Abstract: In a pumping arrangement for a chamber, a regenerative pumping mechanism comprises a rotor and a stator having an annular channel within which rotor blades rotate to urge fluid along the channel. The channel has a stripper, a channel inlet positioned adjacent one end of the stripper and through which fluid from the chamber enters the channel, and a channel outlet positioned adjacent the other end of the stripper and through which pressurised fluid leaves the channel. The stator further comprises a fluid bypass in the form of a bore having an inlet and an outlet on either side of the stripper. A valve allows fluid entering the channel to selectively diverted through the bore to the channel outlet. This can allow the performance of the pump to be varied without changing the speed of rotation of the rotor, and thus allow the pressure in the chamber to be accurately controlled.