Double tanks and manifold question

[Solly]

Hi, I am new to double tanks setup, just got the kit for my BC, hired an extra regulator and 2 tanks (no manifold) and just kept alternating to breathe from each of the tanks.

I was looking on a manifold to have my setup complete and I was lost, I found too many manifold description.. dual, rotation, isolation ...etc. I thought it is just a way to connect the 2 tanks, is there really a difference and one of them is superior to others?

one other question, if I am to design a manifold (before I am into diving), I would have connected the 2 tanks together and just have 1 regulator taking from both tanks in the middle of the manifold rather than 2 as all manifolds are ... but after being a diver I know that double tanks is the first step towards some tech diving which is all based upon redundancy hence having 2 regulators is needed even if they are both sharing the same air source... so my question is, is there any other reason beside redundancy to have 2 air outlets of the manifold rather than just one?

A final question, why should I need a manifold over my basic setup of 2 tanks, 2 regulators and alternate breathing to balance the air in the 2 tanks every couple of ten bars?

 

[Hickdive]

... so my question is, is there any other reason beside redundancy to have 2 air outlets of the manifold rather than just one?

It is just for redundancy but redundancy in both regulators and gas, see the rest of my answer below.

A final question, why should I need a manifold over my basic setup of 2 tanks, 2 regulators and alternate breathing to balance the air in the 2 tanks every couple of ten bars?

With an isolation manifold if one regulator fails it can be effectively shut off from both cylinders but you can still access the remaining gas in both the cylinders via your other regulator.

With independent cylinders, if one regulator fails then you can no longer access the gas in the cylinder it is connected to.

 

[micklock]

I dive independent doubles, I like the ease of hauing them around as singles and I have three tanks so on the second dive I swap in a full tank. I breath 1000psi off the first tank then 2000psi off the second tank then switch back to the first tank. My reason for diving doubles is solo diving and cold water, my dives are NDL dives.

 

[fire_diver]

Independant doubles are fine, but it does include a higher task loading. Using an isolation manifold makes the dives so much easier, but it costs more (buying the manifold) and requires some practice to be able to close the isolator in case of an emergency.

Pros and cons with either option.

Maa salama

 

[UCFKnightDiver]

I dive independent doubles, I like the ease of hauing them around as singles and I have three tanks so on the second dive I swap in a full tank. I breath 1000psi off the first tank then 2000psi off the second tank then switch back to the first tank. My reason for diving doubles is solo diving and cold water, my dives are NDL dives.

You really break apart your doubles (bands) every dive? Or do you use some kind of soft banding system for the tanks? Seems like sidemount would be easier for you but meh.

 

[micklock]

You really break apart your doubles (bands) every dive? Or do you use some kind of soft banding system for the tanks? Seems like sidemount would be easier for you but meh.

I use these Ultimate Velcro Double Bands by Capt. Dan Berg it's easy to change tanks with the hoop and buckle style cam bands.
I tried sidemount on a shore dive and liked it but I didn't have all the right lenght hoses. For boat diving in the Great Lakes I would rather go with backmount.

 

[mksmith713]

The more I learn about this, the more independant doubles sounds like the way to go.
Valve shut offs are a PITA when you rarely practice them for an emergency.
I'd hate to have to do them every dive as a matter of fact.

How painful is it to have to swap out a single tank from a rig using tank bands with independant doubles?

 

[UCFKnightDiver]

with the velcro bands that micklock's using it looks like it would be relatively easy, but with solid stainless steel bands in would be a major PITA.

 

[DA Aquamaster]

I dove independent double for quite a while with travel bands due to some logistical issues where two single tanks were a lot more practical than manifolded doubles.

It was considered very uncool at the time, but that has changed to some extent with the rise in populatity of side mounting.

Gas management is not significnatly greater. You start on the left tank and use 1/3rd of the capacity. Then you switch to the right tank and use 2/3rds of its capacity (after you use the first third of this tank, you should be at your turn point on the dive). Then you switch back to the left tank to use the second third of it's capactiy (at that point you should be at the surface or at your first deco gas). This leaves 1/3rd in reserve split bewteen both tanks, and it also ensures that at any point in the dive, you have an amount of gas equal to what you used to get to that point to get you back out. This also ensures that you have enough exit gas in either tank in case you were to lose the contents of the other tank.

You can increase the reserve at the end of the dive by adjusting the size of the "thirds" you use on the dive, but you still only require two gas switcehs.

Some divers, and in particular the recetn crop of side mount divers, will argue till the cows come home about the need for more frequent gas switches, but none of them have any valid relationship to increased safety as the point where it really matters is at or near the point of maximum penetration and that is covered just as well with 2 gas switches as it would be with 4. It's not an argument you can win because those who don't get it either lack the spatial relations ability to get it, or are going to go to their grave supporting what someone else taught them.

Trim issues may consitute a valid reason for the more frequent switches and increased work load re-stowing hoses when side mounting, but the differential is not normally enough to create a trim problem with back mounted independent doubles.

 

[Solly]

well, I use SS bands with along screw to connect the bands to the backplate, removing the setup and back to single tank setup would only take 3 minutes, getting it back would take no more than 5 minutes (if on dryland or the sea is calm and I am on a boat) or something like 10 minutes with high care if the sea is rough.. so it is not a big deal anyway... setting it up for the first time took sometime as I had to assemble some nuts on the tanks side, however removing it and reinstalling would be easier as I now just unscrew the nut on my back's side and thats it ....
here is a photo of the setup, I just unscrew the nut that appears under the Poseidon logo in one photo then the whole setup is free from the BC in one piece as seen in the other photo.