I. Model Meaning (More than D631-333C)

D631: 631 Series Two-stage Mechanical Feedback Servo Valve

335: Flow Code → 120 L/min @ 35 bar (Same as 333C, Maximum of the Series)

C: Standard Valve Body, FKM Sealing

F: Special Configuration (External Pilot / Low Leakage / Power Generation / Nuclear Power Level)

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

Rated Flow: 120 L/min

Maximum Working Pressure: 315 bar (4,500 psi)

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

Step Response (100%): ≈ 25 ms

Hysteresis: ≤ 3%

Resolution: ≤ 0.5%

Internal Leakage (Zero Position): < 2.5 L/min (The leakage of F configuration is significantly lower)

Temperature Range: −20 ℃ ~ +80 ℃

Filter Requirements: NAS 6–7 Grade

III. Key Points of F Configuration (Different from Ordinary 333C)

External Pilot Supply Oil (X Port): Independent Pilot Pressure, Suitable for High Pressure / High Flow Systems

Zero Position Leakage Lower: < 2.5 L/min (For ordinary C, approximately 4 L/min), Energy Saving, Low Heat Generation

Anti-Vibration / Anti-Impact Reinforcement: 15 g Three-Axis Vibration, Common in Power Generation / Steam Turbine DEH

Material Upgrade: Valve Core Corrosion Resistant Alloy, Sealing Compatible with Anti-Fuel Oil (EH Oil)

IV. Typical Applications (F Configuration Focus)

Steam Turbine DEH, Main Steam Valve / Regulating Steam Valve (EH Oil System)

Nuclear Power / Thermal Power: High Pressure High Flow, Long-Term Continuous Operation

Metallurgy: Thick Plate Rolling Mill, High Pressure Roll Gap Control

Heavy Load Testing: 200–500 Ton Level Fatigue / Structural Loading