Abstract: The invention relates to a piston pump for thick matter, in particular for high-solids sewage sludge, coal sludge and concrete. The piston pump has at least one delivery cylinder (16) which contains a motor-driven or hydraulically driven delivery piston (20) and which has an orifice (12) which communicates alternately with the interior of a material feed container (10) and with a pressure delivery line (30) in a slide-controlled manner in accordance with the movement of the delivery piston (20). In order to significantly increase the degree of filling of the at least one delivery cylinder (16), an annular nozzle (32) opening into the delivery cylinder (16) in the region of the orifice (12) is provided, and this annular nozzle (32) is connected to an external pressure line (34) to which a lubricant can be admitted.