A process fluid recycle system for compressor assemblies to recycle process fluid vapor flowing from one or more compressors to gear case(s) through shaft seal(s). The flowing process fluid is recycled back to the low pressure inlet of the compressor assembly by way of a recycle conduit. Coalescing filters are provided to separate oil mist from the process fluid vapor. Oil vapor and water vapor can also be removed, where necessary, by suitable oil and water vapor traps. During startup and shutdown or other times when low pressure transients occur that could cause a back flow of gear oil from the gear case into the compressor(s) by way of the shaft seal(s), an anti-back flow compressor is operated to ensure that the pressure within the gear case will be less than within the compressor.