The Mighty Thor
Contributor
I was wondering if switching a verturi switch all of the way open does anything to affect your consumption of air. Anyone?
Does a Venturi Switch affect your SAC rate?
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If it doesn't increase your resistance significantly then no. You are still breathing the same. Now, if changing it causes you to have to forcefully suck your air out of your reg (not likely) I would say probably yes.
grausch
Registered
According to my Open Water course the answer is no.
If you think about it logically, whenever you inhale, your lungs expand. This in turn causes a pressure difference which effectively moves the seat from the orifice in your second stage allowing air to flow to the mouthpiece. Once the pressure has equalised, the seat is pushed back by a lever and this then presses the seat against the orifice, effectively stopping the flow of air.
Based on the fact that the pressure differential actually causes the air to flow, it makes sense to not try to impede the airflow in any way.
What the venturi does accomplish, is that it allows you to set a lower cracking resistance on your second stage to make breathing easier while reducing the likelihood of freeflows on the surface. Some manufacturers use different methods to accomplish the same goal. I do not know how efficient they are as I primarily know how my own reg functions (Apeks ATX 200).
As a test, you can purge your regulator under water and see/feel where the air goes when the venturi is moved. I found that in the open position all the air goes out the mouthpiece, but in the closed position some air also escapes from the exhaust.
Cheers
Gunter
Edit: Corrected some bad grammar.
If you think about it logically, whenever you inhale, your lungs expand. This in turn causes a pressure difference which effectively moves the seat from the orifice in your second stage allowing air to flow to the mouthpiece. Once the pressure has equalised, the seat is pushed back by a lever and this then presses the seat against the orifice, effectively stopping the flow of air.
Based on the fact that the pressure differential actually causes the air to flow, it makes sense to not try to impede the airflow in any way.
What the venturi does accomplish, is that it allows you to set a lower cracking resistance on your second stage to make breathing easier while reducing the likelihood of freeflows on the surface. Some manufacturers use different methods to accomplish the same goal. I do not know how efficient they are as I primarily know how my own reg functions (Apeks ATX 200).
As a test, you can purge your regulator under water and see/feel where the air goes when the venturi is moved. I found that in the open position all the air goes out the mouthpiece, but in the closed position some air also escapes from the exhaust.
Cheers
Gunter
Edit: Corrected some bad grammar.
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