1st stage fail into BC?

[FFMDiver]

I read a dive story on the web where a major failure in the first stage sent high pressure downstream into LP hoses, overcoming the valve in the power inflator and dumping tons of gas into a BC and sending the diver screaming to the surface.

Can anyone tell me if this could potentially happen on Poseidon Odins or are there built-in prevention mechanisms? Thank you.

 

[CincyBengalsFan]

bmuise once bubbled...
I read a dive story on the web where a major failure in the first stage sent high pressure downstream into LP hoses, overcoming the valve in the power inflator and dumping tons of gas into a BC and sending the diver screaming to the surface.

Can anyone tell me if this could potentially happen on Poseidon Odins or are there built-in prevention mechanisms? Thank you.

This can in fact happen to the first stage.

But it can't happen to the power inflater on the BC. They have weak points designed in them to blow out in case this event was to happen. There is no way a BC power inflater can take much pressure over 200 PSI. I've tested them myself in the shop on my slow days....It just won't happen.

Sounds like a false story to me.

 

[DA Aquamaster]

A second stage utilizing a downstream design will freeflow at anything over the normal intermediate pressure and prevent any excessive air pressure in the low pressure hoses. Same with most pilot valve designs as they are also slightly biased toward one side to open and allow a freeflow if the normal IP is significantly exceeded.

Theoretically, a econd stage with a perfectly balanced pilot valve design would not neccesarily freeflow and could cause a higher than normal IP. But even in that case a runaway power inflator is unlikely. Simple inflators use the same kind of valve that is used in your car tires (a Schrader valve) and more pressure just closes them tighter. Balanced inflators are (like pilot valve or balanced regulators but in the opposite direction) a bit biased toward one side rather than totally balanced and will again close slightly tighter with higher intermediate pressure. The inflator body or an LP hose would blow before the BC would begin filling.

Besides, if it did, all you would have to do is disconnect the inflator. That's one of the reasons why they have quick disconnects in the first place.

 

[FFMDiver]

makes sense folks, especially the disconnect.
Thanks.

 

[matt_unique]

This happened to one of my friend's students. First stage failed and inflated his drysuit like the stay-puff marshmallow man. He was shot to the surface feet first. Watch out for that!

--Matt

 

[CincyBengalsFan]

matt_unique once bubbled...
This happened to one of my friend's students. First stage failed and inflated his drysuit like the stay-puff marshmallow man. He was shot to the surface feet first. Watch out for that!

--Matt

I've never fooled with to many drysuit inflators. Thanks for letting us know about that.

 

[Charlie99]

matt_unique once bubbled...
This happened to one of my friend's students. First stage failed and inflated his drysuit like the stay-puff marshmallow man. He was shot to the surface feet first. Watch out for that!

--Matt

Do you happen to know whether he was using his breathing gas for suit inflation, or if this was a separate argon bottle?

If he had 2nd stage regulators on the same first as his drysuit inflator, then the 2nd stages should have gone into freeflow first.

On the other hand, if someone had a separate cylinder and/or 1st stage for suit inflation, and then failed to put on an overpressure relief valve, what you describe is the normal consequence of a 1st stage failure.

 

[neil]

Charlie99 once bubbled...

On the other hand, if someone had a separate cylinder and/or 1st stage for suit inflation, and then failed to put on an overpressure relief valve, what you describe is the normal consequence of a 1st stage failure.

I doubt it. As DA and Cincy said, overpressure in a BC hose is most likely to close the Schraeder valve tighter. The hose would likely fail first. Do an experiment. Put on some face and hearing protection, gloves and heavy clothes. Put a BC hose onto a HP port on a regulator (yes, you'll need an adaptor), hook it up to a BC and let 'er rip! Let me know if the BC inflates.

Neil

oop, forgot the disclaimer:
Anyone who actually tries this has only themselves to blame for damage or injury, and I don't really recommend it as it is a truly dangerous and foolhardy act. But I still want to know if the BC inflates.

 

[Diver0001]

DA Aquamaster once bubbled...
<snip>

But even in that case a runaway power inflator is unlikely. Simple inflators use the same kind of valve that is used in your car tires (a Schrader valve) and more pressure just closes them tighter.

When it's on the inflator the Shrader valve is pushed into the "always open" position. More pressure won't close it harder unless you unclip it.

R..

 

[DA Aquamaster]

Umm...No. The base of the Schraeder valve lives on the pressurized side of things in an inflator and you have to press the inflator button to open the valve. (essentially the same as pressing the little valve stem in your car tire but with a large button attached.) If it were reversed the inflator button would have to be sealed against the IP as well and would be much harder to press.

In a balanced inflator, the valve stem is o-ring sealed at both ends in a chamber at IP and air is allowed to pass from the IP pressue chamber to the BC side when the inflator button is pressed. The valve it held closed by a return spring. Failure can occur in this situation if the return spring is lost and the inflator button is then pressed as there will be no pressure to return the valve to the closed position. But again, this has nothing to do with failing and inflating due to higher than normal IP.