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 appliions demanding high-performance hydraulic control.

Common failures can be egorized 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.

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).