I. Model Meaning

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

346: Flow Code → 75 L/min @ 35 bar (High flow setting in the series) Moog Inc.

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

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

Rated Flow: 75 L/min Moog Inc.

Maximum Working Pressure: 315 bar (4,500 psi)

Frequency Response (−3 dB, 90°): ≈ 50 Hz

Step Response (100%): ≈ 30 ms

Hysteresis: ≤ 0.2%

Resolution: ≤ 0.1%

Internal Leakage (Zero Position): ≈ 1.2 L/min (Built-in Pilot, Higher than F Type)

Temperature Range: −29 ℃ ~ +135 ℃

Filter Requirements: NAS 6–7 Grade

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

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

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

D631-333C 120 Internal ≈ 4.0 Industrial ultra-high flow rate

D631-335CF 120 External < 2.5 Power generation / Nuclear EH oil

D631-346C 75 Internal ≈ 1.2 High-pressure, medium-flow, low-leakage industrial standard

Four. Features and Applications

Features

✅ Internal preload, simple system oil circuit, low cost

✅ Zero position leakage is low (≈ 1.2 L/min), energy-saving, low heat generation

✅ Excellent hysteresis / resolution (0.2%/0.1%), suitable for high-precision closed-loop

✅ Resistant to high pressure 315 bar, suitable for heavy-duty industry

Typical Applications

Metallurgy: Rolling mill reduction, roll gap control

Heavy-load testing: Material fatigue, structural loading (75–100 ton level)

Machine tools: High-precision hydraulic servo feed

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