① Maximize the sealing resistance to ensure that leaking steam is fully consumed within the steam bend passage and expansion chamber.
② Minimize the radial clearance between moving and stationary components, but prevent them from rubbing against each other. Consideration should also be given to minimizing the contact area and frictional heat generated should friction occur, while increasing thermal resistance to prevent thermal deformation of surrounding components.
③ The axial clearance between moving and stationary components should ensure that they do not rub against each other during the entire start-up and shutdown process of the turbine unit, allowing for thermal expansion differences and relative mechanical displacement.