double tank equipment

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When moving to doubles, training of some sort is required IMO. Many qualified instructors will teach a doubles workshop over an afternoon for very little money. It's worth it! If you don't get formal training, please please find a qualified mentor who can cover the training informally.

I had a buddy new to doubles run out of air on me (so they thought). They had simply left their manifold closed, failed to notice their gauge wasn't moving, and never tried their alternate when the airflow stopped from their primary. Luckily I was there to donate and we ended the dive. On the surface while inspecting their gear they turned the manifold ... we all heard the whoooosh as the air equalized between the two tanks!

Doubles are not just a larger single. There are things to learn ... one way or another. Please take the time to get that training, whether it be formally or informally.
 
This is getting out of hand. Maybe it is because I read pages 1-3 then 12-15 to see where the thread went. After reading the remaining pages, I have found Tobin to be generally well mannered, logical, and consistent in his posts. The information he provides is always top notch and very clearly communicated. I don't see the anger or blowhardedness* that some people are apparently sensing in his posts.

Tobin has been clear that there are all kinds of training and that he never said one should go do a doubles course. I am a diver just starting on his tech career and I found the original question to have a strong hint of someone who "just didin't know". I am not saying that as a negative or to demean them, but reading any number of tech threads on this site in conjunction with a google search on "DIR equipment or tech set up" would have provided loads of material on the proper reg set up and basic equipment. For those that argue this is the place to ask such questions, I agree, but I am also one to do as much research as
i can before I ask the questions.

Agilis clearly has a lot of diving experience, but he doesn't have much technical experience. Rather than admit his was wrong about the operation of a manifold (very first topic covered in TDI intro to tech manual btw) he chose to argue semantics and all about how experienced divers should easily be able to figure it out. I actually started yelling at the screen because HE is the prime example of an experienced diver that should have been able to figure it out, but was completely asshat wrong. Intelligence, willingness to learn, and experience are great, but there are loads of things you need to be thoroughly taught in order to know.

Rather than admit? Rather than admit? Either you are joking or you did not read my posts.

I admitted both my mistake and the fact that I knew nothing about isolation manifolds, immediately and at least a dozen times subsequently. I repeatedly made it clear that I had no experience with isolation manifolds or with technical diving. I never claimed I did.

You are correct, a diver of my experience should be able to figure it out, and I quickly did, when I took the trouble to look at a diagram of one, after it became clear that the manner in which I assumed (and I used that word) they worked was incorrect. My assumption was not based on an incorrect interpretation: it was based on no information, only an assumption and on experience with an earlier iteration of doubles manifolds and cheater bars.

My experience with diving technology pretty much ended in the 90s. Almost all of my equipment, excepting a computer, dates from the 80s and 90s. At my age I have no intention of engaging in technical diving, or anything beyond recreational diving. I learned scuba on my own in the 60s and was formally certified in 1972 after a couple of months of classroom, pool, and open water instruction as was required for Open Water NASDS certification back in those dark days.

At 73 I'm happy to still be able to do recreational diving, especially since most of my diving is solo. In fact, the need for lighter tanks, better weight distribution, and a sleeker, lower profile was what led me into this discussion. My first sentences made it clear that I was not interested in tech diving or isolation manifolds. This was on the first page of this long string.

I cannot comprehend how anyone can say I was arguing semantics only because of what I wrote about the definition of valves. I wrote that my definition was idiosyncratic, my own perception, and not the way in which most divers define them in connection with isolation manifolds.

Simply put, in isolation manifolds I count the section of what is in effect the bottom part of a K valve, the part that screws into each cylinder neck, as a valve, or at least part of a valve. I was certainly not arguing for the general adoption of my perception of what constitutes a valve. Other than the valve issue, I can't imagine what constituted semantic argument in anything I wrote..

A competent diver should be easily able to figure out how these manifolds work. I had zero experience or contact with these manifolds until the manner of operation was explained to me in a post; explained clearly though not graciously. After looking at some diagrams last night they are even simpler than I thought.

I'm not sure what I was so completely asshat wrong about that you began "yelling at the screen". I apologize for getting you so upset. I suggest you refrain from listening to the coming presidential campaign debates lest you break a vein in your head.

I must admit that I almost yelled at my own screen when I reread my posts. I am upset with myself for allowing myself to be baited into imitating the unpleasant tactics of an unpleasant individual.

I also realize that my long posts were a waste of time. Few will actually read them, so careful explanation is evidently a waste of time.
 
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When moving to doubles, training of some sort is required IMO. Many qualified instructors will teach a doubles workshop over an afternoon for very little money. It's worth it! If you don't get formal training, please please find a qualified mentor who can cover the training informally.

I had a buddy new to doubles run out of air on me (so they thought). They had simply left their manifold closed, failed to notice their gauge wasn't moving, and never tried their alternate when the airflow stopped from their primary. Luckily I was there to donate and we ended the dive. On the surface while inspecting their gear they turned the manifold ... we all heard the whoooosh as the air equalized between the two tanks!

Doubles are not just a larger single. There are things to learn ... one way or another. Please take the time to get that training, whether it be formally or informally.


I had something similar happen to me. I was about 10 minutes into a dive when I noticed that my gas consumption was unusually good. 15 minutes into the dive, the SPG hadn't moved. I realized something was wrong.

I did a flow check (checked the status of each of the valves, for those who are uninitiated). I turned the isolator and could hear gas flowing from one tank to another. I thumbed the dive right then and there.

Why did I thumb the dive? By practice, I check the right post (as you wear them) where the primary reg sits for pressure and O2% when I pick up my tanks after a fill. By practice, I also usually also check the isolator position to make sure that the fills where done with the isolator open. In this case, whatever reading I get from the right cylinder for pressure and O2% would also apply to the left cylinder. However, in this instance, I had a shop with less doubles savvy staff fill my tanks. Also, they do partial pressure fills for nitrox.

So when I opened the isolator and heard gas rushing into the right cylinder, I was no longer confident that I knew what I was breathing. I trusted nothing at that point. Its possible that I got confused during my pre-dive check and closed the isolator. Though unlikely, it's also possible that the dive shop could have inadvertently filled the left cylinder with a higher O2% while the isolator was closed and neither the dive shop nor I caught the error.

So I thought the prudent thing to do was to call the dive.

Its the kind of thing that maybe some of the more experienced divers would think is intuitive but in reality, when it happens underwater, thinking through all the consequences of something like opening the isolator might not be that straight forward.
 
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I had something similar happen to me on a dive. I went on a dive, I was about 10 minutes into the dive when I noticed that my gas consumption was unusually good. 15 minutes into the dive, the SPG still hadn't moved. I realized something was wrong.

I did a flow check (checked the status of each of the valves, for those who are uninitiated). I turned the isolator and could hear gas flowing from one tank to another. I thumbed the dive right then and there.

Why did I thumb the dive? By practice, I check the right post (as you wear them) where the primary reg sits for pressure and O2% when I pick up my tanks after a fill. By practice, I usually also check the isolator position to make sure that the fills where done with the isolator open. In this case, whatever reading I get from the right cylinder for pressure and O2% and pressure would also apply to the left cylinder. However, I had a shop with less doubles savvy staff fill my tanks. Also, they do partial pressure fills for nitrox.

So when I opened the isolator and heard gas rushing into the right cylinder, I was no longer confident that I knew what I was breathing. I trusted nothing at that point. Its possible that I got confused during my pre-dive check and closed the isolator. Though unlikely, it's also possible that the dive shop could have inadvertently filled the left cylinder with a higher O2% while the isolator was closed and neither the dive shop nor I caught the error.

So I thought the prudent thing to do was to call the dive.

Its the kind of thing that maybe some of the more experienced divers would think is intuitive but in reality, when it happens underwater, thinking through all the consequences of something like opening the isolator might not be that straight forward.

Any tank that's used for nitrox should be checked prior to a dive to make sure you know what you are breathing. The mix of the remnant portion of the previous refill may be misremembered, and the mix of new fills cannot be taken on faith.

By introducing a gas during the dive the mix of which you could not test and could not be sure of, calling the dive was, I think, unavoidable, and the reason perfectly clear.
 
Any tank that's used for nitrox should be checked prior to a dive to make sure you know what you are breathing. The mix of the remnant portion of the previous refill may be misremembered, and the mix of new fills cannot be taken on faith.

The situation was actually worse than that.

The SPG sits on the [-]right[/-] left post as I wear the tanks and therefore reads pressure from the [-]right[/-] left tank if the manifold is closed. The SPG was reading *full* at the beginning of the dive. So even if I trusted the previous fill which, as you say, cannot be trusted, there had to be gas introduced into the right tank as part of the fill process - the end result of which, I never analyzed. For all I know, they could have put O2 into the right tank which made the mix incredibly rich.

There is usually no need to check both posts for O2% and pressure if the manifold is open, especially if the tanks have been sitting for a while after the fill.
 
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The situation was actually worse than that.

The SPG sits on the right post and therefore reads pressure from the right tank if the manifold is closed. The SPG was reading *full* at the beginning of the dive. So even if I trusted the previous fill which, as you say, cannot be trusted, there had to be gas introduced into the right tank as part of the fill process - the end result of which, I never analyzed. For all I know, they could have put O2 into the right tank which made the mix incredibly rich.

There was case in Florida IIRC where trimix was PP blended in doubles. One side ended up with near pure He. Resulted in death.

Not at all "comical"

Tobin
 
There was case in Florida IIRC where trimix was PP blended in doubles. One side ended up with near pure He. Resulted in death.

Not at all "comical"

Tobin

Tobin, can you keep me honest on this? We don't need to check both posts for O2% after a fill if the isolator is open due to something like ideal gas laws. Is that right? Even if the tanks were filled separately with the isolator closed, if you open the isolator, in time the gas between both tanks will eventually, what's the word, mix?
 
Tobin, can you keep me honest on this? We don't need to check both posts for O2% after a fill if the isolator is open due to something like ideal gas laws. Is that right? Even if the tanks were filled separately with the isolator closed, if you open the isolator, in time the gas between both tanks will eventually, what's the word, mix?

it can take a hot minute for the gases to mix once you open the isolator. In my experience if gas A is filled on the left post and gas B is filled on the right, analysis will be funky. Takes some time and shaking of the tanks to get things to mix evenly and settle out.

Iirc the case Tobin is referencing happened at Eagles nest. She switched from her travel gas to backgas, breathed 100% helium and blacked out. I thought she survived but with some neurological deficit but I could be wrong.
 
it can take a hot minute for the gases to mix once you open the isolator. In my experience if gas A is filled on the left post and gas B is filled on the right, analysis will be funky. Takes some time and shaking of the tanks to get things to mix evenly and settle out.


The % of gases in each cylinder will effectively never balance. The "mixing front" is ~.070" diameter and the conduit is long. There was some real world testing done a few years ago and the percentages at each post essentially never changed, over many many days. Russell Edge did the tests IIRC.

Iirc the case Tobin is referencing happened at Eagles nest. She switched from her travel gas to backgas, breathed 100% helium and blacked out. I thought she survived but with some neurological deficit but I could be wrong.

You may be right, but as I recall she eventually died.

Tobin
 
it can take a hot minute for the gases to mix once you open the isolator. In my experience if gas A is filled on the left post and gas B is filled on the right, analysis will be funky. Takes some time and shaking of the tanks to get things to mix evenly and settle out.

The % of gases in each cylinder will effectively never balance. The "mixing front" is ~.070" diameter and the conduit is long. There was some real world testing done a few years ago and the percentages at each post essentially never changed, over many many days. Russell Edge did the tests IIRC.

Thanks guys. Somehow I missed this when it was covered in my open water class.:stirpot:
 
https://www.shearwater.com/products/teric/

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