Why use doubles?

[DA Aquamaster]

An extruded o-ring is one potential issue, a burst disc failuire is another. Both would leave you gasless in fairly short order with a 130 cu ft single as compared to a small set of either isolator manifolded doubles or indendent doubles with a similar total capacty.

Of course, you could also argue that a burst disc failure combined with a broken isolator could leave you gas less as well with manifolded doubles, but it is a matter of how many simultaneous failures do you want to plan for before you decide its just not your day.

 

[JeffG]

If a set of doubles contains the same volume of gas as a single tank with the following set-up, what would be the DIR reason to use doubles?

For Open water NDL type dives there is no reason to use doubles. For Overhead type dives doubles (with an Isolation valve) provides some redundancy in the case of catastrophic gas loss.

Quite frankly, for an open water ndl dive, I wouldn't use that T valve. Just a normal valve. The only problem it solves is a freeflow on one reg while adding some minor complications. I would live with the freeflow issue and remove the minor complications. (Minor complication would be a turned off valve.)

 

[24940]

Quite frankly, for an open water ndl dive, I wouldn't use that T valve. Just a normal valve. The only problem it solves is a freeflow on one reg while adding some minor complications. I would live with the freeflow issue and remove the minor complications. (Minor complication would be a turned off valve.)

It would eliminate the need for a dedicated singles rig and its associated costs. Not related to DIR, but it is more practical.

 

[JeffG]

It would eliminate the need for a dedicated singles rig and its associated costs. Not related to DIR, but it is more practical.

or help the lazy slobs that don't want to swap a hose or two.

very DIR

 

[300bar]

An extruded o-ring is one potential issue, a burst disc failuire is another. Both would leave you gasless in fairly short order with a 130 cu ft single as compared to a small set of either isolator manifolded doubles or indendent doubles with a similar total capacty.

Of course, you could also argue that a burst disc failure combined with a broken isolator could leave you gas less as well with manifolded doubles, but it is a matter of how many simultaneous failures do you want to plan for before you decide its just not your day.

Of course you could also say, an extruding O-ring will only happen during a fill and not on a dive.And those ****** burstdiscs,well WE don't use them. No need, no use.
And a extruding (valve) O-ring will give you more then enough time to make a safe assent in a OW dive.

 

[John_B]

.....

 

[24940]

or help the lazy slobs that don't want to swap a hose or two.

very DIR

Yeah, or that.....

The main issue with the valve is the fact that it's not standardized. I seem to recall JJ advocating the use of H valves for singles, but that doesn't seem to be the norm. In singles diving, most will be using a standard DIN valve.

 

[Vie]

I seem to recall JJ advocating the use of H valves for singles, but that doesn't seem to be the norm.

JJ did write "...single tank divers who choose to dive in deeper areas or in overhead environments must also adhere to equipment redundancy, and use a "Y" or "H" valve to allow two first stages to be affixed to a single tank."

Otoh, this was written a long time ago and is definitely not what GUE advocates/teaches - I think JJ gave up that idea along with the orange/yellow wetsuit (see page 58 of Doing It Right: The Fundamentals of Better Diving for pic).