TABLE OF CONTENTS The steam turbine requires that seals be provided at a number of locations to minimize the leakage of steam between and past stationary and rotating components. These seals can be arranged, or classified, in one of three main groups:
On those stationary components that enclose, and possibly carry steam path components. These include the casings, both inner and outer, and the diaphragms or stationary blades. Such components are used for both high and low (including sub-atmospheric) pressure application
On the rotating components, which compromise basically the rotor, which carries and locates the rotating blades, together with the stage hardware associated with these rows. It can also include some "shrunk-on" components, such as wheels or discs, coupling flanges, and thrust collars
The other, basically stationary equipment, which is included to support, connect, and control the unit operation
The steam path is defined as those components included in the first two groups, which expand the steam and extract work from it. The components of these two groups operate in close proximity, but must maintain a running clearance sufficient to prevent hard contact. In operation, steam leakage occurs between the stationary and rotating components of the unit. This leakage steam represents a bypass of the blade system, and therefore is a waste of the energy that is available from the working fluid. To limit such leakage, sealing arrangements are made within the unit to prevent or minimize this loss.
There are three major locations within the steam path where seals are employed:
