I. Model Meaning

D631: 631 Series Two-stage Mechanical Feedback Servo Valve

F550: Flow Code → 150 L/min @ 35 bar (Maximum flow setting of 631 Series)

F: Externally Mounted Pilot Supply Oil, FKM Seal, High Pressure Version (Power Generation EH / High-Pressure Heavy Load Specialized)

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 Stability at High Flow)

Step Response (100%): ≈ 30–35 ms

Hysteresis: ≤ 0.5%

Resolution: ≤ 0.2%

Zero-Position Leakage: ≈ 2.0 L/min (Controllable in High Flow Valves)

Pilot Supply Oil: Externally Mounted (Requires Independent X Port for Oil Supply)

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 Lead-in Method Zero Leakage L/min Primary Application

D631-F550F 150 External ≈2.0 Power generation EH, ultra-high flow pressure, heavy-duty actuator

D631-502F 150 External ≈2.0 Power generation EH, ultra-high flow pressure (standard version)

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

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

D631-730C 30 Internal ≈0.8 Precision closed-loop, small to medium flow, general industrial

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

Four. Features and Applications Characteristics

✅ Ultra-high flow rate (150 L/min) + external pilot, driving heavy-duty actuators without pressure

✅ FKM seal + high-pressure version, resistant to temperature and corrosion, suitable for harsh working conditions

✅ High stability at high flow rate + low hysteresis, preferred for power generation EH / heavy industry closed-loop applications

✅ External pilot for independent oil supply, suitable for high-pressure and high-flow systems, convenient for maintenance

Typical applications

Power industry: Steam turbine EH system, main steam valve / regulating valve control, large oil actuator drive

Heavy machinery: Large press machine, forging equipment, main drive of metallurgical rolling mill

Industrial high pressure: High-flow high-pressure closed-loop, heavy-duty actuator position / speed / force control

Shipbuilding / heavy industry: Large hydraulic steering gear, anchor gear, heavy platform lifting control