I am no well/pump expert but have changed a pressure switch a couple times on this unit since 1995. Lost water and replaced pressure switch Monday evening and this am when I got up and no water. An hour after I switched the power off, switched it on an the pump started running. Even though it is a 20-40 switch, the pump is running and the guage reads ~52 when it goes off. I tried adjusting the small nut to make it shut down sooner but that has no effect. When I turned the large nut counter cw the pump shut off. Later when water was used, it seemed pump would come on every time when normally this would not be required. At at some point, the pump would not go off and I shut power again. I checked the valve on top, drained tank and pressure is now~t 34. I am beginning to wonder if I bought a defective pressure switch. I have always gone to the same Bowen supply but this time although the switch looks the same it is not the SquareD brand I am familiar with, still have box from previous as I had drawn picture for hooking wires back up on it.