Inspection and Repair Process

Our process involves a teardown of your MOOG D633-521B, mineral bath cleaning, and reassembly with quality parts to restore operation.

About Our Shop

We stock common wear parts in-house, so most rebuilds don’t require outside sourcing. Less waiting, faster turnaround.

Specializing in MOOG D633-521B servo valve technology for over five decades

Frequently Asked Questions

If the main housing or board is intact, repair is usually the better option. We can restore most units to working condition with tested parts.

Yes. Our repairs include a 12-month warranty on parts and labor covering parts and labor.

Not required, but removing excess oil or loose debris before packing helps keep things clean in transit.

Yes. If the unit can’t be repaired, we contact you with options before doing anything further.

Standard turnaround is 1-3 weeks. Rush options are available for time-sensitive situations.

Rebuild Steps

We disassemble every valve, inspect it inside and out, and clean all moving parts. Components that fail inspection are swapped out before the valve is rebuilt and tested.

  • Cleaning: Units go through a mineral bath, with ultrasonic cleaning used for delicate internals.
  • Final Performance Verification: After reassembly, each valve undergoes bench-testing against published performance specs.
  • Seal and Gasket Replacement: Worn seals and gaskets are replaced with new components during every rebuild.
  • Teardown: Every valve is disassembled for internal inspection.

Testing and Bench Verification

With over a dozen dedicated flow test stands and a Hagenbush proportional valve system, we verify flow curves, hysteresis, frequency response, and more. Performance reports and graphs are available for purchase on request. Our operational testing verifies spec-level operation.

Technical Specifications

Every MOOG D633-521B we service is tested under typical applications. Our diagnostics verify performance against published specifications. Technical diagrams and Cycle life data are available for purchase upon request.

Repair, Rebuild and Exchange Options

Beyond standard maintenance, we offer specialized repairs for your MOOG D633-521B unit. Our disassembly process includes reassembly to spec and internal inspection, using only replacement replacement components.

Maintenance Tips

  • Use only manufacturer-recommended hydraulic fluids to protect internal valve surfaces.
  • Keep hydraulic fluid clean and at proper levels for consistent valve operation.
  • Check system pressure regularly to verify it stays within the MOOG D633-521B rated operating range.

Let Us Repair Your MOOG D633-521B

Request pricing, availability, and turnaround for your MOOG D633-521B. NC Servo provides hands-on repair with a 1-year warranty. Contact us to request your repair.

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NC Servo is an independent third-party repair facility. We are not affiliated with, endorsed by, sponsored by, or authorized by MOOG or any original equipment manufacturer (OEM), nor do we claim to be a MOOG service center. All brand names, trademarks, model numbers, and part numbers referenced on this page are the property of their respective owners and are used solely for identification and compatibility purposes.