Molecular drag pump
From Wikipedia, the free encyclopedia
A molecular drag pump is a type of vacuum pump that utilizes the drag of air molecules against a rotating surface.[1] The most common sub-type is the Holweck pump, which contains a rotating cylinder with spiral grooves which direct the gas from the high vacuum side of the pump to the low vacuum side of the pump.[2] The older Gaede pump design is similar, but is much less common due to disadvantages in pumping speed.[3] In general, molecular drag pumps are more efficient for heavy gasses, so the lighter gasses (hydrogen, deuterium, helium) will make up the majority of the residual gasses left after running a molecular drag pump.[4]
The turbomolecular pump invented in the 1950s, is a more advanced version based on similar operation, and a Holweck pump is often used as the backing pump for it. The Holweck pump can produce a vacuum as low as 1×10−8 mmHg (1.3×10−6 Pa).