The water ring vacuum unit is primarily composed of a Roots pump as the main pump and a water ring pump as the preliminary pump in series. The water ring pump chosen for the water ring vacuum unit is more advantageous as a preliminary pump than other vacuum pumps, as it not only overcomes the drawback of low exhaust rate at a certain pressure due to the single water ring pump's pressure difference limit (the unit's pressure difference limit is significantly higher than that of the water ring pump), but also retains the Roots pump's ability to work quickly and achieve a higher exhaust rate. It is capable of effectively removing large quantities of condensable steam, especially when the mechanical vacuum pump with gas-sealed oil seal does not have sufficient capacity to remove condensable steam, or when the solvent used can degrade the pump oil, affecting performance, or when the vacuum system does not allow oil contamination. If equipped with explosion-proof motors and electrical equipment and operated under the corresponding safety regulations, it can also remove flammable and explosive gases.