Independent third-party repair of the standalone servo and proportional valves running boom extension, load moment systems, and outrigger control on rough-terrain, all-terrain, and crawler cranes. Component-level rebuild and bench verification on the same hydraulic stands the shop has run since 1975.
Mobile crane proportional valves are standalone electro-hydraulic units, not modular sectional control stacks. Below are four common contexts seen at the bench.
N110
Rough-terrain cranes
Parker D1FP and Rexroth 4WRPH proportional valves on boom extension and outrigger circuits, used on confined-access construction sites.
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All-terrain cranes
Moog D633 / D634 and Rexroth 4WRPH servo valves running boom extension, load moment systems, and load positioning on complex lift work.
N130
Crawler & lattice boom cranes
High-flow Moog servo valves and Rexroth 4WRPH bodies on boom hoist, load moment, and auxiliary winch circuits where downtime stops the project.
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Load moment indicator circuits
Closed-loop bodies with electronic feedback used in LMI systems for controlled boom extension and load positioning on Liebherr LTM and Grove GMK cranes.
Each unit is opened, inspected, and rebuilt at the component level. Failed parts come from inventory or pulled off donor units. Bench verification before ship.
N210
Pilot stage rebuild
Torque-motor pilot stages, nozzle flapper assemblies, and pilot-pressure trim cleaned and aligned against documented procedures.
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Spool & sleeve service
Spool wear, jobsite-contamination scoring, and lap restoration on Rexroth 4WRPH, Parker D1FP, and Moog D633 / D634 bodies.
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Coil & feedback work
Burned drive coils, feedback wire repair, LVDT verification, and amplifier-card service on closed-loop LMI bodies.
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Bench testing
Hagenbusch and digital hydraulic stands for flow, hysteresis, and frequency response. Performance data available for purchase.
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Donor parts service
19,000+ unit in-house pool. Aftermarket and donor parts for older Liebherr, Tadano, Terex, Grove, and Manitowoc hardware no longer supported by the OEM.
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Repair scope
NC Servo handles bench-level component work on the valve hardware. The repair is not a certification: NC Servo does not provide, renew, or represent FM, FAA, or any other approval. Reinstallation, system validation, load testing, and determining suitability for return to service — including any certification that applies — remain solely the responsibility of the customer or qualified field technician.
Mobile crane hydraulics run through long lift cycles in dusty, dirty environments. The failures we see most often fall into the categories below. Recognize one? A part number is enough to start.
Torque-motor pilot drift, nozzle plugging from contamination, and null shift after long boom-extension service.
Spool and body
Spool wear, contamination scoring, sluggish action on cold starts, and internal leakage past the spool on Rexroth 4WRPH and Parker D1FP / D3FP bodies.
Coil and feedback
Burned drive coils, feedback wire wear at the pilot, LVDT signal drift, and amplifier-card faults on load moment indicator circuits.
Connector and electrical
Damaged connectors, harness strain on telescoping booms, and contamination on the connector pins after years of jobsite service.
N500 Workflow
From part number to ship-back
Same four-step path through the shop whether the unit is a Rexroth 4WRPH off a Liebherr LTM or a Moog G761 off a Grove RT.
N510
Get in touch
Give us a call or email with the part number, the crane it came off, and a photo of the nameplate if it helps.
N520
Bench review
Tech opens the unit, inspects pilot and spool, and runs it on the hydraulic stand to confirm what failed.
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Cost & approval
We call back with the cost and a rough turnaround. Nothing is started without your sign-off.
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Repair, test, ship
Failed components replaced from inventory or off donors, the valve verified under pressure, and shipped back.
N600 Common questions
Common questions about mobile crane valve repair
Application-specific questions. For brand-specific FAQs, see the dedicated brand page in the brand list above.
What types of mobile crane servo valves do you repair?
Standalone servo and proportional valves used in mobile crane hydraulic control: Rexroth 4WRPH, Parker D1FP / D3FP, and Moog D633 / D634 servo valves. These are the electro-hydraulic valves used for boom extension, load moment systems, and outrigger control, not modular sectional valve stacks.
Do you offer field service for mobile crane valve replacement?
Bench repair is the standard service. You ship the valve in for rebuild and testing. Field service can be arranged for on-site needs but is not the typical offering.
Can you repair valves from older mobile cranes no longer supported by the OEM?
Yes. Legacy servo valves from older Liebherr, Tadano, Terex, Demag, and Grove cranes come through regularly. Stock varies by part number, so give us a call about a specific unit.
What mobile crane brands come through the shop?
Liebherr LTM / LTR / LR, Tadano ATF / GR / GT (and Mantis), Terex / Demag AC / CC / Superlift, Manitowoc and Grove RT / TMS / GMK, Link-Belt RTC / TCC, and other manufacturers worldwide. Focus is on the standalone control valves, not the main directional control valve banks.
Do you repair load moment system valves?
Yes. Load moment systems use servo valves (typically Moog or Rexroth) for controlled boom extension and load positioning. Bench repair is on the valve hardware only; load testing, LMI calibration, and return-to-service certification remain with the crane owner or qualified inspector. Both come through the bench regularly.
What if the valve is beyond economic repair?
If the valve is not fixable, we will let you know and help source a replacement.
What is the warranty?
One year on parts and workmanship for repairs and rebuilt units. Standard exclusions apply for contamination, improper installation, and out-of-spec operation. Flushing and filtering the hydraulic system before reinstalling a repaired valve is recommended.
N700 More from NC Servo
Related repair coverage
Other industry-specific pages, the broader category hubs, and the brands seen most often on mobile crane hydraulics.
Give us a call or send a part number with the crane it came off. We'll check the donor pool, suggest a rebuilt match if we have one, and walk through repair or cross-brand options if we don't.
