Breathing / Air management - Tips&Tricks.

[paddler3d]

I would like to hear more about this. I would think that increasing the opening on the regulator orifice would pass the same volume of compressed air, just at a lower pressure differential. I dunno... maybe physics is different underwater?

I just got the Vance Harlow book on Regulator Maintenance and of course I don't have the book here with me, but there is a section on how venturi assisted models work and you take apart, maintain, so on so forth.

I'm doing this from memory, but I'll reconfirm later. The venturi changes the second stage by increasing or decreasing the cracking pressure. As a diver that is nice, because we can compensate for depth. Most of us, likely have it set to the max which I believe decreses the cracking pressure. We have it just below the free flow point. We have the second stage delivering us a lot of air when we don't need it. It is almost like force feeding us the air. We decrease the cracking pressure to our actual work load and we are more efficient in the delivery of air.

I was supposed to go diving this weekend, but we had a family emergency and that go scrubbed, but I was going to set my reg to an increase in the cracking pressure and see if I could have noticed anything.

I'll quote the book later, but I think I close on understanding what his was saying and relating it.

 

[TSandM]

As long as the second stage is not freeflowing at all (meaning no bubbles escaping from the mouth) then lowering the cracking pressure will not increase the amount of gas that leaves the tank per minute of time. You will inhale and exhale the amount that you need to keep your CO2 normal -- the only difference is that you will do less work to achieve that. However, INCREASING the cracking pressure beyond a certain point will make it difficult to inhale full, increasing the likelihood of rapid, shallow breathing which wastes gas.

As several people have already pointed out, the key to lowering your gas consumption is relaxed efficiency, and not hurrying. Making efficient use of your propulsion (i.e. making sure that the thrust from your kick pushes you where you want to go, and that half your effort isn't pushing you up in the water column when you don't want to go there) and using efficient propulsion techniques (eg. frog kicking, which includes a glide phase which is a resting phase) will go a long way toward extending your gas supply. It takes time and a little effort to become efficient, but the payoff is tremendous.

 

[Sonic04GT]

I would like to hear more about this. I would think that increasing the opening on the regulator orifice would pass the same volume of compressed air, just at a lower pressure differential. I dunno... maybe physics is different underwater?

I am curious as well. I have an Atomic B2 with the user adjust knob on the side. In the manual it states that once you are underwater this should be opened all the way for easist breathing. It is only there so you can lessen the sensitivity to push through rough surf or while surface swimming, situations likely to cause freeflow. They even mention specifically that opening it partially will not save you air, but instead cause you to breath harder to get the air you need.

 

[paddler3d]

I would like to hear more about this. I would think that increasing the opening on the regulator orifice would pass the same volume of compressed air, just at a lower pressure differential. I dunno... maybe physics is different underwater?

I found it.

Vance Harlow's SCUBA Regulator Maintenance and Repair, Chapter 1: How a Regulator Works, p.21

Sorry if that is not following the MLA.

"Venturi Assist

...In a 2nd state with venturi assist, the incoming air is blasted directly at the mouthpiece opening so it sucks the rest of the air in the second stage along with it. The lowers the pressure in the diaphragm chamber, which gives the diaphragm action a bit of a boost and makes it easier to sustain flow once it has been initiated.

There's nothing new about venturi assist - most of the old double hose regulators had the air jet positioned to blast the outgoing air directly into the house to the same - the short-lived double hose DX Mistral actually had a little hose going up inside the big hose that shot the air right in the diver's moth (which most users hated).

A little venturi assist is a very nice thing, but too much can dry out a diver's mouth, give an unpleasant feeling of being "force fed", and waste air."

It goes on bit farther about the levers on the 2nd stage.

I have felt that my reg, Apex ATX 100 has definitely given me more than enough air at whatever depth, or tank pressure I had, but I always felt like I would end up with dry mouth, also I'm a bit heavy on the air. I saw this and it peaked my interest.

I apologize for not getting everything correct the first time around.

 

[Bubbletrubble]

To clarify, the difference between cracking pressure and Venturi assist functions in a second stage regulator is:
- Cracking pressure: pressured required to initiate flow of gas
- Venturi assist: a feature involving the angle of a flow vane which makes it easier to sustain the flow of gas once it has been initiated.

Therefore, one should be able to turn the Venturi assist knob from plus to minus (and vice versa) and not notice any difference in the cracking pressure.

As can be expected, increasing the work of breathing could translate into an increased metabolic requirement, resulting in greater gas consumption.
It goes without saying that free-flow incidents prove costly in terms of gas consumption.
The take-home message is to make sure that your regs are properly adjusted. Then the reg shouldn't have any appreciable effect on one's air consumption.

To address the OP's question, the best things one can do to improve air consumption include:

• Relax. Relax. Relax.
• Spend as much time as you can hovering. Hovering requires very little energy. You see more this way, too.
• Move very slowly through the water. Technically, this kinda goes with the previous bit of advice.
• Dive. Dive. Dive. The more you dive, the easier it is to do all of the above.

Have fun and dive safe.