My well system has worked problem free for the past 11 years. It has a
submersible pump at 220' with a pressure switch of 30/50psi. When
full, the pipes hold the pressure without leakdown. But recently, the
instant the pump kicks on the pressure drops to 0 for a split second,
then back to 30 and rising. The 0 pressure is noticeable in a water
stream also, kind of like a burp.

My first thought was a check valve, but the water pressure is constant
when the pump is off. Unless the pump has it's own check valve? But
then everything happens so fast there's no time for the water column to
fall. The pressure tank precharge is ok. Any suggestions?

Bob S.