The screws in a rotary screw unit compress oil to produce the compressed air, says Worman. "Any particulate contamination can change the surface of the rotors so they won't mate up with each other," he points out. "You will also have added costs due to increased service intervals and greater filtration."
Before you make any final decisions, ask yourself how much air you need and at what psi; what types of tools you will be running; how many tools you will be running; and how often you need compressed air.
"It's not always that cut and dried," says Pettigrew. "There are advantages to each one."