Hello, first I don't know alot about the workings of pumps, tanks and sand filters. But seeing that I have all of the above and have incured a problem I guess I need to learn. I had to replace the bladder tank(old one sprung a leak). New tank is a Wellsaver LPT 20, 20 gallon from Lowes. The pump is an Ace Hardware 1hp deep well jet pump, GE made. This is used to fill my sand filter. The old tank ,I forget the brand, is larger than the new tank. I'm not sure of the size mabe 30 gal? Got every thing hooked up easy enough and switched on the pump and it begain filling the sand filter but the bladder tank did not fill. After filter was full, pump kept switching on and off without filling bladder tank. When pump is running it shows about 40-45lbs of pressure but falls to 0lbs when pump stops.
Sorry for being long winded but family needs water.
Hope I given enough info. I look forward to your replies.

Thanks. Tim