Description
Key Technical Specifications
- Model Number: D691 E2052A
- Manufacturer: Moog Inc. (Industrial Motion Control Group)
- Valve Type: Two-stage PQ servo-proportional valve (integrated flow/pressure control)
- Actuation Principle: ServoJet jet pipe pilot (permanent magnet torque motor) + sliding spool power stage
- Size Classification: ISO 4401 Size 04 (NG8) – 4-bolt flange (M8 x 1.25)
- Flow Capacity: 100 L/min (26.4 gpm) at Δp=70 bar
- Maximum Operating Pressure: 350 bar (5075 psi) – continuous service
- Electrical Interface: ±10V/4-20mA switch-selectable input (12-bit resolution), 24V DC ±10% supply, ±10V LVDT feedback + 4-20mA pressure output
- Connector Type: 10-pin DIN 43650 A (IP65 when mated with sealed boot)
- Response Time: 10ms (90% step response); 7ms (high-response “H” variant)
- Operating Temperature: -20°C to +70°C (-4°F to +158°F)
- Fluid Requirements: Mineral oil (ISO VG 32–68), NAS 1638 Class 5, max 85°C fluid temp
- Mounting Torque: 22 Nm (16.2 ft-lbs)
- Weight: 4.5kg (9.9 lbs)
- Certifications: CE, RoHS compliant; ATEX/IECEx optional (Zone 2 hazardous areas)
MOOG D691-Z2708G
Field Application & Problem Solved
In mid-sized industrial hydraulic systems—think injection molding hold pressure control, steel mill auxiliary roll actuation, or medium-duty component test rigs—the biggest frustration is balancing PQ precision with system simplicity. Generic two-stage valves require external PQ controllers that add wiring, lag, and failure points. A Ohio injection molder lost $120k/year to scrap because their external controller couldn’t sync flow and pressure during the hold phase, leading to part sink marks. A Pennsylvania steel mill dealt with 4-hour downtime events when external PQ modules failed, halting auxiliary roll adjustments.
This valve fixes that by packing full PQ control into the valve body. You’ll find it in: injection molding machines (maintaining ±1.5% pressure accuracy to eliminate sink marks), steel mill auxiliary rolling stands (controlling roll force and position for sheet edge quality), paper machine actuator control (web tension and edge guiding), and medium-duty test rigs (dynamic load profiles for automotive components). Its core value is integrated precision + low maintenance—the ServoJet pilot resists contamination 50% better than nozzle-flapper designs, and no external controllers mean 30% fewer wiring-related issues. For the Ohio molder, it dropped scrap rates from 6% to 0.8%. For the steel mill, it cut PQ-related downtime by 85%.
Installation & Maintenance Pitfalls (Expert Tips)
- Fluid Cleanliness: NAS 1638 Class 5 Is Non-Negotiable: The ServoJet pilot’s 0.4mm jet pipe orifice clogs with NAS 6 oil. I replaced two valves at a Michigan paper mill where the client used 10µm filters—each failure cost 3 hours of production. Fix: Install 5µm absolute filters (β10 ≥ 100 per ISO 16889) and test oil cleanliness every 1800 hours. De-aerate oil to prevent cavitation in the pilot.
- Single-Point Grounding Eliminates Pressure Drift: Rookies ground the valve and controller at different points, creating ground loops that corrupt PQ signals. A Wisconsin molder had inconsistent hold pressure until we re-grounded everything to the same machine frame point. Fix: Use shielded twisted-pair for control signals, ground only at the controller, and keep signal cables 25cm away from power lines.
- Pilot Pressure: Maintain 7–11 Bar: Too low (≤5 bar) slows response; too high (≥14 bar) wears the torque motor prematurely. A Tennessee test rig’s load profiles were erratic until we adjusted the pilot regulator to 9 bar. Fix: Install a dedicated gauge on the pilot supply and check biweekly—fluctuations indicate a clogged filter or faulty regulator.
- Null Adjustment: No Load, No Pressure: Adjusting null with system pressure on the ports causes drift when loads change. I spent 2.5 hours troubleshooting a Kentucky mill’s roll drift until I realized the tech calibrated with 180 bar on the actuator. Fix: Depressurize the system, apply 0V/4mA, and adjust the null screw until feedback reads 0V (±0.01V). Lock with the jam nut and recheck after 20 minutes of run time.
- Mounting Torque: 22 Nm Exact—Not 25: Over-torquing warps the valve body, binding the spool and increasing hysteresis. An Indiana test rig’s valve had 0.3% pressure error until we retorqued bolts to 22 Nm with a torque wrench. Use the cross-tightening sequence (1-3-2-4) to distribute force evenly.
MOOG D691-Z2708G
Technical Deep Dive & Overview
The D691 E2052A is a self-contained PQ control solution engineered for mid-sized industrial systems where space and reliability matter. At its core, it uses a two-stage design: a ServoJet jet pipe pilot and a sliding spool power stage, with all PQ logic integrated into the valve’s onboard electronics—eliminating the need for external control modules.
The ServoJet pilot is the critical innovation: instead of a traditional nozzle-flapper, it uses a rotating jet pipe that directs pressurized fluid to two receiver nozzles, creating differential pressure to shift the power spool. This design is self-cleaning (small particles are flushed through the jet pipe), reducing clogging failures by 50% compared to nozzle-flapper pilots. The permanent magnet torque motor precisely modulates the jet pipe position, translating electrical commands into smooth, repeatable spool movement.
The power stage’s hard-chromed spool (0.004mm clearances) minimizes leakage and ensures consistent flow control. A built-in LVDT tracks spool position in real time, while an A-port pressure sensor feeds pressure data to the integrated microprocessor. The electronics execute PQ coordination algorithms—users can select flow priority, pressure priority, or balanced mode—delivering sub-2% control accuracy without external hardware.
The spring-centered spool provides a fail-safe: power loss sends the spool to neutral, blocking flow to actuators and preventing equipment damage. The ISO 4401 Size 04 flange fits standard mid-sized manifolds, making retrofits straightforward. Unlike generic PQ valves, it’s rugged enough for 24/7 industrial operation, with IP65 protection shielding against dust and water jets. For field service teams, it’s a low-maintenance workhorse—fewer components to troubleshoot, built-in diagnostics, and contamination resistance that stands up to real-world fluid conditions.
