Pumps are devices used to move fluids, such as gases, liquids or slurries. A Pump displaces a volume by physical or mechanical action. A common misconception about pumps is the idea that they create pressure. Pumps themselves do not create pressure, they only displace fluids causing a flow. The added resistance to the flow causes pressure. Because of their wide variety of applications, pumps do have a plethora of shapes and sizes. Pumps can be differentiated in two major groups: rotodynamic pumps and positive displacement pumps. Their names describe the method for moving a fluid.