Freddy wrote:With the power and pressure off the system the air pressure in the tank is set at 2 pound less than cut in because....
After the power is back on & the tank is full, as you use water, the pump does not run at first. The air pressure pushes the water out of the tank, as the bladder pushes the water out, the pressure drops, drops, and just before the bladder empties the tank, the pump comes on. If the air pressure was equal or more then the cut in pressure, the tank would empty, pressure would drop to zero for an instant, water at the faucet would stop briefly, then the pump would come on with a slam. By having 2 pounds of air pressure below cut in, it insures an uninterrupted supply of water and a smooth transition from pump off to pump on. With it set that way, the tank does not quite empty before the pump comes on.
<edit for typo & addition of last sentence>
Thanks. I never knew that. I always set the bladder for 2 pounds less than the switch but never really knew why.