A tracer-gas leak detector includes an analysis unit and a primary pump whose inlet is connected to an inlet orifice of the detector via a first pipe equipped with a first valve. A secondary pumping set has an inlet connected to the analysis unit and an outlet connected to the inlet of the primary pump. The primary pump is a dry pump. The secondary pumping set includes two secondary pumps of the mechanical type separated from each other by a second valve. The secondary pump that is proximate to the dry primary pump is the second secondary pump and includes a dynamic seal stage at its outlet. A second pipe connects the inlet of the second secondary pump to the first pipe downstream from the second valve. A third valve is disposed on the first pipe between the outlet of the second secondary pump and the junction where the second pipe meets the first pipe. The third valve is controlled by a pressure sensor placed at the inlet of the second secondary pump.