application and features 1. starting up directly from atmosphere pressure for evacuation. 2. used either solely as rough pumps, or in combination with other high vacuum pumps as backing pumps. 3. they find wide applications in the fields of metallurgy, chemical, light industry, medicine, electronics and lsi industries. 4. they can not be used for evacuating the oxygenic, poisonous and explosive gases and gases which can react with pump oil easily. neither can they be used as compressor and transmission pump.