7 Gland sealing system
7.1 Function and system layout
Glands and seals are used on turbines to prevent or reduce the leakage of steam or air between rotating and stationary components that have a pressure difference across them, for example, where the turbine shaft is extended through the cylinder endwalls to the atmosphere.
When the cylinder pressure is higher than atmospheric, there will be a general steam leakage outwards: if the cylinder contains steam below atmospheric pressure, the tendency is for air to leak inwards and the sealing system is designed to prevent the air from entering the cylinder and the condenser.
As most of the steam leakage from glands does not pass through the turbine stages, a loss of power output is involved and every effort is made to reduce this power loss by an efficient arrangement of seals and glands.
In the more recent larger steam-turbines, the labyrinth gland is in general use, although the carbon ring gland and the water seal gland may be found in older turbines. The labyrinth gland acts as a restrictor to both steam and air leakage.