What is The Purpose of A Free Flow?

[shotthebreeze]

Hi guys,

I understand that a regulator that free flows is usually in the best interest of a diver if something goes wrong with that piece of equipment. I was told to consider it a saftey feature. Now, what is the reason for the free flow if you flip the mouth piece upside down? Its it to simulate if you spit it out of your mouth for some reason?

 

[cudachaser]

Huh???

 

[shotthebreeze]

I confused myself when I wrote that question out. Let's stick with the basic question...Why does a regulator free flow when it hits the water upside down?

 

[Stingray Brett]

The Pressure is pushing the air up so its not actually a safety feature.

But when it free flows without doing anything they do that so u still can breath instead of not releasing any air and you dieing.

Or thats at least what i think is the reason

 

[Charlie99]

A 2nd stage freeflows when the mouthpiece is up because there is pressure on the diaphram at the front.

What you are probably missing is a basic understanding of how a 2nd stage regulator works. There is a big rubber diaphram in the front of the regulator. It is attached by a lever to a small valve and valve seat. When you suck on the regulator to get some air, that suction pulls in the diaphram, which opens up the valve and delivers the air. Putting the diaphram face down while the mouthpiece is out of the water (or if the reg is full of air) puts the same sort of pressure on the diaphram and causes the reg to deliver air. BTW, the purge button of a regulator is nothing more than a way to manually push in the diaphram.

You can avoid freeflow by adjusting the regulator so that you have to suck harder to get the air. This is normally done with the octopus regulators, and that's why they don't freeflow when out of your mouth. But this means that you have to suck harder to start the air flow. Some regulators have an "cracking pressure adjustment" knob that sets how hard you have to suck on the reg to start the air flow.

There is another adjustment on many regulators call "venturi". To make breathing easier, the air that comes out of the regulator is directed against a little plate that tends to pull in the diaphram some more. (Or it can be done with a shaped passages and the venturi effect, but it has the same effect as if air were hitting a little plate that pulls on the diaphram.) Often this venturi effect can be switched on and off with an adjustment that is marked "surface/dive" or "+/-".

Does this answer your question? Or just confuse you more?

Charlie Allen

 

[spectrum]

Hi guys,

I understand that a regulator that free flows is usually in the best interest of a diver if something goes wrong with that piece of equipment. I was told to consider it a saftey feature. Now, what is the reason for the free flow if you flip the mouth piece upside down? Its it to simulate if you spit it out of your mouth for some reason?

I think you're trying to get too many answers with one question.

Nearly all regulators are designed to fail to a delivery (free flow) state. This is in effect a safety feature. If something is going to go wrong you are better off with lot's of air for a little while than getting shut off cold turkey.

When you flip the second stage mouth side up in the water you are placing the diaphragm an inch or 2 underwater and above the mouthpiece, those few inches of water column pressure simulate the draw of your lungs and this causes the regulator to deliver air. Once you start the flow the venturi effect is all to happy to keep it going. I don't see that behavior as a safety feature.

As far as spitting the mouthpiece out you are on your own.

Pete

 

[Jeff Toorish]

I think there is a concept that if a diver passes out and loses his or her mouthpiece the free flowing 2nd stage would alert other divers nearby of a problem. I honestly don't think this is an intended feature, more like something divers should be aware of.

Jeff

 

[scuba70]

The safety feature comes into play if the reg malfunctions while in your mouth. Modern second stages are designed to free flow if there is a malfunction, thereby giving you air. This is a better alternate to having it malfunction and not delivering air. Obviously you will end the dive and breathe from the reg as you have done in your training. If you haven't tried this before, since some agencies don't teach this in OW, it's best to try it in a controlled environment such as a pool. It's a cool skill to practice, but it uses air in a hurry! Better to try it before you actually need to do it.

 

[rawls]

Downstream regulators are designed to freeflow as opposed to upstream designs. Most regulators are downstream which means the valve on the second stage opens with the flow of air. If a downstream valve fails it almost always fails in the open position which is called a fail safe design. This design feature causes the second stage to freeflow and the diver is therefore never cut off from his or her source of air. One of the things that is taught in scuba classes is breathing from a free flowing regulator. When you turn the diaphragm down and it freeflows that is a good example of how sensitive a downstream reg is. When the mouthpiece is turned down the diaphragm is at a slightly lower pressure. When the mouthpiece is turned up the diaphragm senses the slightly higher pressure and is giving you a breath based on the higher pressure it senses...Boyle's Law. When your mouth isn't over it the reg will freeflow...Again it shows how a downstream regulator senses the difference in only a small change in pressure...

 

[John_B]

And a downstream regulator that fails open can still be breathed off of while conserving gas by feathering the valve open and closed. Assuming you can reach your valves and have practiced this at some point in confined water. Uh, nevermind. :14:

John