My "new" independent doubles setup

[Open Ocean Diver]

In an emergency I would think it would be a little more difficult to remove your rig in the water.

 

[AfterDark]

In an emergency I would think it would be a little more difficult to remove your rig in the water.

In 3 dimensions I would think it would be easier, it could either float or sink away from me, after undoing the harness and removing the necklace over my head or from the regulator itself if necessary. Also the two 40" hoses on either side of the AIR make a BIG loop. Some posters mentioned not being able to reach the valves which in turn I replied that I can remove the rig for that purpose. In a runaway free flow from a HP failure that tank is lost to that dive. Closing the valve would be nice to prevent water entering the tank but that's all. It isn't life threating to lose a tank if air/dive time management was done correctly. Taking the rig off U/W is something I haven't found necessary to do outside of practice drills many years ago.

 

[John C. Ratliff]

In 3 dimensions I would think it would be easier, it could either float or sink away from me, after undoing the harness and removing the necklace over my head of from the regulator itself if necessary. Also the two 40" hoses on either side of the AIR make a BIG loop. Some posters mentioned not being able to reach the valves which in turn I replied that I can remove the rig for that purpose. In a runaway free flow from a HP failure that tank is lost to that dive. Closing the valve would be nice to prevent water entering the tank but that's all. It isn't life threating to lose a tank if air/dive time management was done correctly. Taking the rig off U/W is something I haven't found necessary to do outside of practice drills many years ago.

It's easier to take it off and put the scuba unit on over-the-head, rather than removing the regulator loop. That way, you can continue breathing throughout the process.

Concerning the runaway free flow from a HP failure, the tank may not be lost. But using it is another situation. If you get it turned off, and you have a real problem with lack of air, you could actually do a doff and don while on a decompression stop, for instance, and switch regulators. Cousteau showed doing this in the 1960s with the Conshelf II project in the film, World Without Sun. But if you do this, then after the dive the regulator would need servicing.

Here's a recent dive where I had to conduct a doff and don exercise to put my tank back into the BCD backpack:


SeaRat

 

[AfterDark]

It's easier to take it off and put the scuba unit on over-the-head, rather than removing the regulator loop. That way, you can continue breathing throughout the process.

Concerning the runaway free flow from a HP failure, the tank may not be lost. But using it is another situation. If you get it turned off, and you have a real problem with lack of air, you could actually do a doff and don while on a decompression stop, for instance, and switch regulators. Cousteau showed doing this in the 1960s with the Conshelf II project in the film, World Without Sun. But if you do this, then after the dive the regulator would need servicing.

Here's a recent dive where I had to conduct a doff and don exercise to put my tank back into the BCD backpack:



SeaRat

I wonder how divers with no ditchable weight or that have all their weight on the BCD do that without floating upside down while hanging onto their rig?

I'm not all that concerned with taking the rig off it is my best floatation device even without air for the auto inflator after all. After a few dives I may do it just for the experience. During the afore mentioned HP failure, I'd just let the air vent out the OVR close the inline for that side and end the dive using the remaining tank. There is also an octo on the secondary (right) tank that is isolated from the AIR and the left tank.

My diving is shore diving mostly above 50FSW. I dive a big loop mostly, I'm either going out or on my way back either way what's left in one tank will get me at least to the surface if not all the way back to the starting point at any time during the dive..

 

[Gone for diving]

Unless you plan to take off your gear.
I think it pretty unlikely.... maybe 99% of the time....

But Diving aluminum tanks sidemount... is quite doable...

 

[John C. Ratliff]

I wonder how divers with no ditchable weight or that have all their weight on the BCD do that without floating upside down while hanging onto their rig?..

I’m sure doffing over the head is doable with weights in the BCD (which is what I think you meant by saying, “no ditchable weights,” but it would need to be a quick move, and end with hugging the scuba/BCD close to you.

SeaRat

 

[AfterDark]

I’m sure doffing over the head is doable with weights in the BCD (which is what I think you meant by saying, “no ditchable weights,” but it would need to be a quick move, and end with hugging the scuba/BCD close to you.

SeaRat

I read this no ditchable weight stuff from the balanced rig crowd quite often. Words mean things to me. When I read the words "no ditchable weight" or "non ditchable weight" I take it to mean weight that cannot be removed by the diver during a dive. If I'm wrong well I'm wrong, but that is what I mean when I post no ditchable weight, weigh affixed to the tank or pockets attached to tanks, weight that can't just be released quickly and cleanly. Such a diver may become very buoyant after taking off their rig if that is where the weight located. The same with diver that has ditchable weight in pockets on their rig and none on their bodies.

I did a dive today and had all 3 types, 6lbs bolted to my DTA, 12lbs on a belt and one 2lb weights in 2 pockets, which gave me 16lbs of ditchable weight, 4lbs of which I can dump 2lbs at a time if a wish. This dive was done with my "new" independent doubles. They worked fine and as expected the 2nd stage on the right tank needs reconfiguration it was sticking out so far I could see it my side windows. It was suppose to be under my arm. Other than that getting it on was as expected, AIR over the head, sit down and don the tanks. Doffing it was a little awkward but doable. I used both inline valves in on and off positions and ended the dive with a 200 psig difference between the tanks, which could easily be a gauge difference. So I didn't die....this time.
I give it 2 thumbs up

 

[Gone for diving]

used both inline valves in on and off positions and ended the dive with a 200 psig difference between the tanks

Little confused....
Did you leave both valves on or did you alternate?

 

[AfterDark]

Little confused....
Did you leave both valves on or did you alternate?

Both actually for different lengths of time. I had an air loss accident at home so started off with uneven tanks. I closed the lowest one and used the higher pressure tank until they were even then opened both up for the rest of the dive and ended with 200psig difference between the tanks.

I haven't rinsed my gear yet but when do I'm going to check both tanks with the same SPG to see if the difference is gauge or just is different either is fine with me, IMO that's close enough. Also will recheck the IPs on the both 1st stages now that each has had at least one dive.

Right now it's 91F and humid so I'll wait for the rinse.

So here's the post rinse data, both 1st stages are still 130psi IP @600/800psi so I'll assume they are still both 130 @3000psi. Both gauges mounted on either tank gave me the same readings so there is a 150-200psi difference in the way the tanks drain with both inlines' open at the same time. Compared to normal ID air balance that's almost even. There is normally a 500psi difference before regulator switches. This is a better balance, with no intervention on my part if both tanks start off even and the inlines' are open from the start. I did notice a difference in air delivery when using one side as opposed to both sides at the same time which is noticeably better. Also if the pre-dive/dive switch on the AIR is in pre-dive mode and both sides are pressurized you wouldn't notice until you put the switch in dive mode! Then WOW! Is that what I've been missing?

A few more dives and I'll have the donning and doffing down and the second 2ndstage hose routing resolved. So once everything is set, and I'm solo diving picture taking or metal detecting or picture taking at night I can have my hands free to do that. I won't even need to open and close inline valves never mind do regulator switches! No more keeping track of 500psi reg switches just normal glances at my SPGs like a single tank dive. This will reduce my task loading quite a but.

 

[AfterDark]

Here is what I think has changed for the better by the AIR modification to my ID's

Reduction in task loading, there is no longer a need to execute regulator switches at 500PSI and do the extra monitoring of the SPGs to facilitate those switches.

Hands free ID’s usage: My hands are now free to do what I went underwater to do.

The air pressure in both tanks remains better balanced than before the modification using 2 second stages and doing switches.

If I need to donate to another diver the right side inline valve can be closed off to the AIR second stage, giving the other diver exclusive access to the air in the right hand tank. (until I decide otherwise)

The setup now has a slight reduction in redundancy due to the common connection at the second stage.
Because of this the tanks are no longer 100% independent but each tank can be individually isolated from the second stage by the inline valves giving the setup the separation it needs to be redundant.

Some gear used was manufactured by: @James79 owner, operator, Chief/Head and Only Engineer of: (click on attachment)