PURPOSE: To prevent the reverse flow of the fluid or to reduce the quantity of the reverse flowing fluid and to suppress the V-cut abrasion of the titled tube to thereby reduce the durability thereof by a method wherein the inner diamter of the tube is reduced gradually from the sucking end toward the discharge end of the tube.

CONSTITUTION: The inner diameter of a pumping tube is reduced gradually as the tube extends from its sucking end to its discharge end and accordingly, the volume of the fluid (that is, the section enclosed by A4, A5, C5 and C4) actually sucked by the tube until a roller reaches the point C from the point A is smaller than a design volume of the fluid in that condition (that is, the section enclosed by A3, A5, C5 and C3), the former comes to be equal to or nearly equal to a design volume of the fluid from the point B to the point C (that is, the section enclosed by B3, B5, D5 and D3). Consequently, the sucked fluid is completely or substantially filled into that section so that the reverse flow of the fluid is prevented or reduced, the tube is not damaged and the durability thereof is improved to a remarkable degree.