On Feb 14, 8:24 pm, "Lou" wrote:
But how can it suck air into a tank that is full of water without
forcing some of that water out somewhere? Wouldn't there have to be
much less pressure inside the tank than outside? Since liquids cannot
be compressed, there would have to be air already in the tank for a
pressure differential.

Which do you do first, turn the main on and then open the faucet?
or
Open the faucet and then turn the main on?

Does it either way. With the main on first, you can hear water
entering the tank so the air is in the tank prior to any valve being
opened. The more I think about it & discuss it, I'm leaning to air in
the water as it enters the tank, then separating as it sits. Water
comes from a saturated sand aquafir so I can understand how water
movement down there could induce air into the mix.