new setup, 2 first stages vs 2 bottles??

[h90]

I am just planning+purchasing some new toys....
As I want to be as independent as possible I buy a compressor and tanks.

My first plan was to go with 15 liter 300 bar steel tanks. So one tank is enough for two relaxed dives. As I might go to some places per bus, I don't want to go with 2 heavy Alu tanks. (all warm water)

I thought of a TAG valve and using 2 first stages.

Setup 1:
First first stage: My Mares Abyss+Transmitter Uwatec Aladin Air X Nitrox+BCD hose.
Second first stage: My old Mares Abyss (now Octopus) + pressure gauge.

Now I got an alternative idea:

Setup 2
Mono valve, 1 first stage 1 regulator
But a second small 300 bar bottle (1-3 Liter).

While I think the 2nd Setup is better, does it has an advantage in real life?
It only helps if the tank fails. The only two reasons I can think of is, dirt inside that block the valve. Possible??
Or out of air, but I see no possible technical way that an out of air can develope.

Any ideas???

 

[Blackwood]

My first plan was to go with 15 liter 300 bar steel tanks. So one tank is enough for two relaxed dives. As I might go to some places per bus, I don't want to go with 2 heavy Alu tanks. (all warm water)

You have aluminum tanks bigger and heavier than that? That's about 60% more capacity than any aluminum tank I've ever seen.


What's a TAG valve? I assume it's either a Y or an H. Before you invest, think through how you'd route the hoses with your two first stages. I made the mistake of buying an H valve without going through that exercise. There's no way (with my regs) that isn't a CF. I have a plug in the secondary port now and always use it with one first stage.

Two first stages on a single valve are pretty much covering you if one reg fails closed. A free flow failure (extruded o-ring, for example) is much more likely. In that case, you're losing gas with setup #1, but have a redundant, independent source with setup #2.

 

[Puffer Fish]

I think it depends on the type of diving you are doing... I use a small pony when going below 30 meters.. but shallower, I don't. I have a couple of tanks of a similar size, and they work great for doing two dives.

 

[h90]

I mean to use 1 steel 300 bar 15 liter instead of 2 Alu 80. So one steel is lighter than 2 aluminium tanks. That was the reason to go with that exotic setup.

That is the TAG: Tauchversandhaus - Aqualung Din Ventil TAG-Ventil 230 bar Aqualung TAG Ventil
It looks like a Y but not symmetric....And you are right, I didn't consider the hose routing yet.

yes free flow would be a reason. But (from what I read), there should be plenty of time to shut the free flow valve. But a complete separate air source would make it much more easy. I guess on a surprise free flow there is a good chance to shut the wrong valve first.

You have aluminum tanks bigger and heavier than that? That's about 60% more capacity than any aluminum tank I've ever seen.


What's a TAG valve? I assume it's either a Y or an H. Before you invest, think through how you'd route the hoses with your two first stages. I made the mistake of buying an H valve without going through that exercise. There's no way that isn't a CF. I have a plug in the secondary port now and always use it with one first stage.

Two first stages on a single valve are pretty much covering you if one reg fails closed. A free flow failure (extruded o-ring, for example) is much more likely. In that case, you're losing gas with setup #1, but have a redundant, independent source with setup #2.

 

[Blackwood]

Gotcha.

With my regs (ScubaPro Mk25), that would likely route well since I have a bottom port. Not sure about regs lacking that port. In thinking about it, consider proximity to the cylinder. I have one of these:

It looks fine and dandy without the cylinder in the photo, but in reality there's very little clearance between the bottom of the first stage and the crown of my tank. To get it to work (i.e. have one second stage per first stage), I have to mount the regs sideways (perpendicular to the axis of the cylinder). It's ridiculously convoluted.




With what I think is a more complete understanding of what you're doing, I wouldn't personally suggest #1 or #2.

#1 doesn't seem to buy you much (unless you're prone to freeflows), and #2 means you're starting your second dive with your gas spread into one less than full tank (whatever is left from the first dive) and one small tank. I'd get a big cylinder and be done with it. If you want the second as a pony tank, go for it.

 

[trappist]

I'm a European diver... and we are teached that, when we lead dives, we should have 2 sources of gas. In Europe this turned everyone (or almost) into using either the H-valve (some older Y valves can be found although most new ones are all H), or using doubles (not as common either). Almost no one uses a pony over there. The H or Y allows you to have 2 separate sources of air, if one fails you can turn it off or get your buddy to do so. The approach is similar to doubles but with only one tank, which makes it a little harder to turn it off yourself.
I personnally like the idea as it allows me a complete redundancy for smaller weight and more streamline.
I invested in the same setup - 15l - 232 bars (3442psi - X8 XS Scba 119cf) and I loved it. But I was never able to make 2 dives on it... I either dove too deep or too long for that

This said, I do not know any 15l 300bars steel tanks... to my knowledge 300 bars tanks are carbon tanks (like the ones used by firemen). Lighter, requires more weight but provides indeed more gas...

On the routing of hoses, I reapplied most of what is done in the DIR approach (I'm not one of them but some of their principles are good). I have no issues, have complete redundancy between both, except probably if I dive wetsuit (only have the inflator on one regulator - the backup one to minimize load on the breathing one). Hope this helps.

 

[Blackwood]

I'm a European diver... and we are teached that, when we lead dives, we should have 2 sources of gas. In Europe this turned everyone (or almost) into using either the H-valve (some older Y valves can be found although most new ones are all H), or using doubles (not as common either). Almost no one uses a pony over there. The H or Y allows you to have 2 separate sources of air
...
I personnally like the idea as it allows me a complete redundancy for smaller weight and more streamline

I'm sorry, but that's simply not true. An H or Y provides two access points to a single source of air. You do not have complete redundancy.

 

[h90]

Gotcha.

With my regs (ScubaPro Mk25), that would likely route well since I have a bottom port. Not sure about regs lacking that port. In thinking about it, consider proximity to the cylinder. I have one of these:

It looks fine and dandy without the cylinder in the photo, but in reality there's very little clearance between the bottom of the first stage and the crown of my tank. To get it to work (i.e. have one second stage per first stage), I have to mount the regs sideways (perpendicular to the axis of the cylinder). It's ridiculously convoluted.




With what I think is a more complete understanding of what you're doing, I wouldn't personally suggest #1 or #2.

#1 doesn't seem to buy you much (unless you're prone to freeflows), and #2 means you're starting your second dive with your gas spread into one less than full tank (whatever is left from the first dive) and one small tank. I'd get a big cylinder and be done with it. If you want the second as a pony tank, go for it.

I understand the problem on your two valves. When imagine a tank, the second one is very very close to it.

My plan is only to use the big tank (15l 300 bar) and use the small one as pony.
The beauty of the first setup is: less weight and less cost.

 

[h90]

I'm a European diver... and we are teached that, when we lead dives, we should have 2 sources of gas. In Europe this turned everyone (or almost) into using either the H-valve (some older Y valves can be found although most new ones are all H), or using doubles (not as common either). Almost no one uses a pony over there. The H or Y allows you to have 2 separate sources of air, if one fails you can turn it off or get your buddy to do so. The approach is similar to doubles but with only one tank, which makes it a little harder to turn it off yourself.
I personnally like the idea as it allows me a complete redundancy for smaller weight and more streamline.
I invested in the same setup - 15l - 232 bars (3442psi - X8 XS Scba 119cf) and I loved it. But I was never able to make 2 dives on it... I either dove too deep or too long for that

This said, I do not know any 15l 300bars steel tanks... to my knowledge 300 bars tanks are carbon tanks (like the ones used by firemen). Lighter, requires more weight but provides indeed more gas...

On the routing of hoses, I reapplied most of what is done in the DIR approach (I'm not one of them but some of their principles are good). I have no issues, have complete redundancy between both, except probably if I dive wetsuit (only have the inflator on one regulator - the backup one to minimize load on the breathing one). Hope this helps.

300 bar steel tanks are a long time around, but not as common.
15 liter steel are very very rare, but there is a German shop which offers it. Approx. 250 Euro. Much cheaper than carbon and I didn't saw a 15 Liter Carbon yet.

 

[lowviz]

Gotcha.

With my regs (ScubaPro Mk25), that would likely route well since I have a bottom port. Not sure about regs lacking that port. In thinking about it, consider proximity to the cylinder. .............

With some good suggestions from various sources over the years, I ended up with a way to eliminate loops and still keep the valves clear. MK17's don't have a bottom port but this config is clean and you get the long hose on a high performance port. (two SPG's -I know you are going to ask)

>>The whole value of an H-valve (for me) is to be able to go back-and-forth between a single tank and doubles without having to change hoses around on the regs.