Thinking if one was to ferment in a controlled sealed fermenter, say a Brewtools, would there be enough co2 given off to purge a keg, King or otherwise of air, ready for an airless transfer to cut down on the costs of bottled co2?
What I do is keep the temperature within limits, take gravity readings, and as it is in an open fermenter look at the surface of the stuff to see what's going on. That's where the experience comes in.
I'd check that the relief valve is working properly, if it isn't and there is too much pressure from secondary fermentation it can blow off around the tap seal. It has happened with my lower tap King Keg.