I have a new pressure tank and 40/60 pressure switch.. when the cut out psi of 40 kicks on well pump my pressure drops to zero
Then 3secs. Later goes to 40 and water runs. I checked psi in new tank empty and it is 38 psi which is right.. what else could be problem?called the plumber back and he wants to get in my well says its check vavle in there bad... I'm holden off till I get some more input from people

If you have a leaking check valve you should be constantly losing pressure when no water is being used. This would be because water is constantly flowing back down the well when the pump is not operating. I have a little problem understanding how you pressure gauge could ever show 0 pressure if you pressurized the empty tank to 38#. Could you have a faulty pressure gauge. They are cheap and easy to replace. Before doing anything else I think I would replace it.

MT, you are not the only one to ever post that problem. It shows up here from time to time. In fact, mine will do it from time to time, though not for three seconds... just for a fraction of a second. Is your gauge on the tank itself, or on the water line leading into the tank?