Suitable for sampling of liquid medium with zero pressure and certain negative pressure, reverse purge and needle assembly purge, vacuum interface type, the outlet end is connected to a vacuum source, and the reverse purge is performed before sampling, with the aid of vacuum suction at the outlet end The medium flows into the sampling bottle, and the needle assembly is purged after sampling. A gear box is used in the system to control two ball valves at the same time, making the sampling process easier and safer for the operator