2SK series water ring vacuum pumps and 2SK-P1 series two-stage water ring vacuum pumps—atmospheric jet pump units are used to extract air and other non-corrosive, water-insoluble, and non-solid particles-free gases in order to obtain a higher vacuum in a closed container. The 2SK series is suitable for working conditions where the suction pressure is lower than -0.08MPa. 2SK-P1 series liquid vacuum pump is suitable for working conditions where the suction pressure is lower than -0.096MPa. When equipped with an atmospheric pump, the ultimate vacuum can reach -750mmHg. The working vacuum range is -0.03-0.08MPa.