The sampler is essentially a pneumatically driven metering pump. The sampling mechanism is a turbular stem with an inner concentric capture tube and a piston. Each cycle first captures a precise volume of sample and then pumps it through a back pressure valve to a sample to a sample collection receiver. The sampler can be operated up to a maximum of 30 grabs/min.
The in-line sampler installed in a correctly designed system will take representative grabs of sample at a pre-determined rate normally relative to the pipeline flow rate. The compositevof the 1,000 to 10,000 grabs collected during a pipeline transfer provides a reprasentative sample of the oil batch, for lab analysis and reference. The rate of the sampler is normally controlled by a flow computer which measures flow in the main export pipeline.