I. Model Meaning (Sequentially)

D631: 631 Series Two-stage Mechanical Feedback Servo Valve

Z: Standard Non-Explosion-proof Type (General Industrial Environment)

556: Flow Code → 55 L/min @ Δp=35 bar; The last digit 6 = Special Customization (Zero Position / Gain Fine-Tuning + Medium Leakage)

A: External Pilot Supply Oil, FPM (Fluorine Rubber) Sealing, Medium Leakage Valve Core

In one sentence: Z556A = Non-Explosion-proof + 55 L/min Ultra-Large Flow + External Pilot + FPM Sealing + Custom Zero Position

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

Rated Flow: 55 L/min (631 Series Ultra-Large Flow Gear)

Maximum Working Pressure: 315 bar

Frequency Response (−3 dB, 90°): ≈ 45–55 Hz (Typical Value for Ultra-Large Flow)

Step Response (100%): ≈ 30–35 ms

Hysteresis: ≤ 0.3%

Resolution: ≤ 0.1%

Zero Position Leakage: ≈ 0.50 L/min (Medium Leakage Customization, Lower than Standard 550C)

Pilot Supply Oil: External (Requires Connection to X Port)

Explosion-proof Grade: None (Z = Non-Explosion-proof)

Sealing Material: FPM (Fluorine Rubber), High Temperature Resistance / Corrosion Resistance

Temperature Range: −20 ℃ ~ +120 ℃ (Upper Limit for FPM Sealing)

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

III. Comparison of D631Z556A with 407C/550C (Ultra-Large Flow Gear) Table

Project D631Z556A (Customized Outer Pilot) D631Z407C (Customized Inner Pilot) D631Z550C (Standard 55 L/min)

Rated Flow Rate 55 L/min 40 L/min 55 L/min

Pilot Method External (X port) Internal (P port) External (X port)

Sealing Material FPM (Fluororubber) NBR (Nitrile rubber) NBR (Nitrile rubber)

Zero-Position Leakage ≈0.50 L/min (Customized Leakage) ≈0.35 L/min (Low Leakage Customized) ≈0.70 L/min (Standard)

Frequency Response 45–55 Hz 50–60 Hz 45–55 Hz

Price Baseline + 30% (Extra Large Flow Rate + Outer Pilot + FPM) Baseline + 25% Baseline + 20%

In one sentence: D631Z556A is a "External Pilot + FPM Sealing + Custom Zero-Position Version" with a 55 L/min flow rate: maximum flow, high temperature resistance, superior zero-position leakage compared to standard 550C, and the highest price, suitable for scenarios with extra large flow rate, high temperature, and high precision.

Four. Features and Applications Characteristics

✅ 55 L/min Ultra-high Flow Rate: 631 series has a maximum flow limit, suitable for large-displacement actuators

✅ External Pilot (A): Independent pilot oil supply, allowing low-pressure pilot to drive high-pressure main valve, flexible system design

✅ FPM Seal (A): Resistant to high temperatures (+120℃), resistant to hydraulic oil/chemical corrosion, suitable for harsh conditions

✅ Special Customization (6): Zero gain/offset fine-tuning, leakage optimization in the middle, balancing flow and energy consumption

✅ Non-explosion-proof Z-type: Suitable for ordinary industrial environments, with lower cost than explosion-proof K-type

Typical Applications

Ultra-high Flow Rate Closed-loop: Heavy-duty presses, large injection molding machines, die-casting machines, hydraulic machines

High-temperature Conditions: Metallurgical hot rolling lines, glass forming machines, high-temperature testing equipment (+100℃ environment)

External Pilot System: Dual oil circuit design of main high pressure + low pressure pilot, energy-saving control

High Precision and Heavy Load: 55 L/min level hydraulic cylinders/motors, requiring high-temperature stability + zero position accuracy