I. Model Meaning

D631: 631 Series Two-stage Mechanical Feedback Servo Valve

730: Flow Code → 30 L/min @ 35 bar (Medium and Small Flow, Precise Control Grade)

C: Built-in Pilot Supply Oil, NBR Seal, Standard Zero Position (General Industrial / Precise Closed-loop Preferred)

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

Rated Flow: 30 L/min

Maximum Working Pressure: 315 bar

Frequency Response (−3 dB, 90°): ≈ 60–70 Hz (Excellent Dynamic Performance for Medium and Small Flow)

Step Response (100%): ≈ 20–25 ms

Hysteresis: ≤ 0.3%

Resolution: ≤ 0.1%

Zero Position Leakage: ≈ 0.8 L/min (Extremely Low Leakage in Small Flow Valves)

Pilot Supply Oil: Built-in (Draws oil from Port P)

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 Pre-charge Method Zero Leakage L/min Primary Application

D631-730C 30 Internal ≈0.8 Precision closed-loop, low-flow high-pressure, general industrial

D631-404C 15 Internal ≈0.4 Ultra-precision, extremely low leakage, laboratory / test bench

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

D631-335CF 120 External <2.5 Generating EH, large flow, high stability

D631-502F 150 External ≈2.0 Generating EH, extremely large flow, high pressure

IV. Features and Applications Characteristics

✅ Small flow rate (30 L/min) + Built-in pilot, system simplified, cost low

✅ Extremely low zero-point leakage (≈0.8 L/min), energy-saving, low heat generation

✅ High resolution, low hysteresis, preferred for precise position/velocity/pressure closed-loop control

✅ Built-in pilot without external X port, convenient installation and debugging

Typical applications

Industrial automation: Precision presses, injection molding machines, die-casting machines for closed-loop control

Testing equipment: Material testing machines, fatigue test benches, dynamic loading systems

Metallurgy: Roll-down, tension control, precise roll gap adjustment

General high-pressure: Small flow rate, high precision, high stability closed-loop scenarios