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Your Manifold - open or closed


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#31 PerroneFord

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Posted 05 October 2008 - 04:59 PM

There are two schools of thought when doing shutdown drills.

School one teaches you to isolate the gas immediately, as you will save at least half your available gas. So you isolate the gas while you still have freeflow or other flowing loss of gas. In this school of thought, being able to get the isolator closed as quickly as possible has merit. Thus we see things like people just opening the manifold one turn or two. Along with the requisite issues that may bring along with it.

The other school of thought says that in all likelihood the post that will fail is the one that is being used during the dive, while the dormant post (the one that is just handling your backup reg, SPG, and perhaps drysuit inflation) is very unlikely to develop problem. So that valve drill teaches to shut down the right post first. In this school of though, shutting the isolator quickly doesn't really carry much weight because you will likely have stopped the problem with your first action.

In any event, there is a lapse of time from when you get a post shut down, to the flow of gas stopping. If you are set in trying to fly through the drill, you will likely NOT be patient in allowing that flow to stop before you turn the post back on. Thus you will get through the entire drill and still not solve the problem, and have to redo the drill slower the second time through. Been there, done that.

#32 Capn Jack

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Posted 05 October 2008 - 06:15 PM

In any event, there is a lapse of time from when you get a post shut down, to the flow of gas stopping. If you are set in trying to fly through the drill, you will likely NOT be patient in allowing that flow to stop before you turn the post back on. Thus you will get through the entire drill and still not solve the problem, and have to redo the drill slower the second time through. Been there, done that.

THANKS for the words Perrone. Let me try to read it back, "build a pause into the real-world situation to see if you've fixed the problem before proceeding to the next valve."

I think Bill mentioned that, but I appreciate the additional insight.
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#33 Diverbrian

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Posted 05 October 2008 - 06:43 PM

I am of the full open/full shut school as that way you can easily check the valve position. I do dive with the manifold open for reasons of wanting an equal draw out of both tanks without having to fuss with anything unless an emergency is going on. Also, if I isolate one regulator for a freeflow with the purpose of letting it thaw and restarting it a couple of minutes later (common procedure in Great Lakes diving), I don't have to worry about which one of my back tanks has the most gas out of it.

What I believe PF was referring was the possibility of having that valve shut completely from manuevering in an overhead and not being aware that it shut. There are issues where divers have nearly panicked with a full tank of bottom mix in the other side and thinking that they were out because their indication was an pressure gauge at zero and they didn't know that their manifold valve was closed.

Having mentioned that, I do believe that there are advantages and disadvantages to both approaches of open/closed manifold. It is up to the individual diver to determine which set of risks they want to deal with.

I will agree with Capt. Jack's instructor that time IS important in valve drills no matter what approach you use. I just don't feel that I lose enough time by leaving valves at full positions to make it worth the time that I would lose in verifying their positions in an emergency.
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#34 Diverbrian

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Posted 05 October 2008 - 06:46 PM

There are two schools of thought when doing shutdown drills.

School one teaches you to isolate the gas immediately, as you will save at least half your available gas. So you isolate the gas while you still have freeflow or other flowing loss of gas. In this school of thought, being able to get the isolator closed as quickly as possible has merit. Thus we see things like people just opening the manifold one turn or two. Along with the requisite issues that may bring along with it.

The other school of thought says that in all likelihood the post that will fail is the one that is being used during the dive, while the dormant post (the one that is just handling your backup reg, SPG, and perhaps drysuit inflation) is very unlikely to develop problem. So that valve drill teaches to shut down the right post first. In this school of though, shutting the isolator quickly doesn't really carry much weight because you will likely have stopped the problem with your first action.

In any event, there is a lapse of time from when you get a post shut down, to the flow of gas stopping. If you are set in trying to fly through the drill, you will likely NOT be patient in allowing that flow to stop before you turn the post back on. Thus you will get through the entire drill and still not solve the problem, and have to redo the drill slower the second time through. Been there, done that.


Sorry, I missed this page that had your post. I didn't mean to put words into your mouth (as it were) with my previous post.
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#35 Diverbrian

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Posted 05 October 2008 - 06:47 PM

In any event, there is a lapse of time from when you get a post shut down, to the flow of gas stopping. If you are set in trying to fly through the drill, you will likely NOT be patient in allowing that flow to stop before you turn the post back on. Thus you will get through the entire drill and still not solve the problem, and have to redo the drill slower the second time through. Been there, done that.

THANKS for the words Perrone. Let me try to read it back, "build a pause into the real-world situation to see if you've fixed the problem before proceeding to the next valve."

I think Bill mentioned that, but I appreciate the additional insight.


That is a good statement.
A person should be judged in this life not by the mistakes that they make nor by the number of them. Rather they are to be judged by their recovery from them.

#36 VADiver

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Posted 06 October 2008 - 11:14 AM

In any event, there is a lapse of time from when you get a post shut down, to the flow of gas stopping. If you are set in trying to fly through the drill, you will likely NOT be patient in allowing that flow to stop before you turn the post back on. Thus you will get through the entire drill and still not solve the problem, and have to redo the drill slower the second time through. Been there, done that.

THANKS for the words Perrone. Let me try to read it back, "build a pause into the real-world situation to see if you've fixed the problem before proceeding to the next valve."

I think Bill mentioned that, but I appreciate the additional insight.


That is a good statement.



Slow is smooth and smooth is fast.

#37 Scubatooth

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Posted 06 October 2008 - 11:31 AM

Vinny that last comment goes for several things beyond diving, including marksmanship :)

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