Moog Servo Valve with G3/8 Outlet Port Lip Seal or Mechanical Seal and

Product Specification

D634-319C D634-341C
D631-333C D661-556C
D661-571C D661Z556C
G761-3004 D661-4789
D072-559A G631-3005 Industrial hydraulic servo valve MOOG, made in Germany, imported with original packaging

FAQ:

• 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) .

Purchasing and Services

8. Can I get a specific valve that is not listed in your standard catalog?

Yes, MOOG is known for its ability to provide custom solutions. They can modify product components to enhance performance or meet specific application requirements .

9. What documentation is provided with a new or repaired servo valve?

A detailed test report is typically provided with new valves or after a professional repair. This report verifies that the valve's performance meets specifications. Key parameters tested include :

• Flow Characteristics

• Null Bias and Hysteresis

• Internal Leakage

• Frequency Response

10. Where can I get technical support or purchase these valves?

You can contact MOOG or their authorized distributors and partners worldwide for technical support, sales, and service. When inquiring, it is helpful to provide the complete valve model number (e.g., G761-3003B) and the part number for accurate assistance .