The RUVAC series of Roots vacuum pumps are often used where great volumes have to be pumped. When combined with dry or oil-sealed forevacuum pumps, Roots vacuum pumps are used to effectively increase the pumping speed at low pressures, thus extending the operating pressure range of the forevacuum pump. This pump combination can be capable of improving the attainable ultimate pressure of a pump system by a factor of 10. RUVAC roots pumps are available in three series with different motor drives.