1st and 2nd stage freeflow questions

While doing some testing w/ my new rig last week I was brushing up on some skills and one of them was simulating a free flow of the 2nd stage w/ purge valve. I recalled a few years ago during OW PADI cert we were sipping air and I got competent at it. However I proved how rusty I was doing so w/o practice for some time. So for the sake of argument I left the reg in my mouth and held purge and I was able to breath just fine off the freeflowing regulator. My questions pertaining to a 2nd stage free flow are as follows:

1. Why does PADI teach the sipping method when you can breath off a freeflowing reg w/o a problem.
2. Do you feel it is safer to pull a freeflowing reg from you mouth that is providing air but making a bunch of bubbles or take it out of your mouth and hope you've mastered sipping a freeflowing reg? I know if I was in a situation where I had to sip under duress w/o practicing for 2 years (like my simulation last week) I probably would have drown.

I'm also curous about 1st stage free flows. My understanding of this is that it is usually due to freezing but if this happens am I understanding correctly that the entire tank pressure will be on the seat of the regulator? Can the regulator seat actually withstand that kind of pressure?? What would occur If I were to breath a tank w/ a 1st stage free flow situation? Would the excess air just flow out the exhaust as a 2nd stage freeflow does? At 20 times the normal operating pressure at the regulator I'm really curious what happens w/ a 1st stage freeflow.

Thanks

Dave

TT_Vert:

1. Why does PADI teach the sipping method when you can breath off a freeflowing reg w/o a problem.

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I've been wondering that for a few years since it was created. PADI is not alone in this.

You have learned a simple and useful skill. Possibly the reason for their method is where you said, "However I proved how rusty I was doing so w/o practice for some time".... Maybe many people find these skills hard to retain? What would be harder to remember? The simpler method of "keep it in your mouth and breathe what you want", or take it out and "sip" as needed?

You are correct. But agencies will teach what they teach....

TT_Vert:

I'm also curous about 1st stage free flows. Can the regulator seat actually withstand that kind of pressure??

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On the second stage? I would instead worry about the LP hose.

If the first stage is free flowing, then there is no pressure on the HP seat because it is open. A free flow in the first stage is caused by the HP seat getting stuck in the open position for some reason. The way the first stage works is that the intermediate pressure is balanced by the main spring. When you take a breath, the IP drops a bit and the main spring's force becomes the greater of the two. The spring then pushes the HP seat away from the orifice and allows air to flow from the tank until the IP rises again. If you breathe a tank down to a pressure below the IP setting of the reg (135 to 150 psi) the HP seat opens and stays open. During storage, there is no IP and the HP valve is in the open position until the reg is put on the tank and pressurized. Even then, there isn't much pressure on the seat itself. The HP seat is never exposed to the entire pressure of the tank. The only exception to this is, possibly, a broken main spring and I'm not sure about that. In any event, a broken main spring means no air flow, not free flow.

You don't have to be concerned about the LP hose during free flow. The second stage LP seat is in a downstream valve and any over pressure condition simply pushes the seat open and lets the air flow through and you have your free flow condition.

Is there some cutaway or diagram of the first stage on this site somwhere I could take a look at to visualize the operation of the first stage to better understand things?

Thansk
Dave

Paladin:

You don't have to be concerned about the LP hose during free flow. The second stage LP seat is in a downstream valve and any over pressure condition simply pushes the seat open and lets the air flow through and you have your free flow condition.

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Unless you run across an old vintage upstream second and test it without knowing what you have. It was only amusing in hindsight and I did learn a lot more about regulators, and testing.

TT_Vert:

Is there some cutaway or diagram of the first stage on this site somwhere I could take a look at to visualize the operation of the first stage to better understand things?

Thansk
Dave

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Scuba Regulators
It shows the downstream as a first stage but you can change HP air to IP air and IP to breathing and it could be a second, the concept is the same.



Bob
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PhD School of Hard Knocks

This might help.

File:First stage cutaway parts.gif - Wikipedia, the free encyclopedia


Animated:


http://upload.wikimedia.org/wikipedia/commons/c/c8/First_stage_animation.gif

TT_Vert:

1. Why does PADI teach the sipping method when you can breath off a freeflowing reg w/o a problem.

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PADI only requires you to breathe from a free-flowing regulator. Sipping is just one technique that many instructors offer. If keeping the mouthpiece partly in your mouth works best for you, do it.

knotical:

PADI only requires you to breathe from a free-flowing regulator. Sipping is just one technique that many instructors offer. If keeping the mouthpiece partly in your mouth works best for you, do it.

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I was keeping the entire mouth in my mouth.

TT_Vert:

I was keeping the entire mouth in my mouth.

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I do it the same way. I just push my tongue to the front to help control the airflow into my mouth.

TT_Vert:

I was keeping the entire mouth in my mouth.

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Some 2nd stage may deliver so much gas that a divers may not be able to simply keep the mouthpiece in their mouth. They will deliver much more air than you can use and all the excess often can not exit through the exhaust valve. So the diver must allow the rest to exit through his mouth. A slip up can result in the regulator being launched from the diver's mouth if the lips are not sufficiently relaxed to allow the excess to vent.

I have found that I can hold the 2nd in my hand to keep it under control and keep the mouthpiece in my mouth with my mouth open and relaxed. But it might take a little practice.