Does this sound like a good idea ?

Muddweller

I know its late, and I should have been in bed hours ago but this came to me in a flash of inspiration (no pun intended) or was that desperation. When I converted my draeger I did away with the OPV, and opted for nose venting instead but this gave issues when ascending on bail out what with having to open the mouthpiece every few meters or so.

So what if I drill the barrel of my mouthpiece and insert a small mushroom valve or somethin like a mask purge valve, when mouthpiece is open the valve would be facing the inside of the housing and is sealed from the outside but when mouthpiece shut, the valve is open to the water and can vent.

I know this would give a farily rapid loss in bouyency but that can be compensated more easily than rapid increased bouyancy I would have thought. Should I just go to bed


Nite all

Karl

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It'll be reet

diverrob

My first thought is no. I would have issues with drilling a hole in my mouth piece. Also when you were on the surface pre/post dive you would lose all of the gas in the CL. This would be a waist of gas and after the pressure equalized between the CL and the outside there would still be a chance of water ingress into the loop. In a BO situation this would not be a concern to me but on a normal dive while on the surface I would hate to subject my loop to a potential leak prior to the dive. Just my thoughts though.

Rob

GKAM

...actually, this may not be a bad idea after all.

If I understood what you are saying, it is already been implemented on the FROG Rebreather



It is also being suggested by Alex for the Open Revolution Rebreather project.

Check out http://www.rebreatherworld.com/photo...oto/827/cat/38 for some pictures.

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Stay #

AD_ward9

The trick in making it work, is you must be able to adjust the pressure on the valve, so control when it lifts.

The normal OPD must lift with less than 40mbar (EN14143:2003 Section 5). The max breathing resistance is 25mbar. This means that both counterlungs are fully expanded by the time the OPD fires. If you have an adjustable OPD, it will all work quite nicely: just set the lift pressure to 10mbar during ascent. On the surface this is fine, as typical resistance at 1ATM is under 10mbar.
Cheers
Alex

zèècalcoene

Hello,

I converted my Dolphin and placed the OPV in inhale bag where the normally blanked P-port sits.
I did disable the 'manual' function of the OPV by placing 2 off the shelf O-rings inside the valve.
I wouldn't recommend removing the OPV in a Dolphin for various reasons.
1) pos pressure test with an alternative OPV (as discussed above) would give a lot of gas loss
2) In case of bailout, something will burst due to pressure increase during ascent.
3) In case of a sudden rapid ascent (shouldn't be a long distance ex. 2m), if you don't deal quick enough with the squirel cheaks..minor lung damage can occur..

With my OPV fitted and the manual function blocked, I found quite a bit of
small leaks in breathing loop..during pos test...
I use 2 small tooth picks and stick them in between the actual valve and the housing of the OPV... In this way I can inflate my breathing loop without the OPV venting..
Small leaks that would have normally passed 'a regular' pos test.. were found in due coarse and fixed..
So far, after 3 yrs diving my Dolphin, never had a flood..

best regards

Ivan

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mCCR Dolphin Diver

Muddweller

Thats very interesting Stay, thanks for that.


I did try the OPV in the inhale bag but found it too bulky and would depress against the shell (didn't get round to modding it cos I'd already decided to ditch it).

Thanks for all your comments.
Karl

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It'll be reet