When the vacuum is on for most of the shift. An ejector consumes compressed air the whole time it runs, and compressed air is an expensive way to move volume; a motor-driven unit converts electricity directly. The crossover is a duty-cycle question rather than a size question, which is why the same pick head is served by an ejector on one line and a pump on another.

The proportion of a given period the unit may run before it has to stop and cool. Continuous-rated units may run indefinitely; intermittent-rated ones carry a percentage and a reference period. Ignoring it does not trip the machine, it shortens the motor life, so the failure appears months later as a unit that has been quietly overheating.

Because these units run near people for long periods, unlike an ejector that fires for a second at a time. A dry running element and a cooling fan together can dominate the sound level of a packing station, and the published figure is measured at a stated distance under a stated load - both of which change what is heard on the floor.

The pumping element itself. Anything drawn off the workpiece - board dust, film scraps, powder - passes straight into the element unless it is stopped first, and abrasive dust in a dry running unit removes the clearances the vacuum depends on. Filter condition is the single largest factor in how long one of these lasts.

It matters anywhere carryover would contaminate the product or the environment being evacuated, which includes printing, electronics assembly and packaging of unwrapped goods. Oil-free units trade some ultimate vacuum for the absence of carryover, and they remove an oil change from the maintenance schedule.

Yes, and that is the usual reason to centralise. A single larger generator feeding a manifold is more efficient than several small ones, but every head then shares the same vacuum reserve, so a leak at one station is felt at all of them. Reservoirs and non-return valves at each head limit the interaction.

Yes. The cooling air path has to be clear and the unit set in the orientation the manufacturer specifies. Motor ratings assume free airflow around the housing, and units recessed into a cabinet or stacked against a panel run hotter than their rating allows. Where enclosure is unavoidable, the cabinet needs its own ventilation.