Yes, you can ferment, say, a 5 gal batch in your 14.5 gal conical. The CO2 gas from fermentation will fill the head space and protect your beer from oxidation. The only drawback is that you'll have less head pressure available to push out your yeast. Dumping more frequently will resolve that issue, or you can simply use the pressurization feature to push it out.
What is the pressurization feature and how is it used?
Hi Skip - you simply place the included barbed elbow into the airlock stopper hole and connect a hose to your CO2 tank. Turn it on slowly to pressurize the tank. You'll hear the pressure relief valve lift and hiss if you get too much pressure on it. That's it!