Gland seal systems very important to main and auxiliary turbines.Turbine shafts must exit their casings in order to couple up or connect with the unit that the turbines drive (reduction gears, pumps, etc.) The main and auxiliary gland seal systems enable the turbine to be sealed where the shaft exits the casing; in effect keeping "air out and steam in."
The purpose of gland seal system is to prevent the leakage of air from the atmosphere into turbine casings and prevent the escape of steam from turbine casings into the atmosphere.
The gland sealing system provides low pressure steam to the turbine gland in the final sets of labyrinth packing. This assists the labyrinth packing in sealing the turbine to prevent the entrance of air into the turbine, which would reduce or destroy the vacuum in the associated condenser. Excess pressure (excess gland seal) is removed by the gland seal unloader.
Since there are times when steam escapes from the seals, a gland exhaust system is provided. The gland exhaust system consists of low pressure piping connected to the gland area between the last two outer sets of labyrinths which receives and prevents steam from escaping to the atmosphere. This system collects the steam and directs it to a condenser for further use in the steam plant.
Most steam turbines have a shaft sealing system which uses carbon rings to isolate the rotor assemblies on both ends with steam injected to prevent air in-leakage in to the turbine. The leakage would reduce turbine efficiency and flow into the condenser downstream of the turbine further reducing system efficiency. This gland steam must be removed by an ejector or exhaust fan to prevent it from flowing back into the turbine.