independent double tanks or isolator valve doubles.

[Roy Moore]

I'm thinking of doubling up my steel 100's. but I'm torn beteen being able to use them as singles also.what are the views on using a joined isolator valve set up as to using independent tanks with seperate valves.does anyone use doubles as two independent tanks?what are the pros and cons of both?

 

[Curt Bowen]

I'm thinking of doubling up my steel 100's. but I'm torn beteen being able to use them as singles also.what are the views on using a joined isolator valve set up as to using independent tanks with seperate valves.does anyone use doubles as two independent tanks?what are the pros and cons of both?

I went from using back mounted doubles to sidemount cylinders a couple years ago for cave diving. I also use this system for some wreck diving and deeper resort diving when traveling with my rebreather is not possible.

 

[drbill]

A thread on another web site raised an issue that I thought was well worth considering since I've thought about the same question.

Independent doubles will not be breathed down equally which introduces an unbalanced set-up as one tank is drained. This can be remedied with a manifold.

 

[Bob_B]

Independent doubles will not be breathed down equally which introduces an unbalanced set-up as one tank is drained. This can be remedied with a manifold.

From what I have read, you have to alternate your breathing from the tanks. I think there is a post on here that I was reading as well.

 

[Rick Murchison]

Gas management is more complicated with independents, and if you lose one you lose all the gas in that cylinder.
On the plus side, they're cheaper and if managed properly can offer more configuration options (sidemount) and gas options (CAUTION - independent doubles using different gasses requires rock-solid planning and gas management)
Rick

 

[Hoosier]

Occasionally I dive with the independent double. Rick addressed the point well.
The most critical skill you have to master is the gas managment. I don't think any tech divers are using this set up though, it is very versatile set up for the rec. limits.

Pros: Very flexible and versatile rig. With the travel band, you can make the double anywhere in the world in 5min.. You don't need to get the manifold and worry free about its maintenance. You can expect the same back up and features like a conventional double rig. Always have more air than anyother rec. diver without showing up a tech rig.

Cons: Need to master the gas management and switch the regulator in underwater as planned. Need two SPGs. For a perfect set, you need to have a left handle valve. It is more prone to the warm water environment unless you are using a totally BC inflator tank like argon tank. It is hard to find your buddy using the same air capacity. Some divers keep picking a quarrel with your set up...

 

[DA Aquamaster]

The best gas management approach with independent doubles is to breathe the first tank down 1/3rd, then switch to the second tank and breathe it down 2/3rds, before switching back to the first tank for the 2nd 3rd. This leaves 1/3rd in each tank as a reserve.

This management plan uses 1/3rd of each tank on the way in, and 1/3rd of each tank on the way out. More importantly, since you only used 1/3rd of each tank on the way in, you have 2/3rds in either tank to get you back out and it ensures you will have enough gas in either tank at any point in the dive to get you back to the surface or your first deco gas in the event you lose access to the contents of either tank.

This approach also requires only 2 regulator switches and very little math (switch at 2000 on the first tank, 1000 psi on the second with 3000's).

With a set of travel bands you can use single rental tanks no matter where you travel.

Another advantage is that the tanks are fully indpendent and there is no absolute requirement to close a tank or isolator valve to prevent losing all your gas as could happen with manifolded doubles. It's still a good idea, but it's not an absolute neccesity.

I prefer a left handed valve on the left hand tank, but when traveling, turning the left tank backwards accomplishes the same thing if you cannot reach a right handed valve on your left tank.

The major downside is the heat you take from divers who are apparently overloaded by the requirement to make 2 regulator switches during the dive and to monitor another SPG.

 

[WarmWaterDiver]

I have done as Hoosier and DA Aquamaster posted, and I have also used manifolded doubles. I have typically used the independant doubles within recreational dive profiles using EAN32 or EAN28 in both tanks when diving on vacation. The Blue Hole in Belize is one such dive for me (EAN28 that time). A shore dive entering at Angel City to the Hilma Hooker in Bonaire on another occasion (EAN32 that time).

A UK dive magazine had an interesting article about using two different gas mixes in independent doubles a while back, regarding Red Sea diving.

http://www.divernet.com/equipment/1104divertests.shtml#quantum

I usually use Dive Rite metal bands & bolts as the travel bands don't work well for me. I always take some tools in the checked baggage so this doesn't add to my tool requirements.

My twin steel 100's at home are manifolded, but haven't seen much use by me due to where I've been living the last 2 residences.

 

[Hoosier]

I'm thinking of doubling up my steel 100's. but I'm torn beteen being able to use them as singles also.what are the views on using a joined isolator valve set up as to using independent tanks with seperate valves.does anyone use doubles as two independent tanks?what are the pros and cons of both?

BTW, I have another set of the new travel band, Aqua Explorer double band. Please let me know if you are interested in......

 

[matt_unique]

I considered the same before I went with a manifold.

I appreciate the advantages of each.

With independents - you have to switch regs periodically to properly use the gas (no biggie) and you *could* do nothing in the event of a failure and still have half your gas.

With manifolded doubles - you have access to all the gas depending upon the type of failure but you *must* close the isolator or you can loose all the gas. Short of a nightmare entanglement scenario this is no biggie. In the end I liked the idea of access to all my gas.

I totally respect the advantages to each system though.

--Matt