1. Model Code Definition

• D634: Series, direct‑drive servo valve (DDV), ISO 4401‑05 (NG10) mountingMoog Inc.

• K: Explosion‑proof version (Ex de IIB+H2 T4/T3), for Zone 1/2 hazardous areas

• 2004: Flow rating & revision (2000 series, 4th high‑precision revision)

• C: Design revision level

2. Basic Data

• Brand: MOOG

• Type: Single‑stage, pilotless direct‑drive servo valve (DDV)Moog Inc.

• Mounting: ISO 4401‑05 (NG10)Moog Inc.

• Drive: Permanent magnet linear force motor (bidirectional direct drive)Moog Inc.

• Feedback: Integrated LVDT spool position closed‑loop

• Electronics: Integrated 24 VDC PWM drive, “de” explosion‑proof

• Protection: IP65

• Weight: ~6.3 kg

• Certifications: ATEX II 2G Ex de IIB+H2 T4/T3; IECEx BVS 13.0126X

3. Hydraulic Specifications

• Max working pressure (P/A/B): 350 bar (5,000 psi)

• Max T‑port pressure: ≤50 bar (standard); 350 bar optional (with Y‑port)Moog Inc.

• Rated flow (Δp = 35 bar): 100 L/min (26.4 gpm)

• Peak flow: 180 L/min

• Null leakage: 2.5–7 L/min

• Fluid: ISO 11158 mineral hydraulic oil

• Fluid temp: −20 °C to +80 °C (−4 °F to +176 °F)

• Viscosity: 15–100 mm²/s (recommended); 5–400 mm²/s (allowed)

4. Electrical Specifications

• Supply voltage: 24 VDC (operating range 18–32 VDC)Moog Inc.

• Max operating current: 2.5 A

• Control signals: ±10 V, ±10 mA, 4–20 mAMoog Inc.

• Connector: 6‑core + PE ground

• EMC: Compliant with EC directives (tested)

5. Dynamic Performance

• Full‑stroke step response: ≤20 msMoog Inc.

• −3 dB bandwidth: 20–32 Hz (improved vs. 2003C)

• Hysteresis: <0.20% full scale (lower than prior models)

• Resolution: <0.08% full scale

• Temperature drift: <1.2% full scale

6. Key Features

• ✅ Pilotless design: No pilot oil needed; simpler piping, lower internal leakageMoog Inc.

• ✅ Pressure‑independent dynamics: Stable performance regardless of system pressure fluctuationsMoog Inc.

• ✅ LVDT closed‑loop: Real‑time spool position feedback for ultra‑high positioning accuracy

• ✅ Spring centering: Fail‑safe (spool returns to neutral on power loss)Moog Inc.

• ✅ Enhanced precision (2004C): Optimized spool throttling edges; best‑in‑class flow linearity and low hysteresisMoog Inc.

• ✅ Explosion‑proof: ATEX/IECEx certified for flammable/hazardous environments

• ✅ Standard mounting: NG10 (ISO 4401‑05) for easy drop‑in replacementMoog Inc.

7. Typical Applications

• Offshore oil & gas, chemical, and petrochemical hydraulic systems

• Mining machinery and hazardous‑area electro‑hydraulic controls

• High‑precision closed‑loop control (position/velocity/pressure/force) in explosive zones

• Combustible media processing equipment

• Energy & process industries requiring ATEX/IECEx compliance

8. Revision Differences (2001C → 2004C)

• 2001C: Base version, standard linearity

• 2002C: Enhanced low‑frequency stability

• 2003C: High precision, better linearity, lower hysteresis

• 2004C: Top‑tier performance; highest linearity, lowest hysteresis/drift, wider bandwidth for critical closed‑loop applications