Woodward 8904-931

Digital guide

Product Introduction: Part number 8904-931 belongs to Woodward’s 8904-series valve-and-actuator combined assemblies and is configured as a complete 3103 stainless-steel gas metering valve mated with a TM-55P proportional electrohydraulic actuator. Designed for industrial gas turbine fuel control, the TM-55P actuator receives command signals from an electronic controller and, through an electrohydraulic proportional drive system, precisely positions the rotating metering sleeve of the 3103 gas valve to achieve high-accuracy gas flow metering and regulation.

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Technical Specifications:

Part Number: 8904-931
Manufacturer: Woodward
Equipment Type: Actuator and valve combined assembly
Valve Type: 3103-series stainless-steel gas valve
Actuator Type: TM-55P proportional electrohydraulic actuator
Drive Method: Electrohydraulic proportional drive
Position Feedback: Built-in electrical position sensor (optional RVDT, synchro, or potentiometer)
Control Compatibility: Compatible with Woodward analog and digital control systems

Functional Features:

Actuator and valve are pre-matched at the factory, with matching calibration completed before shipment to reduce on-site commissioning workload.
The TM-55P proportional actuator is driven by a torque motor servovalve, with internal mechanical feedback ensuring precise positioning.
The 3103 gas valve adopts a rotating sleeve and shoe throttling structure, providing excellent contamination resistance, and is designed to operate with sour gas (high sulfur content gas) that causes problems for other gas valves.
The valve design includes an inlet guide tube that directs gas contaminants to the metering port, reducing contaminant accumulation inside the valve body.
The metering sleeve support bearings are fully sealed from the gas to protect internal mechanisms.
The actuator automatically shifts toward the minimum-fuel direction upon loss of electrical power, providing fail-safe protection.
Internal parts are made of through-hardened stainless steel for corrosion and wear resistance.

Application Scenarios:

Fuel control for industrial gas turbine generator sets.
Fuel management for gas compressor drive packages.
Gas supply regulation in combined heat and power (CHP) systems.
Gas flow control in distributed energy stations.
Gas power units on marine vessels and offshore platforms.

Performance Parameters:

Actuator output torque: 38 N·m @ 2758 kPa (28 lb-ft @ 400 psi); 95 N·m @ 6895 kPa (70 lb-ft @ 1000 psi)
Actuator weight: approx. 6.6 kg (14.5 lb)
Actuator angular stroke: maximum 45 degrees
Valve flow range: 23 to 18144 kg/h (50 to 40000 lb/h)
Gas supply pressure: up to 600 psig (4137 kPa)
Differential pressure range: 25 to 600 psi (172 to 4137 kPa)
Gas temperature range: -40°C to +149°C (-40°F to +300°F)
Hydraulic oil supply pressure: 2758 to 8274 kPa (400 to 1200 psig)
Hydraulic oil viscosity range: 0.6 to 400 cSt
Hydraulic oil filtration: 10 micron nominal
Ambient temperature range: -40°C to +121°C (-40°F to +250°F)
Explosion-proof certification: UL Listed Class I, Division 1, Groups C & D; CSA Listed C22.2; CENELEC Zone 1 Group IIC ATEX

Material Composition:

Actuator housing: High-strength aluminum alloy
Actuator internal parts: Through-hardened stainless steel
Valve body: Precision-cast stainless steel
Metering sleeve and shoe: Through-hardened stainless steel, precision lapped
Seals: Fluoroelastomer (FKM) or other gas-resistant elastomers
Hydraulic seals: Preformed packing rings to prevent accumulation of magnetic contaminants

Structural Features:

The actuator and valve are directly connected via an adapter with no intermediate transmission linkage.
Rotating sleeve and shoe metering structure with excellent flow-loss characteristics.
Double-acting servo piston provides powerful driving force; the TM-55P actuator provides a minimum valve slew time of 100 milliseconds and a time constant of 25 milliseconds.
Hydraulic inlet fitting incorporates a 70 micron absolute filter for additional contamination protection.
Optional electrical position feedback sensor (RVDT accuracy ±0.16°).
Compact overall structure for easy installation within the turbine compartment.

Working Principle: The electronic controller sends an electrical command signal to the torque motor servovalve inside the TM-55P actuator; the servovalve generates a differential pressure that drives the second-stage spool valve, regulating hydraulic oil flow to both ends of the double-acting servo piston. The TM-55P is an electrohydraulic, proportional actuator which converts electric control input to angular shaft output for positioning the rotary fuel metering sleeve of the valve. Its essential element is a torque motor servovalve which generates a differential pressure applied to both ends of, and to operate, 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.

Installation Requirements:

Handle and install the assembly with care to avoid damaging seals, mounting surfaces, and factory adjustments.
Hydraulic and gas connection ports must be protected with plastic caps or covers when not connected to permanent piping.
Confirm that the hydraulic supply pressure is within the specified range before installation.
The hydraulic system must be purged of trapped air to prevent abnormal initial operation.
A filter meeting requirements must be installed at the gas inlet.
Shielded cable must be used for electrical connections with proper grounding.

Usage Precautions:

Hydraulic oil cleanliness is critical to actuator service life; the specified filtration level must be maintained.
Gas contaminant content must be strictly controlled: concentration of solid particles smaller than 10 microns must not exceed 30 ppm, and those larger than 10 microns must not exceed 0.3 ppm.
Regularly inspect hydraulic system pressure and oil condition.
Avoid operation under overpressure, overtemperature, or out-of-range viscosity conditions.
Regularly check the sealing of electrical connectors and the stability of position feedback signals.