Screw Rotor Profiles of Variable Lead Vacuum and Multiphase Machines and Their Calculation Models

Twin screw machines are mechanically simple and reliable, having only two moving parts, while their manufacturing cost is low and, as a result of optimization of their rotor proportions and profiles, their efficiency is high. Consequently, they are now used widely both as multiphase and vacuum pumps.

This study gives the results of an investigation of how their performance is affected by changing the rotor lead, i.e. the axial step along the rotor wrap, from a constant value to a variable one. A number of different configurations have been considered and it is shown that, for machines with a large wrap angle, a variable lead results in greater displacement and improved efficiency.