A turbine inlet supplies compressed air to drive a turbine impeller. There is a compressor impeller and a compressor inlet connected to supply air to be compressed to the compressor impeller. The compressor impeller delivers air to a compressor outlet. The compressor outlet is connected to the turbine inlet. A turbine outlet is connected to a first connection connected to an aircraft. The turbine impeller is connected to the compressor impeller by a drive shaft including a radially outwardly extending thrust disk, and thrust bearings provided on each side of the thrust disk. A cooling air inlet is connected to pass air along the thrust bearings, then radially inwardly and then axially along the shaft. The cooling air is directed to a cooling air outlet. The cooling air outlet is connected to a second connection maintained separate from the first connection. An environmental control system is also disclosed.