OPV location on bmcl

hippytyre

hippytyre

New Member
Just getting my bmcls sorted out and trying to figure out where to put the opv.

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If I put it there it'll double as a water dump but maybe would better the other side of the under the mav?


Also what's the best way to get the holes into the cordura and lungs.


Cheers.
 
IMHO not there unless you want to lie flat on your back or ascend feet first to vent excess gas from the loop if you bail out.
 
Wouldn't the excess pressure vent wherever I put it? I don't see why it would have to be at the top to vent it.
 
feel free to try it in any position you like but ask yourself where the vent is positioned on your wing and why it is where it is.

if you shut the mouthpiece and seal the loop the only vent point you have is the opv and if fitted at the lowest point it will vent only once the gas in the loop has filled the lungs to the opv position. you could take out the OPV in that position and leave the hole and the lungs will still not vent the gas while ascending, they will fill with gas and act as a lift bag with the gas trapped at the highest point until that expanding gas reaches the dump position. as you ascend you will have no way of dumping that gas and as the gas expands you'll become more and more buoyant.

in normal operation it won't matter as you can let it vent aound the mouthpiece but in a bail out situation you can't dump the expanding gas in the loop and the excess buoyancy will stop you from holding your stops.
 
It's a choice or compromise you'll need to make.

If you want to dump water through the OPV it needs to be at the bottom of the lung - BMCLs I'm thinking are going to be a bit of a challenge to dump and roll up like the OTSCLs.

If you want to keep the lungs empty on bailout, the OPV needs to be at the top of the bubble.

Sadly, there's no perfect spot for doing both.
 
I used bmcl's on my vision for 5 years before moving to a revo in 2012. My opv was mounted in the original hole position of the inner bag ie half way up. I ran N@90 mavs from the bottom holes round my waist band. Because the bottom parts on the bmcl are flat then most of the air is held in the top shoulder part anyway. What you need to realise is that due to the design you are being kept on near minimum loop volume by the physical size of the case. On the surface I could only get one full breath from the lungs when my drysuit & wing were fully inflated. Due to this there is very little buoyancy change caused by the lungs, also because the bottom of the case has very little volume it holds very little water in the event of a leak or flood.
I ran a pull cord over my shoulder for the dump but after a while I got fed up with it & removed it. Dave Thompson who gave me the pattern told me the most critical thing was to still have the "T" pieces on the top of your shoulder ( if viewed standing upright).
Some people may remember years back on RBW that Phi was going to sell these with Dave's blessing, the design differed only that on the sides was a section with eyelets & a draw string so that you could adjust the capacity(volume) of the casing to suit the individual divers lung volume. Unfortunately Dave decided that due to CE concerns that it was wiser not to sell them at that time .
 
The AP BMCL have the dumps at the bottom of the bag. They work well as water dumps too. I have OPV's on my wing just above my butt which are used when in trim (head slightly down) I dont see why the BMCL OPV couldnt vent in the same position? or is everyone assuming a bailout is going to be done in a vertical orientation much like the PADI Controlled emergency swimming ascent?
 
Good question, I bought a couple of Dive Rite OPV / Dumps to put onto a set I have had made up and will probably put them in the same position as the JJ. When trying the AP BMCLs, which keep the big AP dumps, it did feel it could dig in to your back. The Dive Rites are smaller. But now i am confused by the rubber gasket it comes with and how the whole sandwich arrangement works with the inner outer and fitting!
 
hippytyre;165712 Also what's the best way to get the holes into the cordura and lungs. [/QUOTE said:
Small, Sharp scissors, cut the inner lung hole undersize so its a stretch fit and the Cordura 0.5mm undersize so its a tight fit- this way you won't suffer any "extrusion" on +ve pressure test or the bailed out ascent Mike is worried about :-)

I wouldn't worry about the bailed out ascent- it works when its at the bottom and you can use the DSV too if you are concerned- How often do you do a bailed out ascent? Enough to comprise performance in other scenarios? Not sure that's worth the worry.
Click to expand...
 
Ben, with your stuff, have you seen the odd double gasket that comes with some OPV /dumps? It is a bit like, how to explain, a Ceylon Mothership? From an OMS document, they suggest, that the gasket sits on the inside if the inner and outside if the outer, so my hole will have to be a little wider than the fittings seen anything like that?
 
no reason why a bailout ascent can't be done flat. I was really thinking about lifting an unconscious diver in a controlled buoyant lift. how do lift him flat? he's head up and you're head up.
 
Dave1w said:
Ben, with your stuff, have you seen the odd double gasket that comes with some OPV /dumps? It is a bit like, how to explain, a Ceylon Mothership? From an OMS document, they suggest, that the gasket sits on the inside if the inner and outside if the outer, so my hole will have to be a little wider than the fittings seen anything like that?
Click to expand...

Those gaskets are common on alot of BCD's (I like your Ceylon Mothership description :-)

I would still cut the hole "tight" for the required size (the width of the Mothership hub)
On the plus side I find that type of gasket seals very well with minimal torque on the valve so easy to self install without tools or other nonsense.
 
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