BOV - Quick Disconnects & Air Flow

w ripley

On OC it was easy -- 1 charged tank, 1 first stage, 1 hose, and 1 second stage. The system was designed to supply enough gas at every depth.

Now its becoming difficult to stay away from quick disconnects with any off-board tanks.

As I look at a QD for my BOV supply hose, I don't see many with the air flow ratings published, so naturally I'm wondering whether or not the QDs will reduce the air flow -- so that at depth the OC BOV just won't get enough gas to do any good?

For example, assume your RMV to be 280+/- L/m for a moderate workload at 5 ata with a SAC rate of 25 L/m. Double the depth or have a heavier workload, of course, and the gas supply needed to breathe soars.

Taking the Swagelock QCs, as an example, the published "water" flow rate is 4 gal/m or 15 L/m for the QC4, 6 gal/m or 22 L/m for the QC6, and 10 gal/m or 37 L/m for the QC8.

If you need 280 L/m to be on OC (BOV) from the above example and the QC6 is only supplying 22L/m, isn't there a problem? Can you compare water flow rates and pressurized air flow rates in this way? If not, then does someone have the conversion formula or tell me where Swagelock publishes its "air" flow rates?

Thanks,

Bill

Lancer4545

Hey Bill,

I can't see any reason for wanting a QD for your BOV, if you put a flow-stop on it has a knurled screw on fitting on the end you can very easily attach or remove. I wouldn't dive without a FS as the BOV will free-flow like mad when you jump in or your bobbing around on the surface.

Lance

__________________
You can run but you can't hide!

ISC Appointed Megalodon Dealer for East Australia
http://www.closedcircuitdivers.com.au
info@closedcircuitdivers.com.au

diverklondike

Lance,

There are a couple different reasons for needing an QD in this type of application. Some people choose plug their BOV to an offboard source. Others choose to plug there BOV into a manifold and have a hose with a QD to pipe in offboard.

These comments were not meant to side track the thread but only to clarify that there are a number of reasons to have a QD involved in the BOV conversation.

Dive Safe.

Mark

Dave Sutton

Do a topic search. This has been discussed at length. QD's are part and parcel of the thinking Rebreather divers kit and ought to be understood. Seach "CEJN" here and you'll find threads dedicated to the topic along with some ideas on how to plumb BOV's, etc.


Dave

.

__________________
.

"All animals are equal, but some animals are more equal than others"


Professional Small Boy: Never Successfully Cubicled.

diverklondike

Thanks Dave...

Bill... This thread provides some good information. I did a similar search on "QC-6"

http://www.rebreatherworld.com/rebre...gelok-qc6.html

Mark

Dave Sutton

Wondering if an article might be in order since this is a common question.


Dave

__________________
.

"All animals are equal, but some animals are more equal than others"


Professional Small Boy: Never Successfully Cubicled.

w ripley

Mark:

Thanks. I read that thread, and the related others I could find, before posting and it does a great job explaining how to put everything together. Unless I missed something, it still does not clarify just how much air volume will go thru the quick disconnect fittings.

I did receive an off-line reply from a friend I met diving this past year and he said he took his QC6 to 100m and breathed using that line as hard as he could and it delivered enough air. I can do the math and see how much gas the system was providing, and that helps a lot. Definately, the QC6 allows enough gas to pass to operate a second stage in real life at 100m. Thanks for that data.

Now, has anyone done the same thing any deeper than that?

Hopefully, you see my question. If you are going to design a life-support system, emergency or otherwise, shouldn't you be able to put it together with pieces based on their specs?

Sorry if I'm being a pain.

Bill

Dave Sutton

Any Swagelok application specialist will be happy to help people designing hadware to do the math. Call your Swagelok distrbutor, ask to talk to their application guy, and ask. They have engineering data sheets on everything. Flow calculations are not rocket science.

IHMO, Using the QC series for rebreather QD's is old-school. Using CEJN compatable fittings allows modular systems to be developed that are far more flexable. They are smaller as well. Similatly to Swagelok, application data sheets are available from CEJN for their hardware and from Hansen and others who manufacture parts that interchange with CEJN.

Respectfully disagree with the prior poster who opined that a flow stop is better on a BOV than a QD. A flowstop does one thing. A QD does several, among them (1): ability to stop a free flow, (2): Ability to plug buddy-gas to the BOV, (3): possible ability to plug 02 to the BOV, and (4) ease of breakdown of the DSV/hose set from the rig for maintenance/washing/drying.


Dave


(never saw anyone wearing an 02 mask in a CJ-6, BTW......)

.

__________________
.

"All animals are equal, but some animals are more equal than others"


Professional Small Boy: Never Successfully Cubicled.

diverklondike

Bill,

Not an issue...

Two points from my side...

1) I personally have tested my QC-6 configuration at 275 fsw. This included changing gas for the BOV at depth high work rate breathing. It worked fine...

2) Several people that I dive with also use the same QC configuration.

The net is that there are lots of ways to approach this. With out a doubt you need to consider what configuration your dive buddies use. It's not a must but it can simplify things some what.

Dive Safe...

Mark

Hanssing

I actually did a simple outline for one, since I triede to make up my mind about how to plub the rEvo, and where to get the parts - don´t think thats exactly new to you though

I'll email it to you, and you can have a look - its very preliminary, just what could be in one.

Nicolai

__________________
Woohooo - I can change my rEvo!
Its going to be bitchin' tricked out piece of gear