This book is derived from chapter 5.1 of the main book "Dredging Technology Book1: The Basics". In order to keep track of things section numbers and formula numbers are kept the same as in book 1.The centrifugal pump and its drive react to changes in the valve opening as follows:1) Blocking the flow causes the pump pressure to rise, however at the same time the drive uses less fuel and delivers less power and starts to rotate faster. Generating the high pressure apparently is not a problem for the drive. 2) Increasing the flow by removing the outgoing hydraulic resistance causes higher fuelconsumption and slower rotation speed.Generating less pressure is apparently a problem for the drive.It is these phenomena that the operator and engineer must understand very well whenthey use a centrifugal pump and drive. In this book the how and why of the working of a centrifugal dredge pump with a diesel drive or electric drive is explained in detail. Following subjects are described: - Changing the impellar diameter to adapt to a changing pipeline length .- Situation at the suction side of the pump.- The "cavitation" phenomenon, which is the start of the boiling of the fluid. - The working of the diesel motor and electro motor. - The influence of the motor characteristic on the pump characteristic. The theory of an Ejector pump is described, complete with the pump characteristic and the efficiency curve. The advantage of an ejector pump is the absence of moving parts. One has to take special attention to the nozzle design and nozzle maintenance. (see Book 1 chapter 1.8) An important conclusion is the very low theoretical max pump efficiency of 29%.