Every industrial vacuum furnace system uses a primary (aka mechanical) pump, which is also commonly referred to as a “backing” pump when either used in series with a booster pump, or used with both a booster and secondary (“high vacuum”) pump combination, such as a diffusion pump. These primary pumps are further divided into “wet” pumps (e.g., oil sealed rotary vane style or liquid ring pumps) or “dry” pumps (e.g., claw, hook or screw). Of the dry primary pumps, the most common types are the claw pump and the screw pump.
Dry pumps are being increasing popular as an alternative to oil sealed rotary vane pumps for many medium and high vacuum applications (e.g., in low-pressure vacuum carburizing where fine granular soot is carried from the process into the pump). Designers and users of vacuum furnaces must have a good understanding of how claw and screw pumps operate. This includes the principles of operation, pump design, sealing, operating characteristics, features, purging, and ancillary devices.
