DIR- Generic Doubles Gas Management?

[buildhuntcook]

I am newly interested in moving into back-mounted doubles and looking into the different systems. I have talked with several advanced technical as well as cave divers and I have a newby question about how the gas is managed on a set of back-mounted twin cylinders. Everyone in my local area uses a long hose configuration, i.e. GUE/UTD/ISE with a manifold. I went to a PADI shop looking into tech courses as they are the only ones that offer technical courses in my area (the advanced divers in my area were trained elsewhere) and now I am really confused about how to breathe from back-mounted doubles. From what I can gather the manifold is open all of the time and the tanks are breathed down as if they were one big tank with a really large volume. The primary regulator stays in the mouth all of the time. If there is an issue then the appropriate response to find/shut down the problem is addressed. The PADI guys I talked to described using the back-mounted doubles basically as two independent systems and requiring redundant EVERYTHING. They described breathing down each tank 500 psi and then switching regulators and leaving the manifold closed and shutting off each tank. Is this the correct method according to PADI? I feel like this defeats the purpose of the manifold being able to share gas with each regulator. The introduction of redundant everything in my mind would make it much harder to find a problem. If you have a redundant bladder in your BC and it auto-inflates then the diagnosis is more steps than knowing your bc is inflated from just your right post. I asked what they did in the event of a buddy being out of gas and having to donate if the valve was shut every time they switched and they said you turn it on. If there is an event on the regulator you are breathing from then equalizing the pressure across the manifold introduces high pressure at depth that could potentially cause more problems. Am I just way overthinking this? Is this the PADI approach to technical diving? Again I am new to this journey and I just want to feel confident about the place I am going to seek training. Any advice or experience is greatly appreciated.
Thanks in advance

 

[tbone1004]

Doubles are traditionally treated as one large tank. Isolation is done in extremely rare circumstances *rare to the point that I haven't heard a report of someone having to isolate in over a decade*.

Independent doubles are sometimes used and those are treated like sidemount tanks for gas management however that is also extremely uncommon.

 

[Trace Malinowski]

Before isolation manifolds, doubles were connected with a crossbar that had one outlet in the center of a fixed crossbar. A malfunction anywhere would cause a complete loss of gas.

To eliminate this risk, divers eliminated the crossbar and attached the first stages to two independent doubles that were banded together. A catastrophic loss of gas would no longer drain the entire supply. One cylinder would be left. For gas management and balance purposes, each tank was breathed down to a certain point then the diver would switch regulators.

A better method of utilizing independent doubles was to sidemount them. Sidemounting is growing in popularity because 1) It allows cave divers more versatility and access to tight spaces and tunnels. 2) It's what the cool kids do and others want to be cool.

When the isolation manifold was invented, it combined the simplicity of one large volume of gas in the cylinders with the safety of being able to close an isolator on the crossbar to create two independent cylinders with a few turns of a knob.

With the DIR philosophy, gas management is normally divided into all gas is usable, 1/2 gas is used outbound and 1/2 gas is used to return, 1/3 of the gas is used out with 1/3 used to return and 1/3 left in reserve, or 1/6 is used out with 1/6 used back and 4/6 are left in reserve. These volumes are calculated after rock bottom gas is determined. Rock bottom is the minimum amount of gas needed to get 2 divers from maximum depth to the surface in recreational diving, or to the first gas switch in technical diving, or to the surface or first stage bottle when cave diving.

In DIR diving, we leave the isolator open and breathe from the long hose coming off the right post. In an emergency, the long hose is donated from the mouth to the out-of-gas diver, and the donor switches to the backup regulator worn on a necklace with the first stage connected to the left post. The auto inflator is connected to the right post and feeds the buoyancy compensator which is a back-inflation BCD called a wing. There are a couple of advantages to having the buoyancy come off the right post related to post roll-offs and runaway BCD inflation issues. The SPG comes from the left post along with the backup reg. Again, there are a couple of advantages to having the SPG on the left including post roll-offs and stage bottle management.

There is no need for an SPG on the regulator on the right tank because if you have a problem you are going home. You've already calculated emergency gas and in an emergency, it will be there.

 

[NothingClever]

@Alaskan Scuba Dude

I find your posts are frequently unhelpful.

If you’re not a technical diver, I’d ask that you refrain from posting here. Asking questions to learn is welcome.

If you do hold a technical qualification, I’d ask that you focus on strengthening the conversation rather than distracting it. I realize you may be intending to be funny but I think miss the mark more often than not.

 

[john120283]

Have you looked into having an instructor travel to you? A lot of the GUE instructors are willing to travel to teach classes.

I took my Fundies class locally and traveled to Vancouver Island for Tech 1

 

[grantctobin]

I am newly interested in moving into back-mounted doubles and looking into the different systems. I have talked with several advanced technical as well as cave divers and I have a newby question about how the gas is managed on a set of back-mounted twin cylinders. Everyone in my local area uses a long hose configuration, i.e. GUE/UTD/ISE with a manifold. I went to a PADI shop looking into tech courses as they are the only ones that offer technical courses in my area (the advanced divers in my area were trained elsewhere) and now I am really confused about how to breathe from back-mounted doubles. From what I can gather the manifold is open all of the time and the tanks are breathed down as if they were one big tank with a really large volume. The primary regulator stays in the mouth all of the time. If there is an issue then the appropriate response to find/shut down the problem is addressed. The PADI guys I talked to described using the back-mounted doubles basically as two independent systems and requiring redundant EVERYTHING. They described breathing down each tank 500 psi and then switching regulators and leaving the manifold closed and shutting off each tank. Is this the correct method according to PADI? I feel like this defeats the purpose of the manifold being able to share gas with each regulator. The introduction of redundant everything in my mind would make it much harder to find a problem. If you have a redundant bladder in your BC and it auto-inflates then the diagnosis is more steps than knowing your bc is inflated from just your right post. I asked what they did in the event of a buddy being out of gas and having to donate if the valve was shut every time they switched and they said you turn it on. If there is an event on the regulator you are breathing from then equalizing the pressure across the manifold introduces high pressure at depth that could potentially cause more problems. Am I just way overthinking this? Is this the PADI approach to technical diving? Again I am new to this journey and I just want to feel confident about the place I am going to seek training. Any advice or experience is greatly appreciated.
Thanks in advance

Mind posting the shop and instructor name?

 

[formernuke]

As stated above. Plus....
For tech classes don't do PADI. I don't know who wrote there tech programs but he or she was definitely smoking something.

It is worth traveling to get a good tech instructor.

If all the other tech divers in your area are traveling for certs, there is a reason.

 

[Robert H. Diver]

Yea don’t do tech with padi.

 

[Whitrzac]

Padi isn't the problem here, its the instructors outdated thinking.

 

[buildhuntcook]

Mind posting the shop and instructor name?

There are only a few shops in my area and this shop is associated with the sheriff's department so I would rather not. Lol.