Some question about doubles

[WhiteSands]

I did a doubles mini course recently to learn how to setup and use doubles (in OW only). I must have been a bad student 'cos now I have many questions

Not much change to S-drill, but now there is valve drill.

Ok so I've practised the valve drill repeatedly. But funny thing is, how do I use it? After the course I realise I have no idea, because I was just taught the steps of the drill and made to practice it by rote, but no application.

I guess I can figure out simple stuff. If right post leaks, shut off and go to necklace. Same for left post, shut off but remain on long hose. But when do I shut off the center knob (what's it called again)?

Also some questions on the hardware. If I shut off right post, gas from right tank is still accessible through the manifold, correct? It just doesn't send gas to the longhose 2nd stage?

The centre knob isolates the two cylinders, effectively making them independent? When will I need to do that?

Thanks for your help.

 

[rongoodman]

In the DIR world, the valve drill isn't a trouble shooting procedure, it's just practice in manipulating the valves. Dealing with failures comes later, in Tech 1. Here's a discussion from a few years back, but I can't find anything newer. Other agencies have their own methods of dealing with problems, e.g., some want you to isolate first and then troubleshoot. Where did you take your doubles course?

Basically, you will have to isolate if you have a leak which can't be solved by simply shutting down a post, such as an O-ring extrusion on a tank.

 

[kr2y5]

As far as I can understand, carrying doubles and all the rules of gas planning are supposed to provide redundancy on the assumption that you will only lose about half of your gas. A freewlowing regulator can drain a tank in less than a minute, or both tanks if the isolator is open. Unless you can close the isolator immediately during an emergency, both tanks will drain, and there will be no effective redundancy, just more ballast to carry back on the boat ladder.

 

[PfcAJ]

Needing to isolate is a rare thing.

Things like a leaking tank o-ring, manifold oring, and burst disk need to be isolated. Also if you break a knob on the ceiling and dislodge a reg (or it free flows), you'd need to isolate.

Its really uncommon, but when you need to do it it's going to make a big difference in how much gas you save.

 

[rongoodman]

http://www.globalunderwaterexplorers.org/files/Standards_and_Procedures/Valve_Manual_Ver2.2.pdf

 

[TSandM]

It's really important to understand how a manifold works, and I'm a little disappointed that you got through the doubles mini without that being clear.

Essentially, a manifold is a pipe connecting the two tanks. There are two outlets in the pipe, one on each side, where you can put regulators. Each outlet has a valve. So the tanks are connected to one another all the time, whether the post valves are open or closed. Either post can access all the gas in both tanks; that's the big advantage of manifolded doubles, because no matter what your first or second stage does, you can still access all your gas through the other post.

In the middle of the manifold bar is another valve, which is the isolator. This valve does what its name implies -- it "isolates" the tanks from one another. If the isolator is closed, each post can only access the gas in the tank on that side. Isolation is only used when closing a post won't solve the problem, which means the leak is upstream of the DIN connection. As AJ points out, there are not many potential problems upstream of the regs, and failures in those places are VERY rare, so isolation is not something one would commonly have to do.

In GUE diving, we are taught to attempt to locate the leak and close the appropriate post first, and if that doesn't solve the problem, we isolate. Other agencies teach to isolate first, on the theory that, once you have done so, even if you dawdle on getting the post closed, you can't lose more than half your gas, nor can you if you have misidentified the source of the leak, or it is upstream of the post. In fact, in GUE diving, you begin to signal your team at the moment you hear the leak, and by the time you have your post closed, it is HIGHLY likely you will have at least one teammate who is LOOKING at your valves and manifold, and can instantly inform you if you are closing the wrong thing.

The valve drill in Fundamentals is a rote activity, just practicing accessing the valves, and opening and closing them (and keeping track of which ones you have closed and opened!). Solving failures with valve closures shows up in the technical classes like Tech 1 and Cave 1. In open water, in general, you can manage a leak as you would with a single tank -- either abort the dive, or go on someone else's gas and abort.

 

[WhiteSands]

http://www.globalunderwaterexplorers.org/files/Standards_and_Procedures/Valve_Manual_Ver2.2.pdf

Dear all,
Thank you for the great tips. Sir, this is great information, thank you! Exactly what I need!

---------- Post added April 21st, 2014 at 09:29 AM ----------

It's really important to understand how a manifold works, and I'm a little disappointed that you got through the doubles mini without that being clear.

Essentially, a manifold is a pipe connecting the two tanks. There are two outlets in the pipe, one on each side, where you can put regulators. Each outlet has a valve. So the tanks are connected to one another all the time, whether the post valves are open or closed. Either post can access all the gas in both tanks; that's the big advantage of manifolded doubles, because no matter what your first or second stage does, you can still access all your gas through the other post.

In the middle of the manifold bar is another valve, which is the isolator. This valve does what its name implies -- it "isolates" the tanks from one another. If the isolator is closed, each post can only access the gas in the tank on that side. Isolation is only used when closing a post won't solve the problem, which means the leak is upstream of the DIN connection. As AJ points out, there are not many potential problems upstream of the regs, and failures in those places are VERY rare, so isolation is not something one would commonly have to do.

In GUE diving, we are taught to attempt to locate the leak and close the appropriate post first, and if that doesn't solve the problem, we isolate. Other agencies teach to isolate first, on the theory that, once you have done so, even if you dawdle on getting the post closed, you can't lose more than half your gas, nor can you if you have misidentified the source of the leak, or it is upstream of the post. In fact, in GUE diving, you begin to signal your team at the moment you hear the leak, and by the time you have your post closed, it is HIGHLY likely you will have at least one teammate who is LOOKING at your valves and manifold, and can instantly inform you if you are closing the wrong thing.

The valve drill in Fundamentals is a rote activity, just practicing accessing the valves, and opening and closing them (and keeping track of which ones you have closed and opened!). Solving failures with valve closures shows up in the technical classes like Tech 1 and Cave 1. In open water, in general, you can manage a leak as you would with a single tank -- either abort the dive, or go on someone else's gas and abort.

Thank you TSandM for the detailed write-up. I looked at the diagram of the left/right valves on the first page of the PDF RonGoodman provided and I understood how it works. I think this diagram would have been very useful for the class.

Ok now I understand the valve drill is just to get me comfortable in manipulating the valves. More practice for me!

---------- Post added April 21st, 2014 at 09:32 AM ----------

It's really important to understand how a manifold works, and I'm a little disappointed that you got through the doubles mini without that being clear.

Essentially, a manifold is a pipe connecting the two tanks. There are two outlets in the pipe, one on each side, where you can put regulators. Each outlet has a valve. So the tanks are connected to one another all the time, whether the post valves are open or closed. Either post can access all the gas in both tanks; that's the big advantage of manifolded doubles, because no matter what your first or second stage does, you can still access all your gas through the other post.

In the middle of the manifold bar is another valve, which is the isolator. This valve does what its name implies -- it "isolates" the tanks from one another. If the isolator is closed, each post can only access the gas in the tank on that side. Isolation is only used when closing a post won't solve the problem, which means the leak is upstream of the DIN connection. As AJ points out, there are not many potential problems upstream of the regs, and failures in those places are VERY rare, so isolation is not something one would commonly have to do.

In GUE diving, we are taught to attempt to locate the leak and close the appropriate post first, and if that doesn't solve the problem, we isolate. Other agencies teach to isolate first, on the theory that, once you have done so, even if you dawdle on getting the post closed, you can't lose more than half your gas, nor can you if you have misidentified the source of the leak, or it is upstream of the post. In fact, in GUE diving, you begin to signal your team at the moment you hear the leak, and by the time you have your post closed, it is HIGHLY likely you will have at least one teammate who is LOOKING at your valves and manifold, and can instantly inform you if you are closing the wrong thing.

The valve drill in Fundamentals is a rote activity, just practicing accessing the valves, and opening and closing them (and keeping track of which ones you have closed and opened!). Solving failures with valve closures shows up in the technical classes like Tech 1 and Cave 1. In open water, in general, you can manage a leak as you would with a single tank -- either abort the dive, or go on someone else's gas and abort.

Thank you TSandM for the detailed write-up. I looked at the diagram of the left/right valves on the first page of the PDF RonGoodman provided and I immediately understood how it works. Your writeup made it even clearer. I think this diagram would have been very useful for the class.

Ok now I understand the valve drill is just to get me comfortable in manipulating the valves. More practice for me!

Oh yes, I know this is beyond my level, but I am curious why GUE choose to close the posts first before the isolator. Is it because of the rarity of failures that requires the closing of the isolator or is there other reasons for doing so?

I would like to understand the thinking behind it, thanks.

 

[PfcAJ]

A failure is MOST LIKELY a regulator failure of some sort. Lots of business going on with regulators; plenty of o-rings, moving parts, etc, so that's the 'go to' option.

In the real life, if you shut down a post that you think it leaking, breath it down/purge it, and the bubbles don't stop, SHUT THE ISOLATOR. Let your buddy come over and sort out what's wrong.

Also, read this:
Life Ending Seconds • ADVANCED DIVER MAGAZINE • By Curt Bowen
Its a big deal.

 

[WhiteSands]

A failure is MOST LIKELY a regulator failure of some sort. Lots of business going on with regulators; plenty of o-rings, moving parts, etc, so that's the 'go to' option.

In the real life, if you shut down a post that you think it leaking, breath it down/purge it, and the bubbles don't stop, SHUT THE ISOLATOR. Let your buddy come over and sort out what's wrong.

Also, read this:
Life Ending Seconds • ADVANCED DIVER MAGAZINE • By Curt Bowen
Its a big deal.

Thank you Sir.

 

[Cyprian]

This is certainly not as thorough as the GUE Valve Manual that Ron posted above, but its a nice short little video that provides a general overview:

https://www.facebook.com/photo.php?v=10201659222862924

If you cannot see the video from the link, just go to Dive Gear Express FB page and look for a manifold video that they shared.