Diving with two tanks

[NC Wreck Diver]

I was thinking doubles would used for diving deep wrecks like the Speigel and such. Those arent on reg setups?

having to use two regs, you also need two computers yes? Kinda seems to defeat the purpose of having doubles.

Be more specific Mike. I dive only doubles, each with an isolation manifold, with the typical two ports. With my isolation valve open, it's just like one big tank. On my primary port, I have a MK25/A700, my power inflator hose, my SPG console, and if I'm in a drysuit, my inflator hose for that. On my other port, I have my MK10/G250, dedicated as my octo. I put a longer than normal yellow LP hose on this, and that second stage is on a necklace so I can grab it in a second. If my primary MK25 was to have a problem, I shut down the isolation valve, and use the MK10 to surface (I could use an SPG on the octo, but I don't use one). For more redundancy, I sling a 30 cu. ft. bailout bottle with a MK2Plus/R295A that is tied down with a bungee cord. This has a short (6") HP hose with an SPG too. I would be very comfortable diving the Speigel with this set up. I just have to decide what my O2 Nitrox mix would be, depending on depth and MOD of 1.4. Not that it really matters........but I have an AIR2 also on my BC.

I dive with one computer, but two would be nice. I'll buy that newer computer soon, but money is a little tight.

I don't understand your post? Are you thinking of using a deco bottle with a higher O2 content (shallower MOD). Let me know.

 

[MikeSK]

I was just confused...

Its always been my understanding that double were used more for having more gas to do deeper dives. If you can use two tanks as one big one, that's what i was confused about as the other replies kinda made it seem like that wasn't possible or something.

Like, I saw a video the other day of the Speigel and nearly everyone was on doubles. I didn't quite understand is all having to have two regs. I thought the reg would attach in the center of the two tanks.

 

[NC Wreck Diver]

I was just confused...

Its always been my understanding that double were used more for having more gas to do deeper dives. If you can use two tanks as one big one, that's what i was confused about as the other replies kinda made it seem like that wasn't possible or something.

Like, I saw a video the other day of the Speigel and nearly everyone was on doubles. I didn't quite understand is all having to have two regs. I thought the reg would attach in the center of the two tanks.

No worries Mike. It used to be like that. I did have some Sherwood Selpac's with one port. Not a lot of redundancy if something goes wrong. With isolation manifolds, you have much more flexibility. I carry a lot of gas. And the 30 gives me more. I always let time be my limiting resource, not gas. There are no fill stations U/W!

If you have any other questions, post them. These guys on SB are always very helpful. I wish I had this back in the 80's...............

 

[MikeSK]

Here's a probably silly question..

If the valve is open, will a computer detect the correct amount of gas? If its closed, and tank one is used up, and you switch, will it detect a full tank again?

The answer would seem to be an obvious yes..but...

 

[Blackwood]

Here's a probably silly question..

If the valve is open, will a computer detect the correct amount of gas? If its closed, and tank one is used up, and you switch, will it detect a full tank again?

The answer would seem to be an obvious yes..but...

If you're diving with manifolded or independent doubles (i.e. two first stage regulators), then no unless you have a pressure gauge on each first stage. If you are diving with a single outlet crossbar (i.e. one first stage regulator), then yes.

This might be another head banging question but I have to ask it. If you needed to, could you remove your first stage off one trank and put it on another tank while under water? Or would this mess everything up. Of course I was planning on purging my second stage.

Yes, you can. You may have to get your stuff serviced and tumbled afterwards, but it's better than having your body serviced I guess.

as others said yes you can have 2 tanks hooked up together. You would need to use a manifold of some type.

Not necessarily; he could run an independent rig.

 

[MikeSK]

How is it normally done for deep wrecks like Speigal? as two independent, or as one big tank? I would think the later..granted, most of Speigal can be done one singles, but I'm just using that as an example.

 

[Blackwood]

How is it normally done for deep wrecks like Speigal? as two independent, or as one big tank? I would think the later..granted, most of Speigal can be done one singles, but I'm just using that as an example.

I've never been diving in Florida, but I imagine it's pretty much like it is here over there.

These days, most people who back mount doubles have them connected with an isolation manifold ("one big tank you can cut in half").

 

[MikeSK]

So with that setup, you need two regs? one for each side.

Or can you just open up one side so both tanks flow through the left or right?

(sorry for the endless seemingly silly questions )

 

[PfcAJ]

You need training from a person, not the internet. This isn't working out, but ill take a swing:

Doubles (with an isolation manifold) give you more gas that can be breathed without switching regs. The neat bit it that it gives you complete redundancy should something break. It needs to have two regs so you can access your gas no matter what.

By convention, the valve that ends up behind your right shoulder is called the right post, and the other shoulder is the left post. If either reg malfunctions/breaks/ whateva, you can close the post and breath the other reg.

Should a burst disk go, or a tank neck o ring, or you break a valve knob of and dislodge a reg, you can close the isolator and save half you gas. Those failures are insanely rare, but we plan for the worst and hope for the best. The isolator is left open at ALL times until you need to close it or are practicing. This needs to be checked before you fill, after you fill, before you gear up, and once you're geared up, and any time anyone touches your valves. Its very important.

You only need one SPG, and it goes on the left post. Your long hose goes on the right post, along with your inflater for your wing. Backup reg goes on the left post, along with your drysuit inflater. This is all you need to do ANY type of diving where you can fit with tanks on your back. From 400' wrecks to cave diving, ice diving, you name it, this WORKS.

 

[Blackwood]

Or can you just open up one side so both tanks flow through the left or right?

That pretty much defeats the purpose. If you want to use one 1st stage, get a big single.

As PfcAJ said, it's set up to give you access to all your gas even in the event of a regulator failure. Yes: with the isolator open, I can breathe down both cylinders through the regulator on my right post (as I generally do). But I have that left post regulator in case I lose my primary, in which case I breathe down both cylinders through it (unless the right goes in such a way that it's dumping gas, in which case I'll isolate so that it doesn't dump gas from the left).

If I am donating gas I'm using both simultaneously, but that's the exception rather than the rule.