D634-381C D634-383C
D633Z7397 D634-385C
D634-386C D634-387C
D634-388C D634-389C
D634-390C D634-391C Original German MOOG hydraulic valve, electro-hydraulic servo valve controls flow and pressure

FAQ:

Frequently Asked Questions (FAQ): MOOG Electro-Hydraulic Servo Valves

Product Overview

1. What is a MOOG Electro-Hydraulic Servo Valve and how does it work?

A MOOG Electro-Hydraulic Servo Valve is an electro-hydraulic conversion and power amplification component. Its primary function is to receive analog electrical control signals and then proportionally adjust the output flow and pressure of hydraulic fluid based on these signals, thereby achieving precise control of hydraulic actuators . Essentially, it converts tiny electrical signals into high-power hydraulic output, making it a core component in electro-hydraulic servo systems .

Most MOOG servo valves are two-stage valves. In the first stage, an electrical signal is sent to a torque motor, which moves a flapper between two nozzles, creating a pressure differential. This pressure difference acts on a spool (the second stage), moving it to control the main hydraulic flow to the load. The valve may use mechanical feedback (e.g., a spring) or an electrical feedback system (LVDT sensor) to ensure the spool position accurately corresponds to the input command signal .

2. What are the main advantages of MOOG Servo Valves?

MOOG servo valves are known for several key advantages :

• High-Precision Control: They offer exceptional control accuracy, which can reach about 0.1%, suitable for demanding applications.

• High Dynamic Performance: They feature fast response times, often in the millisecond range, allowing for high-speed and high-precision control.

• High Reliability and Stability: Designed with advanced technology and materials for stable long-term operation, even in harsh environments.

• Variety of Designs: Available in various series, including standard two-stage, high-performance two-stage and three-stage, and direct-drive valves (DDV) to meet different performance needs.

• Fail-Safe Functionality: Some models include a fail-safe feature that moves the valve to a safe position in case of a power failure or system fault .

Series and Specifications

3. What are the main series of MOOG Servo Valves?

MOOG offers a comprehensive range of servo valves. Some prominent series include :

• G761 Series: A popular two-stage flow control valve with mechanical feedback. Known for fast response and robustness, it is widely used in various industrial applications .

• D630 Series (e.g., D634, D636, D637): These often feature direct drive by a linear force motor (DDV) or advanced control. The D636/D637 series, for example, comes with a fieldbus interface and integrated digital electronics for high flexibility .

• D660, D661, D662 Series: Classic two-stage servo valves with a wide range of industrial uses .

• 72 Series: Standard response two-stage valves with a field-replaceable pilot valve filter and the option for external pilot pressure control .

The table below summarizes the key features of some common series:

Series Example Key Characteristics Typical Applications / Features
G761-3003B Two-stage, mechanical feedback, high response Industrial machinery (e.g., metal forming presses)
D634-341C Pilot-operated, closed-loop spool control with LVDT Precision control systems
D636/D637 Direct Drive (DDV), linear force motor, fieldbus interface No pilot leakage, high dynamics, programmable
72 Series Standard response, replaceable pilot filter Power generation (steam/gas turbines)

4. What are the typical operating parameters for MOOG Servo Valves?

While specifications vary by model, general operating parameters can include :

• Maximum Operating Pressure: Up to 4000-4500 psi (approx. 31.5 MPa) for many models.

• Flow Control Range: From a few liters/minute (e.g., 3.8 L/min) to very high flows (e.g., 3800 L/min), depending on the valve size and type .

• Input Signal: Typically a current signal (e.g., ±40 mA) or a voltage signal. Modern valves may accept digital fieldbus commands .

• Coil Resistance: Typically, each coil in the torque motor has a specific resistance, for example, in the range of 72-88 Ω .

• Operating Temperature: A common range is -20°C to 80°C .

Applications, Troubleshooting, and Maintenance

5. Where are MOOG Servo Valves commonly used?

MOOG servo valves are used in a wide array of industries that require precise motion control :

• Industrial Machinery: Metal forming equipment (press brakes, shears, injection molding machines), wood presses, and plastic machinery.

• Power Generation: Control of steam turbine valves, gas turbine fuel systems, and guide vane control.

• Test and Simulation: Automotive and aerospace test rigs, flight simulators.

• Other Fields: Robotics, material handling, and other applications demanding high-performance hydraulic control.

6. What are the most common failures and how can they be diagnosed?

Common failures can be categorized by the valve's internal components :

• Torque Motor Issues:

◦ Broken Coils: Result in no current, valve does not respond.

◦ Contamination in Air Gap: Causes the armature to stick, preventing valve movement.

◦ Loose Fasteners or Worn Parts: Can lead to increased null bias or instability.

• Nozzle/Flapper Stage Issues:

◦ Clogged Nozzles or Orifices: Often caused by oil contamination, leading to reduced frequency response, poor resolution, and system instability.

• Spool Amplifier Stage Issues:

◦ Spool Sticking: Caused by contaminated oil or a deformed spool, resulting in distorted response or complete seizure.

◦ Cutting Edge Wear: Increases internal leakage, causes null shift, and reduces stability.

System-level symptoms caused by these failures include :

• Cylinder Refusal to Move: Often due to a stuck servo valve.

• Uncontrolled Valve Movement: Sudden full opening/closing of a cylinder without a command change, often due to a clogged nozzle.

• Cylinder Oscillation ("Cylinder Hunting"): Can be caused by high internal leakage, poor resolution, or instability in the valve's null zone.

• High Cylinder Lag.

Quanzhou Yisenneng Hydraulic Electromechanical Equipment Co., Ltd. has been established for many years and has now developed into an international trading company supplying various hydraulic machinery parts, oil pumps and valves. We are one of the few Chinese companies with multiple products and channels. Main focus: quality assurance! The price is the lowest in the industry! Quality management procedures are implemented in accordance with international standards and are implemented throughout the production process. In terms of channels, we have gathered the most complete variety of products in the world; in terms of quality, all products meet international standards; the lowest price in the industry is the highest; the fastest delivery on credit, and a complete after-sales system; remember Good service is the key to cooperation with customers. We strive to achieve high quality standards, provide competitive prices, and ensure timely delivery. In this way, our products have been recognized by the market and satisfied by customers in the past years. Our goal is to meet the needs of our global customers. Here you can enjoy a one-stop shopping experience, the customer is God, you want all of us, I wish you a happy shopping trip.