I just recently replaced my old 1.5 HP Sta Rite lawn sprinkling pump with a new Wayne 2 HP lawn pump. The old pump was controlled by a pressure switch (no pressure tank) and worked fine. The new pump, with the same pressure switch, short cycles continously, even with all zones closed. Because the new pump is bigger, and likely more efficient, does this mean I now need a pressure tank? How do you determine what size?