Conventionally, in a rotary pump such as can be used for transporting liquid foods, a rotary drive shaft is formed with its leading end in a spline shaft, a spline hole formed through a rotor is engaged by the spline shaft of the rotors of the pump within a pumping chamber in a main rotor casing, and a fastening nut of the rotors is engaged and fixed at the end of the rotor drive shafts projected outwardly from the rotor, and a concave casing cover receives the rotor segments and the rotor fastening nut.
In such a conventional rotary pump, a transported liquid flows in the pumping chamber, enters into the concave part inside the casing cover through a space between the rotor and the casing cover, and tends to be retained in that concave part, becoming trapped therein. Since the so trapped food can spoil, the pumps of this type have to be frequently disassembled and the pump with the concave part inside the casing cover cleaned after a day's use of the pump. Reassembly of such pumps after their disassembly, and their cleaning requires the expenditure of considerable time and labor thus increasing the cost of the product.