| http://www.w3.org/ns/prov#value | - In a first preferred mode of operation, electronic control means responsive to a sensed vacuum level are operable to drive a brushless DC stepper motor which in turn drives an eccentric shaft coupled to a two-stage diaphragm pumping mechanism at a high speed to quickly evacuate the vacuum chamber (400 RPM) and at a low speed, such as about 60 RPM, for continuous operation and long life of the dega
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