Abstract: A sealed piston pump having in an open cavity of the pump body, a circular single-piece set formed by a central cylindrical piston. The piston is coupled by a rod to a driving member while the piston in an alternating motion along its longitudinal axis. A ring is placed on the pump body which is hollowed out with an annular channel and a deformable thinned part connecting the piston to the ring. The single-piece set and the pump body are fixedly joined to each other in an imperviously sealed way. The single-block set is made of a synthetic material that is flexible and mechanically and chemically resistant. The pump can be advantageously used in ink-jet printers.