Prism and Drager flapper valves...

silent running

Anybody ever compared them side by side for thickness and diameter?

I ask because I'm interested in the Pelagian BOV which is the shortest/most compact one and it uses Drager flappers. I used to dive the Drager Dolphin and Atlantis and IIRC, the Drager flappers were slightly thicker and bigger than the Prism's, but it's been a long time since I had my hands on them.

Thanks, -Andy

DeepBlueInnovation

Hi Andy,

They are different, I can't remember by how much, but they were definitely a thicker material and a smaller diameter. I had Drager hoses on the Prism for a while as they were the only adapters I had for my BOV.

Cheers,

Ben.

silent running

Hi Ben, thanks for the info. WOB is my concern, I don't want any incresse in WOB if I switch out my Prism DSV for a BOV as IMHO, it's not worth it at that point. I tried the Divematics which uses flappers that are almost identical to the Prism's and had comparable WOB. But the height/profile meant that I kept hitting the CL elbows when I turned my head, damn! Otherwise, the Divematics BOV would be a great choice.

I wonder if I could convince Andy/Rebreatherlab to make a version that uses Prism flappers...

Any other Prism divers besides me interested in a compact BOV that won't restrict your head movements/ergonomics and has comparable WOB to the stock DSV? -Andy

Rebreatherlab

Hi Andy,

The problem is that there are not so many Prisms out there to make it viable to make a new design.

Having said that it would be interesting to see a Prism DSV with cages (if used) and the flappers. I doubt WOB breathing would be that much of a difference as the Draeger flappers are also flat. The main difference lies in flat vs. standard exhaust valves as they are designed to excert a small force againts the flow direction where as the flat valves do not. Theoretically the thinner and larger diam. the better, but if the larger diam. flappers are larger than the hose diam. it will not make much difference. What is the inside hose diam. on the Prism?

If I had all the pieces in front of me and it would be possible to only change the inside of the Pelagian BOVs spigot bore I could do it for only a few orders and not need to charge extra for it. If the outside spigot size have to be made larger then quite a few changes in the machine code would be needed and then it would not be worth it unless charging extra and that extra would be significant, I am afraid.

Maybe wait for Oceanic? They might work up a BOV for the Prism 2?

Andy

__________________

www.rebreatherlab.com

silent running

Hi Andy, thanks for the post. I know we have discussed this before, but the more I thought about plunking down another $1000 for a BOV that may not breathe as well my stock DSV, the harder it was to part with the money.

I'll measure the inside hose diameter and the flapper cage, maybe take a picture of them too. It would be good to know once and for all if it's possible to adapt your BOV to the Prism.

I wish Oceanic would work up a BOV for the Prism 2 as I think it would be a major selling point, but nobody's mentioned such a thing yet... -Andy

Rebreatherlab

I am doing a Pelagian Instructor course in Miami in the end of April. Take a short holiday and we can swap parts around and see. You could also try the BOV with a Pelagian and see how nice in breathes.

Andy

__________________

www.rebreatherlab.com

silent running

Great idea and thanks for the invitation Andy, except that I will be in Indonesia from April 24th to May 12th.

DeepBlueInnovation

Just to resurrect an old thread, why not manufacture adapters like the nato pod uses? that way it is easy to manufacture the one bov and just make a range of adaptors. In the last photo in this link you can see the Inspo ones screwed on. Andy if you like the BOV it wouldn't be hard to get someone with good lathe skills to machine one up.

Cheers,

Ben.

silent running

Hi Ben, just got back from another trouble free 50 hrs of Prism diving in Indo. If I understand correctly, are you suggesting making adapters for the Pelagian BOV? I'm not sure about the way the BOV is constructed and if this could be done without adding a significant amount of bulk to the BOV who's appeal is partly it's small size.

But your mentioning the NATO pod brings up other points I have to consider. I recently saw a NATO FFM with the BOV/OC setup that Peter Readey brought with him to the BTS show in March. While the OC reg used on it is not a very good one, it is at least in the optimal low profile and decent breathing position-45 degrees from the diver's mouth axis. This is the only way I can think of to get a BOV that will be closest to having the same WOB as a regular OC 2nd stage, while still having a low profile. None of the current BOV's orient their 2nd stages this way: They are either mounted underneath the barrel, which can't be good for WOB in OC mode or on the front, sticking out into the breeze like a weather vane and a liability in any real current. The front mounted 2nd stages also have free flow potential and will require a shutoff, which doesn't make switching from CC to OC any easier and which is part of the appeal of a BOV.

My feeling at this point is that until somebody comes out with a BOV that orients the 2nd stage closer to a 45 degree angle, I won't try one again as there's too many drawbacks in terms of OC performance, size and additional complexity. After spending this last trip diving in even more heavy current than usual, I can't imagine having anything even slightly more bulky sticking out in front of my mouth. Nor after all that hard work, do I want to compromise any of the ease of breathing on the Prism DSV... -Andy

DeepBlueInnovation

The photos below detail the adaptors. I haven't got a reg on the pod at the moment as I am considering putting an Xtreme on. You can see that while these have a sizable thread on them which makes them bulky, the adapter itself is really just a sheath that fits over the existing connection. It would be very easy to make a standard BOV and then just screw on the adaptors for specific units without changing the size of the bov significantly. These adaptors have standard Drager flapper valves.

IMGP2380.JPG

IMGP2370.JPG

IMGP2378.JPG


Cheers,

Ben.