OC / CC DSV, Which one and why?

[johnv]

an O/C DSV has a LP lead to a second stage of some sort on the mouthpiece. The CCR mouthpiece is seperated from it by some kind of sealing system. Imageine that on your inspiration mouthpiece, the little hole you blow the water out of when the mouthpiece is closed had a second stage on the end (and was a bit bigger), you exhale water through the exhalation valve, but when you inhale you get gas not water. when you go O/C the CCR part is closed, and when you go CCR, the O/C part is closed.

the loop / ccr / electronics has nothing to do with it, only your diluent 1st stage.

John

[Decodiver]

Originally Posted by Pierre Farrugia

May be I explained myself wrongly, maybe better say this in Maltese , when you switch to OC throgh DSV does gas still flow from inhale lung to the exhaust lung through DSV ? Hope this time you can understand what am I trying to ask.

Hi Pierre,

In short the answer is no, certainly with the ones I have seen, however if you do a dil flush you will force the gas quite quickly back around the system and it should vent through the dump valve on the exhale side.

So in essence you can still Dil flush.

Cheers

Dave Cooper

[Decodiver]

Originally Posted by johnv

the loop / ccr / electronics has nothing to do with it, only your diluent 1st stage.

John

This is not correct for the Bob Howell OC/DSV.

It contains a barrel that rotates, sealing the mouthpiece on both sides when you go OC and taking and expelling gas from the second stage under the mouthpiece.

So the loop ceases to be a loop and becomes a horseshoe.

Cheers

Dave Cooper

[johnv]

Originally Posted by Decodiver

This is not correct for the Bob Howell OC/DSV.
So the loop ceases to be a loop and becomes a horseshoe.

It is correct. I think it's taken as read that you have to have some common parts, primarily the bit you stick in your mouth.

However on any O/C DSV (worth having) you don't inhale through the CCR inhale hoze, or exhale through the CCR exhale hoze, making O/C mode independant as I previously described.


To prove this, next time you dive switch to O/C mode then cut off both your handsets, and your inhale & exhale CCR hozes, I bet your DSV still works :-)

John

[Decodiver]

Originally Posted by johnv

It is correct. I think it's taken as read that you have to have some common parts, primarily the bit you stick in your mouth.

However on any O/C DSV (worth having) you don't inhale through the CCR inhale hoze, or exhale through the CCR exhale hoze, making O/C mode independant as I previously described.


To prove this, next time you dive switch to O/C mode then cut off both your handsets, and your inhale & exhale CCR hozes, I bet your DSV still works :-)

John

Hi John,

we are talking at cross purposes here. I agree with you however, the fact that you bail to an OC/DSV does have an effect on the loop and I was answering to your part of the thread where you said

Originally Posted by johnv

the loop / ccr / electronics has nothing to do with it, only your diluent 1st stage.

hence my statement, the effect on the loop is that it is blocked by the mouthpiece assembly and therefore a horseshoe.

You are of course, correct in saying that you do not inhale from, nor exhale into, any of the CCR loop components.

Hope this clarifies.

Cheers

Dave Cooper

[johnv]

Originally Posted by Decodiver

Hope this clarifies.

it certainly clarifies why I'm not cut out to be an instructor - what - didn't I mention you need to put the sofnolime in the canister thingy - oops

John

[nigelH]

Originally Posted by Decodiver

It contains a barrel that rotates, sealing the mouthpiece on both sides when you go OC and taking and expelling gas from the second stage under the mouthpiece.

So if you ascend on the OC setting the inhale counterlung can only vent back through the scrubber to the OPV. I guess it's only pushing against the usual WOB so I don't see any significant consequences other than getting the handsets in a bit of a tizz since the stuff they inject isn't heading toward the cells. However you've already given up on the loop at this point so it is only a buoyancy issue.

Anything else I'm missing?

[Decodiver]

Originally Posted by nigelH

So if you ascend on the OC setting the inhale counterlung can only vent back through the scrubber to the OPV. I guess it's only pushing against the usual WOB so I don't see any significant consequences other than getting the handsets in a bit of a tizz since the stuff they inject isn't heading toward the cells. However you've already given up on the loop at this point so it is only a buoyancy issue.

Anything else I'm missing?

Hi Nigel

You're right, if you're ascending OC you might as well turn the rig off and save your O2 if you can access it, periodically crush the inhale and exhale counterlungs whilst dumping and buoyancy should not be an issue.

Cheers

Dave Cooper

[Pierre Farrugia]

Originally Posted by Decodiver

the effect on the loop is that it is blocked by the mouthpiece assembly and therefore a horseshoe.

You are of course, correct in saying that you do not inhale from, nor exhale into, any of the CCR loop components.

Hope this clarifies.

Cheers

Dave Cooper

This is what I was after, didn'y realise that like this you can invert the flow, so can do a loop flush.

[nigelH]

Originally Posted by Decodiver

You're right, if you're ascending OC you might as well turn the rig off and save your O2 if you can access it, periodically crush the inhale and exhale counterlungs whilst dumping and buoyancy should not be an issue.

Thanks. I have a TX40 on the O2 (with an Apeks FFD) so I'd be tempted to shut the valve and hope I can go O2 rebreather shallow or at least get a safety stop out of it OC. I only really wanted the Bob to get over the sanity breath problem and onto the stage but I had not fully explored the complications of operating a sealed loop. On my mod 2 course we were introduced to venting a loop via the mouthpiece while ascending OC but I only thought of that for a well flooded loop where the OPV was below the water line.

Some time when you are at the Brighton end of you circuit I must invest a beer or so in pumping you for more information. I'm just inland from the Marina.