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Seal gas is usually injected from compressor discharge. During normal operation of compressor seal gas pressure is high enough for maintaining positive flow across labyrinth at process end, which prevents dirty gas ingress from compressor housing.

During compressor start-up/shutdown seal gas pressure is not sufficient for maintaining positive pressure/flow across labyrinth at process end. Also, during pressurized shutdown pressure in housing and seal gas pressure become equal which makes it possible for unfiltered gas to pass through primary sealing surface. This can be eliminated by fitting gas booster in seal gas supply system.

Clean and dry gas is required for DGS and compressor unfaulty operation. Booster is fitted with a small pneumatically actuated piston compressor. Usually instrument air or Nitrogen are used as driving gas.
The system is automatically switched on when seal gas flow rate/ differential pressure gets low and is switched off once seal gas flow rate/ differential pressure gets back up.