particles of up to 50 microns in size must be handled by the subsea pump the fluid film bearings in the subsea pump motor assembly are made of ceramic materials such as silicon carbide or tungsten carbide that have proven effective at withstanding abrasive particles the bearings are designed to have a large fluid film for better particle handling characteristics because the liquid filled motor is above the balance drum any gas that is liberated across this throttling device tends to rise into the motor cavities this gas accumulation could eventually result in partially uncovered upper bearings which could lead to bearing damage and failure the pump motor in this embodiment incorporates a vent in the motor top cap which allows the balance flow to purge out of the top of the motor back to the separator this serves to establish the pressure gradient required across the pump for thrust balance and to sweep free gas continuously out of the motor and back to the separator while this permits some gas flow through the bearings it does not materially affect the fluid properties this strategy requires that the top of the upper motor bearings be below the separator liquid level when the pump is shut down so that the process fluid does not flow back to the separator uncovering the bearings in addition to providing the motive power for transporting.