Question
I have a 1/2 HP shallow well jet pump to a sand point.  The pump fills the pressure tank well but when the tank is full, the pump continues to chatter and doesn't shut off, like "dieseling" on a gasoline engine.  I changed the pressure switch and checked the pressure in the pressure tank to no avail.  Could you tell me what to do about this?


Answer
Thanks for the question.
Is it possible the check valve is leaking?
When this happen the water fills the tank the immediately runs back down the well. The switch responds to the low pressure and starts again. Over and over.
Another thing to check is the pressure setting of the switch vs the tank pressure. With the pump off and system drained, the tank pressure should be 3-4# under the pressure switch setting. example;
pump starts at 32 psi then the tank should be 28-29 psi.
Hope this helps. If you have further question, feel free to ask.

Matt