Abstract: A pump device for metering and/or feeding liquid materials, particularly colorants and plasticizers for molded plastics. The pump consists of a linear metering tube which is straight throughout of length of the compression zone, thereby reducing stress and fatigue on the tube, thus prolonging tube life. The metering tube is compressed by compression rollers attached to an endless drive belt which moves within a track cut into a housing. In another embodiment of this invention, wherein the linear metering tube is inclined slightly, stresses on the tube are distributed over the tube by the gradual compression of the tube. The pump provides for simple, precise, long-life dispensing of polymer additives.