Nearly all of the Proactive sampling pumps from the Proactive poly pumps to the Proactive stainless steel pumps require a controller. Additionally, almost each type of pump requires a different controller. The controller connects the DC power to the pump and controls the power going into the pump. The controller regulates the volume of water that the pump purges. A customer may require a controller because he has a pump but does not have the controller or the customer may want an additional controller on site.