... stage vacuum pumps ( one rotary vacuum pump + one roots vacuum pump) 3. high efficiency Use:This unit ... plant, and transformer manufactory, and it can vacuum pump in vacuum melting, welding, drying, chemical pharmacy. ... the gas which will be reaction to pump oil or cause erosive effect on ferrous ... The unit takes Roots Pump as main pump and spinning vacuum pump as pre-stage pump.(3) A vacuometer is ...