axial position thereof an oil feed passage 54 is provided as a conduit for oil flowing radially inwardly to the bearing surfaces and an oil slinger 50 is provided to sling the oil radially outward from the shaft 36 an annular cavity 56 then functions to receive the oil which is slung off from the bearing 40 and to facilitate the drainage of oil through a passage 57 and back to the sump 58 in order to provide a counteraction to the aerodynamic thrust that is developed by the impeller 37 a 34 balance piston 34 is provided by way of a low pressure cavity 59 behind the impeller wheel 37 a passage 61 is provided in the impeller 37 in order to maintain the pressure in the cavity 59 at the same low pressure as the compressor suction indicated generally by the numeral 60 this pressure downstream of the guide vanes 70 typically varies from around 77 psia at full load down to 40 psia at 10 load since the pressure in the transmission casing is higher i e equal to the compressor suction pressure upstream of the inlet guide vanes 70 or about 78 79 psia than that in the cavity 59 and especially at part load operation a labyrinth seal 62 with its associated teeth 63 is provided between the bearing 40 and the impeller 37 to seal that.