In this example of a servo pump filler (often called a metering pump filler) a rotary gear pump delivers product from the product tank to a container through a filling valve and nozzle. The pump delivers a known volume for each rotation of the drive shaft. A shaft encoder measures the cumulative rotation of the shaft which is directly proportional to the volume of product delivered. A signal from the encoder stops the pump at a set point corresponding to the required fill volume.
Lobe pumps, peristaltic pumps and rotary reciprocating pumps are also commonly used in servo pump filling systems.