Electrohydraulic Power Servo
The Electrohydraulic Power Servo is a three-stage servo valve used in conjunction with a customer-supplied power cylinder to provide very accurate and responsive power cylinder control. The EHPS’s staged design allows for accurate power cylinder position control (accurate EHPS flow control), with the flow capacity to meet required cylinder response times (slew rates).
The EHPS’s stages are as follows:
- Stage 1—a torque-motor servo valve
- Stage 2—a spool/amplification stage with feedback to the first stage
- Stage 3—a spool/amplification stage with feedback to the second-stage
The EHPS is designed to control power cylinders with bore diameter sizes in the range of 100–255 mm (4–10 inches) and servo stroke lengths in the range of 50–305 mm (2–12 inches).
The EHPS’s torque motor accepts a 0–200 mA current signal from an external servo controller (not included) and is calibrated for a null current of 100 mA (used to center the unit’s internal pilot valve). An electronic servo position controller like Woodward’s Servo Position Controller (SPC) must be used in conjunction with the EHPS to control the user’s cylinder, valve, or valve rack. The servo position controller accepts a valve position feedback signal and outputs a position demand signal to the EHPS to perform closed loop control of the unit servo.