dive/pre-dive switch

[skinerd]

Can someone please explain to me how the dive/pre-dive switch on most regs works. By that I mean what does it actually change inside the reg, I know it stops freeflow etc.
Thanks
Andrew

 

[redacted]

There are a least a couple designs for devices with that name. What regulator are you talking about? I believe many regs refer to a venturi assist device as a dive/pre-dive switch. It is a device that impedes or directs the airflow in the mouthpiece area. Other like the Scubapro D series have a dive/predive switch that operates on the lever which controls airflow into the 2nd stage. And there may be others.

 

[skinerd]

It was more of a general question covering all regs, but I am referring to the switch usually on top of the reg. Not the one that adjusts flow.

 

[Diver0001]

All it does is move a little plastic bit inside the reg so the air is directed straight through the mouthpiece to create a venturi effect that makes breathing a little easier.

If you turn it hte other way, then the air is not directed out the mouthpiece and there is no venturi effect.

R..

 

[skinerd]

thanks!

 

[SeaLevelScuba]

PreDive mode - Most common design is that the mechanism obstructs the airflow in the breathing chamber causing backflow against the diaphragm to prevent free flow of the regulator. Breathing resistance is slightly increased due to the lack of a venturi effect on the diaphragm. Another design is that additional pressure is appliead against the diaphragm within the breathing chamber causing the diaphragm to not be suceptible to the venturi effect.

Dive mode - eliminates the obstruction or additional pressure described above to allow the diaphragm to be suceptible to a venturi effect.

The venturi effect is nothing more than creating a lower pressure on the diaphragm caused by the directional flow of air out of the breathing chamber, this lower pressure allows the ambient pressure from outside the breathing chamber to actually assist in depressing the lever delivering more air volume.

This was a simplistic view of the what goes one in a regulator with the min/max, dive/predive, etc levers. These are different from the effort knobs on some regulators.

 

[The Chairman]

The science is great to understand, but you might want to understand the BENEFIT of this device. In the "non-dive" or "surface" position (usually marked by a minus sign), your regulator is far less likely to free flow due to the "back pressure" it creates.

 

[DA Aquamaster]

And in the "Dive" or "+" position, the venturi effect may result in a little more air coming your way than is comfortable, so you may end up with a setting somehwere in the middle. It's a matter of personal preference.