We have a submersible pump in our well which is 65 feet deep with the pressure tank in the garage. For the last year when the pump shuts off at 55 lbs it drops immediately to 45 lbs and gradually drops to 35 in about 15 minutes and cycles again. I have closed the valve between tank and pump and the pressure doesn't drop. Does this sound like a bad check valve(in the pump??) or how about the O ring connection at the pitless adapter? The pump and tank are about 18 years old. I would appreciate any and all help. Oh, by the way, great forum!!