Need help with a turbine issue?

In steam turbines, the servo valves used in servo motors are generally electro-hydraulic servo valves, which consist of a torque motor with two stages of amplification and a mechanical feedback system. The first stage of amplification is a dual-nozzle and baffle system ； The second stage of amplification is a slide valve system, and its principle is as follows: When an electrical signal is sent in from the servo amplifier, current flows through the coils in the armature of the torque motor, generating a magnetic field. Under the action of the armatures on either side, a rotational torque is produced, which causes the armature to rotate; this in turn causes the connected flap to move, with this flap extending between the two nozzles. Under normal and stable operating conditions, the distance between the baffle and the nozzles on both sides is equal, resulting in equal oil discharge areas for the nozzles on each side; therefore, the oil pressure on both sides of the nozzles is equal. When an electrical signal is applied, the armature drives the baffle to rotate; as a result, the baffle moves closer to one of the nozzles, reducing the oil discharge area of that nozzle and thus decreasing its flow rate. This increases the oil pressure in front of that nozzle. Meanwhile, the distance between the opposite nozzle and the baffle increases, leading to an increased oil discharge volume and a reduced flow rate, which in turn lowers the pressure in front of that nozzle. In this way, the original electrical signal is converted into torque, which generates a mechanical displacement signal; this signal is then converted into an oil pressure signal, and it is amplified through the nozzle-baffle system. The oil pressures in front of the nozzles on both sides of the baffle are connected to the two chambers of the lower spool. Therefore, when the oil pressures in front of the two nozzles are not equal, the oil pressures at both ends of the spool are also not equal. The spool moves under the effect of this pressure difference, and the oil ports controlled by the shoulders on the spool open or close, thereby allowing high-pressure oil to flow into the piston rod chamber of the hydraulic actuator in order to increase the opening degree of the steam valve, or allowing the piston rod chamber to be connected to the return oil path so that the oil in that chamber can be drained, which in turn allows the spring force to reduce or close the steam valve. To improve the stability of the control system, a feedback spring is installed in the servo valve. In addition, there is a certain mechanical zero offset when adjusting the servo valve; this allows, in the event of a sudden power loss or signal interruption during operation, the mechanical force to cause the spool to shift to one side, thereby closing the steam valve.

The teacher upstairs has already explained it very clearly, so I won’t say anything more, hehe