Abstract: Centrifugal pump, in particular a hygienic centrifugal pump, provided with a primary and a secondary shaft seal (7,8) at the rear wall (2) of the pump chamber (1). Cooling flushing and barrier fluid is passed to and from a compartment (12) between these seals (7,8), optionally in a flushing fluid circuit. A sensor means (18) is provided in a discharge pipe (16) from the compartment (12) and adapted to measure at least the turbidity, electrical conductivity and temperature of the flushing fluid for activation of an alarm in case of leaking pump fluid through the primary seal (7). As a result the centrifugal pump is more sensitive to leaking pump fluid through the primary seal such that the pump activates an alarm (or optionally shuts down), if the leakage is too extensive.