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Woodward 8904-780

Product Overview
The Woodward 8904-780 is a member of the 3103 gas valve family integrally mounted with a TM-55 series electrohydraulic actuator. Based on the Woodward 3103/TM55 product platform, this combination unit is an electro-hydraulic, stainless steel control valve for use on aeroderivative and industrial gas turbines. The valve is capable of metering gas flow between 50 and 40,000 lb/hr (23 and 18,144 kg/hr). It is designed to be corrosion-resistant and self-cleaning, allowing it to operate in sour gas environments (high sulfur content gas). The TM-55 hydraulic actuator provides robust position control of the 3103 gas metering valve.
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Detailed content

Technical Specifications
  • Manufacturer: Woodward
  • Equipment type: 3103/TM-55 gas fuel control valve (electro-hydraulic, stainless steel)
  • Metering flow capacity: 50 to 40,000 lb/hr (23 to 18,144 kg/hr)
  • Valve design: Rotating metering sleeve and seal shoe in a stainless steel housing
  • Metering port maximum flow areas: 645 mm² (1 in²) and 1290 mm² (2 in²) standard configurations
  • Actuator: TM-55 proportional, open-loop control with a variety of valve position feedback devices
  • Valve slew time: Minimum 100 milliseconds
  • Time constant: 25 milliseconds
  • Maximum inlet pressure: 45 bar (650 psig)
  • Operating temperature: -40 to +121 °C (-40 to +250 °F)
  • Actuator output force at sleeve outer diameter: Over 1334 N (300 lb) of shearing force
  • Flow turndown ratios: Up to 500:1
  • Explosion-proof certification: UL and CSA Approved
Functional Features
  • Self-cleaning valve concept with through-hardened parts and hard surface coatings for high contaminant resistance
  • Capable of operating in sour gas environments that cause problems for other valves
  • TM-55 actuator provides robust position control with high shearing force to remove deposits and cut through light debris such as pipe scale
  • Optional porting configurations and internal mechanical feedback
  • Optional electrical position transducer for accurate position indication
  • Dry coil torque motor with redundant coil options
  • Actuator factory-adjusted for bias in the minimum fuel direction in event of loss of supply pressure or input current
  • Adapter housing provides adjustable maximum and minimum flow stops and an adjustable minimum position indicator switch
Application Scenarios
  • Aeroderivative gas turbines
  • Industrial gas turbines in the 3730 to 37,300 kW (5000 to 50,000 hp) range
  • Gas turbine fuel metering systems in oil field operations with heavily contaminated, unsweetened gas
  • Scheduling flow for acceleration and deceleration control in conjunction with electronic control systems
  • Closed-loop control of engine parameters such as shaft speed, torque, gas temperatures, and pressures
Material Composition
  • Valve body: Stainless steel construction
  • Internal parts: Through-hardened stainless steel
  • Actuator case: Anodized aluminum
  • Actuator internal parts: Through-hardened stainless steel
  • Hydraulic fluid sealed from torque motor by preformed packing ring
Structural Characteristics
  • Rotating metering sleeve and seal shoe throttling structure
  • Inlet guide tube provides smooth flow path and directs heavy contaminant particles through the metering port
  • Shoe is spring and pressure loaded against the sleeve to obtain a self-cleaning action
  • Direct integral mounting of valve and actuator via adapter
  • 40-micron filter fitting at hydraulic supply pressure inlet
  • Optional electrical position transducer (RVDT, linear synchro transmitter, or potentiometer)
Working Principle
The TM-55 electrohydraulic actuator converts electric control input to angular shaft output for positioning the rotary fuel metering sleeve of the valve. The essential element is a torque motor servovalve which generates a differential pressure applied to both ends of, and operates, the second-stage spool valve. Input current to the torque motor gives proportional displacement of the spool valve and subsequent proportional movement of the servo piston. The rotating metering sleeve position determines the open port area for gas metering. The self-cleaning action occurs as the through-hardened stainless steel shoe scrapes deposits off the sleeve as it rotates.
Control Input Requirements
  • Standard Input Signal: 0.020 to 0.200 A coil current from 0° to 45° stroke
  • Coil Resistance: Single — 26 Ω @ 20 °C (68 °F); Dual — 40 Ω @ 20 °C (68 °F)
Performance Characteristics
  • Hysteresis: 2.0%
  • Repeatability: 2.0%
  • Threshold: Less than 0.25% of maximum input current (200 mA)
Installation Requirements
  • Handle with care during component handling and installation
  • Hydraulic and gas connection ports must be protected when not connected to formal piping
  • A filter meeting requirements must be configured at the gas inlet
  • Shielded cables must be used for electrical connections with proper grounding
  • Adequate dither signal recommended on servovalve input to minimize threshold and hysteresis
Usage Notes
  • Hydraulic oil cleanliness is critical to actuator service life
  • Gas impurity content must be strictly controlled
  • Avoid operation under conditions of overpressure, overtemperature, or outside the viscosity range
  • Regularly inspect hydraulic system pressure and oil condition
  • Actuator maintenance intervals shall follow Woodward OEM recommendations

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