4.1.8 Sealing gas
When pumping corrosive process gas, there is a risk that the gas might attack parts of the pump. To counter this danger, sensitive parts must be protected by a continuous flow of inert gas. Pumps are therefore fitted with a special gas inlet system through which gas flows into the pumping system at defined locations. In turbo-molecular pumps, it is principally the bearings and the motor compartment which require protection. The intake of sealing gas in the motor compartment protects against chemical reactions by aggressive gases with corosion-sensitive components of the lubricant or the bearings as well as preventing dust and particles entering the lubricant reservoir and mixing with the lubricant. The use of sealing gas to protect the motor and prevent particles from entering and causing contact between the shaft and the emergency bearings, for instance, is also recommended for lubricant-free turbopumps.
In addition to sealing gas for the bearings, process-capable dry backing pumps also have purge gas injected into individual pumping stages of the process pump. The process-dependent purge gas flow is adjusted using pressure regulators upstream of the calibrated nozzles or flow regulators (mass flow controllers, or MFC) and monitored by pressure sensors and switches.