How Long For Freeflow To Empty Tank?

[JustAddWater]

Thanks all. I just took what I thought would be "a little break" from homework to board dive. (Coincidently, it is an integrated math/science course for my Master degree.) That was an interesting, challenging, and worthwhile discussion. At first, my shoot from the hip response was that the tank would empty 5 times faster at 5 ATA, but Rick's response makes sense. This reminds me of a thread/discussion we had a couple of years ago, regarding the depth it would take for the gas not to flow from a valveless tank.
I think I'll drop this recent question on my class cohorts tomorrow.
Thanks again,
JAW

 

[truva]

i just want to thank everyone, and Rick Murchison in particular, for a very educational
thread.

basically, there is no significant difference in the rate at which at tank free-flows to empy at the surface or under pressure. SAC issues don't have any relevance here.

again, thanks

The question was:

How long would it take for a freeflowing regulator to empty an AL 80 at the surface?

How much less would this time be at ,say, 5ATM (132 feet??)

The answer depends on which part of the 'regulator’ was experiencing the free flow, some people understand the difference some don’t but then I guess on a thread this long we sometimes lose the point. I find it relatively funny that this seems to be such a hard thing to grasp. See a ‘free flowing regulator’ can have two meanings, you have the first stage free flow and the second stage free flow, 2 different issues with 2 different symptoms.

I described how you could test this in a previous post; a hi-performance first stage regulator will keep up with a free flowing secondary. Does this mean it will empty faster than a tank you just opened the valve on at the same depth, of course not. But it does mean that this secondary free flow will empty the tank faster at depth than the free flow would at the surface.

This is as good as I can explain it; we were discussing 2 different possibilities here and the problem I have is that I am the only one that seems to recognize that. I hope I am not.

Thank you,

Truva

 

[JustAddWater]

I wouldn't be surprised to see some more experiment results on this thread real soon. It will be interesting. Unfortunately I won't be able to test my hypotheses during my next dive trip because it will conflict with another experiment I'm running; how many lobster I can fit in my game bag.

 

[truva]

I wouldn't be surprised to see some more experiment results on this thread real soon. It will be interesting. Unfortunately I won't be able to test my hypotheses during my next dive trip because it will conflict with another experiment I'm running; how many lobster I can fit in my game bag.

Then my regulator starts breathing really wet... Does this when I have a nice grouper too. Not sure why maybe I need to run a few more tests.

Good Luck!

Truva

 

[mac_diver]

Truva

It doesn't matter if it is a 1st or 2nd stage freeflow. The controlling factor is the delta p from the tank to the ambient pressure. Perhaps examining what happens in each case will clarify. In a first stage freeflow, the 1st stage valve is stuck open and the intermediate pressure increases to the point that the second stage is forced open. Both valves will remain open and the flowrate is detemined based on the pressure differential from the tank to the sea minus the pressure losses in the valve and regulator. In a second stage freeflow, the second stage valve is stuck open. The first stage valve will open to deliver air to the second stage. Since the intermediate pressure setpoint will not be reached, the first stage valve will remain open. In this case the flowrate will once again be based on the pressure differential between the tank and ambient. In either case, you better find your buddy and head to the surface.

 

[Big-t-2538]

There are two types of free flows here

One is with a first stage free flow, or just opening a tank valve, the other is with a secondary.

They will behave differently more so with the hi-performance regulators.

Truva

Yes, you are right, both of those cases behave differently compared to each other, but each of those cases will perform the same way (within a negligible difference) regardless of depth.

 

[Hobbs]

This might give some good thoughts and info
http://www.divernet.com/technique/0102twins.htm#top

 

[Big-t-2538]

Sure enough....right from the article...

Knowing that the loss rate varied with cylinder pressure, would it vary with depth? We conducted a further experiment to check this, carrying a spare cylinder and regulator on a dive and letting it blow at 30m. The rate of gas loss was unchanged.

 

[truva]

. In a second stage freeflow, the second stage valve is stuck open. The first stage valve will open to deliver air to the second stage. Since the intermediate pressure setpoint will not be reached, the first stage valve will remain open. In this case the flowrate will once again be based on the pressure differential between the tank and ambient. In either case, you better find your buddy and head to the surface.

The IP set point can and should be reached during a secondary free flow, remember this only has to be at the diaphragm. The regulator doesn’t measure the pressure lose through the regulator to the leak. At the point when the available tank pressure can no longer make the IP set-point inside the measured by the regulator at the diaphragm will the first be totally open. I know that my Apeks regulators will keep up with a secondary free flow but like I said looking at an IP pressure gage you may not believe it. Just because it your pressure gage reads 125 PSI or so it doesn’t mean that the pressure never hits 145 PSI in the regulator where it counts or that's all the air the first stage can flow.

Truva

 

[MikeFerrara]

If the IP is reached in the first stage the first stage will close and the flow of air will stop. No first stage can maintain the preset IP with the second stage flowing.