I have shallow well (spring fed) with 40 gallon non-pressurized tank. Tank was full all the way to the top. Pressure gauge showed 0. drained out about half of tank and used air compressor to put 28 pounds in tank. Worked fine for 2 days then lost all pressure in tank again because tank was full to the top. When you open up valve anywhere in house pressure switch kicks on and cycles between 30 (kick on) and 50 (shut off). If you close valve it stops cycling but the pressure gauge shows pressure going down slowly.