Triple Coil Electrohydraulic Servo Valve Assembly

The hydraulic actuator assembly uses a two-stage hydraulic servo valve to modulate the position of the

actuator output shaft and thereby control the gas fuel valves. The first stage torque motor utilizes a triple

wound coil, which controls the position of the first and second stage valves in proportion to the total

electric current applied to the three coils.

If the control system requires a rapid movement of the valve to send more fuel to the turbine, total

current is increased well above the null current. In such a condition, control port PC1 is connected to

supply pressure. The flow rate delivered to the piston cavity of the actuator is proportional to the total

current applied to the three coils. Thus, the opening velocity is also proportional to the current (above

null) supplied to the torque motor.

If the control system requires a rapid movement to close the gas fuel valve, the total current is reduced

well below the null current. In such a condition, port PC1 is connected to the hydraulic drain circuit. The

flow rate from the piston cavity to drain is proportional to the magnitude of the total current below the

null value. Thus, the closing velocity is also proportional to the current (below null) supplied to the torque

motor.