I. Model Decoding

D631: Two-stage mechanical feedback servo valve of the 631 series

Z: Ordinary non-explosion-proof, for industrial normal temperature environment

557: Rated flow rate 55 L/min (Δp = 35 bar); Last digit 7 = High dynamic optimization valve core, high frequency response, low leakage

B: External independent pilot oil supply, NBR nitrile rubber seal

Sentence: Z557B = 55L/min ultra-large flow rate + High response high configuration valve core + External lead + Normal temperature NBR seal

II. Core Parameters (Single side Δp = 35 bar)

Rated flow rate: 55 L/min (upper limit flow rate of 631)

Maximum working pressure: 315 bar

Frequency response (-3dB/90°): 55–65 Hz (high configuration high-speed type)

Step response: 25–30 ms

Hysteresis: ≤0.25%

Resolution: ≤0.08%

Zero leakage: ≈0.40 L/min (low leakage energy-saving)

Pilot method: External X port independent oil supply

Sealing material: NBR nitrile

Working temperature: -20 to +80℃

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

III. 557A / 557B Comparison (Same flow rate, same high response) Table

Parameters: D631Z557A, D631Z557B

Flow rate: 55 L/min, 55 L/min

Dynamic frequency response: 55–65 Hz, 55–65 Hz

Pilot: External, External

Sealing: FPM fluororubber (high temperature resistant - 20~120℃), NBR nitrile (normal temperature - 20~80℃)

Zero position leakage: 0.40 L/min, 0.40 L/min

Price: Higher, More economical

Applicable working conditions: High temperature, harsh oil, General-purpose hydraulic at normal temperature, priority for cost-effectiveness

IV. Product features & Applications Characteristics

Top-level high dynamic valve core: 557 exclusive optimization, fast response, high precision, and more stable zero position

External guide independent oil supply: High and low pressure separation, system energy saving, flexible debugging

Normal temperature economical seal: NBR compatible with conventional hydraulic oil, lower cost

Low leakage: Significantly reduces idle power consumption, long-term energy saving

Non-explosion-proof Z-type: Ordinary factory, no flammable or explosive environment

Typical scenarios

Heavy-duty presses, large-scale injection molding clamping / injection, metallurgical rolling mill lowering, large hydraulic cylinder synchronization, normal temperature high-speed closed-loop hydraulic system