sheck33 once bubbled...
I understand you are diving doubles, correct? If so, i get the impression that you are using 2 SPG's, if so, why?
Separate independent tanks with separate regulators - no manifold involved.
The downside is that it requires regulator switching on dives where you plan to use the additional air from both tanks to ensure you always have enough air in either tank to finish the dive in case of a malfunction with either tank or regulator. An SPG is required on each tank to double check what is remaining as the dive progresses and to ensure you are always leaving 1/3 of the air in reserve.
On shallower or shorter dives that could be done with a single tank, I still carry both tanks to maintain the same configuration I am used to and to provide what amounts to a very large pony bottle as much of my diving is solo.
There are some advantages in that I carry a lift bag and reel strapped with surgical tubing to the right tank in case an ascent line is needed. On a single tank dive all I have to do is switch out the left tank between dives and all the stuff rigged to the right tank stays in place. This and the travel bands themselves allow for the fastest tank changes on the boat.
This setup also allows the use of different air or nitrox mixes in either tank to either add a saftey margin in deco or to accellerate deco. But I don't prefer to do this as anything over nitrox 40 imposes very signifincant depth limits below which the other tank cannot safely be used as a redundant bailout system. I am more likely to sling a 30 cu ft pony with either O2 or Nitrox 70 to accomplish any accellerated decompression.
The configuration is a little odd by most standards but it allows for the same basic configuration whatever the dive profile, which breeds a lot of familiarity. It also maximizes flexibility and minimizes hardware and air fills compared to a more conventional doubles arrangement with an isolator manifold. It also allows me to maintain the same setup when traveling and using rental tanks.
I own 18 tanks but share them with my spouse and son who do not dive deep and have no need for doubles. Doing it this way avoids tying the tanks up in doubles arrangements that no one else would use and has eliminated the need to spend a small fortune on additional tanks and isolator manifolds.
