VT3 GAS 2 and 3 FO2 setting question.

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Dan Watkins

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GAS 1 can be set from 21% to 50% FO2
GAS 2 and 3 can be set from 21% to 100%, but the instructions state:

"The VT3 is programmed to prevent FO2 for GAS 2 and 3 from being set at values lower than the FO2 Set Point for GAS 1. GAS 2 and 3 can only be set to values equal to or higher than the FO2 Set Points for GAS 1 and 2, respectively."

So if I set my GAS 1 to 32%, GAS 2 and 3 cannot be set lower than 32%. If I set GAS 2 to say 36%, GAS 3 cannot be lower than 36%.

I would like to have Nitrox in my main tank (GAS 1), and carry a Pony bottle for emergency ascent that I just keep air in (designated GAS 2). But because of the programming of the VT3, it would not allow me to set an FO2 of 21% for GAS 2.

I just wondered what the reasoning behind this restriction is... Is there generally some concern to switching to a gas with a lower FO2 than the primary tank?
 
https://www.shearwater.com/products/swift/

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