ISI offers electric, hydraulic, and turbine drive brush cleaning systems. In each case, the drive is connected to a high reduction gear box that rotates the screen between internal and external brushes for cylinder screens and rotates external brushes in the case of the cone screens. Electric drives are perhaps our most common drive assembly and have the benefit of being able to have the screen located at great distances from the control panel (e.g., distances of 1 mile (1.6 kilometers) or more are possible). Hydraulic drives are relatively simple and have the benefit of being able to be operated in the dry, but are limited to distances between the hydraulic power unit and screen of around 300 feet (90 meters). Turbine drives are simple and reliable and do not require a power source at the screen. However, because turbine drive brush-cleaning only happens when water is flowing through the screen system, this drive type is selected with careful consideration of site conditions and planned operation of the system.