valve drills - agency differences

[Scubaholic123]

Hi guys

Joined this site so I could specifically ask this question - thank you very much in advance for any answers.

I'm a PADI & SSI MI and am in the process of training to become a PADI Tec 40/45/50 Instructor. Have completed the student training and close to finishing the instructor prerequisites. I'm deliberately not going to disclose where i'm training or who with because I have been very disappointed with the quality of instruction received and much of my training has been self taught. Many people recommended TDI over PADI training, the reason behind my choosing PADI is that other agencies will recognise the credentials and allow me to cross over for minimal cost. PADI won't.

My question is this - my instructor has me doing valve drills in the following order - isolator closed, right post close/breath down/open, left post close/breath down/open and finally reopen isolator. As part of my self tuition I've looked a numerous YouTube clips from Tec instructors from many agencies. I cannot find anyone closing the isolator first. I've asked my instructor (who is a CD) about it and he got pissed off, said his way was best but no further clarification.

Any comments from experienced tec divers would be appreciated. I will keep everything in mind when I'm finally teaching this course.

thanks

 

[KevinNM]

I'm not an experienced tech diver, but the GUE valve drill manual is right valve close and open, isolator close and open and left valve close and open. For troubleshooting, the isolator is the 'I can't stop the leak so I'm going to save what gas I can' option, not the first option.

His unwillingness to explain this seems odd.

 

[kensuf]

I teach isolate first and I know quite a few that do the same. The purpose is to preserve half of your gas and then deal with the problem. In an ideal world, you should try to go for the reg / post that is leaking, but identifying which one is leaking may be difficult, which is why I have them go for the isolator first.

The way I teach it is almost exactly like you describe (isolate, close right, breathe down, open right, close left, breathe down, open left, open isolator), the only difference is I also want my students to verify the reg they are not breathing from is on and functional (purge it) before they shut down the reg they are breathing.

I know others that teach right valve, isolator, left valve.

 

[decompression]

This.....

 

[tursiops]

My training is PADI and TDI. Isolator first, unless you have specific info on where/what the problem is. Save your Gas! Is there a difference in strategy for cave diving versus no (hard) ceiling?

 

[Bric Martin]

His way may, or may not be the best. But if he can't explain why you do something he is not what I want from an instructor.

 

[WarrenZ]

TDI diver here I was thought isolate first unless you were able to bet your life on where the problem is. For example burst hose free flow that you can see and diagnose close the offending reg post if not close isolator then trouble shoot.

 

[kr2y5]

I think the difference comes from the differences in philosophy between those, who put a greater emphasis on team diving (e.g., GUE, UTD), and those, who emphasize self-reliant diving (e.g., TDI).

Here's how I understand it. Hopefully, someone will quickly jump in to correct me right away if I'm wrong about it.

In team diving, even if all gas is lost, there is always (supposed to be) another team member closeby carrying redundant gas. From this perspective, I understand that the "worst case" scenarios, in which one has to isolate, seem to be less of a concern compared to self-reliant diving, because there is always some "cushion" in the form of another team member, and the gas in their tanks.

From the perspective of a self-reliant diver, on the other hand, one generally plans under the assumption there may be no buddy to come to rescue, and consequently, there's a greater emphasis on worst-case scenarios, in which the worst failure has just happened, and you are left to deal with the problem on your own.

The "isolate first" approach is the one that seems to be more compatible with the self-reliant philosophy, since it protects you against the hypothetical bad "sh*t hit the fan and you are left all-alone" scenario. In case one will eventually have to isolate, it maximizes the amount of gas left in the "good" tank, assuming the problem affects only one side. If you close the isolator quickly, you will still have close to half of the gas left, and since you had planned to have enough gas to complete the dive even if you lost half of your gas, you should still be fine, even if you have no buddy around to share gas with.

On the other hand, the "close the post first" approach maximizes the total amount of gas left in both tanks, regardless of whether you guessed it right or wrong. It optimizes for the more common failure scenario at the expense of the less likely scenario. If the consequences aren't too severe (which is presumably the case in team diving, since there's always a teammate around), the latter is an example of what is generally accepted as a sound engineering principle.

 

[2airishuman]

Remember that it's a drill, and is based on the scenario where the leak is serious and the cause of the leak is unknown (rare in practice). Isolating saves the gas on the unaffected side, no matter what the problem is, even if the problem is a blown cylinder neck O-ring or burst disk. Once you isolate, you can't lose more than half your remaining gas, which means that on a rule of thirds dive, isolating promptly will leave you enough gas to complete the dive safely if a leak occurs at any point in the dive.

The other side of the coin is that cylinder neck O-ring and burst disk failures are vanishingly rare once the dive is well underway. If they happen at all, they'll happen early in the dive when there's still plenty of gas. This school of thought holds that you're better off training to close the posts to save gas in the more likely scenarios -- regulator free flows and blown hoses or hose O-rings.

I think being able to reach the valves and operate them quickly is more important than the order in which they're closed.

 

[Scubaholic123]

thank you everyone - appreciate all your replies, view points & information