Accurate prediction of internal leaks in stationary dry Roots vacuum pumps

There exists a calculating method for internal leaks in dry Roots vacuum pu mps. It rests upon the semi-empirical Knudsen-Dong law (Knudsen M, Ann Phys 1909;28:75; Dong W, PhD thesis, Contract no. W-7405-eng-48, University of California, 1956) describing steady rarefied gas flows in the three well-kn own regimes of flow; the only data input is the geometric contour of the st ator and the rotors, and the pressure operating conditions. Using readings taken from a stationary dry Roots pump, it is checked that this calculating method is capable of predicting the conductance of each of the clearances to a few percent, on a pressure range widely covering the transient flow re gime. (C) 1999 Elsevier Science Ltd. All rights reserved.