Regulator failure modes

[InTheDrink]

Ok so I've asked various questions here on what to do if this gas 'emergency' happens (e.g. blown tank o-ring) or that happens (e.g. free flow) and the responses have been very educational and frequently interesting/amusing/riveting.

Thus far my questions/posts haven't conjured up any regs/equipment failure scenarios that will completely and immediately deny a diver gas [for the purposes of this post I am excluding simply running out of gas through not checking gauges or not having gas turned on in the first place].

So what am I missing? Are there any types of equipment failure that will immediately deliver no gas from either primary or backup second stages? Is there anything that can go so badly wrong with the first stage that will completely stop it delivering gas to the seconds?

Thanks,
J

 

[fppf]

Well, there are some older second stages that where "upstream" designs. Almost all first stages still use an "upstream" design.

With an upstream design, the valve is located on the high pressure side of a regulator and opens into the high pressure side. With the older second stages if the first stage had an IP creep they would lock closed. Newer second stages all use down stream designs so they will free flow in the even of IP pressure increase.

With the upstream first stage if the transfer pin between the sensing diaphragm and the seat broke it would shut off all gas supplies.

Failures that would intently and suddenly cut off all gas is rare IMHO. But then again, anything can happen, this stuff is man made and no one is perfect.

 

[Joti]

not really a reg fault, but I've heard of crap in the tank either abruptly or immediately cutting off air during a dive when it migrates its way to the outlet. I think tanks have some kind of dip stick type thing to avoid this but sometimes they get removed.

 

[Web Monkey]

So what am I missing? Are there any types of equipment failure that will immediately deliver no gas from either primary or backup second stages? Is there anything that can go so badly wrong with the first stage that will completely stop it delivering gas to the seconds?

As mentioned, "crap in the tank" will do this, especially if there's no dip tube or it fell out. There are a number of incidents on SB where divers went head-down, and were immediately OOA.

More creepy than being OOA, is that a tank can be so contaminated that it can actually clog the valve or first stage inlet filter. I only have one set of lungs and would prefer to not be the recipient of random tank contamination.

Terry

 

[walke121]

not really a reg fault, but I've heard of crap in the tank either abruptly or immediately cutting off air during a dive when it migrates its way to the outlet. I think tanks have some kind of dip stick type thing to avoid this but sometimes they get removed.

That was the only thing I could think of...

 

[300bar]

fppf might want to look at his post again. upstream and upstream.


J. don't worry about this to much,a major failiure will NOT happen.
All modern regs. are build as failsafe. ie. when poo hits the fan,your reg will start to freeflow. Never will it shut down. There is only one way for a (normal) balanced 1st stage to shut down and that is when some one removes the pin controling the pressure transfer. IT'S NOT GONNA HAPPEN.

 

[300bar]

As mentioned, "crap in the tank" will do this, especially if there's no dip tube or it fell out. There are a number of incidents on SB where divers went head-down, and were immediately OOA.

More creepy than being OOA, is that a tank can be so contaminated that it can actually clog the valve or first stage inlet filter. I only have one set of lungs and would prefer to not be the recipient of random tank contamination.

Terry

I'm sorry Terry, BUT have you ever seen such a tank.

Not very likely, because it takes a decade or so (with severe misuse ie wrong/bad filling), to get so much gue in to a tank, before it will clog up a valve. I only know of 1 insident, and that tank had not been used for over 15 years.

 

[DA Aquamaster]

I am aware of three possible failures where gas delivery could be interupted.

1. I had a buddy who had ice form in the second stage on an ice dive to the point that it blocked the lever and failed closed. A very rare failure, but maybe a good reason to avoid a plastic cased and plastic air barrel regulator if you are ice diving.

2. I know a diver who had a reg fail due to a lever with less than adequate tension that allowed the poppet to slip off the bearing surfaces on the poppet. Again this result in a failure to deliver air, and it is the only failuire of this type I have seen or heard of in about 20 years.

3. I had another buddy who notred the reg stopped delivering air in a head down position. On the surface with the reg inverted, and the purge depressed the reg delivered a cup or so of really dirty looking water. Obviously due to a lot of water in the tank and a missing dip tube.

Failures one and two just require you to switch to the octo and are not life threatening. Failure number three is intermittent in that it only occurred in a head down position, so it again did not result in a total failure to deliver air.

 

[InTheDrink]

Hey Evert, freaky - was just thinking of you. That of course is worrying in itself.

I guess my over arching point was to understand just how badly things can go wrong when diving and the primary answer I have is 'not that bad'. This is not complacency, this is trying to get a thorough understanding of as many of the problems that could occur and their remedies and no problem that I've so far suggested is so bad as to require an earlier solution I considered (breathing BC bladder). I now understand why that solution is neither a good one nor necessary.

Crap in your tank is clearly a hazard and in my experience no-one checks their (rental) tanks apart from how the gas smells or occasionally like me, a CO test too. Debris without a dip stick would clearly present a hazard but like 300bar says, how frequent is this really? I'll still bear it mind tho and try to remember to shake my tank to hear how it sounds.

That aside then - am I cool to say to a newbie, when asked, that there are more or less no ways in which you will run out of gas because of equipment failure in which you won't be able to reach the surface. Keep an eye on your gauges frequently and make sure your gas is on and you'll be just fine.

Silly tho it may seem, it's a reassuring understanding. At least for me it is.

J

 

[Mr Carcharodon]

I'm sorry Terry, BUT have you ever seen such a tank.

Not very likely, because it takes a decade or so (with severe misuse ie wrong/bad filling), to get so much gue in to a tank, before it will clog up a valve. I only know of 1 insident, and that tank had not been used for over 15 years.

I have and have heard reports of others. It happens.