Z-system gas switching

[kundalinichi]

Hi everyone. I am still getting used to my Z-plus system with isolatable manifold, I am tech certified (on backmount) but plan on doing many more 2-tank air sidemount dives before planning to do any multiple-gas dives on the Z-system.

My question for you Z-sidemounters, especially with a isolatable manifold incorporated into your system, how do you switch gasses mid-dive? (Mainly in the sense of "back gas" switch to deco gas) Do you keep a traditional stage setup on your high-O2 deco bottle with a first and second stage, and switch normally? Or do you unplug left side, plug in deco gas, and simulaneaously turn on deco tank\turn off right side tank, and then breathe it off your long hose? I have been putting a lot of thought into gas switching, and I can see many different ways of doing it using the zsystem.

I am wondering, because in my purchasing of the Z-system, I was told that you could input ANY gas into the system, and still be breathing off long hose\backup. But then comes the extra vigilance and keeping up which gas is plugged in and you are breathing off of. Thanks for any input you can give, even if you are just using a Z-distribution block.

 

[rjack321]

Why would you use a switchblock for entirely open circuit diving?

 

[kundalinichi]

Because it acts just as my doubles isolator manifold does, without having to heave the doubles around. I can plug in any tanks I want and have regulator redundancy (although it still can be considered a single point of failure, I know).

 

[Kevrumbo]

(Here in Chuuk Lagoon from 05 to 16Oct and again now 17 to 29Nov)

I've just been switching to deco gas bottles with conventional regs the usual way --been diving backmount doubles for the deeper wrecks beyond 45m with 50% & O2 in the AM; and Z-system doubles sidemount with O2 deco for afternoon dives on wrecks 30m or less in the PM after a 3hr surface interval.

I did bring an extra QC6 hose kit, but only plan on using it as a spare set for bottom mix in case of a cut hose. . .

 

[DA Aquamaster]

There's a progression or escalation of sorts involved, but the isolator does solve the single point of failure issue that kept me from even considering the Z-system for cave diving use.

I spoke with Andrew at DEMA a couple years ago and got the impression that the Z system was originally designed to provide a means for a clean, DIR configured hose routing and back up reg for single tank monkey diving. It does that pretty well, but it obviously also had potential for two tank SM diving as well in terms of allowing a standard DIR hose configuration. The problem was that a second stage freeflow would leave you basically screwed as both regs are plumbed into the (non isolated) distribution block. To resolve that risk, you needed to:

a) add in line shut offs to each second stage, and they add 3 additional dynamic o-rings each, two of which are very prone to damage from sand and salt crystals, and damage to just one of them leaves you open to gas loss. So in effect the additional items needed to mitigate the risk creates even greater risks of their own (not a viable configuration plan); or

b) bring along a separate QD hose and second stage assembly to plug into one of your SM tanks in the event of a second stage failure - and that plan still leaves you without a wing or drysuit inflator. I can live without a wing inflator, but the lack of a DS inflator can be problematic in a cave profile where I have to descend significantly to exit the cave. And the emergency second stage assembly sucks up an entire pocket where it lives under used, often sandy and silty and with unacceptably low odds of actually working if ever needed. (Another non-viable plan.)

Consequently, the isolated distribution block resolves that single point of failure problem and now does allow a true DIR hose configuration with the isolation and redundancy needed to make the whole thing work. However the isolated Z-system still adds a degree of complexity that most SM divers just don't feel is needed. In effect it's an issue of playing the DIR tenet of a consistent hose routing on the team against the tenet of not bringing along anything you don't need to keep things simple and minimizing failure points.

That aside, the whole Z-system idea gets much more controversial again if you now decide to use the Z-system isolator manifold for technical two tank diving AND use it for your gas switches. With a gas switch using a Z-manifold and an isolator to plug in the deco gas, you've now got two tank valves and an isolator valve involved and are now using what is a very non standard gas switch protocol. Given the number of technical divers who have died due to incorrect gas switches, that's just not acceptable to me. And, even if you get past that, your deco gas system has now went from a very simple tank/first stage/second stage system to a tank/first stage/QD/manifold/second stage system.

Personally, I found that the long/short hose issue on mixed teams was much more easily resolved by just diving with a 5' hose on each tank and thus passed on the Z-system concept. However if I dove it, I'd use a standard stage/deco bottle configuration rather than try to plug it into the Z-system.

 

[JamesK]

Bravo! I agree. Your last paragraph says it all. I have switched over to a two long hose configuration on my SM tanks, an encourage those I dive with to do the same. While side mount allows massive amounts of customization, many aspects can still be standardized

 

[DA Aquamaster]

Bravo! I agree. Your last paragraph says it all. I have switched over to a two long hose configuration on my SM tanks, an encourage those I dive with to do the same. While side mount allows massive amounts of customization, many aspects can still be standardized

We're probably part of what is most likely still a minority of SM divers that think standardizing this in SM would be a good thing, and almost a necessity for anyone who may ever find them selves needing to donate gas to a mixed team diver.

But for some, part of the appeal of side mount is the near total lack of standardization, and they'll only go down that road kicking and screaming.

 

[decompression]

I'm in agreement with DA, the addition of more QC6's on the deco bottles adds unnecessary complications (but less chance of reg failure?). And even the non-isolated manifold could be best applied to single tank SM, but does keep to the scalable tennent of UTD. When I first started SM I looked at the many set ups and didn't notice a prevalent "long hose" on both tanks set up. I thought it through and realized that it made sense other than donating your known functioning reg, although it was functioning just a few psi ago. The iso manifold is just a way of diving SM doubles identical to BM doubles. For several reasons, I use individual reg sets on my deco bottles, less complex, less confusion, reduces wrong gas scenario. If you don't use an iso manifold for SM doubles, I'd also like to see a long hose on each tank. Just my 2 psi.

 

[kundalinichi]

Thank you all for your input, I do agree that even though making stage\deco bottles able to plug into the Z system may reduce the bulk of the regs, but the complexity added is really over the top, as you would have to isolate your main air supply. My current 100% O2 bottle setup is the standard rigging\reg config and I am going to keep it that way. I do have a extra stage reg with QC6 on it if I want to add another stage tank of air, but I don't see that happening anytime soon.

I do have the "bailout" reg. a simple HOG reg with a QC6 female attached, and it does indeed take up a big portion of my drysuit pocket.

Enjoy Chuuk, kevrumbo

 

[rjack321]

This.

Because it acts just as my doubles isolator manifold does, without having to heave the doubles around. I can plug in any tanks I want and have regulator redundancy (although it still can be considered a single point of failure, I know).

Does not answer this question.

Why would you use a switchblock for entirely open circuit diving?

Nobody anywhere is using an OC long hose with a bungied backup on their deco bottles. By using a switchblock this is effectively what you are saying you need in order to dive. That wins you:
an extra QC6 on your deco reg
and the most non-standardized OC deco gas switch protocol you could possibly dream up

Nobody has (ever?) died from lack of a long hose and bungied backup on their deco reg. Lots and lots of people have died from bogus gas switches. You can do the risk vs. reward math.

This is completely unrelated to whether you dive a Z system with or without a manifold (which I personally think is a stupid peice of gear parting the naive with their money)