Turbo Expander Bearing Gas Problem

Air bearings are supplied as a pneumatic potentiometer if the intermediate pressure drops there are two possible reasons: - the orifice between supply and bearing is partly clogged by dirt or oil (?) - the clearance increased due to contacts between shaft and bearing either due to shaft oscillations or to contacts at start with low air pressure. There is an other possibility: there are some leaks so that the active flow is decreased.

Is it a cryogenic turbo expander? Can you give details like inlet/outlet temp. and pressure etc. "5 bar bearing gas pressure" is bearing sealing gas for oil lubricated bearing or for gas lubricated bearing. For oil lubricated bearing seal gas pressure depend on gap pressure (pressure acting on back side of impeller) which may vary if inlet or outlet pressure varies. So, please check the variation of inlet and outlet pressure. Most probably lower inlet pressure. Are you getting cold fumes also?