During start, stop and operation of the steam turbine, the cylinder temperature varies greatly. With the temperature changing of the various parts of the cylinder, the parts will expand and contrac. In order to ensure free expansion of the steam turbine and to maintain the cylinder center to be consistent with the rotor center, the sliding-pin systems are provided, the functions are as follows: 

1. To maintain the cyclinder center to be consistent with the rotor, in order to avoid the center changing due to the expansion of the body, thus causing the the vibration of the unit or the friction between the dynamic and the static. 

2. To ensure the free expansion of the cylinder, in order to generate excessive stress and deformation. 

3. To make the axial and radial clearance of the stator and the rotor conform to requirements.