A method of monitoring a WDM optical signal is provided. In real-time, a foregroundbackground separation algorithm is used on the real-time stereo video signal to identify pixels from the stereo video signal that represent the physical foreground object. The insert is adjacent the impeller and serves to minimize catastrophic compressor failure that might otherwise occur as a result of contact between the impeller and compressor chamber wall. A plurality of radial locking pins are arranged radially from the spindle.