I. Model Meaning (Compared with D631K771C)

D631: 631 Series Two-stage Mechanical Feedback Servo Valve

K: Explosion-proof (Ex ia IIC T4/T6), specially designed for safe explosion-proof area by Moog Inc.

771: Flow code → 25 L/min @ 35 bar (General medium flow standard gear)

C: Built-in pilot, NBR seal, standard zero position

A: Custom suffix (Key difference)

A = Low zero position leakage + Improved seal + Zero position accuracy improvement (≤ 0.1%)

Some batches: Electrical connector optimization / Coil insulation strengthening / Low-temperature compatibility (−30 ℃)

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

Rated Flow: 25 L/min

Maximum Working Pressure: 315 bar

Frequency Response (−3 dB, 90°): ≈ 65–75 Hz (Higher than K771C by 5–10 Hz) Moog Inc.

Step Response (100%): ≈ 18–22 ms (Faster) Moog Inc.

Hysteresis: ≤ 0.25% (Better than 0.3% of K771C)

Resolution: ≤ 0.08% (Higher Precision)

Zero Position Leakage: ≈ 0.45 L/min (25% lower than K771C)

Pilot Supply Oil: Built-in (Oil is taken from Port P)

Temperature Range: −30 ℃ ~ +85 ℃ (A suffix for low-temperature strengthening)

Filter Requirements: NAS 6–7 grade / ISO 4406 <14/11

Explosion-proof Grade: Ex ia IIC T4/T6 (Safe, Zone 0/1/2 available) Moog Inc.

III. Key Differences between D631K771CA and D631K771C Table

Project D631K771CA (Customized) D631K771C (Standard) Effect

Zero position leakage ≈0.45 L/min ≈0.6 L/min CA is more energy-efficient and has lower heat generation

Frequency response 65–75 Hz 60–70 Hz CA has faster dynamics and more stable closed-loop

Hysteresis / Resolution 0.25% / 0.08% 0.3% / 0.1% CA has higher control accuracy

Temperature range −30 ℃ ~ +85 ℃ −20 ℃ ~ +80 ℃ CA is resistant to low temperatures, cold regions / suitable for outdoor use

Sealing / Insulation Improved NBR / Enhanced insulation Standard NBR CA has longer lifespan and higher reliability

IV. Features and Applications Characteristics

✅ K explosion-proof intrinsically safe + A high-precision low-leakage, preferred for closed-loop control in explosion-proof zones

✅ 25 L/min medium flow rate + built-in pilot, system is simple and easy to maintain

✅ Low-temperature strengthening (−30 ℃) + high dynamics (75 Hz), suitable for high-altitude / outdoor explosion-proof scenarios

✅ Low leakage + high resolution, energy-saving while improving control accuracy

Typical applications

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

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

Energy machinery: turbine speed regulation, small EH systems, hydraulic stations in high-altitude areas

General high-pressure: medium-flow precision closed-loop, position / speed / force control, explosion-proof zone actuators