Moog Servo Valve with G3/8 Outlet Port Lip Seal or Mechanical Seal and Horizontal Pump Shaft for Hydraulic Systems

Model Numbers: D634-319C, D634-341C, D631-333C, D661-556C, D661-571C, D661Z556C, G761-3004, D661-4789, D072-559A, G631-3005

Made in Germany, imported with original packaging

• Servo valve G761-3004 H38JOGM4VPL
• Amplifier D661-4033 P80HAAF6VSX2-A
• Servo valve D661-4636 G60KOA5VSX2HA
• Servo valve D661-4651 G35KOA6VSX2HA
• Servo valve D661-4469C G75KOAA6VSX2HA
• Servo valve D633-308A R08K01MON
• Servo valve D633-308B R08KO1M0NSM2
• Servo valve G631-3006B H75JOFM4VBR
• Servo valve G761-3600B
• Servo valve D662-4010/D061-8411 D02HABF6VSX2-A
• Servo valve G761-3033
• Servo valve G761-3034

MOOG servo valves are primarily used as actuators in electrical hydraulic servo systems. These systems benefit from hydraulic actuators that offer excellent speed control, high power-to-weight ratio, smooth transmission, and strong interference resistance. The servo valves are essential components in modern high-performance electro-hydraulic servo systems.

• Torque Motor Issues:
  • Broken coils result in no current flow, preventing valve response
  • Contamination in air gap causes armature sticking
  • Loose fasteners or worn parts can increase null bias or instability
• Nozzle/Flapper Stage Issues:
  • Clogged nozzles or orifices (often from oil contamination) reduce frequency response and cause instability
• Spool Amplifier Stage Issues:
  • Spool sticking from contaminated oil or deformed spool causes distorted response
  • Cutting edge wear increases internal leakage and reduces stability

• Cylinder refusal to move (often due to stuck servo valve)
• Uncontrolled valve movement (sudden full opening/closing without command)
• Cylinder oscillation ("hunting") from high internal leakage or instability
• High cylinder lag

• Maintain clean, dry hydraulic fluid
• Use high-quality filters and follow strict oil analysis/replacement schedule
• Design hydraulic system to minimize contaminant accumulation
• Perform regular inspections for leaks and performance changes
• Follow manufacturer's preventive maintenance intervals

• Custom valve solutions available upon request
• Detailed test reports provided with new/repaired valves
• Technical support available through MOOG and authorized distributors