Free flow - what else happens?

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mark01

Contributor
Scuba Instructor
Messages
256
Reaction score
47
Location
Des Moines, Iowa
# of dives
500 - 999
When a first stage feeezes and causes free flow in the second stage, will it also overwhelm the BC valve and/or the drysuit valve? I've never heard of this happening, but a discussion with my local dive shop left me thinking it might.
 
When a first stage feeezes and causes free flow in the second stage, will it also overwhelm the BC valve and/or the drysuit valve? I've never heard of this happening, but a discussion with my local dive shop left me thinking it might.
The second stage is designed as a fail-safe valve. That is, when there is a failure (such as a frozen first stage), it fails open - resulting in a free flow. The BC and drysuit valves are not of the same design, so the same results do not occur (a good thing as those would not be good results with those valves).

Because the second stage serves as a fail-safe, it is very important that no regulator system be used without one. If no second stage is present, you should include some other pressure relief valve to handle overpressures.
 
There is no guarantee the inflator valve won't fail at any time and for any reason including excessive intermediate pressure.

That's why Deep Sea Supply sells these neat little LP Hose Release Flanges that will make it easier to remove the hose.

https://www.deepseasupply.com/index.php?product=45

Mindnumbing though it is, it is worth the time to think about equipment failures (including multiple failures) and consider the implications.

Richard
 
When the first stage freezes open the intermediate pressure rises, but it's limited by the relief offered when the second stage(s) freeflow. Once my diaphram sprung a leak, and when I was checking the system I found that at around 175psi my second stages would begin free flowing.

My BC inflator was unaffected as it's valve held closed at that pressure.
 
You should also keep in mind that an open inflator valve is resulting in a pressure drop, which could in turn result in a freezing of the inflator. A free-flowing inflator is not a good thing on any dive (accept on the surface when i doesn't really matter) and it could be a bit tricky to release the lp-hose at the same time that you are trying to deflate the BC. It's always a good idea to train these things in a controlled environment so that you are comfortable in handling such a failure at depth. Only use small bursts to inflate the BC or drysuit to minimize freezing. To drop from the surface to let's say 80ft or so before filling up the BC to regain neutral boyancy could be a very bad thing to do...
 
Greetings Mark01 and interesting question! I have never personally experienced a free -flow with multiple failures of BC / DS inflators at the same time. It does not mean it is impossible but sounds like interesting training scenario to me.
We do train for all the failures mentioned and have experienced all of them personally at different times. It can be tricky to disconnect inflator hoses especially with 7mm or dry gloves. Thus the importance of training before a failure happens!
If a first stage is cold enough to freeze any continued flow of air from regulator, DS inflator, BC inflator can result in a free flow. In most of the free flows I have witnessed it was a result of bumping the alternate / Octo. regulator which triggered the immediate free flow. The water temperatures were in the 34º to 40º range and at the 70'-110' depths. It really was handled well and resulted in no harm to anyone and when diving in those conditions one needs to expect failures! It goes with the territory.
The best advice I can offer as others have mentioned is to train for and prepare for the conditions in which you dive. This also means you maintain your gear and make sure it is appropriate for the conditions which you intend to dive. Extra attention to safety checks pre and post dives will help curb inflator failures and adjusting regulators correctly can help reduce free flows. Not rule them out! Watch the placement of your Octo. as well try to think of the best spot where it is accessible but not as easy to bump the purge.
Have fun training and safe diving to you!
CamG Keep diving....keep training....keep learning!
 
https://www.shearwater.com/products/peregrine/

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