Well X-Trol 119gal. Old.
Pressure switch set at 40-60.
At rest and without power to the pump after all water has drained from tank, pressure gauge reads 0.
Tank is reading 15lbs of pressure from my air gauge.
Turn pump on, fill tank, turn yard sprinklers on:
Bad Behavior: When pressure falls to 40, pump kicks on. Pressure builds slowly (normally) until about 47 then jumps to 60 immediately. Pump stops. Pressure drops immediately back to 47. Pressure drops slowly (normally) as water is being used until it hits 40 and the pump kicks back on.
Ideas on the status system?
(Edit: I know the tank should hold about 38lbs of air. I topped it off months ago, and the air has dropped to 15lbs)