A “roughing pump” is a vacuum pump used to evacuate a vacuum system at the outset, as the first stage towards achieving a higher vacuum. The term originates from the “rough vacuum range” it works in, which is above 1×10−3 torr (0.1 Pa). Pumps that operate in higher vacuum ranges operate inefficiently at atmospheric pressures, whereas pumps that work efficiently at atmospheric pressure usually cannot produce a vacuum lower than approximately 1×10−3 torr. The process of learning how to use vacuum pumps is often a difficult and time-consuming exercise, in this article you will find important tips to help you operate your pumping system in an energy and cost-saving manner.
“The roughing pump is the component that primes the other pumps in series on the vacuum line, evacuating the system until a pressure level is reached at which a booster pump (known as a lobe-type roots pump) can be activated, followed by other types of diffusion, turbomolecular, cryogenic, ionic and other pumps that can be used when the pressure is reached. Depending on the flow rate, the pumping system is proportioned in relation to system volume, pumping cycle speed, load degassing, and contamination produced by the load (vapors, dust, binders, etc.) in the pump itself. It is, for this reason, that mechanical strength and wear influence the choice of pump type. The first choice concerns the decision to adopt a vane pump or a rotary piston pump.”
SOURCE: TAV Vacuum Furnaces