Second stage connection

[Jack Hammer]

So my concept is as follows:

Different idea for independent doubles

One of the drawbacks of independent doubles (IDs) is the regulator changes. Removing a regulator from one's mouth at 100+ feet is something that some people might advise against.

It can also create the false impression that you may be in trouble. A DM once told me post dive that when he saw me drop my regulator from my mouth @130FSW he began moving towards me thinking I may be narc'd and in need of help. He came over to me after the switch and gave me the OK sign which I returned not knowing why at the time. Anyway, I'm going to rig a configuration that eliminates the regulator switches while using my IDs. It could also be used with sidemount.

Gear needed is a second stage that can be connected at the same time from both the right and left ports, 2 on/off inline valves, 2 90 degree elbows, and 2 40" or to suit LP regulator hoses for BM (SM would be shorter); also 2 1st stages with identical IP's. Also 2 overpressure reliefs one for each 1st stage. Since only one second stage is used, a second 2nd stage is mounted on the right hand 1st stage for an octo. For complete redundancy an AIR type inflator can be added to give the diver a third 2nd stage option .

The left side 1st stage is connected to the left side of the 2nd stage by the elbow assembled with the on/off valve . The right tank is connected to the right side of the same 2nd stage the same way. The 2nd stage is necklaced and the LP hoses are routed under the arms. Tank switches are made by turning the inline valves on and off instead of switching regulators.
There maybe a slight reduction in redundancy but the diver still has 2 second stages that can access either tank thru separate 1st stages so the reduction is slight.
The on/off valve and elbows can be seen as weak points but after using both for 5 years without issues, I have confidence in their reliability. Here are some pictures:


View attachment 674576 View attachment 674577 View attachment 674578

It's like a homemade Z manifold with more options and fittings. I think AG would be proud. This could become quite the rage in the SM and ID communities. I say pair it with a 95# dual bladder bungee wing for perfection

 

[AfterDark]

Just curious what would happen if both LP switches were closed at the same time?

That means the 2nd stage isn't being used no air the switches are closed/off. The same as what happens when you close the tank valve.

 

[AfterDark]

If both valves are left open, one tank will empty slightly faster than the other, as it is impossible to tune the two first stages exactly the same.
This can be a problem or bot.
For me it would not be a problem, provided that one has two SPGs and checks the two pressures often.
When one tank is empty the other will continue supplying air.
In my opinion those two inline valves are superfluous...
The sustem will still be more redundant and safer than using a standard AL80 with just a single valve and a single first stage...
Un fact I am not happy with such a basic setup.
I use a 15 liters steel with double valve and two DIN first stages (MK5) and two second stages (a 109 on the right and a 129 on the left).
Which in the ends provide more or less the same degree of redundancy as the system with an Air1 with two hoses described here.

Don't forget there is also a 109 on the right hand 1st stage to give added redundancy to the system. There are 2nd stages in my setup, only one gets used on an uneventful dive. My aim is to
eliminate regulator changes without sacrificing the redundancy of ID's. I'm not trying reinvent the wheel. Cut from my post: Since only one second stage is used, a second 2nd stage is mounted on the right hand 1st stage for an octo. For complete redundancy an AIR type inflator can be added to give the diver a third 2nd stage option .

 

[AfterDark]

Hey anybody notice the nice OMS double tank adapter in my 1st picture? I found that on Ebay 5-6 years ago, haven't seen another since.

 

[Open Ocean Diver]

That means the 2nd stage isn't being used no air the switches are closed/off. The same as what happens when you close the tank valve.

Sorry meant open, both open.

 

[James79]

Sorry meant open, both open.

If both are open, the 1st stage with higher IP will provide all the air unless the demand is high enough to drop the IP to the lesser 1st stage's IP. In theory, @AfterDark could simplify the system by intentionally setting one first stage with higher IP (like a 10 psi split) and only putting a shutoff on the hose from that one.

Just a thought.

Respectfully,

James

 

[AfterDark]

If both are open, the 1st stage with higher IP will provide all the air unless the demand is high enough to drop the IP to the lesser 1st stage's IP. In theory, @AfterDark could simplify the system by intentionally setting one first stage with higher IP (like a 10 psi split) and only putting a shutoff on the hose from that one.

Just a thought.

Respectfully,

James

If I understand correctly what you are suggesting the system would lose it's independence, it would be like an old school manifold on 2 tanks with no way to isolate one tank from the 2nd stage. If the left 1st stage should fail and there is no switch on that side I can't stop the free flow so it vents out OVR on the 1st stage instead of the 2nd stage. no dice.

 

[James79]

If I understand correctly what you are suggesting the system would lose it's independence, it would be like an old school manifold on 2 tanks with no way to isolate one tank from the 2nd stage. If the left 1st stage should fail and there is no switch on that side I can't stop the free flow so it vents out OVR on the 1st stage instead of the 2nd stage. no dice.

Good catch, I spoke without thinking it through enough! I guess you could still simplify it operationally by running an IP split and leaving the lower IP inline shutoff open, only closing it as an Isolation response... But then you have the complexity of managing maintenance for the IP split.
I guess just forget my suggestion! Lol

 

[AfterDark]

Sorry meant open, both open.

Then the tank with 1st stage with highest IP drains before the other. This of course would be apparent on the SPGs, I normally switch tanks every 500psi so I would notice sooner rather than later which is one of the reasons I do 500 psi switches, it forces me to look at the SPGs early and often. Also the 1st time I went to switch tanks via the inlines I would find both up/on and correct. Either way is fail safe.

 

[AfterDark]

Evidently these years of being able to continue to breathe haven't taught you much in the way of failure modes, statistical bias, or the ability to have a discussion without resorting to "I'm still alive and thus your opinion is invalid" attacks. Of note, if you don't maintain that clusterfhcuk of shutoff valves around your neck, one of them will fail and continue to flow even when "closed."

To confirm, rather than:
"adding an isolator manifold" of four static o-rings and a seat and removing a HP hose, SPG, and two dynamic O-rings (as well as the "need" of the swivels on your first stages)
OR
Being comfortable (or diving with a group that is comfortable a la not the divemaster interaction at 130' ) with you switching regs on a non-manifolded setup

You're chosen:
1) a unicorn reg
2) two elbows (2 static o-ring each)
3) two shutoff valves with two static and 2 dynamic o-rings each
4) an additional LP hose
5) a donation reg that you're not actively using as an octo on your right side
6) potential loss of ability to turn off left hand bottle because of its angle behind your skull
7) and considering adding an Air2 because you think it increases redundancy
And all of the above in addition to yoke first stages and your five after market swivels on your first stages?

Just making sure this is laid bare before someone attempts to mimic your setup and hurts themselves.

Well, unless someone can come with another unicorn regulator there's not much chance of mimicking my setup now is there? That's why it's my setup and not some eles's setup.

Don't forget the spool valves in the 2 SPGs and the 4 O rings on 2 HP hoses. I've got an inflator hose with an O ring and a connection that can both fail. If I don't shave my mask leaks too!