Youtube vid - free flow

[rjack321]

its an application of the universal gas law. pV=nRT. Since pressure is dropping so does temperature. sure, there may be some friction from the gas passing through, but it is greatly outweighed by the loss of heat energy due to the reduction in pressure.

open one of your tank valves in the garage tonight. after your wife is done yelling at you about all the noise, put your hand on the valve. cold or hot?

The postulation is if your isolator is closed and you open it "will it contribute to a free flow?"

Now assume your regs are correctly configured and you have been breathing your right post and the left is still at full pressure. You open the isolator. The left tank cools. But the left tank's gas and valve temp isn't relevant as you aren't breathing on it (and the person in the video wasn't either)

The temp of the gas in the right tank will minutely rise as the left tank discharges into it and its pressure rises. Ergo opening your isolator during a dive makes no difference on the likelihood of a primary reg free flow.

 

[Adobo]

Imagine how this would have gone if they didn't have that platform to kneel on. One of the dives on my Tech 1 was a skills dive at 100' doing valve failures, OOA, etc, but we had been beat into us the two days prior in 30-40ft. Here our video Tech One Class on the Munson - Yahoo! Video

Question for you - at around the 8 minute mark, the team begins to share gas. After completing the donation, the donating diver goes to the back and the recipient goes to the front. The donating diver then picks up the reel and starts reeling in.

Is that the procedure in tech 1? (It's an honest question. "Go take the class and find out for yourself" is a reasonable response.)

 

[Rick Inman]

Just wondering, which tech agency does drills on their knees vertically?

 

[JeffG]

Is that the procedure in tech 1? (It's an honest question. "Go take the class and find out for yourself" is a reasonable response.)

It should always be the single file procedure.

on a line, you should be single file.

For airshares...the donor is in the rear.
for reeling in a reel....the "reeler" should be in the rear.

 

[JeffG]

Just wondering, which tech agency does drills on their knees vertically?

I have the PADI DSAT video. They show the drills on their knees at the bottom of a pool

 

[jjones9527]

Question for you - at around the 8 minute mark, the team begins to share gas. After completing the donation, the donating diver goes to the back and the recipient goes to the front. The donating diver then picks up the reel and starts reeling in.

Is that the procedure in tech 1? (It's an honest question. "Go take the class and find out for yourself" is a reasonable response.)

That was a partial brain fart on my part (I was the donor). The OOA diver always goes in front, so that the donor can keep an eye on them. The OOA diver is also not going to get very far away, as his life line is attached to the guy behind him. Picking up the reel in an OOA is the wrong thing to do. I should have secured it in place, then followed the line out. Reeling it in takes too much time when gas is now an issue.

 

[jjones9527]

I have the PADI DSAT video. They show the drills on their knees at the bottom of a pool

I think one of the DSAT videos or manuals also says to hook your leg around something to avoid buoyancy changes during drills/gas switches.

 

[Adobo]

That was a partial brain fart on my part (I was the donor). The OOA diver always goes in front, so that the donor can keep an eye on them. The OOA diver is also not going to get very far away, as his life line is attached to the guy behind him. Picking up the reel in an OOA is the wrong thing to do. I should have secured it in place, then followed the line out. Reeling it in takes too much time when gas is now an issue.

That's what i figured. In that scenario, it seems the reel would become "disposable".

Incidentally, I wish getting copies of videos from one's class was more common. It seems like there are all kinds of learning opportunities just by re-reviewing the footage.

 

[jjones9527]

Yeah, every time I look at that footage it looks uglier and uglier, but it reminds me of stuff to look out for. Our instructor actually gave us the video and encouraged us to post it up.

 

[lamont]

its an application of the universal gas law.

not quite the whole story.

pV=nRT. Since pressure is dropping so does temperature.

the pressure is dropping, but the volume is increasing. to first order that is much more important than the temperature drop (up to around a 20x drop in pressure, less than a 2x drop in temperature).

technically what happens is here:

Adiabatic process - Wikipedia, the free encyclopedia

since there is limited heat transfer between the expanding gas and the tank it is a nearly isoentropic or adiabiatic process. as the volume expands the work done by the expansion must be offset by a loss of internal energy (decrease in temperature).

if you let a gas expand slowly enough you will get enough heat transfer continuously into the system so that it follows an isotherm instead of an adiabat, the temperature of the gas will not change (but heat must be transferred from the surroundings). the cooling of the gas is because you expand it fast enough so that its temperature has to drop because the surroundings don't transfer heat into it fast enough.