LLigetfa
DIYer, not in the trades
Losing prime under moderate to heavy use suggests that the water level in the well is falling and the pump is sucking air but it could also be a suction side leak that is exacerbated as the level drops. It would be good to know the specifics of how deep the in-well injector was set and what the actual recovery rate is for the well. Without knowing for sure, a 3/4 HP, 10 GPM pump may empty the well casing fairly quickly. With about 60 feet of reserve in the casing, (that would be almost 90 gallons) the existing pump should not have sucked in air so one has to assume the footvalve was not set near the bottom.
When you say "lose water", what specifically happens? If the pump has a low pressure safety cut-off, those can be a source of frustration if/when draw exceeds capacity. If a bladder tank has too much precharge, the bladder will hit the bottom resulting in total loss of reserve, possibly tripping a low cut-off and/or losing the pressure that a jet pump needs to make more pressure. I often read on this forum that the pump doesn't make the pressure, that it is the jet/venturi that does. That is a half truth. The pump provides pressure to the jet which in turn makes additional pressure.
You still have not said what size pressure tank you have and if it is a bladder tank. A large tank can represent a significant draw on the well. From kick-in to kick-out, the drawdown amount is refilled at full pump capacity. At 40/60 a 120 gal tank may require 32 gal in one pump cycle.
When you say "lose water", what specifically happens? If the pump has a low pressure safety cut-off, those can be a source of frustration if/when draw exceeds capacity. If a bladder tank has too much precharge, the bladder will hit the bottom resulting in total loss of reserve, possibly tripping a low cut-off and/or losing the pressure that a jet pump needs to make more pressure. I often read on this forum that the pump doesn't make the pressure, that it is the jet/venturi that does. That is a half truth. The pump provides pressure to the jet which in turn makes additional pressure.
You still have not said what size pressure tank you have and if it is a bladder tank. A large tank can represent a significant draw on the well. From kick-in to kick-out, the drawdown amount is refilled at full pump capacity. At 40/60 a 120 gal tank may require 32 gal in one pump cycle.