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Woodward 8921-018

Product Identification:​ EHPC (Electro-Hydraulic Power Cylinder) — a custom, application-specific linear integrating actuator for steam turbine control valve or valve rack positioning.
Product Overview:​ The 8921-018 is Woodward’s EHPC designed for ease of application and use. It is a linear integrating driver typically used for steam turbine control valve or valve rack positioning. The actuator uses a low-pressure (80–250 psi / 552–1724 kPa) hydraulic oil source, then employs three amplification stages to generate the required output shaft force. As a custom actuator, the EHPC is configured and built for the specific application.
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Detailed content

Working Principle:​ The EHPC receives a 0–200 mA integrating input signal (100 mA null) and uses a low-pressure hydraulic source amplified through three stages to produce precise linear shaft motion. Position feedback is provided via 4–20 mA, 20–4 mA, 0–10 Vdc, or 10–0 Vdc.
Technical Specifications:
  • Supply Pressure:​ 80 to 250 psi (552 to 1724 kPa)
  • Input Power:​ 24 Vdc ±10% @ 2 A
  • Input Signal:​ 0–200 mA integrating input signal (100 mA null)
  • Position Feedback:​ 4–20 mA, 20–4 mA, 0–10 Vdc, or 10–0 Vdc (minimum to maximum cylinder position)
  • Output Shaft Diameter:​ 1.750 in (44.45 mm)
  • Shaft Material:​ Hardened 17-4 PH stainless steel
  • Thread Size:​ 1.250 in –12 UNF-2A
  • Pressure Sensitivity:​ Not less than 2%
Material Composition:
  • Output shaft: Hardened 17-4 PH stainless steel
  • Hydraulic sections: Precision-machined metal bodies with three-stage amplification
Structural Features:​ Linear actuator with integral hydraulic amplification stages, threaded output shaft for valve connection, position feedback transducer.
Application Scenarios:​ Steam turbine control valves, valve rack positioning for mechanical-drive or generator-drive steam turbines.
Installation Requirements:
  • Mount rigidly to the valve or valve rack
  • Provide filtered hydraulic oil supply at 80–250 psi
  • Connect 24 Vdc ±10% power supply at 2 A
  • Wire integrating input signal (0–200 mA) and position feedback per configuration
  • Follow ESD-safe handling procedures
Usage Precautions:
  • Do not remove PCB from control cabinet unless necessary
  • Avoid synthetic clothing; wear cotton or cotton-blend to prevent static buildup
  • Do not touch PCB components or conductors except at edges
  • Keep replacement PCBs in anti-static bags until ready to install
  • Prime mover must have an independent overspeed shutdown device
  • Unauthorized modifications outside specified limits void warranty and may cause injury or property damage

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