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Woodward 8915-679
Product Introduction: The 8915-679 is a linear-motion electro-hydraulic servo actuator developed for speed/governing control of small- and medium-sized steam turbines and turbomachinery. It converts an electronic analog command signal into a high-power linear hydraulic output force to directly drive the steam turbine control valve, achieving continuous speed and load regulation. The actuator integrates the EM35 electronic driver as a single, compact unit — no external servo amplifier is required. It operates from the turbine’s lubricating oil supply and is widely used in power-generation turbines and industrial drive turbine retrofits.
Detailed content
Technical Specifications:
- Control Signal: 4–20 mA analog input
- Hydraulic Medium: Turbine oil (lubricating oil)
- Supply Pressure: 0.21 – 1.03 MPa
- Stroke: 38 mm
- Output Force: 11,200 N
- Power Supply: 24 Vdc
- Operating Temperature: –20 to +70 °C
- Protection Class: IP54
Functional Features:
- Integrated EM35 driver board with built-in 11-point piecewise linearization table to compensate for valve non-linear flow characteristics
- Patented anti-contamination self-cleaning servo valve, tolerant of impurities in turbine oil, reducing jamming failures
- Built-in LVDT position feedback sensor for closed-loop position control with high repeatability
- Fail-safe logic: on loss of power or loss of oil pressure, the actuator moves to the safe fault position
- Anti-side-load design reduces piston-rod leakage caused by lateral forces
Application Scenarios: Main control valve of small/medium turbine generator sets; speed governing actuators for industrial drive turbines (compressors, pump drives); retrofit projects for cogeneration units.
Performance Parameters:
- Full-stroke response time: ≤150 ms
- Positioning accuracy: ±0.25% FS
- Hysteresis: ≤0.5%
- Resolution: 0.1%
Material Composition: Cylinder barrel – high-strength cast steel; piston rod – quenched chrome-plated alloy steel; servo valve spool – hardened stainless steel; housing – cast aluminum + carbon steel combination; seals – oil-resistant fluorocarbon rubber.
Structural Features: Fully integrated monoblock construction — hydraulic cylinder, servo valve, EM35 electronic driver box, and LVDT displacement sensor are assembled as one unit. The oil-port flange is on the side, with the piston rod output downward. The electronic compartment is physically isolated from the hydraulic chamber to prevent oil ingress onto the circuit board.
Working Principle: The control system output 4–20 mA command enters the EM35 driver board, which outputs current to drive the built-in servo valve. Turbine pressure oil enters the servo valve and is proportionally directed to either side of the cylinder to push the piston rod in linear motion. The LVDT continuously acquires the actual piston-rod position and feeds it back to the EM35 driver unit, where it is compared with the command signal for closed-loop regulation, maintaining the output position following the command.
