Adjustment Knobs on Regulators

[mrlipis]

While I understand how these adjustment knobs work, increased or decreased pressure on the diaphragm, and I understand that there is no more or less air pressure delivered, my question is this. If the resistance is less, am I able to suck more air than if the adjustment is set for more resistance? While not delivering more air, am I able to demand more air because of less resistance? Hope this question makes sense. I also know that there is two different types of adjustments, the knob and the lever. For the sake of argument let's address the lever type. I am using an Aqua lung legend (not LX).

Bruce

 

[vixtor]

As far as I know there are two types of adjustments:

1. lever - using venturi effect, its purpose is to mantain the air path open (so the air will flow into your mouth) without requiring you to mantain a lower pressure by sucking. basically it is just a plastic shield that deflects air in a specific manner.
2. knob - this adjusts the diaphragm resistance at inhaling. this means that you require more effort in order to move the diaphragm.

The first one allows you to perform an effort just to open the diaphragm, and then the air path will remain open until you stop breathing, being kept open just by the flow of air.
The knob will adjust the power that you use to suck the diaphragm open. If the regulator does not have the venturi assisted mechanism, you will need to mantain the power during the whole inhalation. If the breathing is venturi assisted, you need this power only for initiating the breath, and then air will come into your mouth without effort.

Regarding your question, you should be able to demand the same ammount of air with or without these systems. Maybe if your muscles are tired because of the breathing effort, you will not have the power to inhale (but I don't think the difference is signifiant enough to matter).

 

[vixtor]

On a second thought, using a regulator that requires more effort in order to provide air, when you are more tired you might start breathing shallowly and tire even more.

 

[PhilEllis]

Adjusting the breathing resistance knob on a regulator simply adjust the amount of effort necessary to begin the flow of air from the regulator. Once that flow begins, all regulators perform different as to the effort required to continue air flow at various levels.

May regulators have a case venturi effect that reduces the effort required to flow various amounts of air. We have a page that describes the dynamic testing of the air flow of a regulator on our regulator bench. Maybe you can read this article and take a look at the graphs to get some understanding of the relationship between "breathing effort require" to maintain a certain volume of "air flow". If you have questions, fire away.

Dynamic Flow Measurement for Scuba Regulators

Phil Ellis

 

[mrlipis]

Phil, good article but this would appear, correct me if I am wrong, to detail the venturi type of adjustment which is generally a knob that turns counter clockwise to eventually achieve a free flow.
It does appear that cubic ft per min does increase. My question however is regarding the lever type of adjustment. To better explain my question, here is a scenario. I am fighting a current and I start raising my heart rate, which in return creates more of a demand for O2. I am sucking on my reg and don't feel that I am getting enough air. By adjusting the LEVER for less resistance, am I in fact getting more air or does it just seem like it as the breathing resistance becomes easier.

I suppose that once the intake valve is completely open the volume of air will not increase and thinking in those terms maybe the question should be, Is the intake valve either open or closed, or does it open partially depending on demand?

Bruce