Pump for pumping liquid in a pulse-free flow

A substantially pulse free, cylindrical pump which operates in a peristaltic manner on a cylinder to give a continuous flow of relatively small quantities of a liquid from an inlet port to an outlet port of the pump, which pump comprises two concentric cylinders in which at least one cylinder is formed from a piezoelectric ceramic material polarized in the radial direction and divided in the axial direction into at least three piezoelectric elements, each of which elements include at least one circumferential ring, separated by circumferential grooves on the surface of the cylinder remote from an annular space between the two cylinders;

• an electrical power supply in separate electrical contact with each ring and a switching device which completes an electrical circuit between the electrical power supply and each ring;
• wherein each element in seccession when energized electrically expands, radially in progressive sequence to fill the adjacent part of the annular space between the two cylinders and forms a moving seal which moves progressively from the inlet port of the outlet port to expel a first quantity of liquid therefrom.