Abstract: A pump may include a rotatable pumping part, a drive shaft, and a coupling for transmitting rotational movement of the drive shaft to the pumping part. The coupling may include a first part which is connected to the pumping part and a second part which is connected to the drive shaft, the first part having an electrically conductive material and the second part having an element for generating a magnetic field. The second part may be moveable relative to the first part to vary the degree of interaction between a magnetic field generated by the element and the electrically conductive material. Movement of the second part relative to the first part may be caused, at least in part, by a fluid controlled actuator having a piston moveable within a cylinder which is substantially non-rotating, such that the drive shaft and the second part are rotatable relative to the cylinder.

Abstract: A pump may include a rotatable pumping part, a drive shaft, and a coupling for transmitting rotational movement of the drive shaft to the pumping part. The coupling may include a first part which is connected to the pumping part and a second part which is connected to the drive shaft, the first part having an electrically conductive material and the second part having an element for generating a magnetic field. The second part may be moveable relative to the first part to vary the degree of interaction between a magnetic field generated by the element and the electrically conductive material. Movement of the second part relative to the first part may be caused, at least in part, by a fluid controlled actuator having a piston moveable within a cylinder which is substantially non-rotating, such that the drive shaft and the second part are rotatable relative to the cylinder.