An apparatus for pumping a fluid, the apparatus comprising a casing, a shaft supported by bearing means to the casing, a pumping means fastened to an end of the shaft, and a slide ring seal arranged between the pumping means and the bearing means, the slide ring seal comprising, - a first end facing the pumping means, - a second end facing the bearing means, - a first rotating slide ring with a slide surface having a first diameter and being arranged to rotate with the pumping means, - a second rotating slide ring with a slide surface having a second diameter and being arranged to rotate with the pumping means, - the first and the second rotating slide rings being arranged in connection with a rotating body, - a first stationary slide surface arranged against the first rotating slide surface and fastened to a stationary structure, - a second stationary slide surface arranged against the second rotating slide surface and fastened to a stationary structure, - the first and the second stationary slide surfaces (1,6) being arranged in connection with a stationary body, - the first rotating slide surface and the first stationary slide surface forming a first pair of slide surfaces, - the second rotating slide surface and the second stationary slide surface forming a second pair of slide surfaces, - the first and the second pair of slide surfaces leaving a liquid cavity therebetween, - the first pair of slide surfaces (1, 2) sealing the liquid cavity from atmosphere, and - the second pair of slide surfaces (6, 7) sealing the liquid cavity from the fluid to be pumped, characterized in that the rotating body is arranged at the first end of the slide ring seal, and the stationary body at the second end thereof, and that the second pair of slide surfaces (6, 7) sealing the liquid cavity from the fluid to be pumped is located radially outer than the first pair of slide surfaces (1, 2). - a first end facing the pumping means, - a second end facing the bearing means, - a first rotating slide ring with a slide surface having a first diameter and being arranged to rotate with the pumping means, - a second rotating slide ring with a slide surface having a second diameter and being arranged to rotate with the pumping means, - the first and the second rotating slide rings being arranged in connection with a rotating body, - a first stationary slide surface arranged against the first rotating slide surface and fastened to a stationary structure, - a second stationary slide surface arranged against the second rotating slide surface and fastened to a stationary structure, - the first and the second stationary slide surfaces (1,6) being arranged in connection with a stationary body, - the first rotating slide surface and the first stationary slide surface forming a first pair of slide surfaces, - the second rotating slide surface and the second stationary slide surface forming a second pair of slide surfaces, - the first and the second pair of slide surfaces leaving a liquid cavity therebetween, - the first pair of slide surfaces (1, 2) sealing the liquid cavity from atmosphere, and - the second pair of slide surfaces (6, 7) sealing the liquid cavity from the fluid to be pumped,