A pump has a housing defining a first pumping chamber and a second pumping chamber. The pump also has a first plunger and a second plunger. The pump additionally has at least one driver operatively engaged with at least one of the first and second plungers to move the at least one of the first and second plungers between first and second end positions. The pump further has a common spill passageway fluidly connectable to the first and second pumping chambers and a selector valve disposed between the common spill passageway and the first and second pumping chambers. The selector valve has a body and a ball valve member operably disposed within the body. The ball valve member is movable between a first and a second ball valve member position to selectively fluidly connect the first and second pumping chambers to the common spill passageway.