I am on a submersible deep well pump. I replaced my bladder tank some time ago, due to the old one being rusted out. There is no check valve in the line between the pump and tank. 3 days after the swap, I started getting air in the lines. I checked and adjusted my tank pressure to the manufacturer's recommendation. At that point, I bled air from the system. I thought I fixed it, but 2 days later, I had air again. I have since bled the system again, only to have the air return. Today, I hooked up a pressure gauge to check for leaks, but the gauge stayed at a constant pressure for 15 min. I opened up the water and allowed the well to pump up to pressure again. When the pump cut off, I put my ear to the well head pipe, and it sounded like water was draining back into the well, but my pressure remained constant. Who has an idea what is causing this. I'm now convinced, this is where my air is originating from.