FRV vacuum roots blower is a positive displacement blower, the negative pressure of which can be adjusted within the allowed range according to the requirements of users. Two groups of impellers rotating in opposite directions are arranged inside the blower shell, as rotate when the gap between the impellers as well as between the impeller and the shell is rather small. When the impellers pass through the suction end, certain air is held between the impellers, the air moves aside to be exhausted from exit end. During the operation, the negative pressure in the pipeline at suction end will increase slowly till to the required value.