Basic Information

• Brand: MOOG

• Model: D634‑551

• Series: D634 (Direct Drive Valve, DDV)

• Type: Single‑stage, pilotless, direct‑operated servo valve

• Mounting: ISO 4401‑05 (NG10)

• Drive: Permanent magnet linear force motor

• Feedback: Built‑in LVDT spool position closed loop

• Electronics: Integrated 24 VDC PWM drive

• Protection: IP65

• Weight: Approx. 6.3 kg (13.9 lb)

Hydraulic Specifications

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

• Max T‑port pressure (no Y port): ≤50 bar (725 psi)Moog Inc.

• Max T‑port pressure (with Y port): 350 bar (5,000 psi)Moog Inc.

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

• Peak flow: ≈180 L/min (47.5 gpm)

• Null leakage: 2.5–7 L/min

• Fluid: ISO 11158 mineral hydraulic oil

• Viscosity: 15–100 mm²/s (allowable 5–400 mm²/s)

• Fluid temperature: −20 °C to +80 °C

Electrical Specifications

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

• Max current: 2.2 A

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

• Connector: 6‑core + PE, IP65Moog Inc.

• Electronics: SMD technology, PWM current output, EMC certified

Dynamic Performance (Typical)

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

• −3 dB bandwidth: 18–30 Hz

• Hysteresis: <0.25% of full scale

• Resolution: <0.10% of full scale

• Temperature drift (ΔT = 55 K): <1.5% of full scale

Key Features

• Pilotless direct drive: No pilot oil supply needed; simpler piping, lower leakage, higher reliabilityMoog Inc..

• Linear force motor: High and stable driving force, pressure‑independent dynamicsMoog Inc..

• LVDT closed‑loop feedback: Ensures high positioning accuracy and repeatability.

• Spring centering: Fail‑safe return to neutral on power lossMoog Inc..

• Low power consumption: Minimal heat generation at nullMoog Inc..

• High contamination resistance: Suitable for harsh industrial environments.

Applications

• Medium‑sized hydraulic presses & forging machines

• Injection molding & die‑casting equipment

• Vibration & fatigue test benches

• Heavy‑duty industrial hydraulic systems

• Precision position, force & speed closed‑loop control