Linear current boosters are used for optimizing the power out of your solar panels to get your Solar Water Pumps turning as early and as late as possible into the day. Linear Currenct Boosters (LCB) are for solar water pumps and solar panels what a car's transmission is used for getting its wheels turning as the engine ramps up power.
In theory, many solar pumps can be powered directly from the right voltage solar panel array. However, in reality, without the linear current booster the pumps works significantly less through out the day. The LCB increases the current (to get the pump's motor moving) at the sacrifice of voltage when your panels are not getting full direct sunlight.
Linear current boosters are rated by the maximum amperage (current) that they can put out. You'll want this maximum amps to be as much or more than the maximum draw of the solar pump. LCBs inherently work at different input and output voltages as part of their optimization.