An adjustment assembly for pump casing of a pump, the pump casing including a main part and a side part having a main axis and a side wall section extending laterally with respect to the main axis. The adjustment assembly is operable to cause relative displacement between the side part and the main part of the pump casing. The adjustment assembly includes a drive device and an actuator which can be activated externally of the pump, the drive device being operable to cause the relative displacement of the side part in response to activation of said actuator, the relative displacement capable of being a combination of axial and rotational movement.