fail safe

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beche de mer

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Is scuba equipment designed to fail safe.


In other words, if a second stage fails, will it free flow, or can it cut off your gas?

What kinds of failure can occur with a first stage?
 
The short answer is, it depends on the regulator.

Apeks regs (that is what I dive) will freeflow upon failure. I believe certain Poseidon regs will shut down when failed. There may be others also that do this.

When you hear of people speaking of "upsstream" and "downstream" reg, this is what they are talking about.


beche de mer once bubbled...
Is scuba equipment designed to fail safe.


In other words, if a second stage fails, will it free flow, or can it cut off your gas?

What kinds of failure can occur with a first stage?
 
MOST second stages fail open. Like DD said, Poseidon regs are known to fail closed - although some of the most recent models may not.

With first stages, it depends on the problem... But most problems that I know of will cause a first to fail closed.

That's why simple is good... The simpler, the better. :)

There's several ways to combat these problems:

1. Have your regs serviced regularly. Of course, this means no guarantees... In fact, most reg failures that I've known of have happened soon after a service. :confused: Nonetheless, servicing and preventative maintenance can go a long way to keeping your regs functioning.

2. Don't dive solo. Have a buddy that's skilled and dependable so that you have a secondary source of gas. Those that dive solo often use a pony or a SpareAir, but those units have a reputation for being less than dependable. Opinions vary, so do your research and make your own choice.

3. Dive with a manifolded pair of doubles whenever you're in a situation where an ESA is impossible. A manifolded set of doubles gives you two second stages, two first stages, two bottles of gas, and the ability to switch, on the fly, to use whatever is working at the time. For example, a failed first stage would not prevent you from using the other... And still be able to allow you access to all of the gas available.

4. Don't forget that your BC inflator can supply you with gas in a pinch... That is, in a way, you actually have three second stages.

Hope that helps. :)
 
1. Bad captured o-ring on a DIN connector.
2. First stage freeze-up when diving in cold water.
3. Sediment/rust clogging a first stage filter.
4. A mechanical failure of some sort--a spring breaks, piston snaps, etc.
5. Defective materials cause a spectactularly catastrophic failure.
 
Even with a downstream 2nd, a lever failure leaves you SOL. Extremely unlikely failure so long as everything was installed correctly. If you are diving without a redundent gas source, you need to be real comfortable with your ability to do a CESA.
 
A Poseidon Odin regulator has an upstream 2nd. The 2nd stage is called a "Jetstream". An overpressure from the first stage will not cause a free-flow, but will instead open a spring loaded relief valve where the hose joins the Jetstream 2nd stage. Were this to happen, you could still breathe through the 2nd stage. You can test the action of the relief valve by pulling on the 2nd stage while the regulator is charged. You will hear air escape when you make a firm pull. The Poseidon is a darned good regulator. It is extremely dependable and will deliver air like no other. For deep, hard diving it is among the best.
 
SeaJay once bubbled...
. Those that dive solo often use a pony or a Spare Air, but those units have a reputation for being less than dependable.
Sea Jay,
I've heard the many Spare Air nightmare stories, but I have not heard of pony bottle failures and am not familiar with this reputation. How is a pony bottle less dependable than any other? How does it's size effect it's dependability? Do you have any stats behind this claim? Not trying to give you a hard time here, I'm really interested.
Thanks!
 
who dives with a 6cf pony nearly cacked himself this summer.

He was on a deep NDL dive, 130' to be exact, spearfishing, and was about out of time. He also was fairly low on gas.

He decided to unstick the anchor from the wreck. Here is where things got nasty; as he huffed and puffed he consumed the remainder of his gas supply in his single tank!

So he switched to the pony; fortunately, he was essentially done with the unsticking, and he began his ascent.

Unfortunately, his breathing rate was SEVERELY jacked from the exertion of unsticking the anchor. At 60' he ran out of gas AGAIN - and this time he was REALLY out, having consumed his pony bottle's contents.

VERY fortunately for him, another spearo was on the line doing deco at 30' with plenty of remaining backgas and he was able to obtain gas from him and complete a normal ascent profile with stops.

Had he been forced to make a CESA from the 60' level, he might have well gotten badly hurt, as he was out of NDL time and had been puffing like a freight train down there, plus, his ascent rate wasn't quite "within the lines" either from what I understand. They were some 20nm out in the gulf at the time - not exactly the right place to have a serious DCS or AGE problem.

Fortunately there was no injury or worse, but he learned that a small pony is frequently not enough.

I have no idea if he has invested in a larger one or given some serious thought to his gas management strategies - you'd hope he's done both!
 
Rick Inman once bubbled...

Sea Jay,
I've heard the many Spare Air nightmare stories, but I have not heard of pony bottle failures and am not familiar with this reputation. How is a pony bottle less dependable than any other? How does it's size effect it's dependability? Do you have any stats behind this claim? Not trying to give you a hard time here, I'm really interested.
Thanks!

I think SeaJay was probably referencing the reliability of the Spare air rather than the pony concept as well. In general pony reliability is no better or worse than a single tank scuba configuration. With the same regulator and valve design, the only difference between your pony and your primary air source would be the size of the tank.

You do want to be sure though that the pony reg is well maintained, tested frequently and has sufficient performance to support you in a high air demand situation at depth. For deep diving your primary reg should be as good as your primary.

Tank size is also important and if I were King, pony bottles less than 19 cu ft would not be sold as a pony of less capacity is often not up to the job and will get divers into trouble with the false sense of security they offer. The example given above is an excellent example of how that can happen and why you should never plan on using the gas in your pony. In my opinion, 30 cu ft should be considered the minimum pony size for deep diving.

Setting up and testing the pony over several dives also uses air from the pony and you will need to top it off occassionally and should check the pressure before every dive. A large pony has an advantage here as it can go longer between top offs before the capacity is reduced to the point where it can no longer be considered adequate. Better yet, practice actually using your pony on the last dive of the day now and then and then get it refilled.
 
Genesis once bubbled...
who dives with a 6cf pony nearly cacked himself this summer.


Everyone had the choice to carry what ever size bottle they want but if I'm carrying my pony, it is 30 cf, I just feel better with the extra gas. It is a bit bigger than a 6 cf but I know that I can ascend from any of my dives with it. If I can't then I have definitely been working too hard.
 

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