i have a 21/2" galvanized casing at a depth of over 100' with a 1" black plastic pipe in the center. the water level is about 30 ' in depth and the pump is an additional 15' from well casing in pump house. I believe it is a 3/4 hp. centrificle pump set at 36lbs on and 52 lbs off.i have a bladder tank(20 gal.?) set at 34 lbs. my problem is it takes 15 to 20 minutes to full pressure and when we run the shower we get great pressure for about 3 minutes and then will gradually slow to a slight trickle, the black plastic pipe is about 50' to the foot valve. what can solve mt problem and maintain pressure. all replies will be appreciated..thanks