Personally, and this is just my opinion, I see no need for more than 1 ball valve. I have 3 intake nipples on mine. 2 are just capped and 1 has a full port ball valve. If I want more air, I'll just uncap one nipple and fine tune with the valve.
Basically if 1 fully uncapped is not enough air, I'll just slighly open the valve. I'm just saying that with only 1 valve, there's still the ability for infinite adjustments from all closed to all open.
Big JT's Smokin' BBQ Competition Team
“If we could change ourselves, the tendencies in the world would also change. As a man changes his own nature, so does the attitude of the world change towards him.
We need not wait to see what others do.” - Mahatma Gandhi