The turbine shaft speed is changed at constant load by adjusting the position of pivot a on piston rod 3 of servomotor 1. This is done with nut 2 which can be moved along the thread of rod 3. As point d is moved upward, valve spool 4 is also shifted upward, directing fluid to the upper end of servomotor 1 and moving valve member 5 downward to increase the supply of steam to the turbine. At constant load, valve member 5 should return to its previous position, and point d, for steady-state operation, always occupies the same position, which corresponds to blocked off ports in the directional valve. Therefore, when point d moves upward, sleeve b of governor 6 must move downward and this takes place only when the speed is reduced.
$4248$CHP,Rg$