LLigetfa
DIYer, not in the trades
It was me that said that. Depending on what the precharge pressure is, when the pressure switch starts the pump, the pressure tank should be almost empty. The precharge on a jet pump system should be about 3 to 5 PSI less than the cut-in pressure so that there is still enough water until the pump starts producing more. If the precharge is too high, there can be a hesitation. If air has collected where that little bit of water should be, that air can cause a loss of prime.The first thing chucky said makes a lot of sense, about a small suction leak allowing air to build up against the diaphragm.