These type of pumps are designed for evacuating from sealed vessel (with pressure not more than 800 mbar) air and nontoxic explosive and fire hazardous gases, which are non-aggressive to the pumped fluid and construction materials, vapors and gas-vapor mixtures which are precleared from condensed moisture and mechanical pollutions with oxygen content not more than in air (21 % by volume) at normal conditions.The pumps can operate only in combination with fore pumps and are intended for pumping in the pressures range from 1,3·102 Pa (1 mbar) to ultimate pressure. The roots pumps are not intended for pumping air, gases and gas-vapor from one vessel to the second one.