ianr33
Contributor
If you have a Venturi adjustment on your reg do you actually use it? My regs are Apeks,they breathe fine with the switch in the minimum position so I just leave it there. One less thing to mess with and less chance of free flows.
Venturi Switch
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DMdoogie
Contributor
I use an Apeks TX 100, I dive in current in West Palm Beach, and it works most of the time. I set the venturi on pre-dive until I get to the bottom, it prevents "bubble blast" when I turn my head into the current to guide the other divers to the reef. In a really stiff current I still need to cup my hand over the purge button. I open the venturi to "dive" when I hit the bottom and face away from the current.
I set it back to "pre-dive" when I reach the surface and have to float while waiting for the pickup.
I agree with you that there is little difference in breathing when used in a gentle current.
Apeks is the only reg I've used where the cracking adjustment knob actually works. Twisting the knob makes a big difference in WOB when fighting a fast current, fighting a fast lobster, rescuing a dumb diver, etc.
DMdoogie
I set it back to "pre-dive" when I reach the surface and have to float while waiting for the pickup.
I agree with you that there is little difference in breathing when used in a gentle current.
Apeks is the only reg I've used where the cracking adjustment knob actually works. Twisting the knob makes a big difference in WOB when fighting a fast current, fighting a fast lobster, rescuing a dumb diver, etc.
DMdoogie
On SP regs I will use the adjustment knob, which does have a significant impact on cracking (inhalation) effort, but the venturi switch stays in the middle.
all4scuba05
Contributor
DA Aquamaster:
ditto.
I also use the adjustment knob on the second stage when swimming into a current, that's what it's for. The dive/predive switch isn't really designed for that.
Here's what is happening inside a typical second stage regulator: (This is a Zeagle, and Apeks is almost just like this one.)
Photos no longer attachable.
See the bottom 2 photos on my instruction page http://www.mobilescuba.com/instruction.htm
In pic # 1, the + Venturi or Dive Position:
Air flows directly up to a defector vane right in front of the mouthpiece, creating the venturi or syphon of air into the mouthpiece. Very easy breathing is the result. In this position a properly tuned regulator will venturi when out of the mouth, in or out of the water.
In pic #2, the -Venturi or Pre-dive Position:
Air is rotated forward into the diaphragm by the blue collar, where it tries to close the valve. But the diver continues working to breathe and overrides the reverse flow. Labored breathing is the result. The regulator will not venturi.
Divers can, and do, use the venturi control either way or anywhere in between.
I prefer to dive in the + Venturi, #1, and adjust down the cracking effort if need be.
Before removing the mouthpiece at the end of the dive, or when gas switching, I just flick it into - Venturi, #2.
Cracking effort adjustment just tightens down or backs off on the spring tension to the seat.
Chad
Photos no longer attachable.
See the bottom 2 photos on my instruction page http://www.mobilescuba.com/instruction.htm
In pic # 1, the + Venturi or Dive Position:
Air flows directly up to a defector vane right in front of the mouthpiece, creating the venturi or syphon of air into the mouthpiece. Very easy breathing is the result. In this position a properly tuned regulator will venturi when out of the mouth, in or out of the water.
In pic #2, the -Venturi or Pre-dive Position:
Air is rotated forward into the diaphragm by the blue collar, where it tries to close the valve. But the diver continues working to breathe and overrides the reverse flow. Labored breathing is the result. The regulator will not venturi.
Divers can, and do, use the venturi control either way or anywhere in between.
I prefer to dive in the + Venturi, #1, and adjust down the cracking effort if need be.
Before removing the mouthpiece at the end of the dive, or when gas switching, I just flick it into - Venturi, #2.
Cracking effort adjustment just tightens down or backs off on the spring tension to the seat.
Chad
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