I. Model Meaning

D631: 631 Series Two-stage Mechanical Feedback Servo Valve

502: Flow Code → 150 L/min @ 35 bar (High Flow, Heavy Industry Grade)

F: External Pilot Supply Oil, FKM Seal, Zero Position Optimization (Power Generation EH System / High Flow Stability Special)

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

Rated Flow: 150 L/min

Maximum Working Pressure: 315 bar

Frequency Response (−3 dB, 90°): ≈ 45–50 Hz (High Flow Dynamic Stability)

Step Response (100%): ≈ 30 ms

Hysteresis: ≤ 0.2%

Resolution: ≤ 0.1%

Zero Position Leakage: ≈ 2.0 L/min (Low for High Flow Valves)

Pilot Supply Oil: External X Port 15–210 bar

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 External/Integrated Mode Zero-Position Leakage L/min Main Application

D631-502F 150 External ≈2.0 Power generation EH, high-flow high-pressure, high-stability closed-loop

D631-335CF 120 External <2.5 Power generation EH, steam turbine electro-hydraulic conversion

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

D631-404C 15 Integrated ≈0.4 Small flow, ultra-high precision, low leakage

IV. Features and Applications Characteristics

✅ Ultra-high flow rate (150 L/min) + external pilot valve, suitable for high-pressure systems with large flow rates

✅ High stability, low drift, reliable long-term operation accuracy

✅ Strong anti-contamination ability, long service life, preferred for heavy industry / power generation harsh environments

✅ External X-port independent pilot valve, flexible system design, compatible with accumulators

Typical applications

Power generation: Steam turbine EH system, main steam valve / regulating valve electro-hydraulic actuator

Heavy machinery: Large press machines, rolling mills, forging equipment with high-pressure and large flow rate closed-loop control

Testing equipment: High-flow hydraulic loading, fatigue test system

Industrial general-purpose: High-pressure, large flow rate, high stability closed-loop control