A pump includes first and second impellers and a sealing element. The sealing element is arranged between the first and second impellers around the drive shaft. The sealing element has a first end transvers to the drive shaft and facing the first impeller and a second end transverse to the drive shaft facing the second impeller. The sealing element has a length along an axis smaller than the distance between the first and second impellers such that the sealing element is movable along the axis between the first and second impellers. The first and second ends of the sealing element have first and second areas transverse to the axis, the first area being larger than the second area such that the force exerted by the lower pressure generated by the first impeller is substantially equal to the force exerted by the higher pressure generated by the second impeller.