The subject of variable Vi is very interesting. As i have said before, i have not any experience with large and/or industrial systems. On dual screw compressors with variable Vi, i clearly see the need for fully independent movement of the capasity slide and the varable Vi slide in order to maintain the best isentropic efficiency at all pressure and load ratios. I have however got the impression that variable Vi is not fully acomplished when the compressor is running in part load. Can someone explain if this is the case and why?