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

 

[Dark Wolf]

My pleasure! I gotta warn you, though. Stockton is usually low vis diving, but great for building core skills. Stockton does have primitive camp sites, I will find out what the rates are.

I am also going to do my first dives at Pomme de Terre lake this fall. I expect conditions similar to Stockton. Both lakes are about 100 feet deep, or thereabouts.

I am going to be at Beaver Lake on the 26th, then Table Rock on the 2nd. But we can sure set something up, and you are welcome anytime. I normally dive Sundays and Mondays.

I will send you a message with my contact details. Email or text is fine. I work a weird schedule, just an FYI.

Look forward to diving with you!

DW

 

[treasurehunter]

I’m 100% for choosing the right instructor ,it really makes all the difference , well worth the travel and extra expenses.
A good tech instructor will develop you into a proficient tech diver where most all gear failures or dive plan not going to plan will become more of a inconvenience than a life or death situation.
You will be proficient and confident in how to set up your gear to your specifications.
My instructor also taught me how to calculate deco in my head using prime numbers in case the shtf and I lose my slate and dive computer.
You will develop a mindset.

Back mount doubles :
The way the manifold works:
1-Your two tanks are connected together as one big tank, and you have access to two regulators and full volume of gas.

2-there is an isolator valve between the two tanks and regulator posts to separate them if need be.

3-right or left post can be closed and you have full access to entire gas volume ,but you now only have access to one regulator.
If you are closing a post it will be a regulator issue or a leaking nob.
Depending on which post you close you might lose the function of your pressure gauge or suit inflator or dry suit inflator.

If you are properly trained, it won’t be detrimental because you will be able to handle it as more of a inconvenience than an emergency.

4- close isolator and you have access to half the gas, one regulator.
If you have to close the isolator ,pretty much means one of your tanks is done for , and you are heading back out.

As for buoyancy redundancy.

If you are diving dry your dry suit is basically your second alternative or for others that use there dry suit as there bcd your wing is your alternate.

If you are diving wet then a dual bladder makes sense , and you don’t have to connect an inflator hose, you have option of oral inflate. Technically a sufficient sized smb is considered a redundant buoyancy device but will be a big pain in the a$$ to try and complete a deco obligation with a smb. So diving wet is the only configuration I would consider a dual bladder wing.

Hope this helps in your quest.

 

[Alaskan Scuba Dude]

Take the course with PADI, and turn the isolation manifold back on when you finish the course.

 

[NothingClever]

@buildhuntcook - I think you’ve received some invaluable guidance from @Trace Malinowski and @Jim Lapenta.

I might’ve missed something in your first post but the only thing I’d add is “What’s the hurry?” or “Can you wait until you move to the PNW?”

With an abundance of instructors up there, your likelihood of successful outcomes dramatically increases.

The other thing - if you pursue technical training, don’t be surprised if the AI and/or DM goals lose some of their shine.

 

[rob.mwpropane]

Take the course with PADI, and turn the isolation manifold back on when you finish the course.

What tf?

 

[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.

 

[Jrock1062]

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.

excellent explanation TY

 

[rx7diver]

... I am headed to Mermet this weekend ...

@buildhuntcook,

If you are located near Columbia MO and you are diving Mermet Springs IL this weekend, I am assuming that you are participating in the Mermet trip that CH is running for Diventures/Captain Nemo's this weekend. I don't know if you know this, but one of the previous owners of Captain Nemo's, DG, received his full cave traniing from Steve Bermen (RIP) at Ginnie Springs a couple of decades ago, IIRC. I don't know how active a cave diver DG is now, but he almost certainly will be happy to chat with you about what he was taught. Not GUE, though, almost certainly.

rx7diver

 

[buildhuntcook]

@buildhuntcook - I think you’ve received some invaluable guidance from @Trace Malinowski and @Jim Lapenta.

I might’ve missed something in your first post but the only thing I’d add is “What’s the hurry?” or “Can you wait until you move to the PNW?”

With an abundance of instructors up there, your likelihood of successful outcomes dramatically increases.

The other thing - if you pursue technical training, don’t be surprised if the AI and/or DM goals lose some of their shine.

There is no real rush. Just seeing what is available near me and what I would be willing to travel to versus waiting to do it when it is easily accessible. I am trying to find out what courses/platform/etc...will help me reach the goals I want without dumping a bunch of money into certs that don't make me a better diver or move me towards my goals. I appreciate all of the input everyone has had on this thread though. It has been invaluable to know what questions to ask and what to look for.

 

[buildhuntcook]

@buildhuntcook,

If you are located near Columbia MO and you are diving Mermet Springs IL this weekend, I am assuming that you are participating in the Mermet trip that CH is running for Diventures/Captain Nemo's this weekend. I don't know if you know this, but one of the previous owners of Captain Nemo's, DG, received his full cave traniing from Steve Bermen (RIP) at Ginnie Springs a couple of decades ago, IIRC. I don't know how active a cave diver DG is now, but he almost certainly will be happy to chat with you about what he was taught. Not GUE, though, almost certainly.

rx7diver

I did indeed attend the trip with CH! I have talked with DG about some of the things on this topic but as he states himself "squirrel!!!" He is more than willing to provide the information but is not always able to provide the attention span lol. Outstanding group of divers there.