Servo valves and proportional valves
Servo valves and Servo-Proportional Valves are electro-hydraulic operate by transforming a changing analogue or digital input signal into a smooth set of steps of movement in a hydraulic cylinder. Servo valves can provide precise control of position, velocity, pressure and force with good post movement dampening characteristics. A low voltage is used control the servo valve. The control voltage is passed into an amplifier which provides the power to alter the valve's position. The valve will then deliver a measured amount of fluid power to an actuator. The use of a feedback transducer on the actuator returns an electrical signal to the amplifier to condition the strength of the control voltage to the servo valve.
Many of the servo values in use today are manufactured by Moog Inc. A typical example of servo valve is the Moog servo valve D631 series. An example of servo valve use is in Blow Moulding where the servo valve controls the wall thickness of extruded plastic making up the bottle or container by use of a deformable die.