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Woodward 8904-786
Product Name: Actuator and Valve Combined Unit (part number 8904-786)
Product Overview: The 8904-786 belongs to the Woodward 8904 series of actuator and valve combined units for gas turbine fuel systems. The combined unit is delivered pre-matched and calibrated from the factory for direct installation into turbine fuel systems, integrating an electro-hydraulic actuator with a gas valve.
Detailed content
Technical Specifications: Based on the 8904 series combined unit architecture (exemplified by related models such as 8904-780):
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Actuator output torque: 30 to 75 N·m (22 to 55 lb-ft)
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Actuator weight: approx. 6.6 kg (14.5 lb)
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Valve flow range: 23 to 18,144 kg/h (50 to 40,000 lb/h)
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Gas supply pressure: up to 600 psig (4,137 kPa)
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Differential pressure range: 25 to 600 psi (172 to 4,137 kPa)
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Hydraulic oil supply pressure: 400 to 1,000 psig (2,758 to 6,895 kPa), allowing ±20% fluctuation
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Hydraulic oil viscosity range: 0.6 to 400 centistokes
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Hydraulic oil filtration: 10 µm nominal
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Gas temperature range: –40 to +149 °C (–40 to +300 °F)
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Ambient temperature range: –40 to +121 °C (–40 to +250 °F)
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Explosion-proof certification: UL Listed Class I, Division 1, Groups C & D; CSA Listed C22.2
Functional Features:
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Actuator and valve pre-matched at factory with basic calibration completed, reducing on-site commissioning
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TM-series integral electro-hydraulic actuator uses torque motor servo valve for rapid response and high control precision
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Rotary sleeve and gate throttle structure provides excellent anti-contamination capability
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Valve design includes inlet guide tube that directs gas impurities toward the metering port, reducing impurity accumulation in the valve body
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Metering sleeve support bearing is completely sealed off from gas to protect internal mechanisms
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Fail-safe: actuator automatically biases toward minimum fuel direction upon loss of power
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All internal parts made of fully hardened stainless steel for corrosion and wear resistance
Material Composition:
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Actuator housing: high-strength aluminum alloy
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Internal actuator parts: fully hardened stainless steel
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Valve body: precision-cast stainless steel
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Metering sleeve and gate: fully hardened stainless steel, precision-ground
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Seals: fluorocarbon rubber (FKM) or other gas-resistant elastomers
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Hydraulic seals: preformed packing rings to prevent magnetic contaminant accumulation
Structural Features: The actuator and valve are directly connected via an adapter with no intermediate transmission link. The rotary sleeve and gate metering structure provides excellent flow resistance characteristics. A dual-acting servo piston delivers powerful driving force. The hydraulic inlet fitting has a built-in 40 µm strainer for additional contamination protection. An electrical position feedback sensor is built into the actuator for closed-loop control. The overall structure is compact for easy installation within the turbine compartment.
Working Principle: The electronic controller sends an electrical command signal to the torque motor servo valve inside the actuator. The servo valve generates a pressure differential to drive the secondary spool, regulating the flow of hydraulic oil to the two ends of the dual-acting servo piston. The piston movement drives the final output shaft to rotate, thereby changing the opening of the valve metering sleeve. The built-in electrical position sensor detects the position in real time and feeds back to the controller, forming a high-precision closed-loop position control.
Application Scenarios:
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Industrial gas turbine generator set fuel control
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Gas compressor drive fuel management
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Combined heat and power (CHP) system gas supply regulation
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Distributed energy station gas flow control
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Marine and offshore platform gas power units
Installation Requirements: Handle with care during lifting and installation to avoid damaging seals, mounting surfaces, and factory calibration settings. Protect hydraulic and gas connection ports with plastic caps or covers when not connected to formal piping. The actuator is delivered pre-calibrated and purged of calibration fluid, ready for installation without additional cleaning or calibration. Confirm hydraulic supply pressure is within the specified range before installation. Bleed trapped air from the hydraulic system to prevent abnormal initial operation. Configure a filter meeting requirements at the gas inlet. Use shielded cable for electrical connections with proper grounding.
Usage Notes: Hydraulic oil cleanliness is critical to actuator life; maintain the specified filtration grade (10 µm nominal). Strictly control gas impurity content. Regularly inspect hydraulic system pressure and oil condition. Avoid operation under overpressure, overtemperature, or out-of-range viscosity conditions. Periodically check electrical connector sealing and position feedback signal stability. Follow Woodward OEM recommendations for maintenance intervals; return to factory for overhaul upon expiry to restore to “like-new” condition.
