I. Model Meaning

D631: 631 Series Two-stage Mechanical Feedback Servo Valve

K: Explosion-proof (Ex ia / Intrinsic Safety), suitable for hazardous areas (Zone 0/1/2)

771: Flow Code → 25 L/min @ 35 bar (Medium Flow, General Industrial Mode)

C: Built-in Pilot Supply Oil, NBR Seal, Standard Zero Position

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

Rated Flow: 25 L/min

Maximum Working Pressure: 315 bar

Frequency Response (−3 dB, 90°): ≈ 60–70 Hz

Step Response (100%): ≈ 20–25 ms

Hysteresis: ≤ 0.3%

Resolution: ≤ 0.1%

Zero Position Leakage: ≈ 0.6 L/min

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

Explosion-proof Grade: Ex ia IIC T4/T6 (Intrinsic Safety, Available for Oil/Gas / Dust Explosion Zones)

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

Model Flow Rate L/min Internal Explosion-proof Zero-Position Leakage L/min Primary Application

D631K771C 25 Yes (K) ≈0.6 Explosion-proof area, steel mills, chemical plants, medium flow closed-loop

D631-730C 30 No ≈0.8 Precision closed-loop, medium and small flow, general industry

D631-404C 15 No ≈0.4 Ultra-precision, low leakage, precision closed-loop

D631-793C 5 No ≈0.25 Ultra-precision, extremely low leakage, laboratory / test bench

D631-346C 75 No ≈1.2 Medium flow, high-pressure industrial standard

D631-F550F 150 External No ≈2.0 Generating EH, ultra-large flow high-pressure, heavy-duty actuator

IV. Features and Applications Characteristics

✅ K is of explosion-proof intrinsically safe design, directly compatible with chemical / oil and gas / dust explosion-proof areas, without the need for an additional explosion-proof box

✅ 25 L/min medium flow rate + built-in pilot, the system is simple and convenient for debugging and maintenance

✅ Low leakage (≈0.6 L/min) + high resolution (≤0.1%), balancing efficiency and accuracy

✅ High pressure 315 bar + standard ISO 05 installation, with strong universality and low replacement cost

Typical applications

Explosion-proof industrial: chemical reaction vessels, oil and gas extraction platforms, equipment in dust environments (aluminum powder / flour)

Metallurgical steel mills: tension control of rolling mills, roll gap adjustment, hydraulic lowering, AGC system

General high pressure: medium flow rate precision closed-loop, position / speed / force control, small and medium power actuators

Energy machinery: water turbine speed regulation, small EH systems, precision loading test benches