Question about isolating doubles

[jduncan]

I'm new to diving doubles, and for the first couple dives I have been just getting comfortable with the feel of the setup. I am using the 7' hose for the primary, and have a short hose for backup.

My question is: What would be a cause for isolating the tanks? If I have an issue with second stage (free flow), I shut the tank valve. If I have an issue with the first stage, or o-ring, etc., I shut the tank valve. The only thing I could think of would be the tank to valve o-ring failure.

I know I am missing something!

J

 

[Nixdax]

If a burst disk goes. Shutting off the valve won't help, but closing the isolator protects half of your gas supply.

 

[jimdiverman]

I don't know what kind of diving you are doing, but let's say you damage the valve on a bulkhead in a wreck or on an overhead in a cave, or you damage the manifold on one side, or lost your burst disk on a tank. I am sure there are several others. In any of these cases, you would close the isolator to try to save half your gas if you were unable to stop the gas from escaping from one tank, and end the dive.

 

[jduncan]

That makes sense - Also, I imagine the manifold itself can fail at the tank connection on either side. That would be an isolation situation as well?

 

[jimdiverman]

That makes sense - Also, I imagine the manifold itself can fail at the tank connection on either side. That would be an isolation situation as well?

You would isolate the twin sets in any situation where you could not stop gas from escaping due to damage to any part of the manifold or to a single valve or a single tank body. Multiple leaks (on both sides of the manifold), and you are breathing free flows and sharing gas until you get to the surface.

 

[jduncan]

I imagine it would be hard to tell WHAT happened - so would one start with the tank valve first, and then move to the isolation valve if that didn't stop the gas leak?

J

 

[jimdiverman]

I imagine it would be hard to tell WHAT happened - so would one start with the tank valve first, and then move to the isolation valve if that didn't stop the gas leak?

J

Have you had a technical diving course, or about to take one? This should be covered in your twinset course by your instructor.

You isolate the tanks first for just the reason that you state... you don't know where the leak is, so you try to save half your gas first. Then you switch to your backup regulator and isolate your primary (right post). If that doesn't stop the gas, switch back to your primary regulator and isolate your backup regulator (left post). Somewhere in that process, you are hopefully going to stop the leak. If not, you need to do your best to find gas from your buddy or alternate sources, and end the dive. (You should end the dive in any case if you have any type of gas loss.)

 

[jduncan]

I just finished the SSI Stress/Rescue. I went to the Intro to Tech seminar at the Boston show, and plan to get a technical course in at some point. Thanks for the answers, they were very helpful.

Jeff

 

[texdiveguy]

I imagine it would be hard to tell WHAT happened - so would one start with the tank valve first, and then move to the isolation valve if that didn't stop the gas leak?

J

Always isolate the tanks first by closing the isolator valve....then proceed to find the leak.

 

[JeffG]

Just to be different.

Turn off the offending valve.

If you cannot determine the offending valve, then try the right post. If that doesn't work, Isolate.