Stenner Classic Series Metering pumps are self-priming and the 3-point roller assembly provides a positive 2-point seal on the pump tube at all times. 45 Series pumps eliminate the need For anti-siphoning Valves and diaphragms. Stenner's adjustable head pumps are built with three detachable components; the motor, feed rate control, and the pump head that can be separated without tools. Outputs are dependent upon the rpm of the motor gears and the size of the peristaltic pump tube. The patented mechanical feed rate control (adjustable models) allows the pump's output to be scaled from 5% to 100% with the simple turn of the dial.