Moog Servo Valve with Splined or Keyed Shaft Type Lip Seal or Mechanical Seal

Product Specification

D792-5018 G771K227
G771-K226 G771-K201
G771-K620 D664-4009
D631-751C D791-4004
B61042005 G631-3703b MOOG Hydraulic Servo Valve Electro Hydraulic Industrial Flow Control and Pressure

FAQ:

What are the main series of MOOG Servo Valves?

MOOG offers a comprehensive range of servo valves. Some prominent series include :

• G761 Series: A popular two-stage flow control valve with mechanical feedback. Known for fast response and robustness, it is widely used in various industrial applications .

• D630 Series (e.g., D634, D636, D637): These often feature direct drive by a linear force motor (DDV) or advanced control. The D636/D637 series, for example, comes with a fieldbus interface and integrated digital electronics for high flexibility .

• D660, D661, D662 Series: Classic two-stage servo valves with a wide range of industrial uses .

• 72 Series: Standard response two-stage valves with a field-replaceable pilot valve filter and the option for external pilot pressure control .

The table below summarizes the key features of some common series:

Series Example    Key Characteristics    Typical Applications / Features
G761-3003B     Two-stage, mechanical feedback, high response    Industrial machinery (e.g., metal forming presses)
D634-341C     Pilot-operated, closed-loop spool control with LVDT    Precision control systems
D636/D637     Direct Drive (DDV), linear force motor, fieldbus interface    No pilot leakage, high dynamics, programmable
72 Series     Standard response, replaceable pilot filter    Power generation (steam/gas turbines)

4. What are the typical operating parameters for MOOG Servo Valves?

While specifications vary by model, general operating parameters can include :

• Maximum Operating Pressure: Up to 4000-4500 psi (approx. 31.5 MPa) for many models.

• Flow Control Range: From a few liters/minute (e.g., 3.8 L/min) to very high flows (e.g., 3800 L/min), depending on the valve size and type .

• Input Signal: Typically a current signal (e.g., ±40 mA) or a voltage signal. Modern valves may accept digital fieldbus commands .

• Coil Resistance: Typically, each coil in the torque motor has a specific resistance, for example, in the range of 72-88 Ω .

• Operating Temperature: A common range is -20°C to 80°C .

Applications, Troubleshooting, and Maintenance

5. Where are MOOG Servo Valves commonly used?

MOOG servo valves are used in a wide array of industries that require precise motion control :

• Industrial Machinery: Metal forming equipment (press brakes, shears, injection molding machines), wood presses, and plastic machinery.

• Power Generation: Control of steam turbine valves, gas turbine fuel systems, and guide vane control.

• Test and Simulation: Automotive and aerospace test rigs, flight simulators.

• Other Fields: Robotics, material handling, and other applications demanding high-performance hydraulic control.

6. What are the most common failures and how can they be diagnosed?

Common failures can be categorized by the valve's internal components :

• Torque Motor Issues:

  ◦ Broken Coils: Result in no current, valve does not respond.

  ◦ Contamination in Air Gap: Causes the armature to stick, preventing valve movement.

  ◦ Loose Fasteners or Worn Parts: Can lead to increased null bias or instability.

• Nozzle/Flapper Stage Issues:

  ◦ Clogged Nozzles or Orifices: Often caused by oil contamination, leading to reduced frequency response, poor resolution, and system instability.

• Spool Amplifier Stage Issues:

  ◦ Spool Sticking: Caused by contaminated oil or a deformed spool, resulting in distorted response or complete seizure.

  ◦ Cutting Edge Wear: Increases internal leakage, causes null shift, and reduces stability.

System-level symptoms caused by these failures include :

• Cylinder Refusal to Move: Often due to a stuck servo valve.

• Uncontrolled Valve Movement: Sudden full opening/closing of a cylinder without a command change, often due to a clogged nozzle.

• Cylinder Oscillation ("Cylinder Hunting"): Can be caused by high internal leakage, poor resolution, or instability in the valve's null zone.

• High Cylinder Lag.

7. How can I maintain my MOOG Servo Valve and prevent failures?

The most critical factor for reliable servo valve operation is maintaining clean, dry hydraulic fluid .

• Oil Filtration: Use high-quality filters and adhere to a strict oil analysis and replacement schedule. Contamination is the primary cause of servo valve failure.

• System Design: The hydraulic system should be designed to minimize dead spots where contaminants can accumulate. The reservoir should be sized appropriately to allow for air and contaminant separation .

• Regular Inspection: Periodically check the valve and system for leaks, unusual noises, or changes in performance.

• Preventive Maintenance: Follow the manufacturer's recommended maintenance intervals, which may include replacing the valve's internal filter (if equipped) .

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