I. Model Meaning

D631: 631 Series Two-stage Mechanical Feedback Servo Valve

793: Flow Code → 5 L/min @ 35 bar (Ultra-low flow, Ultra-high precision gear)

C: Built-in pilot supply oil, NBR seal, standard zero position (Ultra-precise closed-loop dedicated)

II. Core Parameters (Δp = 35 bar / each side)

Rated Flow: 5 L/min

Maximum Working Pressure: 315 bar

Frequency Response (−3 dB, 90°): ≈ 80–90 Hz (Ultra-low flow dynamic perfection)

Step Response (100%): ≈ 15–20 ms

Hysteresis: ≤ 0.2%

Resolution: ≤ 0.05% (Ultra-high precision level)

Zero Position Leakage: ≈ 0.25 L/min (Minimum for 631 Series)

Pilot Supply Oil: Built-in (oil is taken 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

D631-793C 5 Internal ≈0.25 Ultra-precise, extremely low leakage, laboratory / test bench

D631-404C 15 Internal ≈0.4 Highly precise, low leakage, precise closed-loop

D631-730C 30 Internal ≈0.8 Precise closed-loop, medium flow rate, general industrial

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

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

D631-502F 150 External ≈2.0 Power generation EH, extremely large flow rate, high pressure

Four. Features and Applications Characteristics

✅ Ultra-low flow rate (5 L/min) + built-in pilot, the system is extremely simple and easy to debug

✅ Industry's lowest zero leakage (≈0.25 L/min), energy-saving to the extreme, with minimal heat generation

✅ Ultra-high resolution (≤0.05%) + ultra-low hysteresis (≤0.2%), the top choice for ultra-precise closed-loop control

✅ Built-in pilot without external X port, suitable for narrow spaces / integration with precision equipment

Typical applications

Precision testing: material micro-tester, fatigue test bench, dynamic loading system

Laboratory: hydraulic component performance testing, servo control research, high-precision calibration equipment

Industrial ultra-precision: micro force control, precise positioning, micro hydraulic actuator closed-loop

General high-pressure: ultra-low flow rate, ultra-high precision, extremely low leakage closed-loop scenarios