Description
At-A-Glance Executive Brief
- Model: G771K208A
- Brand: Moog
- Part Type: G771 series two-stage electro-hydraulic servo valve
- Lifecycle status: OEM obsolete, superseded by G771K294A; stocked for brownfield power turbine and industrial test rig retrofits
- System compatibility: Works with turbine governor controllers, hydraulic actuators, DCS/PLC analog command signals
- Weight: 3.8 kg
Technical Introduction
Servo valve failure stops hydraulic actuator positioning, leading to loss of turbine governor control, machine shutdown or unstable closed-loop motion. The Moog G771K208A is a two-stage flow-control electro-hydraulic servo valve designed for high-precision closed-loop hydraulic motion control. It converts low-power analog electrical command signals (from turbine control or automation systems) into precisely regulated hydraulic flow to drive hydraulic actuators. The first stage is a jet-pipe pilot stage driving the second-stage spool valve, delivering fast dynamic response, low null drift and repeatable flow metering. It accepts ±10V analog setpoint signals from DCS or governor controllers. Commonly deployed on steam/gas turbine governor hydraulic actuators, material test systems and industrial simulation rigs. Power generation and test facility operators maintain spare units to reduce forced outage risk while planning legacy hydraulic control migration.
- Best Suited For
- Steam and gas turbine governor hydraulic actuator control loops
- Fatigue test benches, structural test rigs and motion simulation systems
- Direct drop-in replacement for existing Moog G771K208A servo valve installations
Core Technical Specifications
| Parameter | Value |
|---|---|
| Part Number | G771K208A (Moog G771 family) |
| Valve Type | Two-stage jet-pipe electro-hydraulic servo valve |
| Input Signal | Analog ±10 VDC |
| Max Operating Pressure | Up to 5000 psi |
| Rated Flow | Up to 40 GPM |
| Pilot Stage | Jet pipe design |
| Features | Low null shift, high dynamic response, closed-loop flow regulation |
| Fluid | Clean mineral hydraulic oil, ISO grade filtration required |
| Mounting | Standard ISO manifold mounting pattern |
| Weight | 3.8 kg |
| Environmental Details | Please refer to the OEM datasheet for complete environmental tolerances. |
Field Engineer’s Tech Notes
- Hydraulic fluid cleanliness is critical. Contamination will cause spool sticking, null drift and premature servo valve failure; maintain proper filter element maintenance schedule.
- Electrical wiring polarity must match original. Reversed signal polarity reverses actuator direction and can trigger machine trips.
- After replacement, perform null adjustment and closed-loop tuning to match governor or motion control loop parameters before returning to service.
Adaptive QA & Testing Protocol
Each G771K208A servo valve is bench tested on a hydraulic servo test stand. We apply ±10V analog command signals to verify linear flow response, hysteresis and null offset. Frequency response and step response are validated. Leakage measurements are taken across rated operating pressure. Electrical coil continuity and insulation resistance are inspected. Full test reports or bench test video clips are available upon request.
Buyer’s FAQ
Q: What is Moog G771K208A used for? A: It is a two-stage electro-hydraulic servo valve that converts analog control signals into modulated hydraulic flow for closed-loop positioning of turbine governor actuators and high-performance test rigs.
Q: What warranty applies for refurbished and NSFP G771K208A? A: Refurbished and NSFP units carry a 12-month hardware warranty. Coverage excludes damage from hydraulic contamination, improper oil filtration, reverse signal polarity or field overpressure transients.
Q: What lead time should I expect? A: Stocked units ship 3–7 business days. If inventory is depleted, lead time increases while we source surplus Moog G771 series servo valves.
Q: What is the direct replacement part for G771K208A? A: Moog’s supersession part is G771K294A for this obsolete valve model.
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