How Long to Drain a 80 Cubic Foot Cylinder - 4 Failures

[grf88]

Untli I checked just now it never occurred to me that my Faber steels didn't have a burst disc - although it's obvious why not.

In North America the valves on Faber Cylinders require a burst disk.

 

[Bob DBF]

my assumption is that if you can't figure out how to oral inflate a BCD on the surface, you probably would be over weighted. Most Newbies start out that way.

Yeah, just pointing out the pluses of getting the weight right as fast as possible, preferably on the first shallow dives after OW class. It's not just theory it can save your a$$.


Bob
----------------
I may be old, but I'm not dead yet.

 

[abnfrog]

The fastest I have seen a tank drain was when my son's first stage diaphragm failed at 80 feet on a high current wreck in the St. Lawrence.

another self rebuild ......hmmm

---------- Post added March 17th, 2014 at 09:54 AM ----------

Fundamentals Of Constant Mass Flow Gas Systems - Rebreather World

This article goes into detail on why you won't see much change with depth on HP failures. (There are a number of other good articles that can help you understand the concept, this was just the first I ran across in a quick search for a decent link.) Gas will be held back by the narrowest point in the system. Flow of gas is generally limited to the speed of sound, so once the gas leaving the tank reaches that speed the flow rate will remain essentially constant. Gas will drain from the tank at a fixed rate until it crosses a a certain threshold. For example, if you fully open a tank valve: (numbers have been completely made up)
A tank at 00 feet will drain at 20 cubic feet per minute until the tank pressure reaches 100 psi, at which point the flow rate will begin to drop.
A tank at 99 feet will drain at 20 cubic feet per minute until the tank pressure reaches 110 psi, at which point the flow rate will begin to drop.
A tank at 198 feet will drain at 20 cubic feet per minute until the tank pressure reaches 120 psi, at which point the flow rate will begin to drop.
So if the flow rate only begins to change at around 100 psi, it's understandable that barely any difference will be seen between a tank draining at the surface and a tank draining at 300 feet.

I know this has been touched on already in this thread, but for the more curious among us I though you might like to better understand the physics behind it.

most people don't have any concept of mass flow ....sonic or sub sonic orifice ...they should read above ..any in reality who cares 60 seconds verses 90 seconds its still fast that's why we train to isolate and shut down