How Long For Freeflow To Empty Tank?

[ianr33]

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??)

 

[H2Andy]

it will go roughly five times as fast at 5 ATM than whatever it is at the surface (actually, it's around 5.1 to 5.2 times faster).

not sure how long it would take at the surface, though. try it out and let us know!

 

[ianr33]

it will go roughly five times as fast at 5 ATM than whatever it is at the surface (actually, it's around 5.1 to 5.2 times faster).

That was my first thought as well,but thinking about it some more I dont believe that is true.
If the Intermediate Pressure (I.P.) on the reg is set to say 150 psi then at the surface gas will be exiting the first stage at 150 +14.7 = 165 (round figures)

At 132 feet the gas leaving the first stage will be at 150 + 132/33*14.7 =209 psi

So I would expect the tank to empty faster by a factor of 209/150 = 1.4 i.e. it would only take 71% (1/1.4*100) as long to empty at 132 feet .

Am I on the right track here??

 

[DA Aquamaster]

I emptied a nearly full steel 72 at 140 ft in around 30 seconds with a MK 15 D400. It was a LOT faster than I expected.

I also recently tested a MK 20 D400 at the surface and found that it dumped air at about 40 cu ft per minute, so I'd estimate it would take two minutes to empty an AL 80 at the surface with a high performance reg.

I think you are on the right track in that the flow rate of the second stage is dependent on the IP. But even assuming it is a linear or nearly linear function (which I suspect it is) you would still need two actual data points to accurately relate the increase in flow rate with the increase in IP. With only one data point, you are not able to determine the slope of the linear function.

I have a new piston coming for one of my Mk 20's. When it arrives I may run a flow test with the D400 at as low an IP as I can get from it and then repeat the test at 145 psi and see if there is a measurable difference. Otherwise it will have to wait until the ice is off and I can run a flow test at 100' to compare with one just under th surface to get a significant difference in IP.

 

[ianr33]

Hi DA Aquamaster

Thanks as always for your insightful comments. And on 2 boards as well,practically simultaneously. I am impressed !!!

 

[H2Andy]

i was working backwards from the NOAA chart for air consumption at depth, assuming a free flow would be similar.

i don't see how it would be different. any thoughts?

 

[truva]

That was my first thought as well,but thinking about it some more I dont believe that is true.
If the Intermediate Pressure (I.P.) on the reg is set to say 150 psi then at the surface gas will be exiting the first stage at 150 +14.7 = 165 (round figures)

At 132 feet the gas leaving the first stage will be at 150 + 132/33*14.7 =209 psi

So I would expect the tank to empty faster by a factor of 209/150 = 1.4 i.e. it would only take 71% (1/1.4*100) as long to empty at 132 feet .

Am I on the right track here??

You need to think of it in absolute pressure if you are going to try that, but you do not seem to account for the change in mass…….

Truva

 

[H2Andy]

I emptied a nearly full steel 72 at 140 ft in around 30 seconds with a MK 15 D400. It was a LOT faster than I expected.

I also recently tested a MK 20 D400 at the surface and found that it dumped air at about 40 cu ft per minute, so I'd estimate it would take two minutes to empty an AL 80 at the surface with a high performance reg.

by my calculation, it will take 2.5 minutes to empty at the surface, based on
a 30 second empty time at 140 feet.

we're not that far off

 

[truva]

would be easier to use because a “balanced” regulator should put the same pressure out relative to ambient no matter what that is. The only thing that changes here is the density of the gas. It should empty slower but not so you would really be able to tell.

Truva

 

[MikeFerrara]

Just look at it based on fluid flow principals.

The flow out of the tank is dependant on the pressure differenntial and the resistance to flow inbetween. All a reg can do is add resistance to flow from the inside of the tank to the outside world.