I just need to reach up and open the BOB dsv lever and nose breathe.



If I need to bail I just have to move the BOB dsv from the side p-port to the front p-port and insert a blanking plug (secured to side of mask with bit of cave line) or blank it with the primary dsv (harder but possible)

[Tipping head to side stops water ingress through side p-port when swapping dsvs ]



Another trick that works really well and totally prevents accidental floods is to use the BOB CL as part of bouyancy. During descent I alternate adding gas manually to both wing as well as BOB.

Used this on the Song Hong exped at it worked like a charm. With the ADV combined with using the bob as part of bouyancy the BOB loop was +ve the whole time during the dives helping to keep water out



*(note: must seal off BOB dsv water vent hole)

Attached Images

NOVA.jpg (19.5 KB, 274 views)

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jaap

"During the dive to verify the bob is working I just need to reach up and open the BOB dsv lever and nose breathe."

How about the added deadspace while doing this? Could it be a problem when deep?

"If I need to bail I just have to move the BOB dsv from the side p-port to the front p-port and insert a blanking plug (secured to side of mask with bit of cave line) or blank it with the primary dsv (harder but possible)"

Doesn't exactly sound like quick & easy thing to do in a stressful situation? Did you have the balls to try it out deep and alone?

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diverreb

Question for you guys using a BOB.....

Pre-breathing is necessary ( 2 -5 minutes on average) to get the Sorb/EAC's warmed up so that the proper scrubbing reactions can take place.

How does that happen with a BOB?

Assume you have an elevated breathing rate at the time of switch-over.... Does that present risks associated with higher CO2 levels?

Just curious.

Richie

Drmike

you only take one or two breaths thru the nose to verify loop isnt flooded small deadspace isnt an issue for couple breaths. In the event you actually bail you swap the bob dsv for the primary one so no increased deadspace.

Whats the rush? whats the panic? Take your time in an emergency keep calm. Breath a few breaths from the attached 2nd stage remain calm and in control - no need to rush rush rush. Rememeber you likely wouldnt bail directly from one loop straight to other due to co2 anyway most likely you would only bail )(without 1st going OC) if primary loop floods. such a flood is almost never instant - user will usually get increasing warning (gurgling) before he bails so shouldnt be stresses

But anyway I disagree - its actually a piece of cake to swap the dsvs.




Its very quick and easy (I practiced it)
With the side OC 2nd stage fitted you can realy take your time (10 secs feels like a lifetime)

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Drmike

my current protocal is to run semiclosed when 1st bail (and sometimes during whole bail) this will help with going to cold scrubber. prebreathe on surface then descend, check when reach max depth and/or at reg intervals.

bob to me is gas extender. I would never plan on going to bob direct from a co2 issue - thats best dealt with (co2) with oc bail gas (which is why i still carry some oc bail gas). once breathing rate has recovered go to bob. to me bob is for uise if primary floods.

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mattmexico

yo

During the Wakulla II cave project we where diving double but independent Cis Lunar MK5P with seperate DSV and came to a procedure to pre-breathe both units on the surface then descend on the bailour rebreather adding dilluent to the primary unit ( at this moment inert ) and keep the ADV active as well.

When reaching max depth we switched over to the primary rebreather setting set point and establishing loop gas, and then kept on going doing the dive knowing that the bailout rebreather is working, has the right setpoint, loop gas and the gas selection is done right.

greetings
Matt

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Nad

About the activation of the scrubber, you say that doing the BOB BA slowly (a couple of breath each time) could also warm up the sofno?
Well better than nothing.

I find this an interesting solution, with FFM.

Nad

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Nad

...I have to write faster.

Nad

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Drmike

Hey Matt, cheers,

What Im doing is prebreathe with manual dila and O2 on surface, then on descent using primary im manually adding dil as well as ADV firing dil into bob. Hit target depth (or at pre determined depth) and check bob (nose breathe ) then every 10 mins or so repeat test. Im not adding any O2 during dive unless I bail

Personally im not fussed what the ppo2 is in the loop as 1) it will always be breathable and not higher than dil ppo2 (which at depth is not far off/same as setpoint) 2) I would never bail to the bob in shallows anyway (its for deep bail) Id go OC so Im not concerned about chances of going to hipoxic loop (besides pre breathe ensures loop will breathable in shallows) 3) it takes seconds to increase/ reduce loop ppo2 once bailed.

cheers
mike

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Drmike

hehe yeh thats something I was hoping/dreaming about but dont know if effect is really significant. but would be nice if it is

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