Pilot valve for steam turbine

摘要

A pilot valve (31) associated with a main valve (32) for the admission of steam to a steam turbine comprises convergent-divergent nozzle (47) formed by a concave deflector (35) that is part of the pilot valve head (33) and a convex portion of the pilot valve seat (34). The nozzle (47) effects that the ratio of the cross-sectional area of the nozzle throat (42) to the cross-sectional area at the nozzle exit varies with valve lift and that the steam flow through the valve is smooth and directed away from critical valve components. This allows a minimisation of erosion of critical valve components and an increase in valve operational lifetime.