Description
Woodward B8251-758
Technical Specifications
- Product Type: Electro-hydraulic linear actuator / servomotor.
- Control Input: Accepts proportional analog current signals (typically 4-20 mA or 0-20 mA) from electronic governors.
- Hydraulic Supply: Requires a clean, pressurized hydraulic oil supply (pressure varies by specific system configuration).
- Feedback Mechanism: Integrated LVDT (Linear Variable Differential Transformer) or potentiometer for closed-loop position feedback.
- Stroke Length: Customizable linear travel distance based on specific prime mover requirements.
Functional Features
- High-Response Positioning: Delivers rapid and precise valve or fuel rack movement to accommodate sudden load transients.
- Closed-Loop Accuracy: Continuously compares the commanded position with actual position feedback to eliminate steady-state errors.
- Fail-Safe Capability: Designed to spring-return to a predetermined safe position (e.g., fuel shut-off) upon loss of hydraulic pressure or electrical power.
- High Force Output: Generates substantial linear thrust to overcome high-pressure steam or fuel system forces.
Application Scenarios
Extensively utilized in diesel and gas engine fuel control systems, steam turbine inlet valve actuation, and turbocharger variable geometry control across power generation, marine propulsion, and mechanical drive applications.
Performance Parameters
- Positioning Accuracy: Typically within ±0.5% of full stroke.
- Dynamic Response: Millisecond-level response time for excellent transient recovery.
- Hysteresis: Minimal mechanical hysteresis ensuring smooth and repeatable valve movement.
Material Composition
Constructed with a heavy-duty steel cylinder barrel, precision-machined stainless steel piston rod, and high-performance elastomer seals compatible with industrial hydraulic oils. The internal LVDT is housed in a robust, vibration-resistant casing.
Structural Characteristics
- Form Factor: Cylindrical, linear-motion actuator with integrated feedback sensor.
- Mounting: Clevis, flange, or trunnion mounting provisions for secure attachment to the prime mover.
- Connections: Hydraulic supply and return ports, plus a multi-pin electrical connector for control signals and feedback.
Working Principle
The electronic governor sends a current command to the actuator’s internal servo valve. The servo valve meters pressurized hydraulic oil into one side of the piston chamber, generating linear force. The integrated LVDT continuously monitors the piston’s exact position and feeds this data back to the governor. The governor adjusts the current until the actual position perfectly matches the commanded position.
Installation Requirements
- Mount securely to the engine or turbine frame to prevent misalignment and excessive vibration.
- Connect hydraulic supply lines using clean, high-pressure-rated tubing or hoses.
- Wire the feedback and control signals using shielded cables, grounded at the controller end.
Usage Precautions
- Ensure hydraulic oil meets the specified cleanliness and viscosity standards to prevent servo valve fouling.
- Never operate the actuator without verifying the fail-safe spring mechanism is functional.
- Perform regular stroke and feedback calibration tests during scheduled maintenance.
