Abstract: The apparatus consists of a plurality of piston pumps having preset displacement ratios. A motor mechanism is connected to each of the pumps. In addition, there is a control mechanism connected to each pump ensuring that all pistons execute their previous stroke completely before being reversed and that they all start their following stroke at exactly the same moment. Furthermore there is another control mechanism controlling the speed of each piston so that all pistons complete their respective strokes simultaneously. A mechanism for adjusting and varying the pump displacement is also provided.