I was wondering about the mechanics of a freeflowing regulator, and should this happen, how to overcome it.
Does the freeflow happen at the 1st or 2nd stages, or both, simultaneously? Is there any way to tell the difference when it happens?
It can happen to both, 1st stages could stick open, but this is really rare and normally shows up immediately after rebuild, more often you might see IP creep from a leaking HP seat in the 1st stage, in this case, you won't get a free flow, but a burp of air from the downstream overpressure valve (aka 2nd stage).
The mechanics of a 2nd stage freeflow is pretty simple, essentially the second stage works as a demand valve. You create demand by inhaling, this applies a differential pressure across the diaphragm, which then moves and pushed the lever which opens the 2nd stage valve and feeds you air. In a non-failure mode of freeflow, the diaphragm is moved by water flowing on the diaphragm which is enough to open the valve and of course since most high performance regulator have a venturi to reduce the work of breathing, this venturi can open the valve further making the freeflow worse. To correct this, turn the regulator mouthpiece down or stick your thumb in the mouthpiece which will put positive pressure on the diaphragm closing the valve and stopping the freeflow.
if that doesn't stop the freeflow you probably have a failure, as far as failure are concerned this is a VERY GOOD THING, its referred to as a fail-safe, as the reg fails to a safe condition, giving you more air not less. If you have this type of failure you need to take it to a qualified service shop for repair.
If it's the primary reg diaphram that is stuck open, can't you switch to your octo and ascend?
best method is to breathe off the freeflowing reg, the air is coming out anyway, use it as you ascend. its a good skill to practice, by holding down the purge button. just don't practice long as air will deplete quickly.
I've read that free flows happen more in colder water. Is this true?
this is called freezing, it occurs in cold water due to adiabatic cooling of expanding air, the colder temps can freeze any moisture in the air (tank) and hold the valve open causing a freeflow. the best solution to that is shut off the air, wait about 15 seconds for the reg to warm and slowly open the tank valve, it should fix itself. To prevent it, always get your air from reputable sources, and minimize use of your inflator or other high air demand items. This is often a practiced skill in ice diving courses.
If it's your 1st stage, do both your primary and octo free flow? What then? I know there is a way to breathe off a freeflowing reg, but I'd like some insight into how, etc.
most likely it will only freeflow off your primary, not the octo. This is because the primary is generally tuned to better performance, which includes a lower cracking pressure, which means it will freeflow first, once the pressure is relieved the other reg is unlikely to also freeflow.
As for breathing off a freeflowing reg, please consult your training book, this is a basic skill that is taught during OW, and is a required performance skill for PADI, so I assume it is in most other agencies as well.
This has not happened to me yet, and I get my reg serviced yearly. But just in case......
Thanks in advance,
Lisa
As far as someone dieing during a CESA, well I am not a forensic scientist nor do I have facts of the case. But, assuming a diver is within their no-decompression profiles it is a conservative factor built in the dive tables to allow for a CESA safely. But, if you don't exhale appropriately during the ascent you will embolize and that will kill you. Remember, CESA= normal ascent rate, keyword being "controlled".
