D634-341C D634-501A
D661-4444C D661-4651
D661-4652 D661-4636
072-1202-10 072-1201-10
D662-4210 D662-4013 MOOG electro-hydraulic servo valve hydraulic valve flow and pressure control

FAQ:

What are the key installation requirements?

Proper installation is critical for performance and longevity.

• Filtration: Install a precision filter with a rating of 5 microns or less upstream of the servo valve. The hydraulic fluid cleanliness should be maintained at a maximum ISO DIS 4406 Code 16/13, with Code 14/11 recommended .

• System Flushing: Before installing the servo valve, the entire hydraulic system must be thoroughly flushed to remove contaminants. Use a flushing manifold and circulate fluid under conditions simulating normal operation .

• Mounting: The valve can be mounted in any orientation, ensuring port alignments match the manifold. The mounting surface should be clean, smooth, and flat. Use the specified screws and torque them to 96 inch-pounds .

• Connections: Use O-ring seal connections (e.g., SAE J1926) and avoid welded fittings. Prefer crimped or 24-degree cone type connections .

4. What are common faults and how can I troubleshoot them?

Common faults can be categorized as follows :

• Electrical Faults: Include power supply failure, cable damage, or poor contact. Check the supply voltage, cables, and connectors.

• Mechanical Failures: Such as a stuck valve spool, damaged springs, or worn seals. Regular inspection, cleaning, lubrication, and part replacement are necessary.

• Hydraulic Faults: Including oil contamination, low oil level, or oil leaks. Regularly replace and filter the oil, check oil levels, and repair leaks.

• Valve Oscillation: Unstable operation may be caused by issues with the servo valve's resolution, wear of the valve port, or incorrect control system parameters.

Here is a brief troubleshooting chart based on symptoms :

Potential Trouble Probable Cause
Servovalve does not follow input command 1. Open coil or coil leads.
2. Clogged inlet filter.
Poor response 1. Clogged inlet orifices or nozzles.
2. Partially clogged filter.
3. "Sticky" spool.
No response to electrical signal Shorted coil assembly.
Low flow gain 1. Incorrect null adjustment.
2. Partially plugged orifice or filter.

5. What does daily maintenance involve?

Routine maintenance focuses on preventing common faults :

• Hydraulic Fluid: Maintain the recommended cleanliness level. Change the oil regularly (e.g., every six months) and keep the oil temperature within the 40°C to 50°C range.

• Filters: Monitor the pressure drop across filters and replace elements periodically or when the pressure drop becomes excessive.

• General Inspection: Regularly check for oil leaks, inspect the valve for unusual noises or vibrations, and ensure electrical connections are secure.

• Sealed Tank: The hydraulic reservoir should be sealed and equipped with an air breather and a magnetic filter .

6. What is "Mechanical Null Adjustment"?

The mechanical null adjustment allows you to calibrate the valve's flow null (the spool position where no flow passes to the actuator when the input signal is zero) independently of other system parameters. This is done by rotating an eccentric bushing retainer pin with an Allen wrench, which can adjust the flow null by at least ±20% . This adjustment should be performed if system components are drifting or stuck in a hardover position .

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