Questions about twinsets.

[Scuba_Nick27]

So I have a question, if you have two tanks connected with a manifold, do the pressures form each tank combine? For example lets say that in each tank there is 3000 psi and 100 cubic feet of atmospheric air, and lets assume that both gasses have identical proportions of other gasses that make up air (nitrogen, noble gasses, etc). Lets say the manifold runs into a pressure gauge halfway between two tanks. Will the pressure displayed on the gauge be 6000 psi or 3000 psi?

That was my first question...

Here is the second question. Since I want to get into technical diving, which includes twinsets, side-mounts and etc. Please provide me with an idea of how things work. Does each side-mount run a separate 1st stage and 2nd stage regulator, or are they connected together? Also, do twinsets run off of one regulator or two separate ones?

Thank you.

 

[runsongas]

no, they equalize. the pressure is not additive like the volume or capacity.

the idea behind isolatable doubles is to have complete redundancy but also access to both tanks in the event of a regulator failure in one tank,, if you closed the isolator, you would have two separate tanks with separate 1st and 2nd stages. in sidemount, the tanks are kept isolated at all times.

 

[divingx]

First question, 3000 psi. The manifold will equalize the pressure in two tanks.

Sidemount has two sets of independent regs including two first stages, two second stages, two spgs and inflator hoses.

 

[Scuba_Nick27]

First question, 3000 psi. The manifold will equalize the pressure in two tanks.

Sidemount has two sets of independent regs including two first stages, two second stages, two spgs and inflator hoses.

Ok, that makes sense now.

 

[Scuba_Nick27]

no, they equalize. the pressure is not additive like the volume or capacity.

the idea behind isolatable doubles is to have complete redundancy but also access to both tanks in the event of a regulator failure in one tank,, if you closed the isolator, you would have two separate tanks with separate 1st and 2nd stages. in sidemount, the tanks are kept isolated at all times.

So in case of redundancy, do you run two pressure guages then? Since each tank is isolated from eachother, how would you know how much pressure you have in one tank or in the other, or in both combined?

 

[runsongas]

generally, no for backmount. because in the case you have a failure and had to isolate, you turn the dive, so it doesn't matter if you can tell how much you have left, you either have enough (if you kept a sufficient reserve) or you don't.

 

[KenGordon]

So in case of redundancy, do you run two pressure guages then? Since each tank is isolated from eachother, how would you know how much pressure you have in one tank or in the other, or in both combined?

They are not normally isolated, only if you have a failure on one side so as to avoid losing all the gas. With independent twins you have two spgs. It is essential to be able to close the isolation valve or the benefits are lost and it should be left closed and dived as independents.

With independents you have to swap regs at appropriate pressures.

 

[Scuba_Nick27]

generally, no for backmount. because in the case you have a failure and had to isolate, you turn the dive, so it doesn't matter if you can tell how much you have left, you either have enough (if you kept a sufficient reserve) or you don't.

They are not normally isolated, only if you have a failure on one side so as to avoid losing all the gas. With independent twins you have two spgs. It is essential to be able to close the isolation valve or the benefits are lost and it should be left closed and dived as independents.

With independents you have to swap regs at appropriate pressures.

Alright, it all makes sense now. Runsongas, you mentioned backmounts. I have a Mares Pure SLS BCD. And I saw a guy with the same BCD diving with a twin set, but he didn't exchange the back-plate to accommodate for the second tank. He simply added a second cam-band and had one tank strapped into one cam band and a second one into the second cam band. Both of his tanks, i'm pretty sure, were steel 100s, and they were bolted together with metal bands. I don't know the reg combination he was running. But the question is, can you do that? Like is it safe to have them like that, because it looked pretty solid to me... or would it be better to buy a backplate for the job?

 

[KenGordon]

Alright, it all makes sense now. Runsongas, you mentioned backmounts. I have a Mares Pure SLS BCD. And I saw a guy with the same BCD diving with a twin set, but he didn't exchange the back-plate to accommodate for the second tank. He simply added a second cam-band and had one tank strapped into one cam band and a second one into the second cam band. Both of his tanks, i'm pretty sure, were steel 100s, and they were bolted together with metal bands. I don't know the reg combination he was running. But the question is, can you do that? Like is it safe to have them like that, because it looked pretty solid to me... or would it be better to buy a backplate for the job?

A commonish configuration here is independent twins on a BCD. Usually there are no steel bands but instead plastic spacing blocks Twinset Cambands | AP Diving which require and extra slot in the BCD plastic back part. AP’ Buddy BCDs are perfect for this, I have an old Spiro one that also works.

Then you just run a pair of first stages, each with one second stage, and SPG and probably an inflator. You have to make sure you have redundant buoyancy too, hence two inflator hoses altogether even with a wetsuit.

Indie twins are not considered ‘cool’ but have some practical advantages in the real world at a certain level.

 

[Scuba_Nick27]

A commonish configuration here is independent twins on a BCD. Usually there are no steel bands but instead plastic spacing blocks Twinset Cambands | AP Diving which require and extra slot in the BCD plastic back part. AP’ Buddy BCDs are perfect for this, I have an old Spiro one that also works.

Then you just run a pair of first stages, each with one second stage, and SPG and probably an inflator. You have to make sure you have redundant buoyancy too, hence two inflator hoses altogether even with a wetsuit.

Indie twins are not considered ‘cool’ but have some practical advantages in the real world at a certain level.

I saw the pictures and that is exactly what he had. So I assume you just attach the twin bands to a single-tank backplate and presto.