I. Model Meaning

D631: 631 Series Two-stage Mechanical Feedback Servo Valve, Moog Inc.

404: Flow Code → 15 L/min @ 35 bar (Low Flow, High Precision Mode)

C: Standard Valve Body, FKM Sealing, Built-in Pilot Supply Oil (Industrial General Configuration)

II. Core Parameters (Δp = 35 bar / Each Side)

Rated Flow: 15 L/min

Maximum Working Pressure: 315 bar

Frequency Response (−3 dB, 90°): ≈ 60–70 Hz (Better Dynamic Performance for Low Flow)

Step Response (100%): ≈ 20 ms

Hysteresis: ≤ 0.1%

Resolution: ≤ 0.05% (Top-level of the Entire Series)

Zero-Position Leakage: ≈ 0.4 L/min (Extremely Low Leakage, Energy Saving)

Temperature Range: −20 ℃ ~ +80 ℃ (Oil)

Filter Requirements: NAS 6–7 Grade / ISO 4406 <14/11

III. Comparison of Key Models in the Same Series (Δp = 35 bar) Table

Model Flow Rate L/min Preload Method Zero Position Leakage L/min Primary Application

D631-404C 15 Internal ≈0.4 Low flow, high precision, low leakage closed-loop

D631-346C 75 Internal ≈1.2 Medium flow, high-pressure industrial standard

D631-335CF 120 External <2.5 Power generation EH system, large flow stability

D631-266C 100 Internal ≈1.8 Power generation / industrial general use

Four. Features and Applications

Features

✅ Extremely small flow rate (15 L/min) + extremely low leakage (0.4 L/min), low heat generation, low energy consumption

✅ Ultra-high precision (hysteresis 0.1%, resolution 0.05%), suitable for micron-level closed-loop control

✅ Internal preload, simple system oil circuit, low cost, fast response

✅ Resistant to high pressure 315 bar, suitable for high-pressure low-flow precision systems

Typical Applications

Precision testing: Material micro-fatigue, high-precision loading (5–20 ton level)

Machine tools: Ultra-precision hydraulic servo feed, micro-displacement control

Aerospace / Military: Low-flow high-pressure closed-loop, high-precision servo control

General industry: High-pressure, low-flow, low-leakage, high-response closed-loop system