A rotary lobe pump comprises a pump body having a driving means and an outer casing, and an insert that can be replaced. The replaceable insert comprises a housing formed of a plastic material and having an inlet port, an outlet port and internal surfaces defining a pumping chamber. The replaceable insert also includes a pair of lobed rotors arranged for rotation within the pumping chamber. The housing includes apertures through which the lobed rotors may be rotationally driven, so that the lobed rotors mesh together for pumping a fluid from the inlet port to the outlet port.

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