OPV mods - options ideas

vlada

In my 85 hrs on a unit, I had 2 complete floods with caustic both time and a number of very wet scrubber dives due to pieces of sorb stuck in OPV. Both times, unit held perfect negative (overnight) and flooded closer to the end of the dive.

Dr. Mike's OPV filter is still finding its way to me, and in the meantime, i am looking for what others have done.

I remember reading about Frankie's scotchbrite solution, but can't find pictures.

Did anyone replace the OPV with some other brand?PMs are welcome as well.

Thanks

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Vlada

www.wrecksandreefs.com

IN468

I had never a full flood but nevertheless to prevent any flood

i did it Frankie´s way

pictures are here

http://www.rebreatherworld.com/ourob...os-owners.html

scroll down..

bletso

If you are diving CCR i would replace any OPV with one from a BC or lift bag. Its only function is to keep the bag from bursting. I just vent though my nose.

If SCR, you really don't have many choices.

Dale

G4SSG

HI
I have now removed the original opv
and replaced it with a si-tech dry suit valve,
yes its the same one fitted too the meg lung
only had two dives with it since mod
working ok at mo
had to cut the hole in lung a little larger
the valve lock nut could only be fitted ,after taking
the breathing hose connection off the lung
martyn

DrJM

it's a very strange issue, after 600h on the no 002 I NEVER flooded the unit, thanks to Mike I recently added for safety the grid

recently a friend of mine had a bad flooding/caustic/cocktail/burn on a second hand unit even with a perfect neg test before ... he bought the hydrophobic mb and also got a grid from Mike

Sitech OPv sounds good plan also, keep us posted on your feelings about the feelings of exhaling the over pressure in the loop

Dive safe (and dry)

J

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Frankie Pellegrino

Dear Vlada
Do you have the canister retention band installed on your canister? If not get one! It could leak from their if the Delran canister expanded quicker then the center section because of the heat of your scrubber. In My Humble Opinion It could cause that mysterious leak. Also the opv filter is a must in my Opinion. Please keep us posted if it happens again …… best of luck.

Also to other Boris divers; this year I checked my first stages Over Pressure Valves and both were set dangerously low. They would crack open at 150 psi. I know other guys in the past posted about them cracking open and loosing all their Dil or O2 Gas. It’s a good idea to bench test them before you start diving deep. Best of luck men and have a kick ass season.I know I will.
Cheers Frankie

aknelson

A strange symptom the leaks. I hope the below give a few hints about my findings.
I had my floods and caustics during the training, and I was irritated.
The factory o-ring kit contains a standard Dome O-ring this one will NOT work on my unit. The 5mm dia. O-ring is simply too small in diameter.
The above fact started a project last Fall. At that time I was reading about removing the o-rings followed by the jubilee-band with the spacers. I was not convinced about the dome leak reasoning.
I agree O-rings will kind a remember the pressure impact and deform. The Parker O-ring hand book has a 100 pages plus just talking about design and background and I would not claim to have found the best solution to the O-ring science. However o-ring peripheral squeeze must be factored into the design. Without the peripheral squeeze a o-ring will not seal.
My work has the required calipers to measure the actual dimensions. I compared the dimension measured with the standard O-ring specification in the Parker Handbook. To my surprise the measurements confirmed there was insufficient O-ring squeeze. The actual dimension did not fit any of the standard O-ring groove specification.
I was left with ordering a 2-457 Neoprene o-ring which turned out to be a bit big. Beside that the groove was too narrow for the 6.4mm standard O-ring. Finally the smaller 2-456 70 shore EDPM worked fine. The Dome has to be pressed on. The dome will not come off by just pulling on it. The 2-456 O-ring deformes around 15-20%. I leave now the Dome O-ring installed for weeks. The positive side effect is no more water inside the dome and no more little white pieces are sitting in the exhalation lung.
I did install the 22mesh SS screen inside the over pressure valve and I still have that stainless steel mesh material around if someone wants a piece. To what I am reading and what I have seen there must have been different groove dimensions in the last four years. What made me wonder is that different units Dome and O-rings will not interchange I did try the interchange. My unit must have been one of the first or second series and I would not use the above as a reference.
Andreas

IN468

I did only one dive with the original O-Ring which was 5,3 mm and had a
partial flood, than i took a 5,7 mm O-Ring and everything was fine
even with the stainless steel band i need the 5,7 mm Ring

Drmike

The situation with the domes is like this;

The center section and domes are made with the correct sized groves and correct sized o-rings. However, due to the size, profile, material properties and design used some domes can expand. They dont all expand, they dont all expand to same extent (which is why different domes/o-ring combos fit on different units). The instability of the dome is inherent in the material and the fact it is a larger thin walled machined part (rather than a (far more expensive to make in small batches) molded fiber reinforded part)

The domes that expand can see their diameter increasing which can if left unfixed eventually cause loss of sealing with the original o-ring when it reaches a certain size.


Solution:

A simple solution is to fit a bigger o-ring. This works for some (depending on degree of expansion and if it stops increasing) .

Theres some speculation that the pressure of the o-ring over prolonged time will speed up or enhance the deformation (which is why I dont store my unit with o-rings installed)

However with just changing the o-ring the dome is still 'free' to continue to expand if its nature is such. In many cases the dome doesnt but in some it continues to distort so that even the large o-ring eventualy loses its seal. To gaurantee no issues ever with expansion (of the original design domes) we ideally need a way to fix the outer diameter of the dome to prevent any or all expansion.


Better Solution :

The stainless steel band clamps provided by the factory fix the dome outer dimension and prevents change in dome diameter - it can even be used (within limits) to 'pull back' an expanded dome to correct size*

Fit the band, fit the original (or larger) o-ring, adjust the band to give the correct seal and forget about it. The best thing with the band is you can adjust it from time to time to make sure seal is always perfect. Fit it and forget it. With the band, deforming/leaking domes is a non issue.



Best/future solution:

I believe (please correct me if im wrong) that the factory has been using a new design of dome for a while with thicker rim to help prevent distortion issues?

I never got around to it but a nice neat solution would be to make up a stainless steel ring the height of the dome ring heat it up and press it over a chilled dome rim rather like the way they used to put rims on barrels. Does the same thing as the stainless bands but looks nicer This should be an easy thing for factory to add to new domes (with circular outer rims)





*to ascertain the correct size what I do is just tighten the band so that I have to push the dome on and off with a reasonable amount of difficulty. Mine is adjusted so I can only just suck the dome down with a negative and blow it off with a +ve



.

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Drmike

Are you using the new opv supplied by factory or the old one with the central spike on the opv base? Since fitting the new one I havent had a flood at all.


For a while I was diving with a liftbag OPV in boris CL. The opening pressure was so high it never opens so flooding is a non issue
I went back to using ccrb opv as i was concerned unit starting up on its own (or injecting at anytime) with the dsv closed would result in burst CLs.

Like I said with the new opv *when i say new it was released well over a year ago) I havent had a flood


Key I think is to keep it clean when filling sorb

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Get a girlfriend you sad twat - a Rebreather is an unfaithful mistress - dont blind yourself to her faults just because she goes down on you