My mom has a deep well jet with a (non-bladder) pressure tank, with no Schrader valve to add air. I'm going to put a new AVC on it this weekend, because they only seem to last 5 years. I'm going to follow this post, so if I'm all wrong, hopefully I find out.

I'd get as much water out of the tank as I can before I "seal it" (trap the air) and add water. Remember Pressure x Volume (of the air) will be a constant. The volume (space) of the air decreases as the pressure increases. Initial pressure(P1) x initial volume of air (V1) = final pressure (P2) x final volume (V2) of air above water. So: P1 x V1 = P2 x V2

For example: When we start, after sealing up the tank, the gauge pressure in the tank is zero, (say 15 pounds absolute/atmospheric), and (say) the tank gets pumped up to 60 pounds (75 pounds absolute). We know the pressure has__ increased __5x, so the volume of air has *decreased* 5x.

If the tank is 48" high and empty of water when we seal it I think this means there will be about 9.5" of air above the water at 60 pounds. (9.5" x 5 = ~48")

If the pump then switches on at 30 pounds (at 1/2 of 60 pounds to keep this example simple) I think this means there will be about 19" (9.5" x 2) of air above water when the pump turns on, so you where able to extract 9.5" of water out of tank between cycles.

My understanding of a Air Volume Control Valve is that it only inserts a small bubble of air into the tank each time the jet pump starts to make up for air in the tank that has dissolved into the water. I don't have a good understanding on when this is too much or too little air to make up for what has dissolved. I would think this depends on how many times the pump starts versus how long the water sits there and can absorb air.