I. Model Breakdown (D633-255A)

D633: D633 Series Direct Acting Servo Valve (DDV), NG6 (03) mounting surface, Moog Inc.

255:

2: Flow Code → 40 L/min (Δp=35 bar) (The maximum flow rate of D633)

5: Electronic / Frequency Response → High Frequency Response (100–120 Hz), Analog Input, Position Closed Loop, Moog Inc.

5: Y Port / Seal → With Y Port (Exhaust), FKM (Fluororubber) Seal, -20 to +120°C

A: Standard Type, No Special Coating, Standard Voltage Version

One Sentence: D633-255A = NG6 + 40 L/min@35 bar + 350 bar High Pressure + Direct Acting without Pilot + 100–120 Hz High Frequency Response + With Y Port (High Pressure Return Oil) + FKM High Temperature Seal

II. Core Parameters (Δp=35 bar)

Rated Flow: 40 L/min (Maximum of D633 Series)

Maximum Pressure: 350 bar (P/A/B/Y Port); T Port (With Y): 350 bar Moog Inc.

Hysteresis: <0.2%

Resolution: <0.1%

Frequency Response (±100%): 100–120 Hz (High Frequency Mode) Moog Inc.

Step Response: ≈10–12 ms

Zero Position Leakage: ≈0.4 L/min (210 bar)

Seal / Temperature: FKM (-20 to +120°C, High Temperature Resistance)

Drive: 24VDC, ±10V or 4–20mA Moog Inc.

Filter: ISO 4406 15/12

Features: No Pilot Hole, Extremely Anti-Pollution, Independent of Dynamic and Pressure, Spring Retention after Power Off, High Temperature Resistance, Compatible with High Pressure Return Oil Moog Inc.

III. D633-255A vs 204 / 231A (Key Differences)

Table

Item D633-255A (40L High Frequency + Y + FKM) D633-204 (40L High Frequency without Y) D633-231A (40L Standard Frequency Response + Y + NBR)

Frequency Response 100–120 Hz (High Frequency) 100–120 Hz (High Frequency) 60–90 Hz (Standard)

Y Port With Y Port (350bar Return Oil) Without Y Port (Internal Leakage, T≤50bar) With Y Port (350bar Return Oil)

Seal FKM (-20 to +120°C) FKM (-20 to +120°C) NBR (-20 to +80°C)

Positioning High Frequency + High Temperature + High Pressure Return Oil All-in-One Capability  High Frequency + High Temperature + Internal Leakage  Standard Frequency Response + Normal Temperature + High Pressure Return Oil

One Sentence: 255A is the "combined upgraded version" of 204 and 231A - simultaneously possessing high frequency, high temperature, and high pressure return oil capabilities, D633 Series with the most comprehensive functions being the flagship model

IV. Application Scenarios

NG6 Mounting Surface, Required 40L/min High Flow + 350bar High Pressure

High Frequency Response (>80Hz) + High Temperature (Oil Temperature 80–120°C) + High Pressure Return Oil (>50bar) All Three Exist Moog Inc.

Precision Press Machines, High-Speed Injection Molding, Casting, Test Machines, Robots, Small Cylinder Diameter High Pressure Control

High Anti-Pollution Requirements, Not Wanting Frequent Maintenance Moog Inc.