36 replies to this topic

[Dive_Girl]

There is a current debate amongst some of my dive buddies regarding diving doubles with the manifold open or closed.

Following are catastrophe scenarios. While I have walked through some of these in conversation before, I'd like to first hear your thoughts on the pros and cons (i.e. pitfalls) in each scenario, or combine some those below, or provide some of your own to support your position of diving the manifold open or closed.

1. You need to share air - you do so donate your long hose and pick up your necklace. Manifold open - you and the other diver dive off your combined backgas. Manifold closed - you and the other diver breathe off separate tanks of backgas.

2. A regulator malfunctions without free flow. Manifold open - you switch to the working regulator and dive off your combined backgas. Manifold closed - you switch to the working regulator and breathe off its tank of backgas.

3. A regulator fails resulting in either an uncontrollable secondary free flow or a first stage free flow. Manifold open - you shut off the valve of the malfunctioning regulator and you dive off the functioning regulator with access to your combined backgas. Manifold closed - you shut off the valve of the malfunctioning regulator and switch to the working regulator and breathe off its tank of backgas.

4. A valve fails or burst disk blows. Manifold open - you shut down the manifold and switch to functioning regulator with access to its tank of backgas. Manifold closed - you switch to the working regulator and breathe off its tank of backgas.

[PerroneFord]

Is there someone out there teaching diving with the manifold closed? That's the craziest thing I've ever heard. I mean, just on the surface of it, with the manifold closed your pressure guage isn't even accurate. It's independent doubles at that point with all the trappings. Including the danger inherent in filling the tanks.

No thanks.

[Dive_Girl]

Is there someone out there teaching diving with the manifold closed? That's the craziest thing I've ever heard. I mean, just on the surface of it, with the manifold closed your pressure guage isn't even accurate. It's independent doubles at that point with all the trappings. Including the danger inherent in filling the tanks.

No thanks.

I didn't mean to cause confusion - this is not a training question. This is about differences in diver methodology (which I find become very staunch amongst divers as they move into extended range diving). There are divers who dive with the manifold closed, breathe down 1/3 of one thank then switch and do the same to the other and then back again. There are gauges on each tank. One reason has been given if a valve or burst disk goes at 200'+ you will not get the manifold closed in time to save enough backgas for a safe ascent to decostops. Another reason is that if you travel and want to dive doubles, they'll likely be banded independents anyway, so if you do not know how to dive this way, you won't be prepared to do extended range dives on these banded independents. A few other reasons are outlined by a closed manifold diver in his blog.

So what are some tangible Manifold open responses to this?

[NJBerserker]

**Disclaimer: I do not dive doubles yet so this is based on my thought process as a diver**

after reading both the blog and what you've posted I still can't see a reason to dive with a closed manifold. Even the author of the blog himself only uses that methodology for training to dive to extreme depths. You listed four scenarios in your first post. Of the four scenarios only the last one (burst disk or valve failure) would benefit from having your manifold closed. It however is also the least likely to happen. Taking a deeper look at that particular scenario, should it occur at 200' feet, you may be down to only your reserve 1/3 if it happens at the end of your dive. In this case you're still chancing it as your respiration rate has probably gone up since you realized you were in trouble. Deeper still we can also assume that at 200 feet you may be inside a wreck or cave. The rapid loss of compressed gas could easily cause a silt-out before you knew what hit you. If you're not diving dry with a separate inflation system you could have buoyancy issues. What I'm gettting at here is that whether or not you have your manifold open or closed, rapid uncontrolled loss of breathing gas will result in a whole mess of serious problems and you can easily be screwed and that if it happens at the wrong time the benefit if any can be quite minimal. Also, the chances of an emergency scenario like the first three you presented where manifold open is more advantageous is sigificantly more likely to occur. Ergo it would make more sense to use that method. If I have made any incorrect statements here please speak up.

[PerroneFord]

NJBersker nailed it.

This kind of backward logic makes technical diving more dangerous that it should be. And generally this kind of crap creeps up from people who either dive solo, have crappy buddies, or who don't actually do the dives they are talking about. I had a real gas failure, in a cave, and ~100ft. It was a non issue. It was a left post failure. I went through standard right post, center post, left post shutdown TWICE because I failed to do it slowly enough the first time to isolate the problem, and still didn't lose more than a few hundred PSI.

Anyone who wants to test this out can take a AL80 down to 100ft and open it up with and SPG on it and watch it drain.


Been there, done that, and I can tell you that a solid buddy and a cool head make this a non issue.


Now, on the issue of diving independents that's fine. But of you are going to dive independents why bother to manifold them? Just get two Al80s or LP95s or whatever, and dive them. You are gaining NOTHING by putting bands and manifolds on them and putting them behind your head.

[Edit: I just went and read the blog. Seems my suspicion was on the money. Solo diver. Discussion over]

Edited by PerroneFord, 23 September 2008 - 06:57 PM.

[bottomtime]

dive with a closed manifold= load gun 1 bullet spin cyl, pull trigger ,,,repeat 6x
or till you inject lead asprin to resolve diving head ache problems

[peterbj7]

I'm wholly with Perrone on this one. Why bother with a manifold if you don't use it? How long does it take you to shut down your valves? - by now you should be able to do it very quickly. You'll lose some gas but that should be minimal, even at 200'. If you can't do it in just a few seconds then you need to practice more.

The only failure where you DON'T want a manifold, on or off, is a catastrophic failure where the valve joins the tank. If that happens you lose all the gas in both tanks, very quickly, and there's nothing you can do about it. But I've never heard of that happening - I have had the odd O-ring leak, but that's hardly catastrophic.

[BubbleBoy]

I was told to dive with the manifold valve open, but, just barely open. That way you can shut it down quickly if necessary.

While it’s easy to imagine gas loss scenarios where a closed manifold would end up advantageous, they almost always depend on the tank with the lower content being the one that becomes unavailable. If the opposite happens, you’re worse off than starting the incident with an open manifold and equal gas in your tanks. To say you’re better off diving with the manifold closed seems to me like flipping a coin and expecting it to always come up heads. A truly conservative diver would assume they always lose the toss, and plan to have only the gas remaining in the lower content tank after the incident. That effectively reduces available gas at all times that your tanks aren’t balanced.

[PerroneFord]

I was told to dive with the manifold valve open, but, just barely open. That way you can shut it down quickly if necessary.

Please think this through. It is an absolute recipe for disaster at the fill station, and honestly, in the water it might save you 3-5 seconds. It's negligible compared to the increased risk of getting half a fill, or worse getting a dangerous fill. I nearly watched someone lose their life from this bit of "tech thinking".

When diving regularly, I can just about get a full valve drill done in 20 seconds. Maybe less. But as I learned when I had to do it for REAL, speed isn't the critical factor. In fact, doing it too quickly may force you to do it twice like it did me. Leave the isolator open at ALL TIMES and check that it is FULLY open prior to your dive.

I had a buddy do a cave dive with me in Wakulla who didn't follow this protocol and he nearly sucked his primary tank dry without realizing it because the pressure gauge was on the left post and obviously it wasn't moving. He was new to doubles. Fortunately, we were safely back on the surface when we realized that his isolator had been closed all dive.

[peterbj7]

Leave the isolator open at ALL TIMES and check that it is FULLY open prior to your dive

There's no need to have it open more than a crack, because it's equalising the pressure between the two tanks all the time, not just when you're breathing. And if it's open the whole way it significantly increases the time a valve drill takes.

Obviously during filling it should be opened more fully - something that the owner/user of the tanks AND the fill operator should both check. After getting back a twinset from filling, it's essential to check the pressure on both tanks even if you think the manifold is open, because debris could be blocking the manifold valve.

Your 20 seconds is of course for a full drill (which for anyone who doesn't know what it is, is all valves shut and all valves opened, though in a logical order). To shut off a single valve to isolate one regulator should take no more than say 5 seconds. If it takes much longer than that then it needs to be practiced until the time comes down.

Edited by peterbj7, 24 September 2008 - 08:26 AM.

[PerroneFord]

There's no need to have it open more than a crack, because it's equalising the pressure between the two tanks all the time, not just when you're breathing. And if it's open the whole way it significantly increases the time a valve drill takes.

Obviously during filling it should be opened more fully - something that the owner/user of the tanks AND the fill operator should both check. After getting back a twinset from filling, it's essential to check the pressure on both tanks even if you think the manifold is open, because debris could be blocking the manifold valve.

I am a firm believer in the KISS principle. Rather than opening, and closing my manifold every time I want gas, why not just leave the thing open. Literally, on closing the center post it might save me 3-5 seconds. I am more than willing to absorb that to keep from having potential issues with me messing up at the fill station, the fill attendant filling my tanks making a mistake, etc. That is a high risk operation that I don't need to make harder.

I completely understand that you have your own way of doing it, and that works fine for you. Since I sometimes have to do drop-off fills here where I live, it is not always feasible for me to monitor the fill operators.

[Dive_Girl]

4. A valve fails or burst disk blows. Manifold open - you shut down the manifold and switch to functioning regulator with access to its tank of backgas. Manifold closed - you switch to the working regulator and breathe off its tank of backgas.

It is this scenario at 200' where the fear factor is dropped with comments such as, do you know how much gas you'll lose at 200' in 10-20 seconds!? Everyone gasps and runs and closes their manifolds. (Note, I have never planned a dive where I would be on my last reserve at 200')

[peterbj7]

Obviously during filling it should be opened more fully - something that the owner/user of the tanks AND the fill operator should both check

Since I sometimes have to do drop-off fills here where I live, it is not always feasible for me to monitor the fill operators

Which is why I said what I do above - YOU open the manifold on your own set fully before handing the tanks in, AND you then check pressures in both tanks after getting them back. Can't be much simpler than that - the only way to simplify it further is to take out one of the steps, which to me is unacceptable.

I'm all for KISS, but it has still to be informed and thoughtful. Operating on autopilot may eventually kill you.

[peterbj7]

It is this scenario at 200' where the fear factor is dropped with comments such as, do you know how much gas you'll lose at 200' in 10-20 seconds!? Everyone gasps and runs and closes their manifolds. (Note, I have never planned a dive where I would be on my last reserve at 200')

There shouldn't be any fear factor. If there is it's a sign of inadequate training. In a crisis it's the poorly learned skills that are forgotten first.

One reason why I don't like the "quickie" tech courses marketed by some agencies. Training needs to be very thorough, just how thorough depending on the student's progress. By making it too easy and approachable we're setting people up for a disaster.

I once had a major catastrophic failure at 320ft. Only the training that had been dinned into me over and over again saved me.

Edited by peterbj7, 24 September 2008 - 10:14 AM.

[PerroneFord]

Operating on autopilot may eventually kill you.

Truer words never spoken. And if you ever saw me prep for a dive... even in the pool, you'd understand that autopilot doesn't exist for me. Those who dive with me can attest to this.