I just intalled a new LP20, purchased from Lowe's. It replaces an old conventional "in one side and out the other side" upright 60 gallon tank that had sprung a leak. Now the pump just runs and runs asif it has lost its prime. If I shut off the pump I can hear the water flow back into pump and stop. I then turn pump back on and it will pump up and shut off.
Any suggestions?

Set the bladder tank pressure at 2 PSI below the cut in point of the control box with the pump shut down and the pressure bled off.. Let's see hor a bladder tank works. In an air system, when the water is being used, pressure comes from the compressed bladder, slowly releasing its pressure against the water surface and the side of the tank, forcing the water out the supply line.When the air differentiaiton valve senses it needs more air, it opens, allowing ambient air to enter. When that happens, it also trips a spring loaded relay to tell the pressure water pump to start sending more water to the tank. That is pushed usually at 20 PSI against the bladder which then starts to be compressed against the air, and reads air pressure against the gauge at 40 PSI. Good luck, Tom

Thanks very much. I was thinking along those lines. The other thought I had was, maybe I have a pipe sizing problem. Pipe from pump to tank Tee is 3/4" and tank Tee is 1". Outlet to building is also 3/4".
Set the bladder tank pressure at 2 PSI below the cut in point of the control box with the pump shut down and the pressure bled off.. Let's see hor a bladder tank works. In an air system, when the water is being used, pressure comes from the compressed bladder, slowly releasing its pressure against the water surface and the side of the tank, forcing the water out the supply line.When the air differentiaiton valve senses it needs more air, it opens, allowing ambient air to enter. When that happens, it also trips a spring loaded relay to tell the pressure water pump to start sending more water to the tank. That is pushed usually at 20 PSI against the bladder which then starts to be compressed against the air, and reads air pressure against the gauge at 40 PSI. Good luck, Tom

maybe I have a pipe sizing problem. Pipe from pump to tank Tee is 3/4" and tank Tee is 1". Outlet to building is also 3/4".
Doubtful! It shouldn't interfere with the operation or the flow. Regards, Tom