Using one of the following methods will ensure that a seal face pressure reversal, which can fail the seal, will not occur:
- A dedicated differential pressure control valve for each seal with a signal select device that will reference the higher value of seal gas reference pressure or primary vent pressure upstream of the primary vent orifice.
- One differential pressure control valve supplying seal gas to each seal in the compressor that senses pressure in the primary vent header downstream of the orifices and set a sufficient high differential pressure (3-4 barg) to ensure that supplied seal gas pressure will always be greater than the maximum flare header pressure. (This alternative is used for large flow compressors where the excessive seal gas flow entering the compressor is still a small percentage of the total compressor flow.)
- Buffer gas (nitrogen or air) supply upsets
- Control valve malfunction
- Carbon ring floating seal hang-up
- Carbon ring floating seal wear
- Bearing housing oil drain system blockage