...If your system was designed properly. You should NEVER EVER have a check valve above ground, or outside of the well! A submersible pump has a valve either built in, or screwed into the top of it! A jet pump uses a foot valve at the bottom of the well, below the jet. If a check valve is used at the tank, heres the scenereo; best case, a drop pipe has rusted through below the water line, and you'd never know it until you lose your pump or jet. No air spurts or warnings. Worse case, a leak developes in the line from your well on a cold, rainy spring weekend. As the water drains back down the well, it creates a vaccuum, drawing in contaminates and polluting your well. You dont know this is happening because that check valve is keeping pressure on your tank and house! I have a submersible pump in my well,200 feet from my house, with the tank under my house, all installed in 1990, and not only are there several yard hydrants on that line, but there are two other houses tee'd into that line as well! All is original, and no check valves anywhere, and no problems either!