Abstract: A portable counterflow helium leak detector has only one pump. The pump is a secondary vacuum pump including an inlet and an outlet. A gas analyzer is connected to the inlet of the pump. The outlet is connected via an inlet valve to a correction orifice for connection to an installation to be tested, the installation being evacuated or being capable of being connected to a primary pump. The detector further includes electronic power supply and control circuit, a power supply, and a display. The detector further includes a first pressure gauge situated between the inlet valve and the connection orifice and an ON/OFF control switch for controlling detector operation. The electronic control circuits cause the inlet valve to open and the secondary vacuum pump to start whenever the detector is powered. The control switch is in the ON position and the pressure measured by the first gauge is below a determined value.