I need a gas valve that only allows one of the two air sources to be coming out of the outlet! The tubes are under pressure. I am open to ANY advise or suggestion!!
That may be expensive in that it might be an uncommon valve. Perhaps it would be better to use two valves and 'Y' their outputs together. You may find a solenoid valve you can use in the automotive industry. An EVAP solenoid http://www.amazon.com/ACDelco-214-1685-VALVE-ASM-EVAP-BRACKET/dp/B0049BROCI is one that handles fumes of the fuel system. I recently discovered two valves on a vehicle that I was working on to have variable ports actuated via stepper motors. - Scotty
The suggestion scottyjr made about using a Y connection with two valves was a good one.
The OP wasn't clear on what type of gases or how much pressure so it's hard to give specific parts advice. Still, here's a link to a surplus medical 12 VDC solenoid valve that can handle gases and liquids (but probably only non-flammable ones) at elevated pressures, $7.50 each. It's just a suggestion and I have no idea if that will fit your needs.